Sunday 21 August: Welcome

A buffet and drinks reception will take place in Holland Hall from 19:00. There will also be an opportunity to register.

Monday 22 August: Molecular Clouds

08:00 Poster boards available

An opportunity to put up your poster in the Forum Street, the Mezannine Level, or the Expolaration Lab 2 (e-posters). Coffee/tea and mini danish will be available in the Forum Street from 08:30.

08:50 Tim Harries and Chris Brunt: Welcome to Star Formation 2016

A mercifully brief welcome address from the co-chairs!

Session Chairs

Chairs: Vera Konyves (morning), Dirk Froebrich (afternoon)

09:00 Stefanie Walch (University of Cologne): Theory review

Molecular clouds condense out of the warm interstellar medium (ISM) on scales of several 100 pc and host filamentary substructures on sub-pc scales. Furthermore, molecular clouds (MCs) consist of molecular hydrogen (H2), which can only be traced indirectly in observations, mostly by means of CO line and dust extinction measurements. Since they are observed to host large non-thermal line widths, the cloud sub-structure seems to be shaped by supersonic turbulence. The crux, however, is that supersonic turbulence is expected to decay in a crossing time unless it can be sustained by some physical process, e.g. stellar feedback. Since the turbulent dynamical state has been observed, the idea of short-lived, dynamically evolving MCs is widely accepted. It is thus likely that the turbulent, internal sub-structure of MCs is imprinted already during their formation process. In this talk I will review the current theoretical understanding of molecular cloud formation and evolution. A 30-minute review of molecular clouds from a theoretical perspective.

09:40 Nicolas Peretto (University of Cardiff): Observational review

The past few years have seen a great deal of spectacular large-scale surveys of star-forming regions across the Galaxy with unprecedented sensitivity and angular resolution. Combined with state-of-the-art interferometric follow-up observations, these surveys are transforming our view and understanding on how interstellar matter is transferred from large diffuse atomic clouds to compact protostellar objects. In this talk, I will review some of the key observational results of the past five years, focussing on the formation, evolution, and fragmentation of interstellar filaments into cores. Tightly related issues such as the formation of molecular clouds, the star formation efficiency, and the importance of feedback will be briefly addressed.

10:20 Masato Kobayashi (Nagoya University): The evolutionary picture of Giant Molecular Cloud mass functions on galactic scales

We formulate and compute the time evolution of giant molecular cloud mass functions on galactic disks. In our model, a network of expanding supernovae and HII regions drives the giant molecular cloud formation and evolution. Such a network provides (i) giant molecular cloud formation and self-growth through multiple episodes of warm neutral medium compression, (ii) giant molecular cloud self-dispersal by radiation from massive stars that are born within those clouds, and (iii) cloud-cloud collisions. Our formulation reflects these three phenomena by coarse-graining them typically over 10 Myrs. We successfully reproduce the observed variation of giant molecular cloud mass functions between arm and inter-arm regions (e.g., M51 by Schinnerer et al. 2013; Colombo et al. 2014a). Our results suggest that the mass function slope is controlled by the ratio of giant molecular cloud formation timescale over its dispersal timescale, whereas the massive end is controlled by cloud-cloud collisions. Future large radio observations with finer spatial resolution and higher sensitivity can observe giant molecular clouds with much lower mass than before, which may put unique constraints on the giant molecular cloud formation/dispersal timescales in different environment on galactic scales. In addition, our results also suggest that some amount (typically a few per cent) of dispersed gas is consumed to form a newer generation of giant molecular clouds. Therefore, we insist that, obtaining a complete picture of gas recycling processes in interstellar medium requires the understanding of the fate of dispersed gas such as CO-dark clouds and optically thick HI gas, which thus needs massive magnetohydrodynamics simulations. In this contribution, we would like to present our results and discuss this new unified picture of giant molecular cloud mass function evolution throughout galactic disks.

10:40 Andrea Bracco (CEA/Saclay): The relative orientation between magnetic fields and filamentary density structures from the diffuse ISM to molecular clouds

Investigating the dynamics of the interstellar medium (ISM) is key to gaining insight into the formation of star-forming filaments in molecular clouds (MCs). A plethora of numerical and analytical models associate the origin of this filamentary structure to the interplay between self-gravity and magnetohydrodynamical (MHD) turbulence in the ISM. However, only few observational constraints exist to favor one specific scenario. Despite the great effort of observers in the last decades, interstellar magnetic fields (MFs) still represent an important unknown in filament formation. Polarized thermal emission at sub-millimeter and far-infrared wavelengths from interstellar dust grains is the most suitable technique to investigate the density-weighted MF-structure in the ISM. Only very recently, the Planck satellite has completed the first all-sky maps of dust polarization at 850 microns, allowing us to probe the correlation between the MF geometry and the filamentary density structure with unprecedented statistics. In this talk I will present results on the relative orientation between the MF and the density structure in the ISM, from the diffuse medium to MCs. The probe of the MF properties in MCs and in their diffuse surroundings is crucial to understand the initial conditions relevant for the formation of star-forming filaments. In the Planck data, filaments seen in total intensity are observed statistically aligned with the MF orientation in the diffuse ISM, while they become statistically perpendicular to the MF in denser regions in MCs. I will discuss the implications of this correlation in the context of filament formation.

11:00 Coffee break

Coffee, tea and cookies

11:50 Simon Glover (Heidelberg University): Hunting for observational signatures of molecular cloud formation

In order to better understand how molecular clouds form in the galactic interstellar medium, we would like to be able to map the structure and kinematics of the gas flows responsible for forming them. However, it is not immediately obvious which observational tracers we should use in order to do this. CO, the workhorse molecule for studies of molecular clouds, is a poor choice, as it traces only relatively dense gas in those portions of the clouds that have already assembled and tells us little about the surrounding gas flows. Numerical simulations suggest that these flows are composed of a mixture of HI and CO-dark H2 and allow us to study the properties of the emission that we expect to detect from them. In this talk, I will present results from a series of recent numerical simulations of cloud assembly and will discuss what these simulations can teach us about the best observational strategies to use when searching for signatures of cloud formation.

12:10 Ana Duarte Cabral (University of Exeter): Observing simulations: Molecular clouds and their journey in the Galaxy

Stars form within molecular clouds, which are formed as a result of the interchange and evolution of gas through a wide range of densities and scales. Therefore, to understand the global processes that lead to star formation, it is crucial to understand the hierarchical organisation of the molecular component of the interstellar medium. However, defining and extracting clouds is not an easy task: molecular clouds are not a discrete well-defined entity - instead, they are part of a continuum of gas that travels through the galaxy, and often a mix of different fractions of atomic and molecular gas components, and different abundances of molecular species such as CO. Moreover, Milky Way studies suffer from yet another issue: a severe line of sight confusion that complicates the identification of “real” individual GMCs. Here I will present our recent work trying to grasp some of these issues, by studying the population of GMCs from a simulation of a portion of a spiral galaxy. We have used a new algorithm (SCIMES) to extract GMCs from both the physical 3-dimensional space, and from an observer’s perspective on CO emission datacubes. I will present the results from comparing the properties of clouds retrieved from the different extractions, as a means to understand the biases inherited from the perspective, resolution and tracer used. I will also explore how different galactic environments can affect GMC properties, namely by following the clouds as they travel from the shear-dominated inter-arm regions into and through spiral arms.

12:30 Eric Keto (Harvard-Smithsonian Center for Astrophysics): A simple description of the energy budget in molecular cloud and their atomic envelopes

The energy budget of molecular clouds and their atomic envelopes is one of radiative equilibrium. For use in 3D numerical hydrodynamics, we develop the simplest possible description of this equilibrium leading to gas temperature. I will describe the model for gas and dust heating and cooling and how the model is benchmarked with observations. The chemical model for the abundances of the major gas coolants, CO, C+, and O, is checked by comparison with spectral line observations made with the Herschel satellite and with the IRAM 30m. The model for the dust is checked against multifrequency observations of submm dust emission also made with Herschel. This model for radiative equilibrium and the gas temperature has recently been incorporated into a 3D SPH code with applications for star formation (Bate and Keto, MNRAS 2015) and the first results, comparison with other more complex models, are described.

12:50 Volker Ossenkopf-Okada (University of Cologne): Column density PDFs as a diagnostic tool

The most simple statistics to characterize the structure seen in maps of interstellar clouds is given by counting the observed intensity or column density values. The resulting probability distribution functions (PDFs) have a characteristic shape determined by the physical processes driving structure formation in the clouds. Measuring these functions is, however, not trivial due to observational limitations. Careful corrections can eliminate the effects of observational noise and line-of-sight contamination. The selection of the map edges is already critical and it turns out that ALMA observations are basically unusable to obtain a reliable statistics. Column density PDFs from dust cover a much larger dynamic range than any molecular-line based PDF, but only the latter ones allow to fully avoid line-of-sight confusion. The major part of the PDFs, usually described by a log-normal function, is often attributed to turbulence, but in fact, the statistics is often insufficient for this assignment. The power-law tail commonly found in the PDFs is caused by the gravitationally driven collapse of filaments and clumps. Different collapse geometries lead to different exponents that are directly measurable. Infrared dark clouds exhibit the same PDF features as more nearby, actively star-forming clouds, proving the same nature of both types of clouds. For a small number of clouds we find, moreover, clear signatures of the phase transitions between atomic and molecular hydrogen and for the imapct of radiative feedback on the column density statistics.

13:10 Lunch break

A buffet lunch with fruit juice, tea and coffee.

14:40 Seamus Clarke (University of Cardiff): Fragmentation of accreting filaments

We use smoothed particle hydrodynamic simulations to investigate the growth of perturbations in infinitely long, initially sub-critical but accreting filaments. The growth of these perturbations leads to filament fragmentation and the formation of cores. Most previous work on this subject has been confined to the growth and fragmentation of non-accreting equilibrium filaments and has found that there exists a preferential fragmentation length scale which is roughly 4 times the filament’s diameter. Our results show a more complicated dispersion relation with a series of peaks linking perturbation wavelength and growth rate. These are due to gravo-acoustic oscillations along the longitudinal axis during the sub-critical phase of growth, when the filament is far from equilibrium. The positions of the peaks in growth rate have a strong dependence on both the mass accretion rate onto the filament and the temperature of the gas. When seeded with a multi-wavelength density power spectrum there exists a clear preferred core separation equal to the largest peak in the dispersion relation. Our results allow observers to estimate a minimum age for a filament which is breaking up into regularly spaced fragments, as well as a maximum accretion rate. We apply the model to recent observations by Tafalla & Hacar (2015) of fragmenting sub-filaments in Taurus and find accretion rates consistent with those estimated by Palmeirim et al. (2013).

15:00 Jouni Kainulainen (MPIA): Fragmentation of the integral shaped filament in Orion A as view by ALMA

High line-mass filaments are birthplaces of high-mass stars and star clusters and thus important for Galactic scale star formation. However, description of their fragmentation and collapse process is yet fundamentally lacking. We have performed the most sensitive fragmentation study of a high line-mass filament to date: we have used ALMA 3 mm continuum data to characterize fragmentation of the Integral Shaped Filament in Orion A down to 1 000 AU scales. The dense cores detected in the data indicate a two-mode fragmentation picture: periodic fragmentation into groups of cores and further fragmentation within those groups. Any current gravitational fragmentation models do not predict such pattern; we discuss possible processes leading to it. We also compare the spatial distribution of dense cores to protostars and stars with disks. The protostars are grouped similarly with the dense cores, while stars with disks have clearly different distribution. This indicates that the maternal grouping of dense cores is retained over the protostar lifetime, but not over the lifetime of stars with disks. This in turn suggests that the distribution of stars looses the memory of its origin rapidly after stars decouple from gas.

