The Environment of High-Mass Young Stellar Objects

Using high-resolution infrared CO spectroscopy new results have been obtained on the environment of high-mass young stellar objects (YSOs). In particular, a new class of neutral, warm and dense outflows has been discovered. The infrared outflows appear a general phenomenon of the activity of high-mass YSOs. With well-defined and often multiple velocities they seem to correspond to episodic and violent mass-loss events from the central source. In addition, a shell of warm, quiescent gas, is formed near the massive star. All these dynamical elements influence the chemistry inside the giant molecular clouds. Beside CO in solid and in gas phase, detection in the infrared has been attempted of simple molecules like CH4, C2H2, H2O and ion H3+ toward few of these sources.

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Dense molecular clouds and associated star formation in the Magellanic Clouds

Proceedings of the International Astronomical Union ◽

10.1017/s1743921307001196 ◽

2006 ◽

Vol 2 (S237) ◽

pp. 40-46

Author(s):

Mónica Rubio

Keyword(s):

Star Formation ◽

Uv Radiation ◽

Molecular Clouds ◽

Massive Star ◽

Dust Emission ◽

Young Stellar Objects ◽

Continuum Emission ◽

Giant Molecular Clouds ◽

Stellar Objects ◽

Ir Sources

AbstractMultiwavelengths studies of massive star formation regions in the LMC and SMC reveal that a second generation of stars is being formed in dense molecular clouds located in the surroundings of the massive clusters. These dense molecular clouds have survived the action of massive star UV radiation fields and winds and they appear as compact dense H2 knots in regions of weak CO emission. Alternatively, we have found that large molecular clouds, probably remnants of the parental giant molecular clouds where the first generation of stars were formed, are suffering the interaction of the winds and UV radiation field in their surfaces in the direction of the central massive cluster or massive stars. These molecular regions show 1.2 mm continuum emission form cold dust and they show embedded IR sources as determined from deep ground base JHKs imaging. The distribution of young IR sources as determined from their Mid IR colors obtained by SPITZER concentrate in the maxima of CO and dust emission. IR spectroscopy of the embedded sources with high IR excess confirm their nature as massive young stellar objects (MYSO's). Our results are suggestive of contagious star formation where triggering and induced star formation could be taking place.

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Formation of high-mass stars in an isolated environment in the Large Magellanic Cloud

Publications of the Astronomical Society of Japan ◽

10.1093/pasj/psz011 ◽

2019 ◽

Vol 71 (2) ◽

Cited By ~ 3

Author(s):

Ryohei Harada ◽

Toshikazu Onishi ◽

Kazuki Tokuda ◽

Sarolta Zahorecz ◽

Annie Hughes ◽

...

Keyword(s):

Star Formation ◽

Large Magellanic Cloud ◽

Magellanic Cloud ◽

Young Stellar Objects ◽

High Mass ◽

Mass Star ◽

Giant Molecular Clouds ◽

Stellar Objects ◽

Stellar Cluster ◽

The Galaxy

Abstract The aim of this study is to characterize the distribution and basic properties of the natal gas associated with high-mass young stellar objects (YSOs) in isolated environments in the Large Magellanic Cloud. High-mass stars usually form in giant molecular clouds (GMCs) as part of a young stellar cluster, but some OB stars are observed far from GMCs. By examining the spatial coincidence between the high-mass YSOs and 12CO (J = 1–0) emission detected by NANTEN and Mopra observations, we selected ten high-mass YSOs that are located away from any of the NANTEN clouds but are detected by the Mopra pointed observations. The ALMA observations revealed that a compact molecular cloud whose mass is a few thousand solar masses or smaller is associated with the high-mass YSOs, which indicates that these compact clouds are the sites of high-mass star formation. The high density and high temperature throughout the clouds are explained by the severe photodissociation of CO due to the lower metallicity than in the Galaxy. The star formation efficiency ranges from several to as high as ∼40%, indicating efficient star formation in these environments. The enhanced turbulence may be a cause of the efficient star formation therein, as judged from the gas velocity information and the association with the lower density gas.

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NIR integral field spectroscopy of high mass young stellar objects

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313000343 ◽

2012 ◽

Vol 8 (S292) ◽

pp. 53-53

Author(s):

K. Murakawa ◽

S. L. Lumsden ◽

R. D. Oudmaijer ◽

B. Davies ◽

M. G. Hoare

Keyword(s):

Gas Phase ◽

Adaptive Optics ◽

Three Dimensional ◽

Young Stellar Objects ◽

High Mass ◽

Spectral Features ◽

Stellar Objects ◽

Integral Field Spectroscopy ◽

Field Spectroscopy ◽

Integral Field

AbstractWe present K-band Integral Field Spectroscopy of six high mass young stellar objects (IRAS~18151–1208, AFGL~2136, S106~IRS4, V645 Cyg, IRAS~19065+0526, and G082.5682+ 00.4040) obtained using the adaptive optics assisted NIFS instrument mounted on the Gemini North telescope. The targets are chosen from the Red MSX Source survey led by University of Leeds. The data show the spectral features of Brγ, H2, and gas phase CO emissions and absorptions with a spectral resolution of R ≈ 5500, which allow a three-dimensional spectro-astrometric analysis of the line emissions. We discuss the results of the ionized jets and winds, and rotating CO torus.

