The Star Formation Newsletter
A community newsletter on Star and Planet Formation research
No. 337 — 20 January 2021
Editor: João Alveswww.starformation.news

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Cover image caption
Detail of the interaction between stellar feedback and the gas in NGC 2174. NGC 2174 is a poorly studied HII emission nebula
located at a distance of about 2 kpc towards the Galactic anti-center (in the constellation of Orion but not associated with thewell known Orion Star Formation region). The region, also known as Sh 2-252, is associated with the young star cluster NGC
2175. Credits: NASA, ESA, and the Hubble Heritage Team (STScI/AURA).
Note from the Editor
The Star Formation Newsletter is now on the web at www.starformation.news. This PDF file contains the monthly Abstracts
and links to the different Newsletter sections. Red text in this PDF is a url link. Submitting an abstract to the SFN is as simple
as entering the arXiv ID (e.g., 2006.10139) in a web form on the SFN web site. We extract the title, authors, and the abstract’s
text directly from the arXiv, so make sure not to remove the LATEX formatting when submitting to the arXiv. If you do, yourabstract will not look great either at the arXiv (which uses MathJax to convert LATEX math symbols to the web) or the SFN.

Abstracts
1.

Filament rotation in the California L1482 cloud
Rodrigo H. Álvarez-Gutiérrez, Amelia M. Stutz, Chi Y. Law, Stefan Reissl, Ralf S. Klessen, Nathan W. C.
Leigh, Hong-Li Liu, Rodrigo A. Reeves We analyze the gas mass distribution, the gas kinematics, and the young stellar
object (YSO) content of the California Molecular Cloud (CMC) L1482 filament. We derive a Gaia DR2 YSO distance of 511+17−16
pc. We derive scale-free power-laws for the mean gas line-mass (M/L) profiles; we calculate the gravitational potential and field
profiles consistent with these. We present IRAM 30 m C18 O (1-0) (and other tracers) position-velocity (PV) diagrams thatexhibit complex velocity twisting and turning structures. We find a rotational profile in C18 O perpendicular to the southern
filament ridgeline. The profile is regular, confined (r . 0.4 pc), anti-symmetric, and to first order linear with a break at r ∼ 0.25
pc. The timescales of the inner (outer) gradients are ∼0.7 (6.0) Myr. We show that the centripetal force, compared to gravity,
increases toward the break; when the ratio of forces approaches unity, the profile turns over, just before filament breakup isachieved. The timescales and relative roles of gravity to rotation indicate that the structure is stable, long lived (∼ a few times
6 Myr), and undergoing outside-in evolution. Moreover, this filament has practically no star formation, a perpendicular Planck
plane-of-the-sky (POS) magnetic field morphology, and POS “zig-zag” morphology, which together with the rotation profile leadto the suggestion that the 3D shape is a corkscrew filament with a helical magnetic field. These results, combined with resultsin Orion and G035.39-00.33, suggest evolution toward higher densities as rotating filaments shed angular momentum. Thus,
magnetic fields may be an essential feature of high-mass (M ∼ 105 M ) cloud filament evolution toward cluster formation.

2.

Dust polarized emission observations of NGC 6334; BISTRO reveals the details of thecomplex but organized magnetic field structure of the high-mass star-forming hubfilament network
BISTRO collaboration - D. Arzoumanian et al. [Abridged] Filaments and hubs have received special attention recently
thanks to studies showing their role in star formation. While the column density and velocity structures of both filaments andhubs have been studied, their magnetic fields (B-field) are not yet characterized. We aim to understand the role of the B-field in
the dynamical evolution of the NGC 6334 hub-filament network. We present new observations of the dust polarized emission at
850µm towards NGC 6334 obtained with the JCMT/POL-2. We study the distribution and dispersion of the polarized intensity(P I), the polarization fraction (P F ), and the B-field angle (θB ). We derive the power spectrum of the intensity and θB along
the ridge crest. Our analyses show a complex B-field structure when observed over the whole region (∼ 10 pc), however, atsmaller scales (∼ 1 pc), θB varies coherently along the filaments. The observed power spectrum of θB can be well represented
with a power law function with a slope −1.33 ± 0.23, which is ∼ 20% shallower than that of I. This result is compatible withthe properties of simulated filaments and may indicate the processes at play in the formation of filaments. θB rotates from2

being mostly perpendicular to the filament crests to mostly parallel as they merge with the hubs. This variation of θB may be
tracing local velocity flows of matter in-falling onto the hubs. Our analysis suggests a variation of the energy balance along thecrests of these filaments, from magnetically critical/supercritical at their far ends to magnetically subcritical near the hubs. We
detect an increase of P F towards the high-column density star cluster-forming hubs that may result from the increase of grainalignment efficiency due to stellar radiation from the newborn stars.