15:20 Kate Pattle (UCLAN): First results of the JCMT BISTRO survey: The magnetic field of Orion A

We present the first results from the BISTRO (B-Fields in Star-Forming Region Observations) Survey. BISTRO is using the newly-commissioned POL-2 polarimeter on the JCMT to map the submillimetre emission from high-column-density regions of nearby star-forming clouds to unprecedented depth in polarised light. BISTRO is producing a large and homogeneous polarisation data set, mapping the magnetic fields in star-forming regions on scales as small as 1000 AU, allowing investigation of some of the most important questions in star formation, particularly the relative importance of magnetic fields and turbulence to the energy balance and evolution of star-forming regions. As a demonstration of the science which BISTRO will achieve, we present early results of observations of the Orion A molecular cloud. We present maps of the magnetic field structure of the OMC 1 star-forming region, along with estimates of magnetic field strengths determined through synthesis with carbon monoxide data taken as part of the JCMT Gould Belt Survey using the Chandrasekhar-Fermi method. We show that the field in the centre of the Orion BN-KL region shows an ‘hourglass’ morphology, with field lines running approximately perpendicular to the central filament. We discuss the consistency of these observations with the recently-proposed model of filament growth in which material is funnelled onto filaments along magnetic field lines, and discuss the interaction between the Orion BN-KL outflow and the local magnetic field. We further show that the polarisation vectors around the Orion Bar are consistent with the Orion Bar being wrapped by a helical magnetic field, and discuss the contribution of magnetic energy to the energy balance of both the Orion BN-KL and Orion Bar regions.

15:40 Huei-Ru Vivien Chen (National Tsing Hua University): Filamentary accretion flows in the IRDC M17 SWex

Although filamentary structures are ubiquitous in molecular clouds, basic observational constraints are needed to clarify the role of filaments in the mass assembling process. We have observed with ALMA the N2H+ and HNC emission in the filamentary accretion flows in the remarkable IRDC complexes, M17 SWex, where a delayed onset of massive star formation was reported in the two hubs at the convergence of multiple filaments of parsec length. We derived the kinematics with the N2H+ emission and found the line widths are smaller than those of ammonia, suggesting a transonic nature of dense gas in the filaments. Slow infall motions are detected along the filaments. Multiple velocity coherent substructures are present in both hubs, likely not yet reaching virial equilibrium.

16:00 Tea break

Coffee, tea and Devon cream tea (plain/fruit scone with clotted cream and strawberry jam)

16:50 Jonathan Henshaw (Liverpool John Moores University): Seeding the Galactic Centre gas stream: initial conditions for the formation of Young Massive Clsuters

The Central Molecular Zone of the Milky Way contains some of the most massive and dense molecular clouds and star clusters in the Galaxy, offering an important window on star formation under extreme conditions. Star and cluster formation in this extreme environment may be closely linked to the orbital dynamics of the gas, the three dimensional distribution of which has been subject to intense scrutiny for several decades. One of the most striking features of the CMZ, noted from the earliest studies, is the complex gas distribution in position-position-velocity (PPV) space. In this contribution, I will present our new systematic approach to studying the kinematics of dense gas in the central 250pc of the Galaxy, demonstrating how this has helped to accurately describe the {l,b,v} structure of the CMZ. I will demonstrate how this analysis can help to distinguish between the three geometries commonly cited within the literature to describe the 3-D structure of the CMZ. Finally, I will present the recent discovery of intriguing oscillatory patterns in the kinematic structure of the dense gas. Perhaps an observational sign-post of gravitational instabilities within the gas, this has, if confirmed, significant implications for understanding the formation of some of the most massive and dense molecular clouds within the Galaxy and may represent the earliest phases in a directly observable (absolute) time sequence for star formation.

17:10 Joao Alves (University of Vienna): Blue streams and local star formation

We construct a 3D map of the spatial density of OB stars within 500 pc from the Sun using the Hipparcos catalogue and find three large-scale stream-like structures that allow a new view on the solar neighborhood. The spatial coherence of these blue streams and the monotonic age sequence over hundreds of parsecs suggest that they are made of young stars, similar to the young streams that are conspicuous in nearby spiral galaxies. The three streams are 1) the Scorpius to Canis Majoris stream, covering 350 pc and 65 Myr of star formation history, 2) the Vela stream, encompassing at least 150 pc and 25 Myr of star formation history, and 3) the Orion stream, including not only the well-known Orion OB1abcd associations, but also a large previously unreported foreground stellar group lying only 200 pc from the Sun. The well-known nearby star-forming low-mass clouds, including the nearby T and R associations Lupus, Cha, Oph, CrA, Taurus, and various low-mass cometary clouds in Vela and Orion, appear in this new view of the local neighborhood to be secondary star formation episodes that most likely were triggered by the feedback from the massive stars in the streams. We find no evidence of an elliptical structure such as the Gould Belt, a structure we suggest is a 2D projection effect, and not a physical ring. We present Herschel data on Ophiuchus where we find that all protostars in Ophiuchus (97%) can be readily associated with a particular source of feedback in the region and that the Ophiuchus filaments (up to 20 pc long) are also formed by the feedback from massive stars, in contrast with the currently accepted filament formation scenario of colliding flows orthogonal to the filament axis. Finally, we do not find N-PDFs to be log-normal, but power-laws.

17:30 Emily Drabek-Maunder (Imperial College London): The JCMT Gould Belt Survey: Understanding the influence of molecular outflows on Gould Belt clouds

Using James Clerk Maxwell Telescope (JCMT) Gould Belt Survey data from CO J=3-2 isotopologues, we present a meta-analysis of the outflows and energetics of star-forming regions in several Gould Belt clouds. The majority of the regions are strongly gravitationally bound. There is evidence that molecular outflows transport large quantities of momentum and energy. Outflow energies are at least 20 per cent of the total turbulent kinetic energies in all of the regions studied and greater than the turbulent energy in half of the regions. However, we find no evidence that outflows increase levels of turbulence, and there is no correlation between the outflow and turbulent energies. Even though outflows in some regions contribute significantly to maintaining turbulence levels against dissipation, this relies on outflows efficiently coupling to bulk motions. Other mechanisms (e.g. supernovae) must be the main drivers of turbulence in most if not all of these regions.

17:50 Enrique Vazquez-Semadeni (RyA-UNAM): Core structure and evolution in globally collapsing molecular clouds

After a brief motivation for the scenario that molecular clouds are in a state of global and hierarchical gravitational collapse, consisting of collapses within collapses, I will discuss the evolution and structure of clumps and dense cores in numerical simulations of cloud formation within this scenario. The clumps exhibit a scaling relation of the form sigma_v^2/R ~ Sigma, where sigma_v is the velocity dispersion, R is the cloud “”radius””, and Sigma is the column density. This relation is similar to that observed for GMCs and massive star-forming clumps, suggesting that the global-collapse scenario correctly describes their internal structure. Concerning the evolution of dense cores,I will also discuss numerical simulations of the prestellar collapse of near-Jeans-mass cores embedded in a multi-Jeans-mass initially uniform background medium. The evolution of these cores closely traces the locus of both low- and high-mass observed dense core ensembles in an M_c/M_BE vs. M_c diagram introduced by Lada et al. (2008), where M_c is the core mass and M_BE is the Bonnor-Ebert mass at the mean density and temperature of the cores. The collapse proceeds in an outside-in fashion, which implies that infall speed estimates based on blue-excess line profiles may underestimate the actual velocities arising in the core.”

18:10 to 19:00 Poster session and drinks reception

The poster session will run from 18:10 to 19:00 and will include a glass of wine/soft drink and snacks. Posters will be in the Forum Street and on the mezzanine level. Don’t forget to visit the e-posters displayed on the Surface Tables in the Exploration Lab 2 (on the mezzanine level of the Forum).

Tuesday 23 August: Protostellar cores

08:30 Coffee/tea and mini Danish

Coffee and tea will be available in the Forum Street from 08:30.

08:50 Tim Harries and Chris Brunt: Notices and updates

Information and updates on the meeting programme and social events.

Session Chairs

Chairs: Simon Glover (morning), Enrique Vazquez (afternoon)

09:00 Kengo Tomida (University of Osaka): Theory review

In this talk I review recent progress in theoretical studies of formation and evolution of stars and disks in collapsing molecular cloud cores. I start from classical problems in the early phase of star and disk formation (i.e. until early Class 1 phase), such as the angular momentum problem, the magnetic flux problem, the magnetic braking catastrophe, the fragmentation crisis, driving of outflows, and so on. In particular, while the angular momentum problem and the magnetic braking catastrophe are now reconciled qualitatively, but they still remain as qualitative problems. Then I move to the later phase of star formation and discuss outstanding topics such as the luminosity problem, episodic accretion, and regulation mechanisms of star formation efficiency in the small scale in different mass regimes, among other things. Also, if time permits, I briefly review recent efforts on theoretical modeling and synthetic observations that enable us to directly compare theories and observations especially using ALMA. At the end I would like to summarize the remaining (and new) problems, (near) future directions, and (quite personal) perspectives.

09:40 Anaëlle Maury (CEA/Saclay): Observational review

While the physical processes regulating the formation and evolution of star-forming cores are believed to largely determine the properties of the resulting young stars, their study has been mostly limited to shallow- and low-resolution observations. The advent of Herschel and large (sub-)millimeter interferometers (ALMA, NOEMA) recently allowed to over-come these limitations, and carry out detailed and/or statistical studies of the cores physical structure and chemical composition, to finally unravel the complex interplay of processes at work to form stars from these cores. I will review recent observational results, showing how the combination of high angular resolution and unprecedented sensitivity allow to finely characterize critical properties such as the angular momentum content, infall rates, pristine disk properties and multiplicity fraction of the youngest star-forming cores.

10:20 Vera Könyves (CEA/Saclay): A census and properties of dense cores and filaments in the Aquila and Orion B cloud complexes

One of the main scientific goals of the Herschel Gould Belt survey ( is to elucidate the physical mechanisms responsible for the formation and evolution of prestellar cores in molecular clouds. Based on Herschel/SPIRE-PACS photometric data, we have recently identified a large sample of such cores in the Aquila (Könyves et al. 2015) and Orion B (Könyves et al., in prep.) molecular clouds.

Our Herschel observations also provide an unprecedented census of filaments in the nearby clouds and suggest an intimate connection between these filaments and the formation process of prestellar cores. We will compare and contrast some properties of the dense cores in the Aquila and Orion B complexes, such as their distributions in the filamentary background, masses, lifetimes, and formation thresholds.

In summary, our Herschel findings support a filamentary paradigm for the early stages of star formation, where the cores result primarily from the gravitational fragmentation of marginally supercritical filaments (cf. André et al. 2014, PPVI).

