Polarization Measurements Across the Balmer Lines of Be and Shell Stars

We have made linear polarization measurements of several Be and shell stars across the Hα and Hβ lines, all of the stars exhibiting polarization in the continuum, the emphasis here being on measurements made of ζ Tau, 48 Per, φ Per, and γ Cas. Three types of results ensue: some stars show no significant change of polarization across the Balmer features (e.g., 48 Per, X Per); some stars show a reduced polarization across the features (e.g., γ Cas, ζ Tau) indicating the presence of intrinsic polarization; some stars show a change in the degree of polarization but with a marked rotation of the direction of vibration (e.g., φ Per, 48 Lib) which can be attributed to a combination of non-aligned intrinsic (circumstellar) and interstellar polarizations. Interpretations of these results are discussed, and we demonstrate the potential power of line profile polarimetry/photometry as an important new method for separating intrinsic and interstellar polarization effects, thus enabling polarization observations to be used as a constraint on models of Be stars.

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Polarization Measurements of Some Herbig Ae/Be Stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900190369 ◽

1990 ◽

Vol 140 ◽

pp. 323-324

Author(s):

S. K. Jain ◽

H.C. Bhatt ◽

Ram Sagar

Keyword(s):

Linear Polarization ◽

Wavelength Dependence ◽

Be Stars ◽

Polarization Measurements

We have measured the linear polarization of 8 bright Herbig Ae/Be stars in UBVRI bands. No unique wavelength dependence of polarization magnitude as well as direction is found in these measurements.

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Spectropolarimetric monitoring of WR140

Symposium - International Astronomical Union ◽

10.1017/s0074180900202544 ◽

1995 ◽

Vol 163 ◽

pp. 506-507

Author(s):

R.E. Schulte-Ladbeck ◽

K. H. Nordsieck ◽

K. S. Bjorkman ◽

M. R. Meade ◽

B. L. Babler

Keyword(s):

Detection Limit ◽

Linear Polarization ◽

Broad Band ◽

Line Emission ◽

Intrinsic Polarization ◽

The Continuum

We report on eight years of spectropolarimetric monitoring of the WR140 binary. The broad-band linear polarization decreased systematically after the 1985 periastron passage. By 1991, it settled to a constant value at which it has remained through the 1993 periastron passage. We do not detect, in data taken after 1989, a line-effect in He II Λ4686. This suggests either that the continuum and the line emission scatter at the same region, or that any intrinsic polarization has been below our detection limit. We conclude that the presently observed polarization of WR140 is consistent with interstellar foreground polarization.

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Recent Results from Ultraviolet and Optical Spectropolarimetry of Hot Stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900214903 ◽

1994 ◽

Vol 162 ◽

pp. 219-229

Author(s):

K.S. Bjorkman

Keyword(s):

Linear Polarization ◽

Optical Data ◽

Time Variability ◽

Be Stars ◽

Circumstellar Envelopes ◽

Polarization Data ◽

Hot Stars ◽

New Models ◽

Be Star ◽

The Continuum

The first comprehensive linear polarization data on hot stars covering the spectral range from 1500 to 7600Å are presented. These results are based on recent observations made with the Wisconsin Ultraviolet Photo-Polarimeter Experiment (WUPPE), combined with ground-based observations from the Pine Bluff Observatory. Implications of the data for models of the circumstellar envelopes of hot stars are discussed, with particular emphasis on the surprising results found for the rapidly rotating Be stars. In particular, WUPPE discovered that the continuum polarization in Be stars decreases into the ultraviolet, which was not predicted by models prior to the observations. Time variability in the optical data is also discussed. Possible interpretations of these results are examined in the light of recent new models for Be star disks.

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Intrinsic Linear Polarization of Be Stars as a Function of v sin i

Symposium - International Astronomical Union ◽

10.1017/s0074180900011438 ◽

1976 ◽

Vol 70 ◽

pp. 277-277

Author(s):

R. Poeckert ◽

J. M. Marlborough

Keyword(s):

Electron Density ◽

Optical Depth ◽

Electron Scattering ◽

Linear Polarization ◽

Apparent Difference ◽

Be Stars ◽

Intrinsic Polarization ◽

Disk Model

The polarization of 48 Be stars has been measured in two bands near Hα with the aim of determining the relation between intrinsic polarization and v sin i. A technique developed by Poeckert (1975) is used to remove the effect of interstellar polarization. It is found that intrinsic polarization depends strongly on v sin i; stars with low v sin i having little or no polarization. We have calculated the i dependence of linear polarization for a disk model envelope and find that the polarization is proportional to τe sin2i when the disk is optically thin (τe is a characteristic electron scattering optical depth). A comparison of the observed relation between intrinsic polarization and v sin i, and that predicted for the disk model is illustrated. We find that an envelope with an electron density of ≤5 × 1011 cm−3 can account for the degree of intrinsic polarization observed in all the program stars. The fact that stars of low v sin i have little intrinsic polarization is evidence for the assumption that these stars are seen pole-on and that the envelopes around these stars are axi-symmetric. No apparent difference between pole-on stars and extreme Be stars was obtained.

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International multiwavelength campaigns on short-term variability of OB stars: optical polarimetry

Symposium - International Astronomical Union ◽

10.1017/s0074180900215799 ◽

1994 ◽

Vol 162 ◽

pp. 530-531

Author(s):

D. McDavid

Keyword(s):

Optical Spectroscopy ◽

Linear Polarization ◽

Wide Band ◽

Be Stars ◽

Short Term ◽

Ob Stars ◽

Intensive Monitoring ◽

Polarization Measurements ◽

Ultraviolet Observations ◽

Short Term Variability

From 1986 through 1992, wide-band optical (B or V filter) linear polarization measurements of eight Be stars and seven O stars were obtained simultaneously with ultraviolet observations from IUE and worldwide ground-based optical spectroscopy and photometry in a series of campaigns designed to study the short-term variability of these objects. Each campaign consisted of intensive monitoring of a few carefully chosen stars over a period of several days and nights, with the greatest possible continuity subject to the limitations of instrument scheduling, weather, and the longitudes of the observing sites.

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Dust and gas in shells around Herbig Ae/Be stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900215465 ◽

1994 ◽

Vol 162 ◽

pp. 392-393

Author(s):

N.V. Voshchinnikov ◽

V.B. Il'in ◽

A.F. Kholtygin

Keyword(s):

Spectral Line ◽

Linear Polarization ◽

Be Stars ◽

Line Profiles ◽

Intrinsic Polarization ◽

Ww Vul ◽

Almost All

Herbig Ae/Be (HAEBE) stars are young objects with strong infrared excesses, variable brightness, intrinsic polarization and complex spectral line profiles. Almost all of these features are due to the presence of circumstellar (CS) shells. We consider the group of HAEBE stars with non-periodic Algol-like minima (UX Ori, WW Vul, etc.). They have irregular brightness drops by 2–3 mag in the visual, accompanied by an increase of linear polarization.

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Study of the HeI λ4471 line-profile of Be stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900214988 ◽

1994 ◽

Vol 162 ◽

pp. 259-260

Author(s):

D. Ballereau ◽

J. Chauville ◽

A. Garcia ◽

J. Zorec

Keyword(s):

Line Profile ◽

Be Stars ◽

The Continuum

In this paper we study the veiling effect and the strength of an extra emission-like component filling partially the HeI λ4471 line of Be stars. It is shown that this component is roughly correlated with the emission in the continuum and in the Hγ line.

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