scholarly journals On the structure and kinematics of molecular clouds from large scale mapping of mm-lines

1991 ◽  
Vol 147 ◽  
pp. 11-20
Author(s):  
J. Bally ◽  
W. D. Langer ◽  
R. W. Wilson ◽  
A. A. Stark ◽  
M. W. Pound
Keyword(s):  
Molecular Clouds ◽  
Large Scale ◽  
Massive Stars ◽  
Vital Role ◽  
Solar Neighborhood ◽  
Young Stellar Objects ◽  
Small Scale ◽  
Molecular Gas ◽  
Main Body ◽  
Stellar Objects

Molecular gas in the interior of the Orion superbubble consists of sheets, filaments, and partial shells in which the active star forming dense cloud cores are embedded. The main body of the Orion A and B clouds and at least 14 smaller clouds in Orion region are cometary in appearance suggesting strong interaction with massive stars in the Orion OB association. While the small scale (< 1 pc) structure of the clouds may be determined primarily by internal magnetic fields, gravity, and the effects of outflows from young stellar objects, the large scale morphology and kinematics is affected by the energy injected by massive stars. Supernovae, stellar winds, and radiation have compressed, accelerated, ablated, and dispersed molecular gas over the last 107 years. Most GMC/OB star complexes in the Solar neighborhood exhibit morphological and kinematic properties similar to the Orion region. We argue that energy injection by massive stars plays a vital role in the evolution of the ISM and may be responsible for much of the observed large-scale structure and kinematics of molecular clouds.

scholarly journals On the structure and kinematics of molecular clouds from large scale mapping of mm-lines

1991 ◽  
Vol 147 ◽  
pp. 11-20
Author(s):  
J. Bally ◽  
W. D. Langer ◽  
R. W. Wilson ◽  
A. A. Stark ◽  
M. W. Pound
Keyword(s):  
Molecular Clouds ◽  
Large Scale ◽  
Massive Stars ◽  
Vital Role ◽  
Solar Neighborhood ◽  
Young Stellar Objects ◽  
Small Scale ◽  
Molecular Gas ◽  
Main Body ◽  
Stellar Objects

Molecular gas in the interior of the Orion superbubble consists of sheets, filaments, and partial shells in which the active star forming dense cloud cores are embedded. The main body of the Orion A and B clouds and at least 14 smaller clouds in Orion region are cometary in appearance suggesting strong interaction with massive stars in the Orion OB association. While the small scale (< 1 pc) structure of the clouds may be determined primarily by internal magnetic fields, gravity, and the effects of outflows from young stellar objects, the large scale morphology and kinematics is affected by the energy injected by massive stars. Supernovae, stellar winds, and radiation have compressed, accelerated, ablated, and dispersed molecular gas over the last 107 years. Most GMC/OB star complexes in the Solar neighborhood exhibit morphological and kinematic properties similar to the Orion region. We argue that energy injection by massive stars plays a vital role in the evolution of the ISM and may be responsible for much of the observed large-scale structure and kinematics of molecular clouds.

scholarly journals Bipolar Outflows and Stellar Jets

1987 ◽  
Vol 115 ◽  
pp. 213-237 ◽  
Author(s):  
Ronald L. Snell
Keyword(s):  
Physical Properties ◽  
High Velocity ◽  
Molecular Clouds ◽  
Early Stage ◽  
Young Stellar Objects ◽  
Molecular Gas ◽  
Bipolar Outflows ◽  
Stellar Objects ◽  
Stellar Jets ◽  
Almost All

A wealth of data is now available on the energetic mass outflows that are associated with young stellar objects. This phenomenon is thought to occur at a very early stage in the evolution of stars of almost all masses. The discovery of this energetic event was first made through observations of the rapidly expanding molecular gas that surrounds many of these young stellar objects. A review of the physical properties, including the energetics and morphology, of the expanding molecular gas is presented in this paper. In addition, the role these energetic winds play in affecting the dynamics of the parental molecular clouds is also discussed. Finally, the results of detailed studies of the structure and kinematics of the high velocity molecular gas are reviewed and the evidence for existance of wind-swept cavities and molecular shells within the clouds are presented.

scholarly journals Small Scale Structure in Nearby Molecular Gas

1997 ◽  
Vol 166 ◽  
pp. 251-260 ◽  
Author(s):  
Edith Falgarone
Keyword(s):  
Molecular Clouds ◽  
Column Density ◽  
Angular Resolution ◽  
Ambient Pressure ◽  
Solar Neighborhood ◽  
Small Scale ◽  
High Angular Resolution ◽  
Molecular Gas ◽  
Hierarchy Of Structures ◽  
Co Emission

AbstractRecent observations at high angular resolution of molecular clouds of low column density have revealed the presence of a conspicuous net of small scale filamentary structures, visible in the 12CO rotational lines only. In addition, the existence of unresolved structure at scales as small as ~ 200 AU in space and/or velocity space is inferred from the spectral properties of the 12CO and 13CO emission. The resolved structures are part of the hierarchy of structures observed in molecular gas in the Solar Neighborhood and appear as non self-gravitating elements confined by an ambient pressure P0/kB ~ 3 × 104cm−3 K. We show why these structures might have their origin in the intermittent structures of turbulence in which viscous dissipation is concentrated in space and time.

