The relation between OB stars, H II regions & molecular clouds

2008 ◽  
pp. 199-206
Author(s):  
Ralph A. Gaume
Keyword(s):  
Molecular Clouds ◽  
H Ii Regions ◽  
Ob Stars

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 Distribution of star-forming complexes and the structure of our Galaxy

2003 ◽  
Vol 212 ◽  
pp. 431-440 ◽  
Author(s):  
Delphine Russeil
Keyword(s):  
Large Scale ◽  
Stellar Population ◽  
Line Of Sight ◽  
H Ii Regions ◽  
Spiral Arms ◽  
Ob Stars ◽  
Star Forming ◽  
Optical Images ◽  
External Galaxies

The determination of the external galaxies morphology is generally based on their appearance on optical images. At these wavelengths young stellar population and their associated H ii regions, which can be grouped into star-forming complexes, appear preferentially located along spiral arms. Hence, it is naturally to use the same tracers to delineate the arms of our own Galaxy. But, where for external galaxies the distribution of star-forming complexes along the spiral arms is generally evident from direct imaging, for our Galaxy the spiral arms are strung out along the line of sight, leading to the superposition and mixing of information from the different complexes in the spiral arms making it difficult to distinguish them. Thus to access to the spatial distribution of young objects, hence to the large scale structure of our Galaxy, it is required first to identify and collect star-forming complexes (molecular clouds – H ii regions – OB stars) and then to determine their distance. In this framework I review the observational results and difficulties concerning the distribution of star-forming complexes and the determination of the structure of our Galaxy.

scholarly journals Continuum Wavelength Emission from Embedded, Young, and Massive Stellar Objects Beyond 1 μm

1990 ◽  
Vol 139 ◽  
pp. 113-114
Author(s):  
Thomas Henning ◽  
Werner Pfau
Keyword(s):  
Molecular Clouds ◽  
Dust Emission ◽  
Average Energy ◽  
Hii Regions ◽  
Point Sources ◽  
Color Temperature ◽  
Stellar Objects ◽  
Ob Stars ◽  
Infrared Background ◽  
Wavelength Emission

One of the components of the galactic infrared background (GIRB) radiation is emission by warm dust grains heated by OB stars embedded in molecular clouds. The main contributors are compact HII regions and comparatively radioquiet infrared (IR) point sources such as the Becklin-Neugebauer object. We present the average energy distribution between 1 and 1300 μm for a sample of BN-type objects. The average color temperature between 60 and 100 μm is ~40 K, which is very similar to the color temperature of the observed warm galactic dust emission (WGDE).

Streaming motions of molecular clouds, ionized hydrogen, and OB stars in the Cygnus arm

2001 ◽  
Vol 45 (1) ◽  
pp. 34-43
Author(s):  
T. G. Sitnik ◽  
A. M. Mel’nik ◽  
V. V. Pravdikova
Keyword(s):  
Molecular Clouds ◽  
Ob Stars

scholarly journals Giant Molecular Clouds in the Galaxy: The Massachusetts-Stony Brook CO Galactic Plane Survey

1987 ◽  
Vol 115 ◽  
pp. 499-499 ◽  
Author(s):  
P. M. Solomon
Keyword(s):  
Molecular Clouds ◽  
Galactic Plane ◽  
Far Infrared ◽  
Formation Mechanisms ◽  
H Ii Regions ◽  
Giant Molecular Clouds ◽  
Star Forming ◽  
The Galaxy ◽  
Two Populations ◽  
Spiral Arm

The CO Galactic Plane Survey consists of 40,572 spectral line observations in the region between 1 = 8° to 90° and b = −1°.05 to +1°.05 spaced every 3 arc minutes, carried out with the FCRAO 14-m antenna. The velocity coverage from −100 to +200 km/s includes emission from all galactic radii. This high resolution survey was designed to observe and identify essentially all molecular clouds or cloud components larger than 10 parsecs in the inner galaxy. There are two populations of molecular clouds which separate according to temperature. The warm clouds are closely associated with H II regions, exhibit a non-axisymmetric galactic distribution and are a spiral arm population. The cold clouds are a disk population, are not confined to any patterns in longitude-velocity space and must be widespread in the galaxy both in and out of spiral arms. The correlation between far infrared luminosities from IRAS, and molecular masses from CO is utilized to determine a luminosity to mass ratio for the clouds. A face-on picture of the galaxy locating the warm population is presented, showing ring like or spiral arm features at R ∼ 5, 7.5 and 9 kpc. The cloud size and mass spectrum will be discussed and evidence presented showing the presence of clusters of giant molecular clouds with masses of 106 to 107 M⊙. The two populations of clouds probably have different star forming luminosity functions. The implication of the two populations for star formation mechanisms will be discussed.

