The structure of stellar hydroxyl masers

Reid, M. J.; Muhleman, D. O.; Moran, J. M.; Johnston, K. J.; Schwartz, P.R.

doi:10.1086/155230

Cited by 79 publications

(66 citation statements)

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“…The OH emission in the 1665 and 1667 MHz lines shows a substantial degree of circular polarization up to 50−80% Claussen & Fix 1982) but linear polarization occurs in only ∼10% of sources (Olnon et al 1980). Highly polarized OH maser features are observed in flaring Miras (Reid et al 1977;Fix 1979;Etoka & Le Squeren 1997), hypergiant IRC+10420 (Benson et al 1979) and post-AGB star OH17.7-2.0 (Szymczak & Gérard 2005). There is a general consensus that the polarization measurements of OH maser emission can Appendices are available in electronic form at http://www.aanda.org be properly explained with the classic model of Goldreich et al (1973) in which the magnetic field plays a key role (e.g., Gray & Field 1996;Elitzur 1996).…”

Section: Introductionmentioning

confidence: 99%

Polarization properties of OH masers in AGB and post-AGB stars

Wolak

Szymczak

Gérard

2011

A&A

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Context. Ground-state OH maser emission from late-type stars is usually polarized and remains a powerful probe of the magnetic field structure in the outer regions of circumstellar envelopes if observed with high angular and spectral resolutions. Observations in all four Stokes parameters are quite sparse and this is the most thorough, systematic study published to date. Aims. We aim to determine polarization properties of OH masers in an extensive sample of stars that show copious mass loss and search for candidate objects that are well-suited for high angular resolution studies. Methods. Full-polarization observations of the OH 1612 and 1667 MHz maser transitions were carried out for a sample of 117 AGB and post-AGB stars. Several targets were also observed in the 1665 MHz line. Results. A complete set of full-polarization spectra together with the basic polarization parameters are presented. Polarized features occur in more than 75% of the sources in the complete sample and there is no intrinsic difference in the occurrence of polarized emission between the three classes of objects of different infrared characteristics. The highest fractional polarization occurs for the post-AGB+PN and the Mira+SR classes at 1612 and 1667 MHz, respectively. Differences in the fractional polarization between the sources at different evolutionary stages appear to be related to depolarization caused by blending. The alignment of the polarization angles at the extreme sides of the shell implies a regular structure of the magnetic field of a strength of 0.3-2.3 mG. Conclusions. Polarized OH maser features are widespread in AGB and post-AGB stars. The relationship between the circular and linear fractional polarizations for a representative sample are consistent with the standard models of polarization for the Zeeman splitting higher than the Doppler line width, whereas the polarized features are the σ components.

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Section: Introductionmentioning

confidence: 99%

Polarization properties of OH masers in AGB and post-AGB stars

Wolak

Szymczak

Gérard

2011

A&A

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“…According to the standard model, i.e., an envelope in radial expansion (Reid et al 1977), these emissions come from the front and back part of the shell respectively. Nevertheless, sometimes one can observe an "intermediate" peak located between the two standard ones.…”

Section: Introductionmentioning

confidence: 99%

Long-term OH variability of Miras

Etoka

Squeren

2000

Astron. Astrophys. Suppl. Ser.

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Abstract. We present here the results and interpretation of a long−term OH variability program conducted with the French Nançay Radiotelescope from 1980 to 1995. It concerns seven Mira stars: R Aql, RS Vir, S CrB, R LMi, RR Aql, U Her and UX Cyg. This study deals with the three OH maser lines observed in the Miras at 1612, 1665 and 1667 MHz. These OH variable stars have periods ranging from 290 to 580 days. The study presents the first insight of the long−term temporal behaviour of OH integrated flux variations as well as spectral component variations. The main aims are to determine the temporal behaviour of the OH maser emission and the longevity and variability of the spectral components. We find that the shapes of the OH curve are closer to the IR than the optical shapes and that the emissions at 1665 and 1667 MHz have a very similar behaviour while the emission at 1612 MHz behaves differently. The 1612 MHz emission shows smoother temporal variations and greater component longevity than the main line emission, leading to the conclusion that the 1612 MHz emission is coming from an outer part of the circumstellar shell and is more saturated than the main line emission. The study also shows the existence of inhomogeneities, especially differences between the front and back parts of the shell can be seen, and that OH variability curves undergo long term variations over several cycles.

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“…For the 1612 MHz line two peaks in the spectrum are frequently observed and interpreted as a blue, approaching maser and a red, receding maser. Also a delay has been observed between the maximum of the blue and the red features (Reid & Muhleman 1977;Herman & Habing 1985). The general trend is that the blue peak maximum occurs before the red one.…”

Section: Masermentioning

confidence: 78%

Mira Variables explained by a planetary companion interaction: A means to drop the pulsation paradigm?

Berlioz-Arthaud

2003

A&A

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Abstract.We emphasize the limits of the classical paradigm explaining the periodic appearance of emission lines by shock waves induced by radial periodic pulsations. In particular, we argue that, if pulsation occurs, it would not be purely radial and the light curve resulting from the contribution of zones at different phases would have a shape different from what we actually observe. The discovery of low mass companions to numerous G stars, some of them very close to the star, led us to look at the fate and the influence of this companion when the star becomes a giant. After Rudnitskij (2000), we suggest that the behavior of the Mira variables is mainly due to the presence of a companion in the tenuous atmosphere of the giant instead of the effect of a pulsating atmosphere explaining the presence of emission lines and the periodicity of these variables. We argue that the presence of a companion may account for the shape of the light curve and the observed phase lag between the maximum visual and the maximum maser light.

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The structure of stellar hydroxyl masers

Cited by 79 publications

References 0 publications

Polarization properties of OH masers in AGB and post-AGB stars

Polarization properties of OH masers in AGB and post-AGB stars

Long-term OH variability of Miras

Mira Variables explained by a planetary companion interaction: A means to drop the pulsation paradigm?

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