NASA Logo

NTRS

NTRS - NASA Technical Reports Server

Back to Results
Intensity-dependent circular polarization and circumstellar magnetic fields from the observation of SiO masersA new aspect of the propagation of astrophysical maser radiation in the presence of a magnetic field is described in which circular polarization is created. The resulting antisymmetric spectral line profile for this circular polarization resembles that produced by the ordinary Zeeman effect when the Zeeman splittings are much less than the spectral line breadth. It is caused by the change, with increasing maser intensity, in the axis of symmetry for the molecular quantum states from a direction that is parallel to the magnetic field to a direction that is parallel to the direction of propagation. When the maser is radiatively saturated, and the rate for stimulated emission is within an order of magnitude of the Zeeman splitting in frequency units, this 'intensity-dependent circular polarization' is greater than that due to the ordinary Zeeman effect by factors as large as 1000. The circular polarization that is observed in the spectra of circumstellar SiO (J = 1-0) masers associated with late-type giants and supergiants may then be caused by magnetic fields as weak as about 10 mG. With the standard Zeeman interpretation of the observations, magnetic fields of 10-100 G are indicated. The lower fields are similar to the limits obtained from the observation of the 22 GHz water masers which are typically somewhat further from the central star. The observed tendency for the fractional linear polarization of SiO masers to increase with increasing angular momentum of the molecular state is shown to be a likely result of anisotropic pumping. Errors are identified that invalidate a recent conflicting claim in the literature about the basic theory of maser polarization in the regime that is relevant here.
Document ID
19950033885
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Nedoluha, Gerald E.
(Naval Research Lab. Washington, DC, United States)
Watson, William D.
(Univ. of Illinois at Urbana-Champaign, Urbana, IL United States)
Date Acquired
August 16, 2013
Publication Date
March 1, 1994
Publication Information
Publication: The Astrophysical Journal, Part 1
Volume: 423
Issue: 1
ISSN: 0004-637X
Subject Category
Astrophysics
Accession Number
95A65484
Funding Number(s)
CONTRACT_GRANT: NAGW-1104
CONTRACT_GRANT: NSF AST-89-19614
Distribution Limits
Public
Copyright
Other

Available Downloads

There are no available downloads for this record.
No Preview Available