3.

Photodissociation Region Diagnostics Across Galactic Environments
Thomas G. Bisbas, Jonathan C. Tan, Kei E. I. Tanaka We present three-dimensional astrochemical simulations andsynthetic observations of magnetised, turbulent, self-gravitating molecular clouds. We explore various galactic interstellar
medium environments, including cosmic-ray ionization rates in the range of ζCR = 10−17 -10−14 s−1 , far-UV intensities in therange of G0 = 1-103 and metallicities in the range of Z = 0.1-2 Z . The simulations also probe a range of densities and levels of
turbulence, including cases where the gas has undergone recent compression due to cloud-cloud collisions. We examine: i) thecolumn densities of carbon species across the cycle of CII, CI and CO, along with OI, in relation to the HI-to-H2 transition; ii)
the velocity-integrated emission of [CII] 158µm, [13 CII] 158µm, [CI] 609µm and 370µm, [OI] 63µm and 146µm, and of the firstten 12 CO rotational transitions; iii) the corresponding Spectral Line Energy Distributions; iv) the usage of [CII] and [OI] 63µm
to describe the dynamical state of the clouds; v) the behavior of the most commonly used ratios between transitions of CO and[CI]; and vi) the conversion factors for using CO and CI as H2 -gas tracers. We find that enhanced cosmic-ray energy densities
enhance all aforementioned line intensities. At low metallicities, the emission of [CII] is well connected with the H2 column,
making it a promising new H2 tracer in metal-poor environments. The conversion factors of XCO and XCI depend on metallicity
and the cosmic-ray ionization rate, but not on FUV intensity. In the era of ALMA, SOFIA and the forthcoming CCAT-prime
telescope, our results can be used to understand better the behaviour of systems in a wide range of galactic and extragalactic
environments.

4.

Linear Stability Analysis of a Magnetic Rotating Disk with Ohmic Dissipation andAmbipolar Diffusion
Indrani Das, Shantanu Basu We perform a linear analysis of the stability of isothermal, rotating, magnetic, self-gravitating
sheets that are weakly ionized. The magnetic field and rotation axis are perpendicular to the sheet. We include a self-consistenttreatment of thermal pressure, gravitational, rotational, and magnetic (pressure and tension) forces together with two nonideal
magnetohydrodynamic (MHD) effects (Ohmic dissipation and ambipolar diffusion) that are treated together for their influenceon the properties of gravitational instability for a rotating sheet-like cloud or disk. Our results show that there is always
a preferred lengthscale and associated minimum timescale for gravitational instability. We investigate their dependence on
important dimensionless free parameters of the problem: the initial normalized mass-to-flux ratio µ0 , the rotational Toomre
parameter Q, the dimensionless Ohmic diffusivity η̃OD,0 , and the dimensionless neutral-ion collision time τ̃ni,0 that is a measureof the ambipolar diffusivity. One consequence of η̃OD,0 is that there is a maximum preferred lengthscale of instability that occurs
in the transcritical (µ0 & 1) regime, qualitatively similar to the effect of τ̃ni,0 , but with quantitative differences. The addition ofrotation leads to a generalized Toomre criterion (that includes a magnetic dependence) and modified lengthscales and timescales
for collapse. When nonideal MHD effects are also included, the Toomre criterion reverts back to the hydrodynamic value. We
apply our results to protostellar disk properties in the early embedded phase and find that the preferred scale of instability cansignificantly exceed the thermal (Jeans) scale and the peak preferred fragmentation mass is likely to be ∼ 10 − 90 MJup .

5.

The sonic scale revealed by the world’s largest supersonic turbulence simulation
Christoph Federrath, Ralf S. Klessen, Luigi Iapichino, James R. Beattie Understanding the physics of turbulenceis crucial for many applications, including weather, industry, and astrophysics. In the interstellar medium (ISM), supersonicturbulence plays a crucial role in controlling the gas density and velocity structure, and ultimately the birth of stars. Here we
present a simulation of interstellar turbulence with a grid resolution of 100483 cells that allows us to determine the position andwidth of the sonic scale (ls ) - the transition from supersonic to subsonic turbulence. The simulation simultaneously resolves
the supersonic and subsonic cascade, v(l) ∝ lp , where we measure psup = 0.49 +/- 0.01 and psub = 0.39 +/- 0.02, respectively.
We find that ls agrees with the relation ls / L = phis Mach(−1/psup ) , where Mach is the three-dimensional Mach number, and
L is either the driving scale of turbulence or the diameter of a molecular cloud. If L is the driving scale, we measure phis =0.42 (+0.12) (-0.09), primarily because of the separation between the driving scale and the start of the supersonic cascade.
For a supersonic cascade extending beyond the cloud scale, we get phis = 0.91 (+0.25) (-0.20). In both cases, phis < 1,because we find that the supersonic cascade transitions smoothly to the subsonic cascade over a factor of 3 in scale, instead of a
sharp transition. Our measurements provide quantitative input for turbulence-regulated models of filament structure and starformation in molecular clouds.

