A Comparison of the Velocity Fields of Young Stellar Objects and of Sharpless H II Regions

1983 ◽  
pp. 73-75 ◽  
Author(s):  
M. H. L. Pryce
Keyword(s):  
Velocity Fields ◽  
Young Stellar Objects ◽  
H Ii Regions ◽  
Stellar Objects

scholarly journals Three generations of stars: a possible case of triggered star formation

2020 ◽  
Vol 496 (1) ◽  
pp. 870-874
Author(s):  
M B Areal ◽  
A Buccino ◽  
S Paron ◽  
C Fariña ◽  
M E Ortega
Keyword(s):  
Star Formation ◽  
Young Stellar Objects ◽  
H Ii Regions ◽  
Stellar Objects ◽  
Three Generations ◽  
The North ◽  
Western Border ◽  
H Ii Region ◽  
New Generation ◽  
North Western

ABSTRACT Evidence for triggered star formation linking three generations of stars is difficult to assemble, as it requires convincingly associating evolved massive stars with H ii regions that, in turn, would need to present signs of active star formation. We present observational evidence for triggered star formation relating three generations of stars in the neighbourhood of the star LS II +26 8. We carried out new spectroscopic observations of LS II +26 8, revealing that it is a B0 III-type star. We note that LS II +26 8 is located exactly at the geometric centre of a semi-shell-like H ii region complex. The most conspicuous component of this complex is the H ii region Sh2-90, which is probably triggering a new generation of stars. The distances to LS II +26 8 and to Sh2-90 are in agreement (between 2.6 and 3 kpc). Analysis of the interstellar medium on a larger spatial scale shows that the H ii region complex lies on the north-western border of an extended H2 shell. The radius of this molecular shell is about 13 pc, which is in agreement with what an O9 V star (the probable initial spectral type of LS II +26 8 as inferred from evolutive tracks) can generate through its winds in the molecular environment. In conclusion, the spatial and temporal correspondences derived in our analysis enable us to propose a probable triggered star formation scenario initiated by the evolved massive star LS II +26 8 during its main-sequence stage, followed by stars exciting the H ii region complex formed in the molecular shell, and culminating in the birth of young stellar objects around Sh2-90.

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

2019 ◽  
Vol 487 (2) ◽  
pp. 1517-1528 ◽  
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.

Molecular Clouds and Star Formation in the Southern H II Regions

1999 ◽  
Vol 51 (6) ◽  
pp. 791-818 ◽  
Author(s):  
Reiko Yamaguchi ◽  
Hiro Saito ◽  
Norikazu Mizuno ◽  
Yoshihiro Mine ◽  
Akira Mizuno ◽  
...  
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Formation Rate ◽  
Point Sources ◽  
Young Stellar Objects ◽  
H Ii Regions ◽  
Stellar Objects ◽  
Order Of Magnitude ◽  
Formation Efficiency ◽  
Active Formation

Abstract We have carried out extensive 13CO(J = 1−0) observations toward 23 southern H II regions associated with bright-rimmed clouds. In total, 95 molecular clouds have been identified to be associated with the H II regions. Among the 95, 57 clouds \ are found to be associated with 204 IRAS point sources which are candidates for young stellar objects. There is a significant increase of star-formation efficiency on the side facing to the H II regions; the luminosity-to-mass ratio, defined as the ratio of the stellar luminosity to the molecular cloud mass, is higher by an order of magnitude on the near side of the H II regions than that on the far side. This indicates that molecular gas facing to the H II regions is more actively forming massive s\ tars whose luminosity is ≳103L⊙. In addition, the number density of the IRAS point sources increases by a factor of 2 on the near side of the H II regions compared with on the far side. These results strongly suggest that the active formation of massive stars on the near side of the H II regions is due to the effects of the H II regions, such as the compression of molecular material by the ionization/shock fronts. For the whole Galaxy, we estimate that the present star-formation rate under such effects is at least 0.2−0.4 M⊙ yr-1, corresponding to a few 10% by mass.

scholarly journals Near-IR integral field spectroscopy of ionizing stars and young stellar objects on the borders of H II regions

2010 ◽  
Vol 510 ◽  
pp. A32 ◽  
Author(s):  
F. Martins ◽  
M. Pomarès ◽  
L. Deharveng ◽  
A. Zavagno ◽  
J. C. Bouret
Keyword(s):  
Young Stellar Objects ◽  
H Ii Regions ◽  
Stellar Objects ◽  
Integral Field Spectroscopy ◽  
Near Ir ◽  
Field Spectroscopy ◽  
Integral Field

scholarly journals THE RMS SURVEY: THE LUMINOSITY FUNCTIONS AND TIMESCALES OF MASSIVE YOUNG STELLAR OBJECTS AND COMPACT H II REGIONS