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Investigating formation of isolated intermediate/massive YSOs in the LMC

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316007936 ◽

2015 ◽

Vol 11 (S315) ◽

Author(s):

Ryohei Harada ◽

Toshikazu Onishi ◽

Annie Hughes ◽

Margaret Meixner ◽

Marta Sewilo ◽

...

Keyword(s):

Initial Conditions ◽

Large Magellanic Cloud ◽

Young Stellar Objects ◽

High Mass ◽

Giant Molecular Clouds ◽

Stellar Objects ◽

B Stars ◽

Stellar Cluster ◽

Neutral Gas ◽

Co Emission

AbstractHigh-mass stars usually form in giant molecular clouds (GMCs) as part of a young stellar cluster, but some isolated O/B stars are observed. What are the initial conditions that lead to the formation of these objects? The aim of this study is to measure the distribution and basic physical properties of the neutral gas associated with isolated intermediate- and high-mass young stellar objects (YSOs) in the Large Magellanic Cloud.As part of the SAGE Spitzer Legacy program for the LMC, we have identified and confirmed YSOs using Spitzer IRAC photometry and IRS spectroscopy. By examining the spatial coincidence between the YSOs and 12CO(1–0) emission detected by the NANTEN mapping survey, we identified more than one hundred intermediate/massive YSOs in the LMC that appear to be isolated, i.e. not associated with CO emission. Deeper follow-up CO observations by our team with the higher resolution by Mopra Telescope (beam=30”) detected CO emission at the YSO positions for ~80% of the isolated LMC YSOs. We obtained ALMA data of some of the targets during Cycle 2. We targeted a small but representative (in terms of their association with neutral gas tracers) sample of the isolated high-mass YSOs that we have been studying in the LMC. All of our 12 targets are separated by more than 200 pc from known CO clouds. Our analysis of the ALMA data shows that a compact molecular cloud whose mass is a few thousand solar masses or smaller is associated with most of the YSOs.

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Principal component analysis tomography in near-infrared integral field spectroscopy of young stellar objects – I. Revisiting the high-mass protostar W33A

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab358 ◽

2021 ◽

Vol 503 (1) ◽

pp. 270-291

Author(s):

F Navarete ◽

A Damineli ◽

J E Steiner ◽

R D Blum

Keyword(s):

Large Scale ◽

Near Infrared ◽

Rotation Axis ◽

Principal Component ◽

Young Stellar Objects ◽

High Mass ◽

Continuum Emission ◽

Rotating Disc ◽

Stellar Objects ◽

K Band

ABSTRACT W33A is a well-known example of a high-mass young stellar object showing evidence of a circumstellar disc. We revisited the K-band NIFS/Gemini North observations of the W33A protostar using principal components analysis tomography and additional post-processing routines. Our results indicate the presence of a compact rotating disc based on the kinematics of the CO absorption features. The position–velocity diagram shows that the disc exhibits a rotation curve with velocities that rapidly decrease for radii larger than 0.1 arcsec (∼250 au) from the central source, suggesting a structure about four times more compact than previously reported. We derived a dynamical mass of 10.0$^{+4.1}_{-2.2}$ $\rm {M}_\odot$ for the ‘disc + protostar’ system, about ∼33 per cent smaller than previously reported, but still compatible with high-mass protostar status. A relatively compact H2 wind was identified at the base of the large-scale outflow of W33A, with a mean visual extinction of ∼63 mag. By taking advantage of supplementary near-infrared maps, we identified at least two other point-like objects driving extended structures in the vicinity of W33A, suggesting that multiple active protostars are located within the cloud. The closest object (Source B) was also identified in the NIFS field of view as a faint point-like object at a projected distance of ∼7000 au from W33A, powering extended K-band continuum emission detected in the same field. Another source (Source C) is driving a bipolar $\rm {H}_2$ jet aligned perpendicular to the rotation axis of W33A.

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Early results from a diagnostic 1.3 cm survey of massive young protostars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921312007594 ◽

2012 ◽

Vol 8 (S287) ◽

pp. 497-501

Author(s):

Crystal L. Brogan ◽

Todd R. Hunter ◽

Claudia J. Cyganowski ◽

Remy Indebetouw ◽

Rachel Friesen ◽

...

