First molecular cloud measurement with Irbene RT-32 radio telescope

2020 ◽  
pp. 39-44
Author(s):  
A ABERFELDS ◽  
A VASYUNIN
Keyword(s):  
Radio Emission ◽  
Radio Astronomy ◽  
Molecular Clouds ◽  
Massive Stars ◽  
Young Star ◽  
Point Of View ◽  
Star Forming ◽  
Emission Point ◽  
Chemical Evaluation ◽  
Molecular Abundances

This paper describes the efforts of the Ventspils International Radio Astronomy Center (VSRC) astrochemist and observation groups to study the formation of massive stars from chemical evaluation and radio emission point of view. By observing all four selected sources chemists group observations can provide important feedback to models, mainly an information for molecules with maser emission. Based on detection of masers in young stellar object (YSO) observations provide information that there are parts of molecular clouds where gas density and molecular abundances are higher by a few orders than in typical young star forming clouds.

scholarly journals Populations of OB-type stars in galaxies

2010 ◽  
Vol 6 (S272) ◽  
pp. 233-241
Author(s):  
Christopher J. Evans
Keyword(s):  
Stellar Evolution ◽  
Massive Stars ◽  
Spectral Synthesis ◽  
High Redshift ◽  
Young Star ◽  
Magellanic Clouds ◽  
Star Forming ◽  
The Galaxy ◽  
External Galaxies

AbstractOne of the challenges for stellar astrophysics is to reach the point at which we can undertake reliable spectral synthesis of unresolved populations in young, star-forming galaxies at high redshift. Here I summarise recent studies of massive stars in the Galaxy and Magellanic Clouds, which span a range of metallicities commensurate with those in high-redshift systems, thus providing an excellent laboratory in which to study the role of environment on stellar evolution. I also give an overview of observations of luminous supergiants in external galaxies out to a remarkable 6.7 Mpc, in which we can exploit our understanding of stellar evolution to study the chemistry and dynamics of the host systems.

scholarly journals Mapping the 13CO/C18O abundance ratio in the massive star-forming region G29.96−0.02

2018 ◽  
Vol 617 ◽  
pp. A14 ◽  
Author(s):  
S. Paron ◽  
M. B. Areal ◽  
M. E. Ortega
Keyword(s):  
Molecular Clouds ◽  
Abundance Ratio ◽  
High Mass ◽  
Local Thermal Equilibrium ◽  
Mass Star ◽  
Galactocentric Distance ◽  
Star Forming ◽  
Physical Conditions ◽  
The Galaxy ◽  
Molecular Abundances

Aims. Estimating molecular abundances ratios from directly measuring the emission of the molecules toward a variety of interstellar environments is indeed very useful to advance our understanding of the chemical evolution of the Galaxy, and hence of the physical processes related to the chemistry. It is necessary to increase the sample of molecular clouds, located at different distances, in which the behavior of molecular abundance ratios, such as the 13CO/C18O ratio, is studied in detail. Methods. We selected the well-studied high-mass star-forming region G29.96−0.02, located at a distance of about 6.2 kpc, which is an ideal laboratory to perform this type of study. To study the 13CO/C18O abundance ratio (X13∕18) toward this region, we used 12CO J = 3–2 data obtained from the CO High-Resolution Survey, 13CO and C18O J = 3–2 data from the 13CO/C18O (J = 3–2) Heterodyne Inner Milky Way Plane Survey, and 13CO and C18O J = 2–1 data retrieved from the CDS database that were observed with the IRAM 30 m telescope. The distribution of column densities and X13∕18 throughout the extension of the analyzed molecular cloud was studied based on local thermal equilibrium (LTE) and non-LTE methods. Results. Values of X13∕18 between 1.5 and 10.5, with an average of about 5, were found throughout the studied region, showing that in addition to the dependency of X13∕18 and the galactocentric distance, the local physical conditions may strongly affect this abundance ratio. We found that correlating the X13∕18 map with the location of the ionized gas and dark clouds allows us to suggest in which regions the far-UV radiation stalls in dense gaseous components, and in which regions it escapes and selectively photodissociates the C18O isotope. The non-LTE analysis shows that the molecular gas has very different physical conditions, not only spatially throughout the cloud, but also along the line of sight. This type of study may represent a tool for indirectly estimating (from molecular line observations) the degree of photodissociation in molecular clouds, which is indeed useful to study the chemistry in the interstellar medium.