3

6.

Physical and chemical structure of the Serpens filament – fast formation and gravitydriven accretion
Y. Gong, A. Belloche, F. J. Du, K. M. Menten, C. Henkel, G. X. Li, F. Wyrowski, R. Q. Mao The Serpens
filament, a prominent elongated structure in a relatively nearby molecular cloud, is believed to be at an early evolutionary
stage, so studying its physical and chemical properties can shed light on filament formation and early evolution. The main goal
is to address the physical and chemical properties as well as the dynamical state of the Serpens filament at a spatial resolutionof ∼0.07 pc and a spectral resolution of .0.1 km s−1 . We performed 13 CO (1–0), C18 O (1–0), C17 O (1–0), 13 CO (2–1), C18 O(2–1), and C17 O (2–1) imaging observations toward the Serpens filament with the Institut de Radioastronomie Millimétrique
30-m (IRAM-30 m) and Atacama Pathfinder EXperiment (APEX) telescopes. Widespread narrow 13 CO (2–1) self-absorption
is observed in this filament, causing the 13 CO morphology to be different from the filamentary structure traced by C18 O and
C17 O. Our excitation analysis suggests that the opacities of C18 O transitions become higher than unity in most regions, and thisanalysis confirms the presence of widespread CO depletion. Further we show that the local velocity gradients have a tendency
to be perpendicular to the filament’s long axis in the outskirts and parallel to the large-scale magnetic field direction. The
magnitudes of the local velocity gradients decrease toward the filament’s crest. The observed velocity structure can be a resultof gravity-driven accretion flows. The isochronic evolutionary track of the C18 O freeze-out process indicates the filament isyoung with an age of .2 Myr. We propose that the Serpens filament is a newly-formed slightly-supercritical structure whichappears to be actively accreting material from its ambient gas.

7.

Water and Methanol Ice in L1544
Miwa Goto, A. I. Vasyunin, B. M. Giuliano, I. Jiménez-Serra, P. Caselli, C. G. Román-Zúñiga, J. Alves
Methanol and complex organic molecules have been found in cold starless cores, where a standard warm-up scenario would notwork because of the absence of heat sources. A recent chemical model attributed the presence of methanol and large organics
to the efficient chemical desorption and a class of neutral-neutral reactions that proceed fast at low temperatures in the gas
phase. The model calls for a high abundance of methanol ice at the edge of the CO freeze-out zone in cold cloud cores. We
performed medium resolution spectroscopy toward 3 field stars behind the starless core L1544 at 3 µm to constrain the methanol
ice abundance and compare it with the model predictions. One of the field stars shows a methanol-ice abundance of 11% withrespect to water ice. This is higher than the typical methanol abundance previously found in cold cloud cores (4%), but is 4.5
times smaller than predicted. The reason for the disagreement between the observations and the model calculations is not yet
understood.

8.

Searching for active low-mass stars in CMa star-forming region: multi-band photometry
with T80S
J. Gregorio-Hetem, F. Navarete, A. Hetem, T. Santos-Silva, P. A. B. Galli, B. Fernandes, T. Montmerle,
V. Jatenco-Pereira, M. Borges Fernandes, H. D. Perottoni, W. Schoenell, T. Ribeiro, A. Kanaan An exotic
environment surrounds the young stellar groups associated with the Canis Major (CMa) OB1/R1 region, which probably wasformed under feedback from at least three supernova events having occurred a few million years ago. We use astrometric datafrom the Gaia-DR2 to confirm the membership of the stars in CMa R1, based on proper motion and parallax, which revealed 514
new members and candidates. The mean age of 5 Myr estimated from the color-magnitude diagram characterizes the sources
as likely pre-main sequence candidates. In total, a sample of 694 stars detected with the T80-South telescope was analyzed
according to different color-color diagrams, which were compared with theoretical colors from evolutionary models, aiming toreveal the objects that exhibit color excess due to accretion processes. Accretion and magnetic activity were also explored on thebasis of empirical flux-flux relation, such as F660 and F861 that are related to Halpha and Ca II triplet emission, respectively. A
low fraction (3 percent) of the sample have Halpha excess and other colors expected for stars exhibiting chromospheric activity.
The number of Class I and Class II objects, identified by the infrared (WISE) colors, indicates a disk fraction of 6 percent,which is lower than the expected for stellar clusters with similar age. A such large sample of objects associated with CMa R1
without evidences of circumstellar accretion can be interpreted as a lack of disk-bearing stars, unusual for young star-forming
regions. However, this may be explained as the result of supernova events.

