H2O Masers In Star-forming Regions Research Articles

Polarization of Astronomical Maser Radiation. III. Arbitrary Zeeman Splitting and Anisotropic Pumping

General solutions of the maser polarization problem are presented for arbitrary absorption coefficients. The results are used to calculate polarization for masers permeated by magnetic fields with arbitrary values of \xB, the ratio of Zeeman splitting to Doppler linewidth, and for anisotropic pumping. The $\xb \to 0$ limit of the magnetic solution reproduces the linear polarization derived in previous studies, which were always conducted at this unphysical limit. While terms of higher order in \xb have a negligible effect on the magnitude of $q$, they produce some major new results. In particular, the linear polarization is accompanied by circular polarization, proportional to \xb. Because \xb is proportional to the transition wavelength, the circular polarization of SiO masers should decrease with rotation quantum number, as observed. In the absence of theory for $\xb < 1$, previous estimates of magnetic fields from detected maser circular polarization had to rely on conjectures in this case and generally need to be revised downward. The fields in SiO masers are \about 2--10 G and were overestimated by a factor of 8. The OH maser regions around supergiants have fields of \about 0.1--0.5 mG, which were overestimated by factors of 10--100. The fields were properly estimated for OH/IR masers ($\la$ 0.1 mG) and \H2O masers in star-forming regions (\about 15--50 mG). Spurious solutions that required stability analysis for their removal in all previous studies are never reproduced here; in particular, there are no stationary physical solutions for propagation at $\sin^2\theta < \third$, where $\theta$ is the angle from the direction of the magnetic field, so such radiation is unpolarized. These spurious solutions can be identified as the \xb = 0 limits of non-physical solutions and they never arise at finite

Planar H2O masers in star-forming regions

view Abstract Citations (70) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Planar H 2O Masers in Star-forming Regions Elitzur, Moshe ; Hollenbach, David J. ; McKee, Christopher F. Abstract The paper examines the planar geometry of shocked material, which is the key property in enabling the high brightness temperatures of H2O masers in star-forming regions. The brightness temperature, beaming angle, and the maser spot size are determined for thin, saturated planar masers under the assumption that the velocity change across the maser due to ordered motions is small compared with the thermal or microturbulent line width. For a given set of physical parameters, the brightness temperature is essentially fully determined by the length of the velocity-coherent region in the shocked plane along the line of sight. Effective aspect ratios (about 5-50) are found that are in agreement with values previously inferred from observed brightness temperatures. Publication: The Astrophysical Journal Pub Date: July 1992 DOI: 10.1086/171574 Bibcode: 1992ApJ...394..221E Keywords: Brightness Temperature; Interstellar Masers; Star Formation; Water Masers; Beams (Radiation); Computational Astrophysics; Physical Properties; Astrophysics; MASERS; STARS: FORMATION full text sources ADS |

Collisional pumping of H2O masers in star-forming regions

view Abstract Citations (33) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Collisional Pumping of H 2O Masers in Star-forming Regions Kylafis, Nikolaos D. ; Norman, Colin A. Abstract The pumping of H2O masers in star-forming regions by collisions with H2 molecules has been studied. It is found that the strong water masers in star-forming regions may not be explained by collisional pumping, unless very large aspect ratios (length/diameter) for the cylinder or small velocity gradients along the axis of the cylinder are assumed. In addition to the 22 GHz water maser, results are presented for other maser transitions of water in the submillimeter range. The detection of these masers with submillimeter telescopes could significantly enhance the understanding of the physical conditions in star-forming regions. Publication: The Astrophysical Journal Pub Date: June 1991 DOI: 10.1086/170071 Bibcode: 1991ApJ...373..525K Keywords: Interstellar Matter; Lasing; Radiative Transfer; Star Formation; Water Masers; Aspect Ratio; Cylinders; Hydrogen; Photons; Submillimeter Waves; Astrophysics; INTERSTELLAR: MOLECULES; MASERS; RADIATIVE TRANSFER; STARS: FORMATION full text sources ADS |

Multiple, narrow lines in the spectrum of an astrophysical maser in a velocity gradient

The emergent radiation spectrum is obtained for an astrophysical maser in the presence of a velocity gradient without making the 'large velocity gradient' (or 'Sobolev') approximation on which previous calculations have been based. Even in the presence of a velocity gradient, the spectral lines of saturated masers are found to remain narrow. More surprisingly, however, the spectrum breaks up into multiple narrow lines. Hence, individual features in the observed spectra of astrophysical masers need not always be interpreted as separate clumps of gas. Specifically, this result may be related to the occurrence of multiple lines from the same location in the H2O masers in star-forming regions and to be the occurrence of numerous, narrow features recently detected in the spectra of circumstellar OH masers.