scholarly journals Spectral shifting strongly constrains molecular cloud disruption by radiation pressure on dust

2018 ◽  
Vol 611 ◽  
pp. A70 ◽  
Author(s):  
Stefan Reissl ◽  
Ralf S. Klessen ◽  
Mordecai-Mark Mac Low ◽  
Eric W. Pellegrini
Keyword(s):  
Star Formation ◽  
Radiation Pressure ◽  
Formation Process ◽  
Molecular Clouds ◽  
Far Infrared ◽  
Young Star ◽  
Star Forming ◽  
Grain Sizes ◽  
Single Temperature ◽  
Spectral Shifting

Aim. We aim to test the hypothesis that radiation pressure from young star clusters acting on dust is the dominant feedback agent disrupting the largest star-forming molecular clouds and thus regulating the star-formation process.Methods. We performed multi-frequency, 3D, radiative transfer calculations including both scattering and absorption and re-emission to longer wavelengths for model clouds with masses of 104–107 M⊙, containing embedded clusters with star formation efficiencies of 0.009–91%, and varying maximum grain sizes up to 200 μm. We calculated the ratio between radiative and gravitational forces to determine whether radiation pressure can disrupt clouds.Results. We find that radiation pressure acting on dust almost never disrupts star-forming clouds. Ultraviolet and optical photons from young stars to which the cloud is optically thick do not scatter much. Instead, they quickly get absorbed and re-emitted by the dust at thermal wavelengths. As the cloud is typically optically thin to far-infrared radiation, it promptly escapes, depositing little momentum in the cloud. The resulting spectrum is more narrowly peaked than the corresponding Planck function, and exhibits an extended tail at longer wavelengths. As the opacity drops significantly across the sub-mm and mm wavelength regime, the resulting radiative force is even smaller than for the corresponding single-temperature blackbody. We find that the force from radiation pressure falls below the strength of gravitational attraction by an order of magnitude or more for either Milky Way or moderate starbust conditions. Only for unrealistically large maximum grain sizes, and star formation efficiencies far exceeding 50% do we find that the strength of radiation pressure can exceed gravity.Conclusions. We conclude that radiation pressure acting on dust does not disrupt star-forming molecular clouds in any Local Group galaxies. Radiation pressure thus appears unlikely to regulate the star-formation process on either local or global scales.

scholarly journals Physical conditions of star forming sites in the S247/252 molecular complex

1991 ◽  
Vol 147 ◽  
pp. 443-444
Author(s):  
C. Koempe ◽  
G. Joncas ◽  
J.G.A. Wouterloot ◽  
H. Meyerdierks
Keyword(s):  
Star Formation ◽  
Molecular Complex ◽  
Molecular Clouds ◽  
Massive Stars ◽  
Giant Molecular Clouds ◽  
Star Forming ◽  
Physical Conditions ◽  
Input Parameters

By now, it is well established that massive stars form in giant molecular clouds. Numerous studies have shown that star formation, instead of being spread uniformly throughout molecular clouds, occurs in dense condensations located within these clouds. The physical conditions in these condensations are therefore critical input parameters for any theory of star formation.