9. Feedback-limited Accretion: Variable Luminosity from Growing Planets
Matías Gárate, Jorge Cuadra, Matias Montesinos, Patricia Arévalo Planets form in discs of gas and dust aroundstars, and continue to grow by accretion of disc material while available. Massive planets clear a gap in their protoplanetary
disc, but can still accrete gas through a circumplanetary disk. For high enough accretion rates the planet should be detectable
at infrared wavelengths. As the energy of the gas accreted on to the planet is released, the planet surroundings heat up ina feedback process. We aim to test how this planet feedback affects the gas in the coorbital region and the accretion rate
itself. We modified the 2D code FARGO-AD to include a prescription for the accretion and feedback luminosity of the planet
and use it to model giant planets on 10 au circular and eccentric orbits around a solar mass star. We find that this feedback
reduces but does not halt the accretion on to the planet, although this result might depend on the near-coincident radial ranges

4where both recipes are implemented. Our simulations also show that the planet heating gives the accretion rate a stochastic
variability with an amplitude ∆Ṁp ∼ 0.1Ṁp . A planet on an eccentric orbit (e = 0.1) presents a similar variability amplitude,
but concentrated on a well-defined periodicity of half the orbital period and weaker broadband noise, potentially allowing
observations to discriminate between both cases. Finally, we find that the heating of the coorbital region by the planet feedback
alters the gas dynamics, reducing the difference between its orbital velocity and the Keplerian motion at the edge of the gap,
which can have important consequences for the formation of dust rings.

10. Measuring Turbulence with Young Stars in the Orion Complex
Trung Ha, Yuan Li, Siyao Xu, Marina Kounkel, Hui Li Stars form in molecular clouds in the interstellar medium (ISM)with a turbulent kinematic state. Newborn stars therefore should retain the turbulent kinematics of their natal clouds. Gaia
DR2 and APOGEE-2 surveys in combination provide three-dimensional (3D) positions and 3D velocities of young stars in theOrion Molecular Cloud Complex. Using the full 6D measurements, we compute the velocity structure functions (VSFs) of thestars in six different groups within the Orion Complex. We find that the motions of stars in all diffuse groups exhibit strong
characteristics of turbulence. Their first-order VSFs have a power-law exponent ranging from ∼ 0.2 − 0.5 on scales of a few toa few tens of pc, generally consistent with Larson’s relation. On the other hand, dense star clusters, such as the Orion Nebula
Cluster (ONC), have experienced rapid dynamical relaxation, and have lost the memory of the initial turbulent kinematics. The
VSFs of several individual groups and the whole Complex all show features supporting local energy injection from supernovae.
The measured strength of turbulence depends on the location relative to the supernova epicenters and the formation history of
the groups. Our detection of turbulence traced by young stars introduces a new method of probing the turbulent kinematics ofthe ISM. Unlike previous gas-based studies with only projected measurements accessible to observations, we utilize the full 6D
information of stars, presenting a more complete picture of the 3D interstellar turbulence.

