scholarly journals Masers in star forming regions

2012 ◽  
Vol 8 (S287) ◽  
pp. 117-126 ◽  
Author(s):  
Anna Bartkiewicz ◽  
Huib Jan van Langevelde
Keyword(s):  
Star Formation ◽  
Young Stars ◽  
Jets And Outflows ◽  
Maser Emission ◽  
Star Forming ◽  
Physical Conditions ◽  
Theoretical Progress ◽  
Star Forming Regions

AbstractMaser emission plays an important role as a tool in star formation studies. It is widely used for deriving kinematics, as well as the physical conditions of different structures, hidden in the dense environment very close to the young stars, for example associated with the onset of jets and outflows. We will summarize here the recent observational and theoretical progress on this topic since the last maser symposium: the IAU Symposium 242 in Alice Springs.

scholarly journals Structure of SiO masers in Orion-KL

2002 ◽  
Vol 206 ◽  
pp. 290-293 ◽  
Author(s):  
Sheperd Doeleman ◽  
Colin Lonsdale ◽  
Paul Kondratko ◽  
Whitney Raas ◽  
C. Read Predmore
Keyword(s):  
Star Formation ◽  
Central Star ◽  
Young Star ◽  
High Mass ◽  
Mass Star ◽  
Maser Emission ◽  
Hii Region ◽  
Star Forming ◽  
Physical Conditions ◽  
Star Forming Regions

The Orion-KL nebula is the closest (450pc) site of high-mass star formation and exhibits powerful outflows associated with protostars. It is also one of only three known star forming regions to exhibit SiO maser emission. Emission in three SiO maser transitions (v=1 J=1 → 0, v=1 J=2 → 1, and v=2 J=1 → 0) imaged by VLBI exhibits an “X” morphology suggesting that the Orion masers form along the outlines of two opposing conical outflows to the NW and SE. At the center of this “X”, VLA observations find emission from an HII region presumably associated with a young star whose wind drives the outflow. The SiO masers probably form along the interface between the stellar wind and surrounding parent cloud. We find that SiO maser emission from different transitions preferentially occurs at different radii from the central star implying that the masers are tracers for physical conditions in the wind-cloud interaction region. On the smallest scales, some individual maser features in each transition overlap both spatially and in velocity providing strong evidence that more than one transition can mase within the same volume of gas.

scholarly journals Millimetre wavelength methanol masers survey towards massive star forming regions

2007 ◽  
Vol 3 (S242) ◽  
pp. 234-235
Author(s):  
T. Umemoto ◽  
N. Mochizuki ◽  
K. M. Shibata ◽  
D.-G. Roh ◽  
H.-S. Chung
Keyword(s):  
Detection Rate ◽  
Massive Star ◽  
Molecular Line ◽  
Maser Emission ◽  
Star Forming ◽  
Methanol Maser ◽  
Physical Conditions ◽  
Star Forming Regions ◽  
Methanol Masers ◽  
Maser Sources

AbstractWe present the results of a mm wavelength methanol maser survey towards massive star forming regions. We have carried out Class II methanol maser observations at 86.6 GHz, 86.9 GHz and 107.0 GHz, simultaneously, using the Nobeyama 45 m telescope. We selected 108 6.7 GHz methanol maser sources with declinations above −25 degrees and fluxes above 20 Jy. The detection limit of maser observations was ~3 Jy. Of the 93 sources surveyed so far, we detected methanol emission in 25 sources (27%) and “maser” emission in nine sources (10%), of which thre “maser” sources are new detections. The detection rate for maser emission is about half that of a survey of the southern sky (Caswell et al. 2000). There is a correlation between the maser flux of 107 GHz and 6.7 GHz/12 GHz emission, but no correlation with the “thermal” (non maser) emission. From results of other molecular line observations, we found that the sources with methanol emission show higher gas temperatures and twice the detection rate of SiO emission. This may suggest that dust evaporation and destruction by shock are responsible for the high abundance of methanol molecules, one of the required physical conditions for maser emission.

scholarly journals SiO Masers in the Star Forming Regions W51 IRS2 and Sgr B2 MD5

1987 ◽  
Vol 115 ◽  
pp. 178-178
Author(s):  
N. Ukita ◽  
T. Hasegawa ◽  
N. Kaifu ◽  
K.-I. Morita ◽  
S. Okumura ◽  
...  
Keyword(s):  
Star Formation ◽  
Excited States ◽  
Line Intensity ◽  
Massive Star ◽  
Massive Star Formation ◽  
Vibrationally Excited ◽  
Maser Emission ◽  
Star Forming ◽  
Star Forming Regions ◽  
Upper Limit