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 Large-scale star formation in Auriga region

2019 ◽  
Vol 492 (2) ◽  
pp. 2446-2467 ◽  
Author(s):  
A K Pandey ◽  
Saurabh Sharma ◽  
N Kobayashi ◽  
Y Sarugaku ◽  
K Ogura
Keyword(s):  
Star Formation ◽  
Spanning Tree ◽  
Large Scale ◽  
Minimum Spanning Tree ◽  
Young Stellar Objects ◽  
Molecular Gas ◽  
Archival Data ◽  
Stellar Objects ◽  
Tree Analysis ◽  
Formation Efficiency

ABSTRACT New observations in the VI bands along with archival data from the 2MASS and WISE surveys have been used to generate a catalogue of young stellar objects (YSOs) covering an area of about 6° × 6° in the Auriga region centred at l ∼ 173° and b ∼ 1.5°. The nature of the identified YSOs and their spatial distribution are used to study the star formation in the region. The distribution of YSOs along with that of the ionized and molecular gas reveals two ring-like structures stretching over an area of a few degrees each in extent. We name these structures as Auriga Bubbles 1 and 2. The centre of the Bubbles appears to be above the Galactic mid-plane. The majority of Class I YSOs are associated with the Bubbles, whereas the relatively older population, i.e. Class ii objects are rather randomly distributed. Using the minimum spanning tree analysis, we found 26 probable subclusters having five or more members. The subclusters are between ∼0.5 and ∼3 pc in size and are somewhat elongated. The star formation efficiency in most of the subcluster region varies between 5 ${{\ \rm per\ cent}}$ and 20 ${{\ \rm per\ cent}}$ indicating that the subclusters could be bound regions. The radii of these subclusters also support it.

scholarly journals Anatomy of Orion Molecular Clouds—The Astrochemistry Perspective/Approach

2021 ◽  
Vol 8 ◽  
Author(s):  
Dipen Sahu ◽  
Sheng-Yuan Liu ◽  
Tie Liu
Keyword(s):  
Molecular Cloud ◽  
Molecular Clouds ◽  
Large Scale ◽  
Chemical Species ◽  
Young Stellar Objects ◽  
Giant Molecular Clouds ◽  
Stellar Objects ◽  
Chemical Conditions ◽  
Cloud Cores ◽  
Physical And Chemical

The Orion molecular cloud (OMC) complex is the nearest and perhaps the best-studied giant molecular cloud complex within which low-mass and massive star formation occur. A variety of molecular species, from diatomic molecules to complex organic molecules (COMs), have been observed in the OMC regions. Different chemical species are found at different scales—from giant molecular clouds at parsec scales to cloud cores around young stellar objects at hundreds of au scales, and they act as tracers of different physical and chemical conditions of the sources. The OMC, therefore, is an ideal laboratory for studying astrochemistry over a broad spectrum of molecular cloud structures and masses. In this review, we discuss the usage of astrochemistry/molecular tracers and (sub) millimeter observations to understand the physical and chemical conditions of large-scale molecular clouds, filaments, and clumps down to cores and protostars in the OMC complex as a demonstration case.

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

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.

scholarly journals Hα emission-line stars in molecular clouds

2019 ◽  
Vol 630 ◽  
pp. A90 ◽  
Author(s):  
Bertil Pettersson ◽  
Bo Reipurth
Keyword(s):  
Molecular Clouds ◽  
Young Stellar Objects ◽  
Be Stars ◽  
Stellar Objects ◽  
Strong Concentration ◽  
Ob Stars ◽  
Star Forming ◽  
Hα Emission ◽  
Objective Prism ◽  
Emission Stars

A deep objective-prism survey for Hα emission stars towards the Canis Major star-forming clouds was performed. A total of 398 Hα emitters were detected, 353 of which are new detections. There is a strong concentration of these Hα emitters towards the molecular clouds surrounding the CMa OB1 association, and it is likely that these stars are young stellar objects recently born in the clouds. An additional population of Hα emitters is scattered all across the region, and probably includes unrelated foreground dMe stars and background Be stars. About 90% of the Hα emitters are detected by WISE, of which 75% was detected with usable photometry. When plotted in a WISE colour–colour diagram it appears that the majority are Class II YSOs. Coordinates and finding charts are provided for all the new stars, and coordinates for all the detections. We searched the Gaia-DR2 catalogue and from 334 Hα emission stars with useful parallaxes, we selected a subset of 98 stars that have parallax errors of less than 20% and nominal distances in the interval 1050 to 1350 pc that surrounds a strong peak at 1185 pc in the distance distribution. Similarly, Gaia distances were obtained for 51 OB-stars located towards Canis Major and selected with the same parallax errors as the Hα stars. We find a median distance for the OB stars of 1182 pc, in excellent correspondence with the distance from the Hα stars. Two known runaway stars are confirmed as members of the association. Finally, two new Herbig-Haro objects are identified.