10:40 Alana Rivera-Ingraham (ESA): Extreme Star Formation in the Galaxy: The Herschel View

The Herschel Space Observatory has provided extensive datasets of unprecedented quality and coverage. The Archive covers regions in a wide range of physical and star-forming conditions across the Galaxy. Here we introduce the latests results from an ongoing large-scale project focused on investigating the processes driving star formation in the most extreme conditions. Compact sources and filamentary structures have been identified and extracted from Herschel maps targeting the most active and densest regions of the Galactic Plane, comprising vigorous, high-mass star and cluster formation. Each structure was characterised according to its physical and environmental properties, ongoing star formation and evolutionary state. The star-forming conditions of these fields have been compared with those derived from the most diffuse, high-galactic latitude fields with none or weak star forming events. Our extensive study provides new evidence in favour of the critical role of external and environmental factors in the overall star formation process, and how these factors contribute to explaining the radically different star formation events in our Galaxy, from isolated low-mass star formation to massive clusters. This evidence will be summarised and discussed in context with theoretical models of cloud evolution.

11:00 Coffee break

Coffee, tea and cookies

11:50 Isabelle Ristorcelli (IRAP / CNRS UPS Toulouse): A statistical analysis of polarized dust emission in the environment of Planck Galactic cold clumps

Magnetic fields are considered one of the key physical agents that regulate star formation, but their actual role in the formation and evolution of dense cores remains an open question. Polarized dust continuum emission is particularly well-suited to probe the magnetic field structure in the dense, cold interstellar medium. Such observations also provide tight constraints on the efficiency of dust alignment along magnetic field lines, which are needed to properly infer the magnetic field properties from observations. With the Planck all-sky survey of dust submillimetre emission in intensity and polarization, we can investigate intermediate spatial scales in the hierarchy of star formation, between global molecular cloud measurements and studies of individual prestellar cores. Planck further enables a statistical analysis of the polarization properties of clumps. We have recently built the first all-sky catalogue of Galactic Cold Clumps (PGCC, Planck collaboration XXVIII 2015), a fraction of which we have studied in detail with our Herschel Key Programme ‘Galactic Cold Cores’. The sources cover a broad range in physical properties and correspond to different evolutionary stages in the star formation process, from quiescent starless clumps and nearby cores to young protostellar objects. I will present new results from our analysis of the polarized 353GHz Planck data for the PGCC sources. In particular, we have studied the variation of the polarization fraction and angle, and the relative orientation between the B-field and the clump elongations. We have also analysed the magnetic field morphology and compared it to structures (filaments, striations) traced at higher resolution with Herschel in the environment of PGCC sources, searching for evolutionary signatures. Finally, I will present a comparison of our results with predictions from MHD simulations that include radiative transfer and the dust radiative torque alignment mechanism.

12:10 Jenny Hatchell (University of Exeter): Taking the temperature of local star-forming clouds with the JCMT Gould Belt survey

Radiative heating by recently-formed (or forming) stars potentially provides a regulatory mechanism for star formation, reducing fragmentation and increasing protostellar masses. I will report on work carried out by the JCMT Gould Belt survey team on the contribution that SCUBA-2 data makes to measuring dust temperatures, on its own and in combination with Herschel measurements.

12:30 Sarah Sadavoy (MPIA): Dust Emissivity in OMC 2/3: Linking the Diffuse Cloud to the Dense Cores

Planck observations have found relatively uniform values for the dust emissivity index of beta ~ 1.8 for diffuse cloud material. Nevertheless, stars form within smaller-scale, denser environments where the dust grains are expected to grow in size, form icy mantles, and subsequently have distinct dust emissivities compared to the diffuse cloud. To explore this expected dust grain evolution, we combined Herschel observations with long-wavelength 2 mm data across a ~ 2 pc long, continuous section of OMC 2/3 at 15000 AU (0.08 pc) resolution. We determine beta and reconstruct simultaneously the filtered-out large-scale emission at 2 mm in this analysis. We find that beta ~ 1.7-1.8 provides the best fit across most of OMC 2/3 with only one protostellar core showing significantly lower values of beta (~1.4). The consistency in beta between the cloud-scale Planck data and our core-scale analysis for OMC 2/3 supports the common assumption of fixed beta indices used ubiquitously in the conversion of (sub)millimeter emission to mass in dense star forming regions. If this consistency is demonstrated in other clouds, then significant changes to dust grain properties may only be apparent on smaller (sub core) scales.

12:50 Chris Wright (UNSW): Magnetic fields via thermal infrared polarimetric imaging

Aligned dust grains within a magnetic field can induce polarization of thermal infrared radiation via emission, absorption or both. The position angle of polarization is directly related to the magnetic field projected on to the plane-of-the-sky. We will present new sub-arcsecond polarimetric imaging observations of embedded Young Stellar Objects made with the CanariCam mid-IR camera/spectrometer on the 10.4 m Gran Telescopio Canarias. By obtaining images across the 10 micron silicate band we can separate emissive and absorptive components of polarization and thus obtain two magnetic field directions, i.e. those within ‘warm’ and ‘cold’ regions of the target. For sources which are also extended we can then obtain a 3-d picture of the magnetic field.

13:10 Lunch break

A buffet lunch with fruit juice, tea and coffee.

14:40 Benoît Commerçon (CRAL ENS Lyon): Outflows and disks formation in massive cores collapse

Discs and outflows are observational features of star formation. While discs and outflows formation is becoming increasingly constrained thanks to radiation magnetohydrodynamics models and observations in the context of low-mass star formation, it is not the case for massive star formation. I will present results of massive magnetized dense core collapse simulations including radiative feedback and ambipolar diffusion. We use the adaptive-mesh-refinement code RAMSES (Teyssier 2002) which includes resistive MHD (Fromang et al. 2006, Masson et al. 2012) and radiative transfer (Commerçon et al. 2011, 2014). I will show how magnetic fields and radiative feedback work together to launch outflows. I will study the formation and properties (early evolution and fragmentation) of the disc around the massive protostars, comforting the standard accretion-discs scenario in the context of magnetised core collapse. Last I will also highlight the limits of ideal MHD with respect to magnetic flux redistribution and outflow formation.

15:00 Yusuke Aso (University of Tokyo): ALMA observations of Keplerian disks around protostars

Keplerian disks around young stars play essential roles in star and planet formation. Even though disks around T Tauri stars have been studied well in the last two decades, the disk formation process prior to T Tauri phase is still not well understood. This is because observations of disks around embedded protostars have been limited. Such a situation, however, has been undergoing a dramatic transformation in the ALMA are.

To understand the disk formation around protostars in detail, we have been observationally studying 8 protostars (6 Class 0 and 2 Class I) with ALMA in mainly C18O (J=2-1) line and 1.3 mm continuum emissions at sub-arcsec resolutions. All the sources show velocity gradients in C18O and detailed analyses using PV diagrams revealed that 4 of them show Keplerian rotation, which is clearly distinguished from rotation of the envelopes. Class 0 protostars tend to have less detectable disks, with lower specific angular momenta. It would be, therefore, suggested that our series of ALMA observations witness disk formation and growth during the protostellar evolution although the results are not statistically significant yet. Dynamical stellar masses estimated from the identified Keplerian rotation are compared with infall motions in their envelopes, finding that some of the infall velocities are significantly slower than the free-fall velocities yielded by their dynamical stellar masses.

The continuum visibility of L1527 IRS, which has an edge-on disk, is fitted by modified disk models without any annulus averaging. This analysis is particularly important for non-axisymmetric structures, such as a disk. The best model suggests that the density of dust is discontinuously enhanced at the boundary between the disk and the envelope. Additionally, the scale height of the disk can be explained by hydrostatic equilibrium. These results clearly demonstrate that ALMA observations can not only search for but also characterize in detail disks around protostars.

15:20 Ben Lewis (University of Exeter): Shaken and stirred - the role of turbulence, magnetism and radiation in the formation of protostars

Expanding on Lewis, et al (2015) and (2016, submitted), which considered only an ideal MHD simulations of the collapse of molecular cloud cores without turbulence, we now use radiation magnetohydrodynamical calculations to explore how the physics of turbulence, magnetism and radiation influence the formation of protostars. We find that the gravitational collapse proceeds in a very different manner in cores with transonic turbulence compared to those with subsonic turbulence across a variety of field geometries and structures. Transonic (i.e. ~ Mach 1) cores are highly disrupted by the turbulent motion which also suppresses the formation of bipolar jets from the first hydrostatic core. Cores with subsonic turbulence still contain a jet, albeit without the symmetry previously seen in non-turbulent calculations and, depending on the magnetic field strength, form pseudo-discs. The inclusion of radiative transfer into the calculations promotes the formation of large discs, compared to the very small and dense discs produced by the MHD only calculations.

15:40 Neil Vaytet (University of Copenhagen): A grid of 1D low-mass star formation collapse models: not all dense clouds form first Larson cores

Stars form within large turbulent molecular clouds from density fluctuations which become gravitationally unstable. Numerical simulations of star formation are becoming ever more sophisticated, incorporating new physical processes in increasingly realistic setups. These models are being compared to the latest observations through state-of-the-art synthetic renderings that can identify the different chemical species present in the protostellar systems. The chemical evolution of the interstellar and protostellar matter is a very active field of research, with more and more chemical databases and reaction solvers becoming available online to the community.

16:00 Tea break

Coffee, tea and Devon cream tea (plain/fruit scone with clotted cream and strawberry jam)

16:50 Yusuke Tsukamoto (RIKEN): Bimodality of Circumstellar Disk Evolution Induced by the Hall Current

We investigate the effect of the Hall current term on the formation of the circumstellar disk using three-dimensional simulations. In our simulations, all non-ideal effects, as well as the radiation transfer, are considered. We found that the size of the disk is significantly affected by a simple difference in the inherent properties of the prestellar core, namely whether the rotation vector and the magnetic field are parallel or anti-parallel. In the former case, only a very small disk (\lt 1 {AU}) is formed. On the other hand, in the latter case, a massive and large (\gt 20 {AU}) disk is formed in the early phase of protostar formation. Since the parallel and anti-parallel properties do not readily change, we expect that the parallel and anti-parallel properties are also important in the subsequent disk evolution and the difference between the two cases is maintained or enhanced. This result suggests that the disk size distribution of the Class 0 young stellar objects is bimodal. Thus, the disk evolution can be categorized into two cases and we may call the parallel and anti-parallel systems Ortho-disk and Para-disk, respectively. We also show that counter-rotating envelopes against the disk rotation appear with a size of ≳ 200 {AU}. We predict that the counter-rotating envelope will be found in the future observations.

17:10 Oliver Lomax (University of Cardiff): Core fragmentation and protostellar multiplicity

Using an ensemble SPH simulations, we follow the evolution of prestellar cores as they collapse and fragment into protostars. The initial conditions for these simulations are constructed to match the observed properties of the cores in Ophiuchus. The protostars that form match the statistics of observed young protostars (IMF and multiplicity statistics, including triples, quadruples, quintuples and sextuples) but only if (i) radiative feedback from protostars is episodic, and (ii) the turbulent velocity field has a significant solenoidal component. A majority of protostars are attended by significant discs, but in multiple systems these discs are often poorly aligned with one another and/or the binary orbit, reflecting the stochastic nature of the accretion flows that feed material into the centre of a core. We also present synthetic spectra and images of multiple systems embedded in protostellar cores. These are calculated using a new Smoothed Particle Monte Carlo Radiative Transfer algorithm.