scholarly journals Metallicity and X-ray luminosity variations in NGC 922

2020 ◽  
Vol 500 (1) ◽  
pp. 962-975
Author(s):  
K Kouroumpatzakis ◽  
A Zezas ◽  
A Wolter ◽  
A Fruscione ◽  
K Anastasopoulou ◽  
...  
Keyword(s):  
Star Formation ◽  
Stellar Population ◽  
Massive Stars ◽  
Star Clusters ◽  
Young Star ◽  
X Ray ◽  
Star Forming ◽  
Star Forming Regions ◽  
Main Driver ◽  
Young Star Clusters

ABSTRACT We present a systematic study of the metallicity variations within the collisional ring galaxy NGC 922 based on long-slit optical spectroscopic observations. We find a metallicity difference between star-forming regions in the bulge and the ring, with metallicities ranging from almost solar to significantly sub-solar ($\rm {[12+\log (O/H)]\sim 8.2}$). We detect $\rm{He\,{\small I}}$ emission in all the studied regions of the bulge and the ring, indicating ionization from massive stars associated with recent (<10 Myr) star formation, in agreement with the presence of very young star clusters. We find an anticorrelation between the X-ray luminosity and metallicity of the sub-galactic regions of NGC 922. The different regions have similar stellar population ages, leaving metallicity as the main driver of the anticorrelation. The dependence of the X-ray emission of the different regions in NGC 922 on metallicity is in agreement with similar studies of the integrated X-ray output of galaxies and predictions from X-ray binary population models.

scholarly journals Structure and Conditions in Massive Star Forming Giant Molecular Clouds

2002 ◽  
Vol 12 ◽  
pp. 140-142
Author(s):  
Jonathan Williams
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Massive Star ◽  
Massive Stars ◽  
The Other ◽  
Giant Molecular Clouds ◽  
Star Forming ◽  
Millimeter Wavelength ◽  
Formation And Evolution ◽  
Self Similar

AbstractMassive stars form in clusters within self-gravitating molecular clouds. The size scale of these clusters is sufficiently large that non-thermal, or turbulent, motions of the gas must be taken into account when considering their formation. Millimeter wavelength radio observations of the gas and dust in these clouds reveal a complex, self-similar structure that reflects the turbulent nature of the gas. Differences are seen, however, towards dense bound cores in proto-clusters. Examination of the kinematics of gas around such cores suggests that dissipation of turbulence may be the first step in the star formation process. Newly formed stars, on the other hand, replenish turbulence through their winds and outflows. In this way, star formation may be self-regulated. Observations and simulations are beginning to demonstrate the key role that cloud turbulence plays in the formation and evolution of stellar groups.

scholarly journals Chemical enrichment from massive stars in starbursts

1999 ◽  
Vol 193 ◽  
pp. 670-678 ◽  
Author(s):  
Henry A. Kobulnicky
Keyword(s):  
Ad Hoc ◽  
Massive Stars ◽  
Spatial Scales ◽  
Young Star ◽  
Fine Tuning ◽  
H Ii Regions ◽  
Chemical Homogeneity ◽  
Star Forming ◽  
Chemical Enrichment ◽  
The Galaxy

The warm ionized gas in low-mass, metal-poor star forming galaxies is chemically homogeneous despite the prevalence of large H II regions which contain hundreds of evolved massive stars, supernovae, and Wolf-Rayet stars with chemically-enriched winds. Galaxies with large WR star content are chemically indistinguishable from other vigorously star-forming galaxies. Furthermore, no significant localized chemical fluctuations are present in the vicinity of young star clusters, despite large expected chemical yields of massive stars. An ad hoc fine-tuning of the release, dispersal and mixing of the massive star ejecta could give rise to the observed homogeneity, but a more probable explanation is that fresh ejecta from massive stars reside in a hard-to-observe hot or cold phase. In any case, the observed chemical homogeneity indicates that heavy elements which have already mixed with the warm interstellar medium (thus accessible to optical spectroscopy) are homogeneously dispersed over scales exceeding 1 kpc. Mixing of fresh ejecta with the surrounding warm ISM apparently requires longer than the lifetimes of typical H II regions (> 107 yr). The lack of observed localized chemical enrichments is consistent with a scenario whereby freshly-synthesized metals from massive stars are expelled into the halos of galaxies in a hot, 106 K phase by supernova-driven winds before they cool and ‘rain’ back down upon the galaxy, creating gradual enrichments on spatial scales >1 kpc.