scholarly journals Star cluster formation in Orion A

2020 ◽  
Author(s):  
Wanggi Lim ◽  
Fumitaka Nakamura ◽  
Benjamin Wu ◽  
Thomas G Bisbas ◽  
Jonathan C Tan ◽  
...  
Keyword(s):  
Cluster Formation ◽  
Star Cluster ◽  
The Other ◽  
Young Stellar Objects ◽  
Molecular Gas ◽  
Archival Data ◽  
Formation Processes ◽  
Collision Process ◽  
Stellar Objects ◽  
Collision Model

Abstract We introduce new analysis methods for studying the star cluster formation processes in Orion A, especially examining the scenario of a cloud–cloud collision. We utilize the CARMA–NRO Orion survey 13CO (1–0) data to compare molecular gas to the properties of young stellar objects from the SDSS III IN-SYNC survey. We show that the increase of $v_{\rm {}^{13}CO} - v_{\rm YSO}$ and Σ scatter of older YSOs can be signals of cloud–cloud collision. SOFIA-upGREAT 158 μm [C ii] archival data toward the northern part of Orion A are also compared to the 13CO data to test whether the position and velocity offsets between the emission from these two transitions resemble those predicted by a cloud–cloud collision model. We find that the northern part of Orion A, including regions ONC-OMC-1, OMC-2, OMC-3, and OMC-4, shows qualitative agreements with the cloud–cloud collision scenario, while in one of the southern regions, NGC 1999, there is no indication of such a process in causing the birth of new stars. On the other hand, another southern cluster, L 1641 N, shows slight tendencies of cloud–cloud collision. Overall, our results support the cloud–cloud collision process as being an important mechanism for star cluster formation in Orion A.

scholarly journals Study of the 13CO/C18O abundance ratio towards the filamentary infrared dark cloud IRDC 34.43 + 0.24

2019 ◽  
Vol 36 ◽  
Author(s):  
M. B. Areal ◽  
S. Paron ◽  
M. E. Ortega ◽  
L. Duvidovich
Keyword(s):  
Molecular Clouds ◽  
Galactic Plane ◽  
Abundance Ratio ◽  
Young Stellar Objects ◽  
Molecular Gas ◽  
Accurate Analysis ◽  
Good Tool ◽  
Dark Cloud ◽  
Average Value ◽  
Far Ultraviolet

Abstract Nowadays, there are several observational studies about the 13CO/C18O abundance ratio ( $X^{13/18}$ ) towards nearby molecular clouds. These works give observational support to the C18O selective photodissociation due to the interaction between the far ultraviolet (FUV) radiation and the molecular gas. It is necessary to increase the sample of molecular clouds located at different distances and affected in different ways by nearby or embedded H ii regions and OB associations to study the selective photodissociation. Using 12CO, 13CO, and C18O J = 1–0 data obtained from the FOREST unbiased Galactic plane imaging survey performed with the Nobeyama 45-m telescope, we analyse the filamentary infrared dark cloud IRDC $34.43+0.24$ located at the distance of about 3.9 kpc. This infrared dark cloud (IRDC) is related to several H ii regions and young stellar objects. Assuming local thermodynamic equilibrium, we obtain: $0.8 \times 10^{16} <$ N(13CO) $<4 \times 10^{17}$ cm–2 (average value $= 4.2 \times 10^{16}$ cm–2), $0.6 \times 10^{15} <$ N(C18O) $<4.4 \times 10^{16}$ cm–2 (average value $= 5.0 \times 10^{15}$ cm–2), and 3 $<$ $X^{13/18}$ $<$ 30 (average $= 8$ ) across the whole IRDC. Larger values of $X^{13/18}$ were found towards portions of the cloud related to the H ii regions associated with the N61 and N62 bubbles and with the photodissociation regions, precisely the regions in which FUV photons are strongly interacting with the molecular gas. Our result represents an observational support to the C18O selectively photodissociation phenomenon occurring in a quite distant filamentary IRDC. Additionally, based on IR data from the Hi-GAL survey, the FUV radiation field was estimated in Habing units, and the dust temperature (T $_{dust}$ ) and H2 column density (N(H2)) distribution were studied. Using the average of N(H2), values in close agreement with the ‘canonical’ abundance ratios [H2]/[13CO] and [H2]/[C18O] were derived. However, the obtained ranges in the abundance ratios show that if an accurate analysis of the molecular gas is required, the use of the ‘canonical’ values may introduce some bias. Thus, it is important to consider how the gas is irradiated by the FUV photons across the molecular cloud. The analysis of $X^{13/18}$ is a good tool to perform that. Effects of beam dilution and clumpiness were studied.

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