17:30 Joana Oliveira (University of Keele): Herschel Spectroscopy of Massive Young Stellar Objects in the Magellanic Clouds

As the nearest gas-rich galaxies, the Large and Small Magellanic Clouds (LMC and SMC) offer the exciting opportunity to bridge the gap between star formation processes on large galaxy-wide scales and on the small scales of individual Young Stellar Objects (YSOs). These metal-deficient galaxies also provide an invaluable window into the star formation process at low metallicity, a region in the parameter space that remains relatively unexplored. I present the results of spectroscopic observations obtained with PACS and SPIRE/FTS onboard the Herschel Space Observatory. The sample of massive SMC and LMC YSOs is well characterised at near- and mid-IR wavelengths, and includes both deeply embedded sources and compact HII regions. The strengths of key gas-phase cooling species ([OI], [CII], H2O, CO, OH) are measured as probes of the physical conditions of the gas surrounding the YSOs. This analysis directly probes the potential metallicity effect, since it quantifies the relative luminosities of the species that promote envelope cooling and thus constrain the cooling budget of the YSO envelopes. The results indicate that while [OI], [CII] and CO are easily and widely detected, H2O and OH may be weak or absent in most YSOs. When compared with massive Galactic YSOs, the Magellanic YSOs clearly exhibit higher photoelectric efficiency (measured by the ratio of line emission to total IR flux), while showing similar [OI]/[CII] ratios; in terms of standard PDR models this suggests a lower G_0/n ratio. The CO ladder is used to constrain the density and temperature of the emitting gas. The spatial extension and morphology of the main emission lines is used to explore the interplay and feedback of the massive YSOs with their environments. I will place such results in context by comparing SMC, LMC and Galactic samples, in order to constrain potential metallicity effects on the star formation process.

17:50 Joseph Mottram (MPIA): Fragmentation and disk formation in high-mass star formation

How do the composition and kinematics of massive star forming environments affect the properties of the high-mass protostars that are forming in them? How is the degree of fragmentation and mass on disk-like scales related to the larger reservoir of dust and gas that they reside in? Are the 10^-4 Msol/yr and higher mass accretion rates and/or flattened envelope structures required by many current theories to form the most massive stars seen in real systems? Does feedback have more of an impact on large or small scales and what is the size (and shape) of the mass reservoir systems forming massive stars? These are all key questions to developing a full, comprehensive and prescriptive theory of how the most massive stars form. What is more, answering them requires multi-scale observations of both the continuum and molecular lines. I will present early results from the CORE NOEMA large program, which is designed to answer such questions by combining observations with multiple PdBI configurations and the IRAM 30m of 20 high-mass star forming regions with L> 10^4 Lsol. As such we have one of the largest datasets to date of high mass star forming regions with sensitivity to emission on spatial scales from ~0.4 pc to <1000 AU, ideal for tackling these fundamental questions.

19:00 Barbeque at Holland Hall

There will be a BBQ for all delegates out on the terrace of Holland Hall. Your conference bag includes a token that you can exchange for a free drink from the cash bar.

Wednesday 24 August: Splinter sessions

08:30 Coffee/tea and mini Danish

Coffee and tea will be available in the Forum Street from 08:30.

09:00 Early-career session (Alumni Lecture Theatre, Organisers: Chris Brunt and Tim Harries)

09:00 Sam Geen (CEA Saclay): Feedback in Molecular Clouds

I present work done using radiative magnetohydrodynamic simulations and analytic theory to better understand the behaviour of feedback processes in turbulent, self-gravitating molecular clouds. In particular I focus on the role of ionising radiation from massive stars in shaping these clouds and the environment into which supernovae subsequently occur. Motivated by the simulations I present a set of analytic models that reproduce the key features of the simulated HII regions and set physical limits on the expansion of HII regions and supernova remnants in cloud environments.

09:15 Jan Orkisz (IRAM/LERMA): Turbulence versus star formation efficiency in Orion B

Star formation in molecular clouds is controlled by many parameters, including gravity, magnetic fields, stellar feedback… The nature of turbulence also plays a key role: compressive motions, as opposed to solenoidal motions, can trigger the collapse of cores, or mark the expansion of Hii regions. Our study focuses on the Orion B molecular cloud, which is extensively observed with the IRAM-30m telescope in a hyperspectral survey covering the 84-115GHz frequency range. At a distance of 400pc, its south-western edge is an ideal laboratory to study star formation: it contains triggered and spontaneous star-forming regions, PDRs, UV-shielded cold-cores… The goal of the survey is to study Orion B with various approaches, such as chemistry, dynamics, statistics, simulations, etc. to make this dataset into a template for observations of galactic and extragalactic GMCs. In this presentation, we show how to observationally derive the fractions of momentum density contained in the solenoidal and compressive modes of turbulence in Orion B, using the 13CO(1-0) data-cube. We successfully implemented a statistical method, developped by Brunt & Federrath (2014) and used so far only on simulations. This allows us to retrieve 3-dimensionnal quantities from the projected quantities provided by the observations, yielding an estimate of the compressive vs. solenoidal ratio in various regions of the cloud. The Orion B molecular cloud being highly supersonic (mean Mach number ~8), the fractions of motion in each mode are close to equipartition. However, the cloud’s motions are on average mostly solenoidal, which is consistent with its star formation rate, the lowest among local GMCs. On the other hand, the motions around the main star-forming regions (NGC2023 and NGC2024) prove to be strongly compressive. We conclude that the compressive or solenoidal motions are indeed correlated to the SFE, which opens a new possibility for star-formation diagnostics in galactic molecular clouds.

09:30 Gwen Williams (University of Cardiff): What can filament dynamics tell us about core formation?

Interstellar filaments represent a key stage in star formation. As they become gravitationally unstable, the densest filaments fragment into cores. The link between filament, core and star formation is one of the main issues of modern astronomy. Infrared dark clouds (IRDCs) help shed light on the subject as they contain the mostly pristine fingerprints of the initial conditions of star formation. SDC13 in particular is an IRDC system of 4 parsec-long filaments, lies 3.6kpc away in the galactic plane, and contains 1000Msun of material. From N2H+(1-0) IRAM 30m data at 27’’ resolution, global longitudinal velocity gradients were observed, corresponding to an increase in velocity width at the centre, which we interpret as gas flows along the filaments fuelling star formation. However, with 0.5pc resolution, our single-dish data is not enough to study the finer scale link between filament fragmentation and core formation. Here we present new JVLA 5’x5’ NH3(1-1) and NH3(2-2) mosaics of SDC13 at 4’’ resolution, probing 0.07pc scales. The ammonia column density map reveal different fragmentation properties for each filament, evidenced by varying collapse timescales and spacings of the cores. By performing hyperfine structure fitting, we resolve stark differences in the velocity field as well, with longitudinal velocity gradients along one filament, and radial gradients across the other. Put together, we interpret these differences as two distinct modes of fragmentation, possibly stimulated by differences in the filaments’ local environment. Also, 2/3 of the starless JVLA cores show peaked velocity dispersion at their centres, contrary to that seen in nearby star forming regions. We believe these are signatures of the fragmentation process itself, indicating the accumulation of gas being accreted into core like structures. This local increase of dynamic pressure could prevent further fragmentation, and contribute to the formation of super-Jeans cores.

09:45 Joseph Booker (University of Toledo): HST Scattered Light Imaging of Orion Protostars: Do Outflows Halt Infall?

A long standing question in the study of protostellar collapse is what halts the infall of a core onto a central protostar. Is the core eventually exhausted by infall, or does feedback from accretion-driven outflows disperse the core? One of the best tracers of the impact of the outflow are the observed cavities carved into the cores. We present a systematic study of near-infrared HST NICMOS+WFC3 1.6μm images, mapping light scattered by dust grains in collapsing cores around low mass protostars with 80 AU resolution. These images are a component of HOPS, the Herschel Orion Protostar Survey, a multi-observatory program designed to obtain 1–870μm photometry, spectroscopy and imaging of a large sample of protostars in the Orion molecular clouds. We map the structure of the outflow cavities for 30 sources by applying a custom edge detection technique to the scattered light images and to radiative transfer models with known cavity geometries. We constrain the shape of the cavities and estimate the fractional volumes of the collapsing cores dispersed by the outflows. We do not find evidence that outflow progressively grow through the Class I phase and question whether feedback plays a major role in dispersing the core, halting infall.

10:00 Bilal Ladjelate (CEA Saclay): Star-formation in the Ophiuchus Molecular Cloud: Similarities and diversity

Our understanding of star formation has greatly advanced in the past 10 years thanks to the help of large photometric multi-wavelength surveys. In particular, the Herschel Gould Belt Survey (André et al. 2010) represents a significant step forward towards a better understanding of the processes happening in nearby molecular clouds. As part of the HGBS, extensive submillimeter continuum images of the Ophiuchus Molecular Cloud (L1688, L1689 and L1709) were produced. A deep census of both prestellar cores and young protostars was obtained using the multi-scale, multi-wavelength source extraction algorithm, getsources (Men’shchikov et al. 2012). The advantage of Herschel is to observe at wavelengths covering the peak of the spectral energy distributions (SEDs) of young protostars and prestellar cores with high sensitivity range. Among the starless cores detected with Herschel, the densest objects are gravitationally bound and can be considered prestellar in nature. In addition to these prestellar cores, Herschel also detects very low-mass unbound cores, which may be transient structures. We found approximately 250 candidate prestellar cores, including 173 with a robust classification Nearly all (99%) of detected prestellar cores are found in zones at A_V ≥ 8, and 8% of them are detected in filaments with column densities above 5 x 10^21 H_2 .cm^-2 These filaments are ubiquitous structures in star-forming regions (André et al. 2014) and their correlation with the detection of prestellar cores is a clue to their importance in the early stages of star-formation in a region not previously known to be filamentary. Harbouring low-mass star formation, at 140 pc, the Ophiuchus star-forming region is a very interesting environment to study a rich sample of prestellar cores in very different environments, L1689 being much less active than L1688, but yet seemingly being in the same physical conditions.

10:15 Coffee break

Coffee/Tea and cookies will be served in the Forum Street.

10:45 Josefa Grossschedl (University of Vienna): Resolved maps of Star Formation Rate and Efficiency in Orion A

The Orion A molecular cloud harbors the closest regions of massive star formation hosting a rich population of YSOs mostly still associated with the cloud. The region is a benchmark for studying star formation and therefore it is critical to have the most reliable and complete sample of the young stellar population. In this work we present a refined catalogue of Young Stellar Objects (YSOs) in Orion A, making use of a new high-resolution, complete, near-infrared imaging survey with VISTA of Orion A (VISION project), complemented with archival data (Spitzer, WISE, 2MASS, XMM- Newton). The new VISTA data allow us to rule out about 5% contaminants in previous samples, mainly galaxies and bright nebulae (e.g., Herbig Haro objects), and re-classify also about 5% of the previously known YSOs. We used mid-infrared data from WISE for areas not covered by Spitzer to get a more complete census and to determine the spatial distribution of YSOs in Orion A in a wide field. This allowed us, for the first time and in a global manner, to construct a map of Star Formation Rate across the entire complex. In connection with the Herschel dust column density map we will further derive a map of Star Formation Efficiencies.