11. Hunting for the elusive methylene radical
A. M. Jacob, K. M. Menten, Y. Gong, P. Bergman, M. Tiwari, S. Bruenken, A. O. H. Olofsson CH2 transitions
between 68 and 71 GHz were first detected toward the Orion-KL and W51 Main SFRs. Given their upper level energies of 225
K, they were thought to arise in dense, hot molecular cores near newly formed stars. However, this has not been confirmed byfurther observations of these lines and their origin has remained unclear. Generally, there is a scarcity of observational data
for CH2 and, while it is an important compound in the astrochemical context, its actual occurrence in astronomical sources
is poorly constrained. The present study, along with other recent observations of the Orion region we report, rule out thepossibility of an association with gas that is both hot and dense. We find that the distribution of the CH2 emission closely
follows that of the [CII] 158 um emission, while CH2 is undetected toward the hot core itself. The observations suggest, rather,that its extended emission arises from hot but dilute layers of PDRs and not from the denser parts of such regions as in the caseof the Orion Bar. This hypothesis was corroborated by comparisons of the observed CH2 line profiles with those of CRRLs,
well-known PDR tracers. In addition, we report the detection of the 70 GHz fine- and hfs lines of o-CH2 toward the W51E,
W51M, W51N, W49N, W43, W75N, DR21, and S140 SFRs, and three of the fine- and hfs lines between 68-71 GHz toward
W3 IRS5. Furthermore, using a non-LTE radiative transfer analysis, we can constrain the gas temperatures and H2 density
to 163 K and 3.4e3 cm−3 , respectively. This analysis confirms our hypothesis that CH2 originates in warm and dilute PDR
layers. Our analysis suggests that for the excitation conditions under the physical conditions that prevail in such regions, theselines are masering, with weak level inversion. The resulting amplification of the lines’ spontaneous emission greatly aids in theirdetection.

12. Eruptive Behavior of Magnetically Layered Protoplanetary Disks in Low Metallicity

Environments

Kundan Kadam, Eduard Vorobyov, Ágnes Kóspál A protoplanetary disk typically forms a dead zone near its midplaneat the distance of a few au from the central protostar. Accretion through such a magnetically layered disk can be intrinsicallyunstable and has been associated with episodic outbursts in young stellar objects. We present the first investigation into theeffects of low metallicity environment on the structure of the dead zone as well as the resulting outbursting behavior of the
protoplanetary disk. We conducted global numerical hydrodynamic simulations of protoplanetary disk formation and evolution
in the thin-disk limit. The consequences of metallicity were considered via its effects on the gas and dust opacity of the disk, thethickness of the magnetically active surface layer, and the temperature of the prestellar cloud core. We show that the metal poordisks accumulate much more mass in the innermost regions, as compared to the solar metallicity counterparts. The duration of
the outbursting phase also varies with metallicity - the low metallicity disks showed more powerful luminosity eruptions with ashorter burst phase, which was confined mostly to the early, embedded stages of the disk evolution. The lowest metallicity diskswith the higher cloud core temperature showed the most significant differences. The occurrence of outbursts was relatively rarein the disks around low mass stars and this was especially true at lowest metallicities. We conclude that the metal content of
the disk environment can have profound effects on both the disk structure and evolution in terms of episodic accretion.

513. Three-dimensional continuum radiative transfer of polarized radiation in exoplanetaryatmospheres

Moritz Lietzow, Sebastian Wolf, Robert Brunngräber Polarimetry is about to become a powerful tool for determining
the atmospheric properties of exoplanets. To provide the basis for the interpretation of observational results and for predictive
studies to guide future observations, sophisticated analysis tools are required. Our goal is to develop a radiative transfer
tool that contains all the relevant continuum polarization mechanisms for the comprehensive analysis of the polarized flux
resulting from the scattering in the atmosphere of, on the surface of, and in the local planetary environment (e.g., planetary
rings, exomoons) of extra-solar planets. Furthermore, our goal is to avoid common simplifications such as locally plane-parallel
planetary atmospheres, the missing cross-talk between latitudinal and longitudinal regions, or the assumption of either a pointlike star or plane-parallel illumination. As a platform for the newly developed numerical algorithms, we use the 3D Monte Carloradiative transfer code POLARIS. The code is extended and optimized for the radiative transfer in exoplanetary atmospheres.
We investigate the reflected flux and its degree of polarization for different phase angles for a homogeneous cloud-free atmosphereand an inhomogeneous cloudy atmosphere. To take advantage of the 3D radiative transfer and to demonstrate the potentialof the code, the impact of an additional circumplanetary ring on the reflected polarized flux is studied. The presence ofa circumplanetary ring consisting of small water-ice particles has a noticeable impact on the reflected polarized radiation. In
particular, the reflected flux strongly increases at larger phase angles if the planetary orbit is seen edge-on because the consideredparticles tend to scatter forwards. In contrast, the degree of polarization decreases at these phase angles.

14.