scholarly journals Chemical evolution of HC3N in dense molecular clouds

2019 ◽  
Vol 489 (4) ◽  
pp. 4497-4512
Author(s):  
Naiping Yu ◽  
Jun-Jie Wang ◽  
Jin-Long Xu
Keyword(s):  
Chemical Evolution ◽  
Molecular Clouds ◽  
Galactic Plane ◽  
Density Ratio ◽  
The Other ◽  
H Ii Regions ◽  
Evolutionary Trend ◽  
Dust Temperature ◽  
Uv Photons ◽  
Cloud Evolution

ABSTRACT We investigated the chemical evolution of HC3N in six dense molecular clouds, using archival available data from the Herschel infrared Galactic Plane Survey (Hi-GAL) and the Millimeter Astronomy Legacy Team Survey at 90 GHz (MALT90). Radio sky surveys of the Multi-Array Galactic Plane Imaging Survey (MAGPIS) and the Sydney University Molonglo Sky Survey (SUMSS) indicate these dense molecular clouds are associated with ultracompact H ii (UCH ii) regions and/or classical H ii regions. We find that in dense molecular clouds associated with normal classical H ii regions, the abundance of HC3N begins to decrease or reaches a plateau when the dust temperature gets hot. This implies UV photons could destroy the molecule of HC3N. On the other hand, in the other dense molecular clouds associated with UCH ii regions, we find the abundance of HC3N increases with dust temperature monotonously, implying HC3N prefers to be formed in warm gas. We also find that the spectra of HC3N (10-9) in G12.804−0.199 and RCW 97 show wing emissions, and the abundance of HC3N in these two regions increases with its non-thermal velocity width, indicating HC3N might be a shock origin species. We further investigated the evolutionary trend of N(N2H+)/N(HC3N) column density ratio, and found this ratio could be used as a chemical evolutionary indicator of cloud evolution after the massive star formation is started.

scholarly journals POLARIMETRY OF INFRARED SOURCES

1981 ◽  
Vol 96 ◽  
pp. 223-236 ◽  
Author(s):  
H. M. Dyck ◽  
Carol J. Lonsdale
Keyword(s):  
Molecular Clouds ◽  
H Ii Regions ◽  
Small Particles ◽  
Stellar Radiation ◽  
Cool Stars ◽  
The Galaxy ◽  
Circumstellar Shells ◽  
Infrared Wavelengths ◽  
Stellar Sources ◽  
Infrared Sources

Polarization at infrared wavelengths has been detected from a number of different objects within the Galaxy. These include young sources associated with molecular clouds and H II regions, cool stars with thick circumstellar shells, bi-polar nebulae, and normal stars suffering interstellar polarization. Typical levels of polarization detected at 2.2 μm are up to 25% for the molecular cloud sources, less than −5% for the cool stars, around 30% for some bi-polar nebulae and less than −2% for interstellar polarization. For the latter three types of source the origin of the polarization is basically understood: it results from scattering of stellar radiation off small particles in the surrounding shell or nebula in the cool stars and bi-polar nebulae and by transfer of flux through a foreground medium of aligned dust grains for the interstellar polarization. The phenomenon of large infrared polarization in the young stellar and pre-stellar sources is less well understood, and it is to this problem that we address ourselves in this review.

12.2 GHz CH3OH Absorption in Southern Molecular Clouds

1991 ◽  
Vol 9 (2) ◽  
pp. 287-288
Author(s):  
R. Peng ◽  
J. B. Whiteoak
Keyword(s):  
Optical Depth ◽  
Molecular Clouds ◽  
Column Density ◽  
H Ii Regions ◽  
Maser Emission ◽  
Dark Clouds

AbstractWe have used the Parkes 64m telescope to observe the 20 → 3−1E absorption of CH3 OH at 12.2 GHz towards 58 Galactic H II regions and dark clouds, yielding 38 detections. The results show that CH3 OH absorbing clouds have a typical optical depth of 0.25 and a column density of 8.4 × 1015 cm−2. CH3 OH absorption is often accompanied by unsaturated maser emission and is closely associated with background H II regions. CH3 OH absorption against the 2.7 K background is also observed in several dark clouds.

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.

Sign in / Sign up

Export Citation Format

Share Document