The maser emission of the J = 1-0 lines of SiO in vibrationally excited states has been detected in two regions of massive star formation, W51 IRS2 and Sgr B2 MD5. The SiO masers apparently coincide with strong H2O masers in each source within the uncertainties of < 5″. Their velocity ranges fall within those of the nearest H2O masers (Figure 1). In W51 IRS2 the maser emission is observed only in the v = 2 state, and the upper limit of the v = 1 line (3σ) is 1/15th of the v = 2 line intensity. The v = 1 emission found in Sgr B2 MD5 is five times stronger than the marginally detected v = 2 emission (Figure 2). Their luminosities are comparable to those from the corresponding maser in Orion.

scholarly journals Constraining How Star Formation Proceeds: Surveys in the Sub-mm and FIR

2009 ◽  
Vol 5 (H15) ◽  
pp. 406-407
Author(s):  
Doug Johnstone
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Mass Star ◽  
Star Forming ◽  
Physical Conditions ◽  
Star Forming Regions ◽  
Dense Cores ◽  
Multi Wavelength ◽  
Low Mass ◽  
High Column

AbstractCoordinated multi-wavelength surveys of molecular clouds are providing strong constraints on the physical conditions within low-mass star-forming regions. In this manner, Perseus and Ophiuchus have been exceptional laboratories for testing the earliest phases of star formation. Highlights of these results are: (1) dense cores form only in high column density regions, (2) dense cores contain only a few percent of the cloud mass, (3) the mass distribution of the dense cores is similar to the IMF, (4) the more massive cores are most likely to contain embedded protostars, and (5) the kinematics of the dense cores and the bulk gas show significant coupling.

scholarly journals Studying Young Stars with Large Spectroscopic Surveys

2015 ◽  
Vol 10 (S314) ◽  
pp. 276-279
Author(s):  
Sarah L. Martell
Keyword(s):  
Star Formation ◽  
Formation Rate ◽  
Mass Function ◽  
Young Star ◽  
Initial Mass Function ◽  
Young Stars ◽  
Star Forming ◽  
Star Forming Regions ◽  
Star Studies ◽  
History Of

AbstractGalactic archaeology is the study of the history of star formation and chemical evolution in the Milky Way, based on present-day stellar populations. Studies of young stars are a key anchor point for Galactic archaeology, since quantities like the initial mass function and the star formation rate can be studied directly in young clusters and star forming regions. Conversely, massive spectroscopic Galactic archaeology surveys can be used as a data source for young star studies.

scholarly journals Low-Mass Versus High-Mass Star Formation

1997 ◽  
Vol 182 ◽  
pp. 537-549
Author(s):  
T. W. Hartquist ◽  
J. E. Dyson
Keyword(s):  
Star Formation ◽  
Young Stars ◽  
High Mass ◽  
Mass Star ◽  
Low Mass Stars ◽  
Star Forming ◽  
Star Forming Regions ◽  
Dense Cores ◽  
Global Properties ◽  
Low Mass

Structures like the clumps identified in the CO maps of the Rosette Molecular Cloud and the dense cores such as those in B5, a cluster of cores and young low-mass stars, are key to considerations of star formation. Whether star formation is a self-inducing process or one that causes itself to turn off depends greatly on whether the responses of the interclump and intercore media to young stars cause the collapse of clumps or cores to be faster than their ablation. We present a naive introduction to the lengthscales over which such responses are significant, mention ways in which the responses might induce collapse, review some of the little that is known of how flows of media around clumps and cores ablate them, and then return to the issue of the lengthscales over which such responses are significant by considering the global properties of mass-loaded flows in clumpy star forming regions.

scholarly journals Star Formation in the Local Milky Way

2015 ◽  
Vol 10 (S314) ◽  
pp. 8-15
Author(s):  
Charles J. Lada
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Milky Way ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Young Stars ◽  
Molecular Gas ◽  
Physical Processes ◽  
Star Forming ◽  
Star Forming Regions

AbstractStudies of molecular clouds and young stars near the sun have provided invaluable insights into the process of star formation. Indeed, much of our physical understanding of this topic has been derived from such studies. Perhaps the two most fundamental problems confronting star formation research today are: 1) determining the origin of stellar mass and 2) deciphering the nature of the physical processes that control the star formation rate in molecular gas. As I will briefly outline here, observations and studies of local star forming regions are making particularly significant contributions toward the solution of both these important problems.