The CALYPSO IRAM-PdBI survey of jets from Class 0 protostars. Are jets ubiquitousin young stars?
L. Podio, B. Tabone, C. Codella, F. Gueth, A. Maury, S. Cabrit, B. Lefloch, S. Maret, A. Belloche, P. André,
S. Anderl, M. Gaudel, L. Testi As a part of the CALYPSO large programme, we constrain the properties of protostellar
jets and outflows in a sample of 21 Class 0 protostars with internal luminosities, Lint, from 0.035 to 47 Lsun. We analysehigh angular resolution ( 0.5"-1") IRAM PdBI observations in CO (2-1), SO (56 − 45 ), and SiO (5-4). CO (2-1), which probes
outflowing gas, is detected in all the sources (for the first time in SerpS-MM22 and SerpS-MM18b). Collimated high-velocity
jets in SiO (5-4) are detected in 67% of the sources (for the first time in IRAS4B2, IRAS4B1, L1448-NB, SerpS-MM18a), and
77% of these also show jet/outflow emission in SO (56 − 45 ). In 5 sources (24% of the sample) SO (56 − 45 ) probes the innerenvelope and/or the disk. The CALYPSO survey shows that the outflow phenomenon is ubiquitous and that the detection rateof high-velocity jets increases with protostellar accretion, with at least 80% of the sources with Lint>1 Lsun driving a jet. The
protostellar flows exhibit an onion-like structure, where the SiO jet (opening angle 10o ) is nested into a wider angle SO ( 15o )and CO ( 25o ) outflow. On scales >300 au the SiO jets are less collimated than atomic jets from Class II sources ( 3o ). Velocity
asymmetry between the two jet lobes are detected in one third of the sources, similarly to Class II atomic jets, suggesting thatthe same launching mechanism is at work. Most of the jets are SiO rich (SiO/H2 from >2.4e-7 to >5e-6), which indicatesefficient release of >1%-10% of silicon in gas phase likely in dust-free winds, launched from inside the dust sublimation radius.
The mass-loss rates (from 7e-8 to 3e-6 Msun/yr) are larger than what was measured for Class II jets. Similarly to Class
II sources, the mass-loss rates are 1%-50% of the mass accretion rates suggesting that the correlation between ejection andaccretion in young stars holds from 1e4 yr up to a few Myr.

The Carina Nebula and Gum 31 molecular complex III: The distribution of the 1-3 GHz

15. radio continuum across the whole nebulaDavid Rebolledo, Anne J. Green, Michael G. Burton, Shari L. Breen, Guido Garay We report the most detailed
1 − 3 GHz radio continuum emission map of the nearest region of massive star formation, the Carina Nebula. As part of alarge program with the Australia Telescope Compact Array, we have covered ∼ 12 deg2 , achieving an angular resolution of∼ 16 arcsec, representing the largest and most complete map of the radio continuum to date. Our continuum map shows aspectacular and complex distribution of emission across the nebula, with multiple structures such as filaments, shells, and fronts
across a wide range of size scales. The ionization fronts have advanced far into the southern and northern region of the Galactic
Plane, as fronts are clearly detected at distances ∼ 80 pc from the stellar clusters in the center. We estimated an ionization
photon luminosity QH = (7.8 ± 0.8) × 1050 s−1 which corresponds to ∼ 85% of the total value obtained from stellar population
studies. Thus, approximately 15% of the ionizing flux has escaped from the nebula into the diffuse Galactic Interstellar Medium.
Comparison between radio continuum and the hydrogen atomic and molecular gas maps offers a clear view of the bipolar outflow
driven by the energy released by the massive stellar clusters that also affects the fraction of molecular gas across the nebula.
Comparison between 8µm and 70µm emission maps and the radio continuum reveals how the hot gas permeates through themolecular cloud, shapes the material into features such as pillars, small shells and arc-like structures, and ultimately, escapes.

616. Chemical analysis of early-type stars with planets
C. Saffe, P. Miquelarena, J. Alacoria, M. Flores, M. Jaque Arancibia, D. Calvo, G. Martín Girardi, M. Grosso,
A. Collado Aims. To explore the chemical pattern of early-type stars with planets, searching for a possible signature of planet
formation. In particular, we study a likely relation between the lambda Bootis chemical pattern and the presence of giant
planets. Methods. We performed a detailed abundance determination in a sample of early-type stars with and without planets
via spectral synthesis. Results. We compared the chemical pattern of the stars in our sample (13 stars with planets and 24 stars
without detected planets) with those of lambda Bootis and other chemically peculiar stars. We have found four lambda Bootis
stars in our sample, two of which present planets and circumstellar disks (HR 8799 and HD 169142) and one without planets
detected (HD 110058). We have also identified the first lambda Bootis star orbited by a brown dwarf (zeta Del). This interestingpair lambda Bootis star + brown dwarf could help to test stellar formation scenarios. We found no unique chemical pattern for
the group of early-type stars bearing giant planets. However, our results support, in principle, a suggested scenario in which
giant planets orbiting pre-main-sequence stars possibly block the dust of the disk and result in a lambda Bootis-like pattern.
On the other hand, we do not find a lambda Bootis pattern in different hot-Jupiter planet host stars, which do not support theidea of possible accretion from the winds of hot-Jupiters, recently proposed in the literature. Then, other mechanisms should
account for the presence of the lambda Bootis pattern between main-sequence stars. Finally, we suggest that the formation ofplanets around lambda Bootis stars such as HR 8799 and HD 169142 is also possible through the core accretion process andnot only gravitational instability [abridged]