2011 ◽  
Vol 730 (2) ◽  
pp. L33 ◽  
Author(s):  
Joseph C. Mottram ◽  
Melvin G. Hoare ◽  
Ben Davies ◽  
Stuart L. Lumsden ◽  
Rene D. Oudmaijer ◽  
...  
Keyword(s):  
Young Stellar Objects ◽  
H Ii Regions ◽  
Stellar Objects ◽  
Luminosity Functions

scholarly journals Compact planetary nebulae: improved IR diagnostic criteria based on classification tree modelling

2019 ◽  
Vol 488 (3) ◽  
pp. 3238-3250 ◽  
Author(s):  
Stavros Akras ◽  
Lizette Guzman-Ramirez ◽  
Denise R Gonçalves
Keyword(s):  
Classification Tree ◽  
Planetary Nebulae ◽  
Young Stellar Objects ◽  
H Ii Regions ◽  
Wide Field ◽  
Stellar Objects ◽  
Isaac Newton ◽  
Sky Survey ◽  
Machine Learning Approach ◽  
Tree Models

Abstract Planetary nebulae (PNe) are strong H α line emitters and a lot of new PNe discoveries have been made by the SuperCOSMOS AAO/UKST H α Survey (SHS) and the Isaac Newton Telescope Photometric H α Survey (IPHAS). However, their resulting list of candidates turned out to be heavily contaminated from H α-line mimics like young stellar objects (YSOs) and/or H ii regions. The aim of this work is to find new infrared criteria that can better distinguish compact PNe from their mimics using a machine learning approach and the photometric data from the Two-Micron All-Sky Survey and Wide-field Infrared Survey Explorer. Three classification tree models have been developed with the following colour criteria: W1 − W4 ≥ 7.87 and J − H < 1.10; H − W2 ≥ 2.24 and J − H < 0.50; and Ks− W3 ≥ 6.42 and J − H < 1.31 providing a list of candidates, characterized by a high probability to be genuine PNe. The contamination of this list of candidates from H α mimics is low but not negligible. By applying these criteria to the IPHAS list of PN candidates and the entire IPHAS and VPHAS+ DR2 catalogues, we find 141 sources, from which 92 are known PNe, 39 are new very likely compact PNe (without an available classification or uncertain) and 10 are classified as H ii regions, Wolf–Rayet stars, AeBe stars, and YSOs. The occurrence of false-positive identifications in this technique is between 10 and 15 per cent.

scholarly journals A 12.2 GHz Methanol Maser Survey toward the 6.7 GHz Counterparts Associated with/without UC H ii Regions

2022 ◽  
Vol 258 (1) ◽  
pp. 19
Author(s):  
Shi-Min Song ◽  
Xi Chen ◽  
Zhi-Qiang Shen ◽  
Bin Li ◽  
Kai Yang ◽  
...  
Keyword(s):  
Detection Rate ◽  
Radio Continuum ◽  
Young Stellar Objects ◽  
High Mass ◽  
Continuum Emission ◽  
H Ii Regions ◽  
Stellar Objects ◽  
Methanol Maser ◽  
Physical Environments ◽  
Methanol Masers

Abstract We report a new survey of the 12.2 GHz Class II methanol masers toward a sample of 367 sources with the 6.7 GHz methanol masers conducted with the Shanghai 65 m Tianma Radio Telescope. This sample has been previously made with observations of the radio continuum emission of UC H ii regions by the VLA. A total of 176 sources were detected with the 12.2 GHz methanol maser, with a detection rate of 48%, including 8 new detections. A lower detection rate (<10%) was determined toward the sources in the Galactic longitude ranges of 60°–180°, revealing that the physical environments from those sources in the Local arm or the tails of Galactic arms do not easily excite the 12.2 GHz masers. In addition, two detections of highly excited-state OH masers at the 13.4 GHz transition were made, one of which is a new detection. Compared to previous surveys, one-third of the detected 12.2 GHz masers show considerable flux variations, implying the possible changes of their physical environments associated with variable radiation fields from their host high-mass young stellar objects. A positive log–log correlation is found between the luminosities of the 6.7 and 12.2 GHz masers in our observed sample, suggesting that both the transition masers have similar excitation conditions. The statistical analysis for the relationships between the methanol maser luminosity and UC H ii region spatial size indicates that the maser luminosities of both the 6.7 and 12.2 GHz transitions have a decreasing trend with the spatial sizes of the associated UC H ii regions, indicating that the Class II methanol masers might fade away with the H ii region evolution.