11:00 Steve Mairs (University of Victoria): How Do Protostars Assemble Mass? A Sub-Millimetre (JCMT) Variability Survey of Deeply Embedded Protostars

Low mass stars form via gravitational collapse in the coldest and densest regions of molecular clouds. Most embedded protostars found in these regions, however, are observed to have accretion luminosities which are an order of magnitude too faint to be explained by steady state accretion. One solution to this problem is to introduce episodic accretion phases wherein the protostar undergoes long, quiescent periods interspersed by bursts of rapid growth. The amplitudes of these accretion bursts are constrained on thousand year and longer timescales and are usually assumed to be driven by gravitational instability in the outer disk. Currently, shorter timescale variations are unconstrained by the models and observations. These timescales, however, should probe accretion processes within the inner disk. In this talk, I will present results from the first six months of the JCMT Transient Survey, an observational program designed to constrain the variability in young, deeply embedded protostars detected in eight fields within the Gould Belt (OMC2/3, NGC 2024, NGC 2071, NGC 1333, IC348, Ophiuchus, Serpens Main, and Serpens South). Observations of each of these regions are taken monthly and will continue for three years, yielding a data set for both variability studies and, in the end, the deepest sub- millimetre observations of each of these regions to date. I will also connect these new results with observations taken by the JCMT Gould Belt Legacy Survey, presenting a variability analysis of these regions over ~4 year timescales. For now, within each individual observation we are able to achieve better than 10% relative uncertainty in source brightness. We anticipate, however, achieving an uncertainty better than 5% in the near future through improved reduction and analysis techniques. Finally, I will discuss two ancillary projects currently underway using ALMA and SOFIA to further constrain the variability of deeply embedded protostars on short timescales.

11:15 Dominika Boneberg (University of Cambridge): The midplane conditions of protoplanetary discs

The mass of protoplanetary discs in gas is a quantity of great interest for assessing their planet formation potential. Disc gas masses are however traditionally inferred from measured dust masses by applying an assumed standard gas to dust ratio of 100. Here we present a novel approach to study the midplane gas by combining modelling of the spectral energy distribution (SED), CO snowline observations and ALMA C18O line emission. All of the modelling steps are crucial to break degeneracies in the parameter space. We apply the technique to the disc around the Herbig Ae star HD 163296, with particular focus on the regions within the CO snowline radius (90 au). Our models unambiguously determine the C180 mass within the CO snowline location and favour a notably low gas to dust ratio (g/d~20). With current and upcoming ALMA C18O data, this technique can be applied to a range of discs and opens up the possibility of measuring gas and dust masses in discs without making assumptions about the gas to dust ratio.

11:30 Julia Roquette (Universidade Federal de Minas Gerais): Near-Infrared variability of disk-bearing stars in Cygnus OB2

Photometric variability is one of the main characteristics of Young Stellar Objects. Exploring its particularities in different wavelengths may provide insights on the ongoing physical process in such objects. In this study, we explored the occurrence and main characteristics of near-Infrared variability in disk- bearing stars in the young OB association Cygnus OB2, 1.4 kpc away from the Sun. We performed a JHK photometric monitoring of the central 0.78 squared degrees of CygOB2, using data observed with the wide-field camera (WFCAM) of the UK Infrared Telescope on Mauna Kea (UKIRT), covering 112 nights spanning 217 days. We explored the variability signatures in a sample of disk-bearing stars in the association. We investigated their variability time scale, their light-curve morphology, and their variations in the color-color and color-magnitude diagrams for JHK filters. We crossed our data with other surveys in the same region, as the Spitzer Legacy Survey of the Cygnus-X Region, the INT Photometric H-alpha Survey of the Northern Galactic Plane (IPHAS) and the Chandra Cygnus OB2 Legacy Survey. We investigated the correlations between our variability characterization and the diagnoses of disk emission and disk accretion activity. We aim to present in this talk our results regarding the variability characterization of such disk- bearing stars, and how they correlate with disk emission and disk accretion activity diagnoses.

09:00 Ages and timescales of young stars (Seminar Room 6, Organiser: Cameron Bell)

A splinter session dedicated to the ages and timescales of young stars. Further information concerning this session, including topics to be discussed and details regarding the submission of contributions, can be found on the session webpage.

09:00 Planet Formation Imager (Seminar Room 4, Organiser: Stefan Kraus)

09:00 John Monnier: Introduction to Planet Formation Imager Project

Following now two decades of work to discover exoplanets, we are approaching a clear understanding of the demographics of exoplanets around solar-type stars in our galaxy. Despite this trove of new data, we lack predictive theories to explain these observations due to the complex non-linear and dynamic processes that lie at the heart of the planet formation process. Progress will require more than the current generation of adaptive-optics coronographs and more than even ALMA imaging in order to peer into planet-forming disks at a range of evolutionary stages with sub-AU spatial resolution. Indeed, long-baseline infrared interferometry will be essential to bring the needed angular resolution and wavelength coverage to see planets forming in situ. The aim of the Planet Formation Imager” (PFI) project is to develop the roadmap for the construction of a new near-/mid-infrared interferometric facility that will be optimized to unmask all the major stages of planet formation, from initial dust coagulation, gap formation, evolution of transition disks, mass accretion onto planetary embryos, and eventual disk dispersal. PFI will be able to detect the emission of the cooling, newly formed planets themselves over the first 10–100 Myrs, opening up both spectral investigations and also providing a vibrant look into the early dynamical histories of planetary architectures. Here I will introduce the Planet Formation Imager (PFI) Project ( and set the stage for a stimulating splinter session where work from the science working group and technical working group will be highlighted. Planning for PFI requires strong connections with current active researchers to both craft the core science drivers and to provide realistic simulated young disks and planetary systems for technical evaluation by the instrumentalists on the project.

09:15 Stefan Kraus: The Science Vision for PFI

This talk will outline the science driver for the Planet Formation Imager (PFI) and the key requirements that the PFI Science Work Group has derived. We make the case that a break-through in angular resolution imaging capabilities is required in order to unravel the processes involved in planet formation. PFI will be optimised to provide a complete census of the protoplanet population at all stellocentric radii and over the age range from 0.1 to about 100 Myr. Within this age period, planetary systems undergo dramatic changes and the final architecture of planetary systems is determined. Our goal is to study the planetary birth on the natural spatial scale where the material is assembled, which is the “Hill Sphere” of the forming planet, and to characterise the protoplanetary cores by measuring their masses and physical properties. We investigated the observational characteristics of these young protoplanets as well as the migration mechanisms that might alter the system architecture. We simulated the imprints that the planets leave in the disk and study how PFI could revolutionise areas ranging from exoplanet to extragalactic science. This talk aims to provide an overview about the breath of science that can be pursued with PFI and serves as introduction to the other science talks in the session that will focus on specific aspects.

09:40 Mike Ireland: A Baseline Design and Technical Roadmap for the PFI

After 2 years of efforts on the Planet Formation Imager concept, a “baseline” design is taking shape as a 1-2km maximum baseline, ~12 telescope array with telescope diameters in the ~3m range. In the first instance, such an array would use direct photon detection in a largely conventional interferometer design, with an expansion option for heterodyne detection at a later stage. I will present this technical vision for the PFI concept on behalf of PFI’s Technical Working Group, focusing on the more novel key technologies and requirements that are needed to achieve the key science goals. These science goals include detecting emission at temperatures as cool as the ice line, detecting Jovian planets up to a 100 Myr age, and resolving structures smaller than a forming Jovain planet’s hill sphere. Based on these key requirements, I will define a cost envelope range for the design, highlight where the largest uncertainties lie at this conceptual stage and where prototyping efforts are needed to reduce risk in a more robust costing of PFI.

10:05 Catherine Espaillat: Detecting and characterising protoplanets with PFI

This talk will summarise the work of our PFI working group on protoplanet detection and characterisation. I briefly review our knowledge about the observational characteristics of protoplanets, considering both the thermal emission of the forming planet and of the viscously heated circumplanetary disk. We will discuss potential line tracers to detect the accretion signatures on the planet and derive sensitivity requirements for detecting protoplanets, both in continuum and line emission.

10:50 Johan Olofsson: Late stages of planetary system formation investigated with PFI

This talk will summarise the work of our PFI working group on protoplanet detection and characterisation. I briefly review our knowledge about the observational characteristics of protoplanets, considering both the thermal emission of the forming planet and of the viscously heated circumplanetary disk. We identify the most promising line tracers to detect the accretion signatures on the planet and derive sensitivity requirements for detecting protoplanets, both in continuum and line emission.

11:25 Sebastian Hoenig: Extragalactic science with PFI

This talk will give an overview of the PFI working group on extragalactic science. I will outline the pioneering work that is done with existing interferometers on AGN and discuss how PFI can probe the crucial physical process in supermassive black hole growth and its relation to the galaxy that are currently out of reach. Another intriguing application of PFI is in cosmology, where the recently demonstrated “dust parallax” measurement method promises direct measurements of the distance to AGN out to a few hundred Mpc, providing a new and independent way of determining the the fate of the universe.

09:00 Computational Star Formation (Seminar Room 5, Organiser: Simon Goodwin)

This session will be devoted to advances in numerical simulation of star formation and protostellar discs. There will be talks on both numerical methods as well as results of simulations.

09:00 Daniel Seifried (University of Cologne)
09:15 Munan Gong (Princeton University)
09:30 Rachel Spowage (Cardiff University)
09:45 Rajika Kuruwita (ANU)
10:00 Claire Esau (University of Sheffield)

10:00-10:30 Coffee

10:30 Duncan Forgan (University of St. Andrews)
10:50 Discussion ‘Where next for computation?’

09:00 Measuring temperatures and densities in star forming regions (Seminar Room 10, Organiser: Jenny Hatchell)

Rationale: Star formation theories predict temperatures and densities for clouds, filaments and cores. Neither temperature nor density is a direct observable. This session aims to bring together researchers interested in extracting these physical properties from observations (e.g. continuum surveys or molecular lines) to discuss useful datasets and methodology (e.g. Bayesian model fitting, radiative transfer models).

9:00-10:30 short talks, each finishing with a summary slide showing the main result(s) and a ‘wish list’ - what the speaker would like to be able to do with his/her method/data/region but doesn’t know how to achieve. Questions at this point will be limited to clarifications.

09:00 Jenny Hatchell (University of Exeter): Introduction

09:10 Yao-Lun Yang (University of Texas): Modeling the Structure of a Class 0 Protostar, BHR71, with 3-D Dust Radiative Transfer Simulations

09:25 Fernando Olguin Choupay (University of Leeds): The physical properties of the prototypical MYSO GL 2591

09:40 Jared Keown (University of Victoria): The Green Bank Ammonia Survey

09:55 Jorge Abreu-Vicente (MPIA Heidelberg): Fourier-space combination of Planck and Herschel images

10:10 Nadia Murillo (Leiden University): The role of temperature and gas heating in multiple stellar system formation”

10:30 Coffee break

11:00-12:00 2-minute presentations of ’wish lists’ from relevant main session talks (Joe Mottram, Katherine Johnstone, Emily Drabek, Jan Forbrich, & Jenny Hatchell), followed by open discussion based on the issues raised.