17. ALMA observations of the early stages of substellar formation in the Lupus 1 and 3

molecular clouds

A. Santamaría-Miranda, I. de Gregorio-Monsalvo, A. L. Plunkett, N. Huélamo, C. López, Á. Ribas, M. R.
Schreiber, K. Mužić, A. Palau, L. B. G. Knee, A. Bayo, F. Comerón, A. Hales The dominant mechanism leading
to the formation of brown dwarfs (BDs) remains uncertain. The most direct keys to formation, which are obtained fromyounger objects (pre-BD cores and proto-BDs), are limited by the very low number statistics available. We aim to identify andcharacterize a set of pre- and proto-BDs as well as Class II BDs in the Lupus 1 and 3 molecular clouds to test their formation
mechanism. We performed ALMA band 6 (1.3 mm) continuum observations of a selection of 64 cores previously identified from
AzTEC/ASTE data (1.1 mm), along with previously known Class II BDs in the Lupus 1 and 3 molecular clouds. Surveyedarchival data in the optical were used to complement these observations. We expect these ALMA observations prove efficientin detecting the youngest sources in these regions, since they probe the frequency domain at which these sources emit most of
their radiation. We detected 19 sources from 15 ALMA fields. Considering all the pointings in our observing setup, the ALMA
detection rate was ∼23% and the derived masses of the detected sources were between ∼0.18 and 124 MJup . We classified thesesources according to their spectral energy distribution as 5 Class II sources, 2 new Class I/0 candidats, and 12 new possible
pre-BD or deeply embedded protostellar candidates. We detected a promising candidate for a Class 0/I proto-BD source andinferred the disk dust mass of a bona fide Class II BD. The pre-BD cores might be the byproduct of an ongoing process oflarge-scale collapse. The Class II BD disks follow the correlation between disk mass and the mass of the central object that isobserved at the low-mass stellar regime. We conclude that it is highly probable that the sources in the sample are formed as ascaled-down version of low-mass star formation, although disk fragmentation may be responsible for a considerable fraction ofBDs.

18. Characterizing the line emission from molecular clouds. Stratified random sampling of

the Perseus cloud

M. Tafalla, A. Usero, A. Hacar Context. The traditional approach to characterize the structure of molecular clouds is to
map their line emission. Aims. We aim to test and apply a stratified random sampling technique that can characterize theline emission from molecular clouds more efficiently than mapping. M ethods. We sampled the molecular emission from the
Perseus cloud using the H2 column density as a proxy. We divided the cloud into ten logarithmically spaced column density
bins, and we randomly selected ten positions from each bin. The resulting 100 cloud positions were observed with the IRAM
30m telescope, covering the 3mm-wavelength band and parts of the 2 and 1mm bands. Results. We focus our analysis on 11
molecular species detected toward most column density bins. In all cases, the line intensity is tightly correlated with the H2column density. For the CO isotopologs, the trend is relatively flat, while for high-dipole moment species such as HCN, CS, andHCO+ the trend is approximately linear. We reproduce this behavior with a cloud model in which the gas density increases
with column density, and where most species have abundance profiles characterized by an outer photodissociation edge andan inner freeze-out drop. The intensity behavior of the high-dipole moment species arises from a combination of excitation
effects and molecular freeze out, with some modulation from optical depth. This quasi-linear dependence with the H2 column
density makes the gas at low column densities dominate the cloud-integrated emission. It also makes the emission from mosthigh-dipole moment species proportional to the cloud mass inside the photodissociation edge. Conclusions. Stratified random
sampling is an efficient technique for characterizing the emission from whole molecular clouds. It shows that despite the complex
appearance of Perseus, its molecular emission follows a relatively simple pattern.

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19.