scholarly journals Global hierarchical collapse in molecular clouds. Towards a comprehensive scenario

2019 ◽  
Vol 490 (3) ◽  
pp. 3061-3097 ◽  
Author(s):  
Enrique Vázquez-Semadeni ◽  
Aina Palau ◽  
Javier Ballesteros-Paredes ◽  
Gilberto C Gómez ◽  
Manuel Zamora-Avilés
Keyword(s):  
Time Scales ◽  
Molecular Clouds ◽  
Large Scale ◽  
Massive Stars ◽  
Formation Rate ◽  
Free Fall ◽  
Star Forming ◽  
Accretion Flows ◽  
The Core ◽  
Mass Segregation

Abstract We present a unified description of the scenario of global hierarchical collapse (GHC). GHC constitutes a flow regime of (non-homologous) collapses within collapses, in which all scales accrete from their parent structures, and small, dense regions begin to contract at later times, but on shorter time-scales than large, diffuse ones. The different time-scales allow for most of the clouds’ mass to be dispersed by the feedback from the first massive stars, maintaining the cloud-scale star formation rate low. Molecular clouds (MCs), clumps, and cores are not in equilibrium, but rather are either undergoing contraction or dispersal. The main features of GHC are as follows: (1) The gravitational contraction is initially very slow, and begins when the cloud still consists of mostly atomic gas. (2) Star-forming MCs are in an essentially pressureless regime, causing filamentary accretion flows from the cloud to the core scale to arise spontaneously. (3) Accreting objects have longer lifetimes than their own free-fall time, due to the continuous replenishment of material. (4) The clouds’ total mass and its molecular and dense mass fractions increase over time. (5) The clouds’ masses stop growing when feedback becomes important. (6) The first stars appear several megayears after global contraction began, and are of low mass; massive stars appear a few megayears later, in massive hubs. (7) The minimum fragment mass may well extend into the brown-dwarf regime. (8) Bondi–Hoyle–Lyttleton-like accretion occurs at both the protostellar and the core scales, accounting for an IMF with slope dN/dM ∝ M−2. (9) The extreme anisotropy of the filamentary network explains the difficulty in detecting large-scale infall signatures. (10) The balance between inertial and gravitationally driven motions in clumps evolves during the contraction, explaining the approach to apparent virial equilibrium, from supervirial states in low-column density clumps and from subvirial states in dense cores. (11) Prestellar cores adopt Bonnor–Ebert-like profiles, but are contracting ever since when they may appear to be unbound. (12) Stellar clusters develop radial age and mass segregation gradients. We also discuss the incompatibility between supersonic turbulence and the observed scalings in the molecular hierarchy. Since gravitationally formed filaments do not develop shocks at their axes, we suggest that a diagnostic for the GHC scenario should be the absence of strong shocks in them. Finally, we critically discuss some recent objections to the GHC mechanism.

scholarly journals Physical conditions of star forming sites in the S247/252 molecular complex

1991 ◽  
Vol 147 ◽  
pp. 443-444
Author(s):  
C. Koempe ◽  
G. Joncas ◽  
J.G.A. Wouterloot ◽  
H. Meyerdierks
Keyword(s):  
Star Formation ◽  
Molecular Complex ◽  
Molecular Clouds ◽  
Massive Stars ◽  
Giant Molecular Clouds ◽  
Star Forming ◽  
Physical Conditions ◽  
Input Parameters

By now, it is well established that massive stars form in giant molecular clouds. Numerous studies have shown that star formation, instead of being spread uniformly throughout molecular clouds, occurs in dense condensations located within these clouds. The physical conditions in these condensations are therefore critical input parameters for any theory of star formation.

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