scholarly journals Masers in Star Forming Regions

1987 ◽  
Vol 115 ◽  
pp. 333-334 ◽  
Author(s):  
R. J. Cohen
Keyword(s):  
Young Stars ◽  
The Other ◽  
Circumstellar Disk ◽  
Molecular Gas ◽  
H Ii Regions ◽  
Star Forming ◽  
Molecular Outflows ◽  
Physical Conditions ◽  
Star Forming Regions ◽  
Cepheus A

OH and H2O masers in star forming regions are important because they are readily detectable indicators of star formation and because they provide unique information on the kinematics and physical conditions in high density regions (106 – 1010 cm−3) surrounding young stars, regions which cannot be studied by other means at present. The Jodrell Bank MERLIN interferometer has been used to map a sample of OH and H2O masers associated with bipolar molecular outflows. The maps of Cepheus A show that the masers are closely associated with the densest compact H II regions at the centre of the flow. The masers appear to be located at the inner edges of the circumstellar disk thought to play a role in collimating the outflow. It is suggested that the H2O masers trace the interaction between the stellar wind and the dense molecular gas, and the OH masers trace shocks propagating into the molecular gas. Rapid and sometimes correlated variations in the maser emission suggest that radiative pumping is likely in this source (Rowland and Cohen, Mon. Not. R. Astr. Soc. in press). Study of the other sources is still in progress.

scholarly journals OH masers and magnetic fields in massive star-forming regions: ON1

2006 ◽  
Vol 2 (S237) ◽  
pp. 452-452
Author(s):  
S. Nammahachak ◽  
K. Asanok ◽  
B. Hutawarakorn Kramer ◽  
R. J. Cohen ◽  
O. Muanwong ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Massive Star ◽  
Zeeman Splitting ◽  
Young Stars ◽  
Star Forming ◽  
Physical Conditions ◽  
Bipolar Outflow ◽  
Star Forming Regions ◽  
The Magnetic Field

AbstractOH masers are sensitive probes of the kinematics and physical conditions, and give unique information on the magnetic field through their polarization. Zeeman splitting of the OH lines can give the magnetic field strength and direction. Observing OH masers with MERLIN we studied the bipolar outflow in the star-forming region ON1, which hosts one of the earliest known ultra-compact (UC) HII regions. The strongest masers lie near the southern edge of the UCHII region in an elongated distribution. The maser distribution is orthogonal to the bipolar outflow seen in HCO+, suggesting that the OH masers may be embedded in a molecular disk or torus around a young B0.3 star, most likely tracing a shock front. An isolated group of 1720-MHz masers is also seen to the East. The magnetic field deduced from Zeeman splitting of the OH maser lines shows a large-scale order, with field values ranging from -0.4 to -4.6 mG. These results add to the growing body of evidence for OH masers associated with molecular disks or tori at the centre of bipolar outflow from massive young stars, and for a significant role played by the magnetic field in generating or channeling the bipolar outflow. Further details are presented by Nammahachak et al. 2006.

scholarly journals The physical conditions and oxygen and nitrogen abundance of 36 SBS galaxies from the SDSS DR7

2013 ◽  
Vol 9 (S304) ◽  
pp. 34-35
Author(s):  
M. V. Gyulzadyan ◽  
V. Z. Adibekyan
Keyword(s):  
Star Formation ◽  
Hii Regions ◽  
High Excitation ◽  
Star Forming ◽  
Physical Conditions ◽  
Star Forming Regions ◽  
Irregular Galaxies ◽  
Uv Excess ◽  
Nitrogen Abundance ◽  
Emission Line Galaxies

AbstractPhysical conditions and oxygen and nitrogen abundances in 36 SBS UV-excess and/or emission-line galaxies from the SDSS DR7 were determined. We have found that SBS 0808+578 is AGN. The others are HII galaxies or HII regions in galaxies. For all objects the oxygen abundance 12+log(O/H) lies in the range of 7.85 ÷ 8.61 and log(N/O) ratio in the range of −1.45 ÷ −0.4. They occupy the same area in the diagram N/O O/H as the high-excitation HII regions. We found no extremely metal-deficient galaxy. Using H-alpha fluxes star formation rates (SFR) for our samples galaxies were determined. Determined SFRs, being in the range of 0.001 ÷ 6 o year−1, are similar of that observed in typical star forming regions in spiral and irregular galaxies.

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