Behavior of Hydroxyl Radicals on Water Ice at Low Temperatures
Masashi Tsuge, Naoki Watanabe Because chemical reactions on/in cosmic ice dust grains covered by amorphous solid
water (ASW) play important roles in generating a variety of molecules, many experimental and theoretical studies have focusedon the chemical processes occurring on the ASW surface. In laboratory experiments, conventional spectroscopic and massspectrometric detection of stable products is generally employed to deduce reaction channels and mechanisms. However, despite
their importance, the details of chemical reactions involving reactive species (i.e., free radicals) have not been clarified because of
the absence of experimental methods for in situ detection of radicals. Because OH radicals can be easily produced in interstellar
conditions by not only the photolysis and/or ion bombardments of H2O but also the reaction of H and O atoms, they arethought to be one of the most abundant radicals on ice dust. In this context, the development of a close monitoring method ofOH radicals on the ASW surface may help to elucidate the chemical reactions occurring on the ASW surface.

20. Distinguishing between different mechanisms of FU-Orionis-type luminosity outbursts

Eduard I. Vorobyov, Vardan G. Elbakyan, Hauyu Baobab Liu, Michihiro Takami Aims. Accretion and luminosity
bursts triggered by three distinct mechanisms: the magnetorotational instability in the inner disk regions, clump infall ingravitationally fragmented disks and close encounters with an intruder star, were studied to determine the disk kinematiccharacteristics that can help to distinguish between these burst mechanisms. Methods. Numerical hydrodynamics simulationsin the thin-disk limit were employed to model the bursts in disk environments that are expected for each burst mechanism.
Results. We found that the circumstellar disks featuring accretion bursts can bear kinematic features that are distinct fordifferent burst mechanisms, which can be useful when identifying the burst origin. The disks in the stellar encounter andclump-infall models are characterized by tens of percent deviations from the Keplerian rotation, whie the disks in the MRI
models are characterized only a few percent deviation, which is mostly caused by the gravitational instability that fuels the
MRI bursts. Velocity channel maps also show distinct kinks and wiggles, which are caused by gas disk flows that are peculiar
to each considered burst mechanism. The deviations of velocity channels in the burst-hosting disks from a symmetric patterntypical of Keplerian disks are strongest for the clump-infall and collision models, and carry individual features that may be
useful for the identification of the corresponding burst mechanism. The considered burst mechanisms produce a variety of light
curves with the burst amplitudes varying in the ∆ m=2.5-3.7 limits, except for the clump-infall model where ∆ m can reach
5.4, although the derived numbers may be affected by a small sample and boundary conditions. Conclusions. Burst triggering
mechanisms are associated with distinct kinematic features in the burst-hosting disks that may be used for their identification.
Abridged.

HII regions and high-mass starless clump candidates II. Fragmentation and induced star

21. formation at 0.025 pc scale: An ALMA continuum study

S. Zhang, A. Zavagno, A. López-Sepulcre, H. Liu, F. Louvet, M. Figueira, D. Russeil, Y. Wu, J. Yuan, T. G.
S. Pillai The ionization feedback from HII regions modifies the properties of high-mass starless clumps (HMSCs, of several
hundred to a few thousand solar masses with a size of 0.1-1 pc), such as temperature and turbulence, on the clump scale. The
question of whether the presence of HII regions modifies the core-scale fragmentation and star formation in HMSCs remains to
be explored. We aim to investigate the difference of 0.025 pc-scale fragmentation between candidate HMSCs that are strongly
impacted by HII regions and less disturbed ones. We also search for evidence of mass shaping and induced star formation in
the impacted HMSCs. Using the ALMA 1.3 mm continuum with a resolution of 1.3", we imaged eight candidate HMSCs,
including four impacted by HII regions and another four situated in the quiet environment. The less-impacted HMSCs are
selected on the basis of their similar mass and distance compared to the impacted ones to avoid any possible bias linked to theseparameters. A total of 51 cores were detected in eight clumps, with three to nine cores for each clump. Within our limited
sample, we did not find a clear difference in the 0.025 pc-scale fragmentation between impacted and non-impacted HMSCs,
even though HII regions seem to affect the spatial distribution of the fragmented cores. Both types of HMSCs present a thermalthfragmentation with two-level hierarchical features at the clump thermal Jeans length λth
J,clump and 0.3λJ,clump . The ALMA
emission morphology of the impacted HMSCs AGAL010.214-00.306 and AGAL018.931-00.029 sheds light on the capacities of
HII regions to shape gas and dust in their surroundings and possibly to trigger star formation at 0.025 pc-scale in HMSCs.
Future ALMA surveys covering a large number of impacted HMSCs with high turbulence are needed to confirm the trend of
fragmentation indicated in this study.

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