12:00 Packed lunches available for pickup from Holland Hall

Packed lunches can be collected from Holland Hall from 12:00. Please note that since they will no longer be refridgerated the sandwiches should be eaten within two hours of collection.

13:00 Social excursions leave from Holland Hall

Please make sure you are wearing suitable clothing, including sturdy shoes for the Dartmoor and Jurassic Coast walks and a waterproof jacket if needed. The ground at Pebblebed Vineyard may also be wet and uneven.

Transport and associated arrangements have been made according to the number of delegates registered for the tours. We therefore ask you to please remain with your chosen event and not attempt to join another tour.

Thursday 25 August: Protostars and clusters

08:30 Coffee/tea and mini Danish

Coffee and tea will be available in the Forum Street from 08:30.

08:50 Tim Harries and Chris Brunt: Notices and updates

Information and updates on the programme and social events.

Session Chairs

Chairs: Mark McCaughrean (morning), Joao Alves (afternoon)

09:00 Nick Wright (University of Keele): Observational review

Over the last few decades our understanding of the properties of young stars and clusters has changed dramatically thanks to many wide-field observations and surveys across the electromagnetic spectrum. Infrared, X-ray and emission-line surveys have greatly increased our census of known pre-main-sequence stars, allowing us to study their distribution and clustering, measure the initial mass function and multiplicity in different environments, and study the ages and star formation histories of different regions. The rise in time domain surveys has also improved our view of episodic accretion and variability in pre-main-sequence stars, while high-resolution imaging has allowed us to study jets and outflows from such objects that exert feedback on their surroundings. In this talk I will review the current observational picture of the properties of young stars and clusters, with a particular focus on how wide-field surveys have contributed to our understanding of this critical phase of stellar lives.

09:40 Stella Offner (Umass Amherst): Theory review

Star formation is governed by the complex interplay of various physical forces, including turbulence, gravity and magnetic fields. In addition, neighboring stars greatly influence each other and their natal cloud by injecting energy into their surroundings (“feedback”). This interaction creates strong coupling between physical processes acting over a broad range of scales. Numerical simulations play an essential role in investigating the complex, nonlinear physics of star cluster formation. In this talk, I will summarize the current state-of-the-art in numerical simulations. I will discuss how numerical results have shaped our understanding of star formation and how different processes impact fundamental quantities like the stellar initial mass function, stellar multiplicity and star formation efficiency.

10:20 Richard Parker (Liverpool John Moores University): The initial conditions of star formation from spatial and kinematic substructure

One of the largest uncertainties in star formation is the initial density and velocity structure of young (1 - 10 Myr) star-forming regions, clusters and associations. Quantifying the initial or maximum density of a region is crucial; a dense region will disrupt the orbits or destroy planetary systems and stellar binaries, and photoevaporate or truncate protoplanetary discs through interactions with massive and low-mass stars. However, the present-day density does not strongly constrain the initial density due to two-body relaxation, which causes a region to rapidly expand and lowers the density by several orders of magnitude within a few Myr. In this talk, I will show that a range of structural diagnostics can constrain both the initial density, and the initial virial ratio of a star-forming region. I will finish by demonstrating the further constraints that Gaia and associated ground-based surveys (e.g. GES) will place on this problem in the near future.

10:40 Isabelle Baraffe (University of Exeter): Consistent models of accretion history and multi-dimensional structure of accreting young stars.

I will present new results for pre-Main sequence and early brown dwarf evolutionary models accounting for the effect of early accretion history. First, I will present self-consistent numerical simulations fully coupling numerical hydrodynamics models of collapsing prestellar cores and evolutionary models of the central protostar or proto-brown dwarf. I will in particular analyse the main impact of consistent accretion history on Li depletion and present a new result regarding the effect of accretion on Li depletion. I will also present the first attempt to describe the multi-dimensional structure of accreting young stars based on fully compressible time implicit multi-dimensional hydrodynamics simulations. I will discuss the relevance of assumptions and treatments of accretion used in 1D stellar evolution codes.

11:00 Coffee break

Coffee, tea and cookies

11:50 Laura Venuti (INAF): Variety of accretion regimes in the young open cluster NGC 2264

Pre-main sequence (PMS) stars are surrounded by disks throughout the first few Myr following their birth. The star-disk interaction is governed by the magnetospheric accretion process. In this talk, we present the results of an extensive u-band accretion survey of the 3 Myr-old open cluster NGC 2264. Performed at CFHT/MegaCam as a part of the CSI 2264 international campaign, the survey provided simultaneous UV+optical photometric monitoring over two full weeks for about 750 young cluster members (of which about 45% have disks). We use the diagnostics of the UV excess, measured over the reference flux level defined by non-accreting members, to investigate accretion properties over the stellar mass range 0.1-1.5 Mo, and infer evidence for a huge variety of accretion regimes within the cluster. While a definite correlation is observed between the average accretion rate M_acc and stellar mass, a significant spread in M_acc values is detected at any given stellar mass. Little contribution to this spread arises from M_acc variability, monitored here over week timescales. We explore and discuss the origin of this large intrinsic spread, which may be associated with a multiplicity of accretion mechanisms: unstable accretion regimes, characterized by short-lived, stochastic accretion bursts, are found to be dominant at the largest M_acc; conversely, stable, funnel-flow accretion regimes, with a steady behavior over many rotational cycles, are found at more moderate accretion rates. In addition, we find a connection between accretion properties and spatial distribution of cluster members: strong accretors are assembled close to the active star forming sites within the cloud, whereas milder accretors and disk-free objects distribute more evenly across the region, possibly as a result of dynamical evolution from their birth sites. This suggests that an intrinsic age/evolutionary spread across the cluster may also contribute to the observed spread in M_acc at any given mass.

12:10 Alicia Aarnio (University of Michigan): Assessing Magnetospheric Accretion in Herbig Ae/Be Stars

In the last few years, large spectropolarimetric surveys have found low magnetic field detection rates in Herbig Ae/Be stars. It has also been recently noted that magnetic field structure and strength dramatically change with increasing stellar mass. These results are very suggestive that the mechanisms for accretion and outflow in Herbig Ae/Be star+disk systems may differ from the magnetospheric accretion paradigm as envisaged for T Tauri star+disk systems. We present the results of our high resolution optical spectroscopic campaign of ~60 Herbig AeBe stars. Our survey includes multi-epoch observations; the timescales sampled range from high cadence (~minutes) to observations taken over several years, probing a wide range of kinematic processes. We find that the strength of variability increases with the cadence of the observations, and over all timescales sampled, the strongest variability occurs within the blueshifted absorption components of the Balmer series lines. We see no inverse P-Cygni profiles, traditionally indicative of ongoing accretion. We discuss the implications of these results in context of recent spectropolarimetric surveys for our understanding of how accretion is occurring in these objects, as well as ongoing radiative transfer modeling.

12:30 Carlo Manara (ESA/ESTEC): Disk evolution in young clusters: accretion, winds, and dynamical properties of young stars and their disks

The evolution of protoplanetary disks in young stellar clusters is regulated by the interplay of various physical processes, such as accretion and winds, and by the interactions with other stars in the cluster. Accretion and winds are best studied spectroscopically. Instruments like the VLT/X-Shooter spectrograph allow us to observe simultaneously the signatures of the accretion process, such as the UV-excess and the emission lines, together with lines tracing winds and outflows, such as helium lines and forbidden lines. At the same time, such spectra allow us to robustly derive the physical parameters of the central objects, such as their temperature and their mass. These processes relate to the disk mass and size, which can nowadays be studied with ALMA. Finally, the coming Gaia data releases will open the field to new studies of dynamical evolution of stars in young clusters by means of kinematical modelling. I will report on the stellar, accretion, and wind properties derived with X-Shooter of the complete samples of low-mass stars in the Lupus and Chamaeleon star forming regions, and discuss the dependence of stellar and accretion parameters with the disk properties obtained with ALMA surveys in these regions. I will also show how we can use Gaia data to study young clusters and the effect of interactions on the evolution of disks.

12:50 Philip Lucas (University of Herts): A population of eruptive variable protostars in VVV

We present the recent discovery of a substantial population of optically hidden eruptive variable protostars in VISTA Variables in the Via Lactea survey (VVV). VVV was the first panoramic time domain survey of the Milky Way in the near infrared. It ran from 2010-2015, observing a 560 sq deg area of the Galactic bulge and plane between 50 and 70 times in the Ks filter. A wide variety of high amplitude infrared variables were detected (DeltaKs > 1 mag) but YSOs represent about half of the population. The YSOs have a variety of light curve types but a substantial proportion can be described as photometric outbursts. Most of these “eruptive” variables appear to be bona fide examples of episodic accretion, similar to the FUor and EXor phenomena. However, their outburst durations and spectroscopic properties are a mix of the FUor and EXor types; those established types are much rarer in the sample. We provisionally refer to these mixed sources as MNors, after the illuminating source of McNeil’s Nebula, V1647 Ori. Eruptive variability is at least an order of magnitude more common amongst class I YSOs than in class II YSOs: we will present a first estimate of the incidence in class I YSOs. Finally I describe the planned “VVVX” extension of VVV to the rest of the southern plane, which is currently at the second and final stage of the ESO public survey selection process.

13:10 Lunch break

A buffet lunch with fruit juice, tea and coffee.

14:40 Matthew Bate (University of Exeter): The dependence of stellar properties on metallicity

I will present the results of four radiation hydrodynamical calculations of star cluster formation that span metallicities ranging from 1/100 to 3 times the solar value. The calculations treat both the thermodynamical evolution of the low-density interstellar medium (including hydrogen and carbon chemistry), and radiation transport which dominates temperatures near protostars. I will discuss the statistical properties of the stars and brown dwarfs that are produced, including how the mass function, multiplicity, and properties of multiple systems depend on the metallicity of the progenitor cloud.

15:00 Tom Megeath (University of Toledo): Low Mass Star Formation in the Diverse Environments of Orion: Result from the Herschel Orion Protostar Survey

Low mass stars from in a diverse range of environments, from isolated dark clouds to dense clusters in close proximity to massive stars. How the low mass star formation process differs between these environments is not well understood. We do know that within this range of environments, the densities of young low mass stars varies by orders of magnitude, yet the initial mass function remains relatively invariant. Comparative studies of protostars in these environments are needed to assess how variation in gas density, turbulence and kinetic temperature affect the fragmentation, collapse and accretion of gas and the formation of stars and disks. I will overivew a survey of protostars in the Orion A & B molecular clouds with the Spitzer, Herschel, Hubble and Apex telescopes, spanning 1.6 to 870 um, as well as follow-up observations in the near-IR and sub-millimeter. The goals of these observations are to characterize multiplicity, infall, accretion, outflow, and disk formation in the diverse environments found in the Orion clouds. These observations find a decrease in the spacing of protostars with increasing gas density, an increase of protostellar luminosity with increasing gas density, and an increase in the number of companions with increasing stellar density. I will discuss how these observations are leading to a better understanding of the physical factors, both external and internal, that control the rate and efficiency at which low mass stars form and ultimately determine their multiplicity and masses.