Keyword(s):

Massive Star ◽

Thermal Emission ◽

Young Stellar Objects ◽

Large Array ◽

Stellar Objects ◽

Very Large Array ◽

Early Results ◽

Wide Range ◽

First Time ◽

24 Ghz

AbstractWe have used the recently-upgraded Karl G. Jansky Very Large Array (JVLA) to conduct a K-band (~24 GHz) study of 22 massive young stellar objects in 1.3 cm continuum and a comprehensive set of diagnostic lines. This survey is unique in that it samples a wide range of massive star formation signposts simultaneously for the first time. In this proceeding we present preliminary results for the 11 sources in the 2-4 kpc distance bin. We detect compact NH3 cores in all of the fields, with many showing emission up through the (6,6) transition. Maser emission in the 25 GHz CH3OH ladder is present in 7 of 11 sources. We also detect non-thermal emission in the NH3 (3,3) transition in 7 of 11 sources.

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Characterizing the radio continuum nature of sources in the massive star-forming region W75N (B)

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1742 ◽

2020 ◽

Vol 496 (3) ◽

pp. 3128-3141 ◽

Cited By ~ 1

Author(s):

A Rodríguez-Kamenetzky ◽

C Carrasco-González ◽

J M Torrelles ◽

W H T Vlemmings ◽

L F Rodríguez ◽

...

Keyword(s):

Massive Star ◽

Radio Continuum ◽

Young Stellar Objects ◽

Stellar Objects ◽

Very Large Array ◽

Star Forming ◽

Thermal Radio ◽

Wide Range ◽

H Ii Region ◽

Continuum Data

ABSTRACT The massive star-forming region W75N (B) is thought to host a cluster of massive protostars (VLA 1, VLA 2, and VLA 3) undergoing different evolutionary stages. In this work, we present radio continuum data with the highest sensitivity and angular resolution obtained to date in this region, using the VLA-A and covering a wide range of frequencies (4–48 GHz), which allowed us to study the morphology and the nature of the emission of the different radio continuum sources. We also performed complementary studies with multi-epoch Very Large Array (VLA) data and Atacama Large Millimeter Array (ALMA) archive data at 1.3 mm wavelength. We find that VLA 1 is driving a thermal radio jet at scales of ≈0.1 arcsec (≈130 au), but also shows signs of an incipient hypercompact H ii region at scales of ≲1 arcsec (≲1300 au). VLA 3 is also driving a thermal radio jet at scales of a few tenths of arcsec (few hundred of au). We conclude that this jet is shock exciting the radio continuum sources Bc and VLA 4 (obscured Herbig–Haro objects), which show proper motions moving outward from VLA 3 at velocities of ≈112–118 km s−1. We have also detected three new weak radio continuum sources, two of them associated with millimetre continuum cores observed with ALMA, suggesting that these two sources are also embedded young stellar objects in this massive star-forming region.

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Molecular environs and triggered star formation around the large Galactic infrared bubble N 24

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz1269 ◽

2019 ◽

Vol 487 (2) ◽

pp. 1517-1528 ◽

Cited By ~ 2

Author(s):

Xu Li ◽

Jarken Esimbek ◽

Jianjun Zhou ◽

W A Baan ◽

Weiguang Ji ◽

...

Keyword(s):

Star Formation ◽

Massive Star ◽

Young Stellar Objects ◽

Collapse Mechanism ◽

Kinetic Temperature ◽

H Ii Regions ◽

Dark Cloud ◽

Stellar Objects ◽

Multi Wavelength ◽

Mass Size

Abstract A multi-wavelength analysis of the large Galactic infrared bubble N 24 is presented in this paper in order to investigate the molecular and star-formation environment around expanding H ii regions. Using archival data from Herschel and ATLASGAL, the distribution and physical properties of the dust over the entire bubble are studied. Using the Clumpfind2d algorithm, 23 dense clumps are identified, with sizes and masses in the range 0.65–1.73 pc and 600–16 300 M⊙, respectively. To analyse the molecular environment in N 24, observations of NH3 (1,1) and (2,2) were carried out using the Nanshan 26-m radio telescope. Analysis of the kinetic temperature and gravitational stability of these clumps suggests gravitational collapse in several of them. The mass–size distributions of the clumps and the presence of massive young protostars indicate that the shell of N 24 is a region of ongoing massive-star formation. The compatibility of the dynamical and fragmentation timescales and the overabundance of young stellar objects and clumps on the rim suggest that the ‘collect-and-collapse’ mechanism is in play at the boundary of the bubble, but the existence of the infrared dark cloud at the edge of bubble indicates that a ‘radiation-driven implosion’ mechanism may also have played a role there.

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