scholarly journals Young Stellar Objects in the Large Magellanic Cloud

1987 ◽  
Vol 115 ◽  
pp. 552-552
Author(s):  
N. Epchtein ◽  
M. A. Braz
Keyword(s):  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Young Stellar Objects ◽  
H Ii Regions ◽  
Type I ◽  
Stellar Objects ◽  
Maser Sources

We present the results of a search for compact infrared objects in the direction of type I OH/H2O maser sources discovered towards H II regions in the Large Magellanic Cloud.

scholarly journals Uncovering distinct environments in an extended physical system around the W33 complex

2020 ◽  
Vol 496 (2) ◽  
pp. 1278-1294 ◽  
Author(s):  
L K Dewangan ◽  
T Baug ◽  
D K Ojha
Keyword(s):  
Physical System ◽  
Large Scale ◽  
Early Stage ◽  
Young Stellar Objects ◽  
Molecular Gas ◽  
H Ii Regions ◽  
Extended System ◽  
Ionized Gas ◽  
Stellar Objects ◽  
Complementary Distribution

ABSTRACT We present a multiwavelength investigation of a large-scale physical system containing the W33 complex. The extended system (∼50 pc × 37 pc) is selected based on the distribution of molecular gas at [29.6, 60.2] km s−1 and of 88 ATLASGAL 870-μm dust clumps at d ∼2.6 kpc. The extended system/molecular cloud traced in the maps of 13CO and C18O emission contains several H ii regions excited by OB stars (age ∼0.3–1.0 Myr) and a thermally supercritical filament (fs1, length ∼17 pc). The filament, which is devoid of ionized gas, shows a dust temperature (Td) of ∼19 K, while the H ii regions have a Td of ∼21–29 K. It suggests the existence of two distinct environments in the cloud. The distribution of Class I young stellar objects (mean age ∼0.44 Myr) traces the early stage of star formation (SF) towards the cloud. At least three velocity components (around 35, 45 and 53 km s−1) are investigated towards the system. The analysis of 13CO and C18O reveals spatial and velocity connections of cloud components at around 35 and 53 km s−1. The observed positions of previously known sources, W33 Main, W33 A and O4–7I stars, are found towards a complementary distribution of these two cloud components. The filament fs1 and a previously known object W33 B are seen towards the overlapping areas of the clouds, where ongoing SF activity is evident. A scenario related to converging/colliding flows from two different velocity components appears to explain well the observed indications of SF activity in the system.

scholarly journals Crystalline silicate absorption at 11.1 μm: ubiquitous and abundant in embedded YSOs and the interstellar medium

2020 ◽  
Vol 493 (3) ◽  
pp. 4463-4517 ◽  
Author(s):  
Tho Do-Duy ◽  
Christopher M Wright ◽  
Takuya Fujiyoshi ◽  
Alistair Glasse ◽  
Ralf Siebenmorgen ◽  
...  
Keyword(s):  
Star Formation ◽  
Interstellar Medium ◽  
Mass Fraction ◽  
Cosmic Ray ◽  
Young Stellar Objects ◽  
Absorption Feature ◽  
H Ii Regions ◽  
Stellar Objects ◽  
Stellar Outflows ◽  
T Tauri

ABSTRACT Utilizing several instruments on 4–8 m telescopes, we have observed a large sample of objects in the mid-infrared (8–13 μm). These comprise a few evolved stars, multiple envelopes of embedded young stellar objects (YSOs) or compact H-II regions, and several sightlines through the interstellar medium (ISM). The latter is where dust resides – and is potentially modified – between its formation in evolved stellar outflows and deposition in molecular clouds. In most objects, we detect not only the well-known 9.7 μm absorption feature of amorphous silicates but also a second absorption band around 11.1 μm whose carrier is attributed to crystalline forsterite. We propose that crystalline silicates are essentially ubiquitous in the ISM and earliest phases of star formation, and are evolutionary precursors to T-Tauri and Herbig stars where such silicates have been commonly found. Modelling shows that in most YSOs, H-II regions and ISM cases, the forsterite mass fraction is between 1 and 2 per cent, suggesting that the younger phases inherit their abundance from the ISM. However, several sources show much stronger features (abundances ≥3 per cent). This suggests that significant processing, perhaps crystallization by thermal annealing, occurs early on in star formation. Most intriguing is the first detection of crystalline silicate in the diffuse ISM. We propose that our observed abundance is consistent with a mass fraction of crystalline silicates of 10–20 per cent injected into the ISM, along with commonly accepted lifetimes against their destruction, but only if cosmic ray-induced amorphization is insignificant over a few Giga years.

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