15:20 Jan Forbrich (University of Vienna): The Orion Radio All-Stars: new perspectives in stellar radio astronomy

The sensitivity upgrades of both the NRAO Very Large Array (VLA) and the NRAO Very Long Baseline Array (VLBA) have begun to provide us with a much improved perspective on stellar centimeter radio emission, particularly concerning young stellar objects (YSOs) and ultracool dwarfs. I will mainly present a deep VLA and VLBA radio survey of the Orion Nebula Cluster (ONC), where we have found 556 compact radio sources, a sevenfold increase over previous studies, and intricate detail on the radio emission of proplyds. We can now better disentangle thermal and nonthermal radio emission by assessing spectral indices, polarization, variability, and brightness temperatures (VLBA). With simultaneous radio-X-ray time domain information (Chandra) and VLBA precision astrometry, this project is providing unpredented constraints on the magnetospheric activity of YSOs across a wide mass range, new insights into the impact of the massive Trapezium stars on their environment, and new astrometric constraints on the ONC itself. Additionally, I will present new VLBA results in ultracool dwarf astrometry. More generally, and beyond providing a new perspective on stellar cm radio emission and physics, this presentation will highlight how VLBI astrometry will allow us to extend the Gaia sample of YSOs and ultracool dwarfs by including embedded objects, distant obscured sources in the Galactic plane, and faint ultracool dwarfs, while providing important opportunities for astrometric cross-calibration with Gaia.

15:40 Nadia Murillo (Leiden University): Do siblings always form and evolve at the same time? Coevality of multiple protostellar systems with Herschel

Multiplicity is common in field stars and protostars. While fragmentation is considered to be the mechanism of formation, the question of when and how this occurs is still open. Previous studies towards pre-main sequence binaries found pairs of non-coeval (different ages) components, with frequencies of 15 to 33%. Is this non-coevality present from the moment of formation or product of dynamical evolution? We address this question by determining the relative evolutionary stages of the components in young embedded multiple protostellar systems. Spectral energy distributions (SEDs) for known multiple protostellar systems in the Perseus star forming region are constructed from literature data and Herschel PACS photometric maps. Inclination effects and the surrounding envelope and outflows are considered in order to decouple source geometry from evolution. This together with the shape and properties derived from the SED are used to accurately determine each system’s coevality. Synthetic SEDs are used to study the frequency of apparent non-coevality due to geometry. Effects of unresolved multiple protostellar systems on SED shapes are also investigated. We find 33% of multiple protostellar systems in our sample to be non-coeval, with higher order multiples showing a tendency to be non-coeval. Random pairing of synthetic SEDs suggest an apparent non-coevality frequency of 17%, however our sample does not show signs of strong geometric effects, hence the observed non-coevality is real. The implications that the non-coevality frequency found in our work has on formation mechanisms and evolution are examined.

16:00 Tea break

Coffee, tea and Devon cream tea (plain/fruit scone with clotted cream and strawberry jam)

16:50 Megan Reiter (University of Michigan): Powerful jets driven by intermediate-mass protostars in the Carina Nebula

We present new spectroscopy and Hubble Space Telescope imaging of protostellar jets driven by intermediate-mass stars in the Carina Nebula. New, near-IR [Fe II] observations of these jets reveal dense gas that is self-shielded from Lyman continuum photons from nearby O-type stars, but is excited by non-ionizing FUV photons that penetrate the ionization front within the jet. Each jet contains a substantial mass of dense, neutral gas that is not seen in Halpha emission from these jets. In some cases, [Fe II] emission traces the jet inside its natal dust pillar, connecting the larger Halpha outflow to the embedded IR source that drives it. New proper motion measurements reveal tangential velocities similar to those typically measured in lower-luminosity sources (100-200 km/s). Combining high jet densities and fast outflow speeds leads to mass-loss rate estimates an order of magnitude higher than those derived from the Halpha emission measure alone. Higher jet mass-loss rates require higher accretion rates, implying that these jets are driven by intermediate-mass (~2-8 Msun) protostars. For some sources, mid-IR luminosities of the driving sources are clearly consistent with intermediate-mass protostars others remain deeply embedded and require long-wavelength, high-resolution images confirm their luminosity. These outflows are all highly collimated, with opening angles of only a few degrees. With this new view of collimated jets from intermediate-mass protostars, we argue that these jets reflect essentially the same outflow phenomenon seen in low-mass protostars, but that the collimated atomic jet core and the material it sweeps up is irradiated and rendered observable. Thus, the jets in Carina offer strong additional evidence that stars up to ~8 Msun form by the same accretion mechanisms as low-mass stars.

17:10 Guido De Marchi (ESA): The Tarantula of low-mass stars

We are studying the recent low-mass star formation in the Tarantula Nebula using the Hubble Tarantula Treasury Project observations. Looking for stars with prominent Halpha excess emission (> 4 sigma, equivalent width > 10A), we have identified more than 20,000 pre-main sequence (PMS) stars over an area of ~180 x 180 pc^2. We are able to detect and study not only the youngest PMS objects, but also those approaching the main sequence, with ages older than ~10 Myr. This is so far the largest sample of individually resolved young low-mass stars.

We find that the distribution of PMS stars is considerably more diffuse than that of massive stars: while many young PMS stars are often close to massive objects, a similarly high number of both young and older PMS objects are clumped in regions with very few or no high-mass stars around. This implies that the conditions for the formation of low-mass stars are more lenient than those required by high-mass stars, and it might even suggest that the relevant processes are quite different. This could have important implications for the concept of initial mass function.

In the central regions, around the R136 cluster, we have already completed the analysis of the physical properties of both younger and older PMS stars. We confirm our previous findings on the dependence of the mass accretion rate on the mass and age of the stars. We show that, in similar conditions of mass and age, in the Tarantula Nebula the mass accretion rates are systematically higher than in the Milky Way, yet still lower than those we measured in active star forming regions in the Small Magellanic Cloud. These findings appear to indicate that the metallicity of the environment may play a significant role in the mass accretion process.

17:30 Lee Hartmann (University of Michigan): Mass functions of star clusters and the upper mass stellar IMF

I will discuss numerical simulations which offer a simple, universal, and robust explanation of the star cluster (initial) mass function - gravitational focusing - with implications for the upper mass end of the stellar IMF.

17:50 Philippe André (CEA/Saclay): The role of interstellar filaments in the origin of the stellar initial mass function

The origin of the stellar initial mass function (IMF) is one of the most debated issues in astrophysics. Two major features of the IMF are 1) a fairly robust power-law slope at the high-mass end known since Salpeter (1955), and 2) a broad peak below 1 Mo corresponding to a characteristic stellar mass scale. In recent years, the dominant theoretical model proposed to account for these features has been the “gravo-turbulent fragmentation” picture, whereby the properties of interstellar turbulence lead to the Salpeter power law and gravity sets the characteristic mass scale (Jeans mass). I will discuss modifications to this picture based on Herschel observations of nearby molecular clouds. The Herschel results point to the key role of the quasi-universal filamentary structure pervading the cold interstellar medium and support a scenario in which star formation occurs in two main steps: First, large-scale compression of interstellar material in supersonic MHD flows generates a cobweb of ~ 0.1 pc-wide filaments in the ISM; second, the densest filaments fragment into prestellar cores above the line mass threshold for gravitational instability. In this observationally-driven scenario, the dense cores making up the peak of the prestellar core mass function (CMF) - likely responsible for the characteristic IMF mass scale - result from gravitational fragmentation of filaments near the critical mass per unit length. The power-law tail of the CMF/IMF arises from the characteristic power spectrum of initial density fluctuations measured along the Herschel filaments (Roy et al. 2015) and from the power-law distribution of masses per unit length observed for supercritical filaments.

19:00 - 23:30 Conference Dinner

The Conference Dinner will take place in the Great Hall, starting with a drinks reception at 19:00. There will then be a three course dinner and at 21:30 we will be entertained by the 13-piece Soul Traders band. A cash bar will be available.

Friday 26 August: Discs

08:30 Coffee/tea and mini Danish

Coffee and tea will be available in the Forum Street from 08:30.

08:50 Tim Harries and Chris Brunt: Notices and updates

Information and updates on the programme and social events.

Session Chairs

Chairs: Janet Drew (morning), Nuria Calvet (afternoon)

09:00 Catherine Espaillat (Boston University): Observational review

We know that most stars were once surrounded by protoplanetary disks. How these young disks evolve into planetary systems is a fundamental question in astronomy and observations of young pre-main sequence stars may provide insights. In this talk, I will review the key constraints on theoretical models provided by observations of the dust and gas in protoplanetary disks. I will discuss disk demographics and evolution as well as disk structure, particularly those disks that contain holes or gaps which many researchers have posited are the footprints of planets. Recent MIR and sub-mm imaging work will be discussed as well as remaining questions in the field of protoplanetary disks.

09:40 Richard Alexander (University of Leicester): Theory review

In this talk I will review our understanding of protoplanetary discs. These discs are of considerable interest, as they are both the primary means of driving protostellar accretion, and also the sites of planet formation. I will briefly discuss disc formation and structure, and then look in detail at the various physical processes - angular momentum transport in the disc, and mass and angular momentum loss in winds - which drive disc evolution. This is a rapidly evolving field, so I will attempt to highlight key recent developments, as well as giving a critical assessment of where the field currently stands. I will conclude by discussing future directions for our study of disc evolution, and the key questions we wish to answer in the coming years.

10:20 Tim Naylor (University of Exeter): A Dynamic Colour-Magnitude Diagram for the Orion Nebula Cluster

We have undertaken time-series multi-colour photometry of the Orion Nebula Cluster over seven nights, with simultaneous multi-fibre spectroscopy. This allows us to construct “movies” of how the positions of stars in colour-magnitude space change with time, and use the spectroscopy to analyse the physical mechanisms driving those changes. Whilst many stars remain largely static in position, some classical T Tauri stars show remarkable peregrinations around the colour-magnitude space. Some changes are clearly due to changes in dust obscuration, though there is evidence for grain growth in the extincting material. The degree of variability is clearly correlated with position in colour-magnitude space with the more variable stars lying below the majority of the pre-main-sequence. As these are the classical T Tauri stars this leads to the remarkable conclusion that in a colour magnitude diagram the heavily accreting stars classical T Tauri stars appear to be older than the disc-less weak-lined T Tauri stars. The simultaneous spectroscopy allows us to show that this is purely an effect of the accretion luminosity.

10:40 Kenny Wood (University of St. Andrews): A Model for (Quasi-) Periodic Multi-wavelength Photometric Variability in Young Stellar Objects

We present radiation transfer models of rotating young stellar objects (YSOs) with hotspots in their atmospheres, inner disk warps and other 3-D effects in the nearby circumstellar environment. Our models are based on the geometry expected from the magneto-accretion theory, where material moving inward in the disk flows along magnetic field lines to the star and creates stellar hotspots upon impact. Due to rotation of the star and magnetosphere, the disk is variably illuminated. We compare our model light curves to data from the Spitzer YSOVAR project to determine if these processes can explain the variability observed at optical and mid-infrared wavelengths in young stars. We focus on those variables exhibiting dipper behavior that may be periodic, quasi-periodic, or aperiodic. We find that the stellar hotspot size and temperature affects the optical and near- infrared light curves, while the shape and vertical extent of the inner disk warp affects the mid-IR light curve variations. Clumpy disk distributions with non-uniform fractal density structure produce more stochastic light curves. We conclude that the magneto-accretion theory is consistent with certain aspects of the multi-wavelength photometric variability exhibited by low-mass YSOs. More detailed modeling of individual sources can be used to better determine the stellar hotspot and inner disk geometries of particular sources.

