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

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.

scholarly journals Dust and gas in shells around Herbig Ae/Be stars

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.

scholarly journals Polarization Measurements Across the Balmer Lines of Be and Shell Stars

1976 ◽  
Vol 70 ◽  
pp. 261-275 ◽  
Author(s):  
I. S. McLean ◽  
D. Clarke
Keyword(s):  
Line Profile ◽  
Linear Polarization ◽  
New Method ◽  
Degree Of Polarization ◽  
Be Stars ◽  
Intrinsic Polarization ◽  
Polarization Effects ◽  
Polarization Measurements ◽  
Balmer Lines ◽  
The Continuum

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.

scholarly journals Polarization Measurements of Some Herbig Ae/Be Stars

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.

scholarly journals Spectropolarimetric monitoring of WR140

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.

scholarly journals Formation and Dissipation of Viscous Disks around Be Stars

2004 ◽  
Vol 215 ◽  
pp. 529-534
Author(s):  
A. T. Okazaki
Keyword(s):  
Smoothed Particle Hydrodynamics ◽  
Rotation Axis ◽  
Be Stars ◽  
Disk Model ◽  
Innermost Part ◽  
Outer Disk ◽  
Particle Hydrodynamics ◽  
Smoothed Particle ◽  
Be Star ◽  
Mass Ejection

Based on the viscous decretion disk model for Be Stars, we study the effect of the torque from the star on the Be star disk, using a 3-D smoothed particle hydrodynamics code and turning on and off the mass ejection from the star. We find that, after the mass ejection is shut off, the innermost part of the disk begins to accrete and the accreting part gradually propagates outward. We also find that the Be disk in misaligned binaries precesses in a retrograde sense when no mass is supplied from the star. If the mass supply is resumed for such a disk, an inner disk is formed with its rotation axis misaligned with that of the outer disk. By the interaction between the inner and outer disks, the outer disk rapidly changes its direction to that of the inner disk.

scholarly journals Dark Matter Dogma: A Study of 214 Galaxies

Galaxies ◽  
2020 ◽  
Vol 8 (2) ◽  
pp. 36 ◽  
Author(s):  
Alan Sipols ◽  
Alex Pavlovich
Keyword(s):  
Dark Matter ◽  
Surface Brightness ◽  
Parametric Models ◽  
Galactic Rotation ◽  
Total Density ◽  
Apparent Difference ◽  
Rotation Curves ◽  
Disk Model ◽  
Radial Profiles ◽  
Baryonic Dark Matter

The aim of this paper is to test the need for non-baryonic dark matter in the context of galactic rotation and the apparent difference between distributions of galactic mass and luminosity. We present a set of rotation curves and 3.6 μm surface brightness profiles for a diverse sample of 214 galaxies. Using rotation curves as the sole input into our Newtonian disk model, we compute non-parametric radial profiles of surface mass density. All profiles exhibit lower density than parametric models with dark halos and provide a superior fit with observed rotation curves. Assuming all dynamical mass is in main-sequence stars, we estimate radial distributions of characteristic star mass implied by the corresponding pairs of density and brightness profiles. We find that for 132 galaxies or 62% of the sample, the relation between density and brightness can be fully explained by a radially declining stellar mass gradient. Such idealized stellar population fitting can also largely address density and brightness distributions of the remaining 82 galaxies, but their periphery shows, on average, 14 M⊙/pc2 difference between total density and light-constrained stellar density. We discuss how this density gap can be interpreted, by considering a low-luminosity baryonic matter, observational uncertainties, and visibility cutoffs for red dwarf populations. Lastly, we report tight correlation between radial density and brightness trends, and the discovered flattening of surface brightness profiles—both being evidence against dark matter. Our findings make non-baryonic dark matter unnecessary in the context of galactic rotation.

scholarly journals Probing the Small Scale Structures around Herbig Be Stars using Hα Spectropolarimetry

2000 ◽  
Vol 175 ◽  
pp. 108-112
Author(s):  
René D. Oudmaijer ◽  
Janet E. Drew ◽  
Graeme Busfield
Keyword(s):  
Accretion Disks ◽  
Electron Scattering ◽  
Detection Rate ◽  
Circumstellar Disks ◽  
Small Scale ◽  
Spherically Symmetric ◽  
Be Stars ◽  
Scale Structures ◽  
Larger Sample ◽  
Small Scale Structures

AbstractWe present spectropolarimetric observations across Hα of a sample of Herbig Be objects. Roughly half of the observed Herbig Be stars show polarization changes across Hα, implying immediately that their ionized, hence inner, envelopes are not spherically symmetric. This pattern, if confirmed by observations of a larger sample, could indicate that the non-detection rate is simply a consequence of sampling randomly-oriented circumstellar disks able to scatter starlight within a few stellar radii, with as implication that the massive Herbig Be stars are still surrounded by accretion disks. In addition, we present preliminary modelling which will assist interpreting the kinematic structure of the electron-scattering region.

scholarly journals Recent Results from Ultraviolet and Optical Spectropolarimetry of Hot Stars

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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