11:00 Coffee break

Coffee, tea and cookies

11:50 Gilles Chabrier (Lyon & Exeter): Formation of proto-stellar and proto-planetary disks in star formation: the key roles of different physical mechanisms

Protostar or protoplanetary disks are the link between the collapse of prestellar star-forming clumps at large scales, and the formation of planet embryos at small scales. Understanding the magnetic, thermal and stability properties of these disks, as well as the key problem of angular momentum transport during the core collapse, are thus mandatory to have a reliable description of protostellar/protoplanetary disks. In this talk, I will present calculations of disk formation that include the most complete relevant physics: non-ideal MHD, turbulence, non-equilibrium chemistry. The output of these calculations, disk properties and outflow signatures, will be compared with recent observations, allowing us to better understand the genesis and the nature of disks.

12:10 Alvaro Ribas (Boston University): Protoplanetary disk lifetimes in nearby star-forming regions

The timescales and relevant parameters for protoplanetary disk evolution are crucial to fully understand planet formation, but a consistent view of this phenomenon has remained elusive given its complexity and limited sample sizes. In this contribution, I will present the most complete study of disk evolution up to date, performed with a sample of more than 2300 YSOs in 22 nearby (<500 pc) star-forming regions and associations. The unprecedented size of the sample and homogeneous treatments applied allowed us not only to derive the most precise measurement of the characteristic disk lifetime so far but also to statistically confirm an important dependence of disk lifetimes with stellar mass. Such a dependence could even lead to differences in the architectures of planetary systems around low-mass and high-mass stars. Finally, I will describe our current efforts on expanding these results with a more detailed subsample and advanced SED modeling techniques.

12:30 Melissa K. McClure (ESO): T Tauri disk gas masses measured from hydrogen deuteride

The total gas mass of a protoplanetary disk is a fundamental, but poorly determined, quantity. A new technique (Bergin et al. 2013) has been demonstrated to assess directly the bulk molecular gas reservoir of molecular hydrogen using the HD J=1-0 line at 112 microns. In this work we present a small survey of T Tauri disk observations of the HD line. Line emission is detected in two cases at >3 sigma significance. Using detailed disk structure models, including the effect of UV gas heating, we determine the amount of gas required to fit the HD line and the amount of dust required to fit the observed disk spectral energy distributions. For both disks, the amount of gas required is more than the MMSN value, and the gas/dust ratio is at least a factor of two lower than that of the ISM. We discuss the implication of this result for these disks’ carbon chemistry and the disk mass probability distribution.

12:50 Stefan Kraus (University of Exeter): Resolving the disc structure of FU Orionis stars

During their formation phase stars gain most of their mass in violent episodic accretion events, such as observed in FU Orionis stars. In this talk I will report on VLTI interferometric observations that allows us study the disk structure around these objects on sub-AU scales.

13:10 Lunch break

A buffet lunch with fruit juice, tea and coffee.

14:40 Katharine Johnston (University of Leeds): A Keplerian-like disc around the forming O-type star AFGL 4176

I will present our ALMA line and continuum observations at 1.2mm with ~0.3” resolution that uncover a Keplerian-like disc around the forming O-type star AFGL 4176. The first-moment maps, pixel-to-pixel line modelling, and position-velocity diagrams of the CH3CN J = 13–12 K-line emission all show a velocity gradient along the major axis of the source, coupled with an increase in velocity at small radii, consistent with Keplerian-like rotation. I will also present APEX 12CO observations that show a large-scale outflow from AFGL4176 perpendicular to the major axis of mm1, supporting the disc interpretation. Finally, we have conducted radiative transfer modelling of the ALMA data, showing that a Keplerian disc surrounding an O7 star, with a disc mass and radius of 12 Msun and 2000 AU reproduces the line and continuum data, further supporting our conclusion that our observations have uncovered a Keplerian-like disc around an O-type star. This work is published in Johnston et al. (2015).

15:00 James Owen (Princeton): Vortices from low-mass planet formation in transition discs

Transition discs are protoplanetary discs that show evidence for dust trapping in their outer regions. Recent high angular resolution mm imaging of these discs has indicated that dust particles, as well being trapped radially, are also concentrated in non-axisymmetric features, and it has been suggested that the dust particles are trapped in a large scale vortex. Since the dust particles that naturally accumulate in transition disc dust traps have Stokes numbers close to unity, there is naturally a large reservoir of pebbles in transition disc dust traps. I will argue that the transition disc dust traps are prime sites for rapid pebble accretion onto low-mass planetary embryos. At the planetary accretion rates expected in nominal transition discs, the accretion luminosity is sufficiently high to heat the surrounding disc to radii well outside the planet’s Hill sphere. This makes the disc locally baroclinic and can lead to vortex formation. I will present this new scenario for vortex formation in transition discs and discuss the long term consequences, while arguing it is perhaps more natural than those scenarios discussed so far.

15:20 Michael Ireland (ANU): High Angular Resolution Mid-Infrared Imaging of Transitional Disks

Transitional and so-called pre-transitional disks consist of an optically thin inner disk and an optically thick outer disk. In some disks, there is evidence for much more complex disk evolution than simply a cleared inner hole. For example, in the case of Oph IRS 48, there is a dust trap in the outer disk and evidence for multiple cavity sizes. We present high angular resolution observations of several disks with the Keck II telescope at infrared wavelengths, primarily 3.7 microns, using adaptive optics and precision calibration techniques including aperture mask interferometry. For Oph IRS 48 and HD 169142, we model the disks using RadMC-3D and show that an azimuthally symmetric disk can model most but not all of the observed structure. In the case of HD 169142, a point-assymetry has been interpreted as direct luminosity from a planet. We discuss alternative explanations from disk emission, showing why interpretation of high angular resolution observations of luminous disk-bearing stars with single telescopes will always be difficult to interpret. A much more ambitious instrument program such as the Planet Formation Imager will be needed to comprehensively disentnagle complex disk evolution from planet formation.

15:40 Pablo Loren-Aguilar (University of Exeter): Toroidal vortices as a solution to the dust migration problem

We have identified a new type of dynamical dust–gas instability in protoplanetary discs that produces global toroidal vortices, due to the process of dust settling. We have investigated the evolution of a dusty protoplanetary disc with two different dust species (1 mm and 50 cm dust grains), under the presence of the instability. We show how toroidal vortices, triggered by the interaction of mm grains with the gas, stop the radial migration of metre-sized dust, potentially offering a natural and efficient solution to the dust migration problem.

16:00 Tea break

Coffee, tea and Devon cream tea (plain/fruit scone with clotted cream and strawberry jam)

16:50 Giovanni Rosotti (University of Cambridge): What is the minimum planet mass that creates observable signatures in proto-planetary discs?

I will discuss the prospects for observing how super-Earths and giant planetary cores shape the proto-planetary disc. While previous theoretical work has shown how they affect the dust surface density much more than the gas one, no proper study has been conducted of what is the minimum planetary mass that produces observable signatures. I address this problem by running multi-fluid gas and dust simulations and generating simulated observations. I’ll highlight in particular how there exists a minimum planet mass that is able to produce a pressure maximum outside its orbit and therefore a dust trap. Planet masses lower than the threshold can still affect the dust surface density, by creating traffic jams in the dust radial velocity; the minimum planet mass detectable is roughly 10-15 Earth masses, but is a strong function of the disc temperature. Finally, I will discuss how it is possible to have an estimate of the mass of the planet from the observations, which involves measuring either the gap width in scattered light observations or the pressure maximum location in sub-mm images.

17:10 Eiji Akiyama (NAOJ): Differential Grain Growth in the Spiral Structure of the LkHa 330 Disc

Grain growth represents an initial step toward planet formation since it involves the coagulation of approximately micron-sized dust residing in protoplanetary discs around young stars. We have conducted H-band (1.6 um) linear polarimetric observations and 0.88 mm continuum interferometric observations toward a transitional disc around the intermediate-mass pre-main sequence star LkHa 330. The observations show a pair of asymmetric spiral arms in the disc. We discuss the origin of the spiral arms and suggest that a massive unseen planet is the most plausible explanation based on recent global hydro simulations. The possibility of grain growth causing the asymmetric structure of the spiral arms was investigated through the opacity index (beta) by plotting the observed SED slope between 0.88 mm from our SMA observation and 1.3 mm from literature. The results imply that grains are indistinguishable from ISM-like dust in the east side (beta ~ 2.0), but much smaller in the west side (beta ~ 0.7), indicating differential grain growth or dust trapping in the spiral arms. Combining the results of near-infrared and submillimetre observations, we find that the spiral arm is geometrically thick, and that grains grow to millimeter size near the disc mid-plane. Future observations at centimeter wavelengths and differential polarization imaging in other bands (Y to K) with extreme AO imagers are required to understand how large dust grains form and to further explore the dust distribution in the disc.

17:30 John Monnier (University of Michigan): GPI observations of Herbig Ae/Be stars

The discovery of transition disks around young stars has provided the opportunity to study planet formation in situ when giant planet formation and growth are most vigorous. Using the Gemini Planet Imager (GPI) in differential polarimetry mode, we have begun a survey to characterize a statistically-significant sample of young disks at each major stage of planet formation, from the youngest “full disk” stage and through pre-transition and transition disk stages. GPI is ideal for this survey due to its unprecedented sensitivity to scattered light emitted between 20-150 AU from the star, a region of the protoplanetary disk where giant planet formation is known to occur. I will report initial observational results and radiative transfer modeling of a few well-known systems. We explore how to combine ALMA and GPI imaging to measure radial variations in the disk’s grain size distribution, outer disk gas pressure scale heights, and chemical snowlines.

17:50 Lee Hartmann (University of Michigan): Conference Summary

The conference summary talk.

18:10-19:00 Drinks reception (Mezzanine level of Forum)

Wine and soft drinks plus snacks will be available to conference delegates prior to Mark McCaughrean’s public lecture.

19:00 Public talk: Mark McCaughrean (ESA) ESA’s Big Year in Space Science 2016

In this talk Professor Mark McCaughrean, Senior Science Advisor at the European Space Agency, will present some key recent results from ongoing missions.

Mark returns to Exeter after a fantastic sell-out talk earlier in the year to deliver a public talk as part of an international astrophysics conference.

The European Space Agency operates and is partner in a fleet of spacecraft studying the Sun, exploring Earth’s magnetic field, orbiting Mars, Saturn, and Comet 67P/Churymov-Gerasimenko, and collecting photons from across the electromagnetic spectrum, from corners of the Universe near and far.

Mark will talk about missions including the Milky Way surveyor Gaia and the gravitational wave technology testbed LISA Pathfinder. He’ll also give a look forward to two big solar system events: Rosetta will end its mission with a controlled impact on the surface of Comet 67P in September, and ExoMars 2016 puts its entry, descent, and landing module onto the Red Planet in October.