scholarly journals The Visual Absolute Magnitude of the Central Objects in Be Stars

2000 ◽  
Vol 175 ◽  
pp. 55-58 ◽  
Author(s):  
A. Moujtahid ◽  
J. Zorec
Keyword(s):  
Absolute Magnitude ◽  
Circumstellar Envelope ◽  
Be Stars ◽  
Circumstellar Envelopes ◽  
Energy Distributions ◽  
B Stars ◽  
Absolute Magnitudes ◽  
Magnitude Difference ◽  
Good Agreement ◽  
The Continuum

AbstractUsing the circumstellar envelope parameters (mean temperature, extent and opacity) derived by fitting theoretical energy distributions to those observed in a sample of 20 Be stars, we estimate the respective magnitude difference ΔV = V – V* of the continuum flux excess produced by their circumstellar envelopes. Using then the HIPPARCOS parallaxes of these stars and the ISM E(B-V) colour excesses derived with the surrounding normal B stars, we estimate the visual absolute magnitude of the central objects in the program Be stars. In most cases the results obtained are in good agreement with the absolute magnitudes obtained from the photospheric (λ1, D) components derived in the BCD spectrophotometric system. There are, however, strong discrepancies in 4 program stars which deserve further studies. The magnitude excess seems to be ΔV ≲ 0 for the higher effective temperatures only. There is no correlation between ΔV and Vsin i, as would be expected if the circumstellar envelopes were strongly flattened.

scholarly journals Hipparcos Positions of B/Be Stars on the HR Diagram

2000 ◽  
Vol 175 ◽  
pp. 117-128 ◽  
Author(s):  
Danielle Briot ◽  
Noel Robichon
Keyword(s):  
Spectral Type ◽  
Rotational Velocity ◽  
Absolute Magnitude ◽  
Be Stars ◽  
Class V ◽  
B Stars ◽  
Luminosity Class ◽  
The Mean ◽  
Absolute Magnitudes ◽  
Hipparcos Parallax

AbstractAbsolute magnitudes of Be and B stars are computed for each spectral type and luminosity class V and IV, using the Hipparcos parallax measurements. Some simulations have been carried out in order to estimate the effects which could bias the mean absolute magnitude calculations. As a result, only stars with σπ/π < 15% have been used. A first result is that B stars are fainter than previous estimations by about 0.5 magnitude on average. We then observe that on average Be stars are brighter than B stars of the same spectral type and this over-luminosity increases with the spectral type. A possible interpretation is proposed based on the fact that the rotational velocity of the late Be stars is near the critical rotational velocity.

scholarly journals On the Characteristics of Circumstellar Envelopes in Be Stars near the Central Object

2000 ◽  
Vol 175 ◽  
pp. 506-509 ◽  
Author(s):  
A. Moujtahid ◽  
J. Zorec ◽  
A.M. Hubert
Keyword(s):  
Density Distribution ◽  
Linear Relation ◽  
Continuum Emission ◽  
Circumstellar Envelope ◽  
Be Stars ◽  
Circumstellar Envelopes ◽  
Energy Distributions ◽  
Central Object ◽  
Density Distributions ◽  
The Mean

AbstractObserved visible energy distributions of Be stars were studied with analytic flux distributions produced by flattened circumstellar envelopes. The theoretical representation of emitted fluxes also allows for density distribution effects in the region where the visible continuum emission/absorption is raised. Two main conclusions were reached: (a) regions responsible for spectrophotometric ”shell” phases have, on average, steeper density distributions than those producing the spectrophotometric ”Be” phases; (b) the mean temperatures of the studied circumstellar envelope regions shows a linear relation with their mean ”inverse” extent R*/R.

scholarly journals TAMS companions of classical cepheids

1994 ◽  
Vol 162 ◽  
pp. 51-52 ◽  
Author(s):  
Nancy Remage Evans
Keyword(s):  
Absolute Magnitude ◽  
Low Resolution ◽  
Classical Cepheids ◽  
The Absolute ◽  
Absolute Magnitudes ◽  
Magnitude Difference

IUE low resolution spectra are an excellent way to determine the temperatures of the hot companions of binary Cepheids. The spectral types of the companions are derived by comparing the spectra with the spectra of standard stars. Absolute magnitudes are calculated from the magnitude difference between the two stars and the absolute magnitude of the Cepheid. In this study, eight binaries containing a Cepheid and a hot companion evolved beyond the ZAMS are discussed.

scholarly journals Absolute Magnitudes and Intrinsic Colours of Non-Supergiant Be Stars

1982 ◽  
Vol 98 ◽  
pp. 33-36
Author(s):  
J. R. Kozok
Keyword(s):  
Absolute Magnitude ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Be Stars ◽  
Large Sample ◽  
Galactic Clusters ◽  
Absolute Magnitudes ◽  
Image Position ◽  
Intrinsic Colour

101 normal Be stars, probable members of 56 galactic clusters and OB-associations, and more than 20 extreme Be stars in the Large Magellanic Cloud were used to derive intrinsic colours of 09-B9 (III-V)e stars. Furthermore, the correlation between the intrinsic colour (U-B)0 and the absolute magnitude of non-supergiant Be stars was confirmed to be and The aim of the present investigation is to enlarge the basis for the determination of intrinsic colours and absolute magnitudes by providing a large sample from the southern sky.

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.

scholarly journals Variation of Anomalous Stages of Ionization with Spectral Type for Be Stars

1982 ◽  
Vol 98 ◽  
pp. 387-390 ◽  
Author(s):  
J. M. Marlborough ◽  
Geraldine J. Peters
Keyword(s):  
Spectral Type ◽  
Uv Spectra ◽  
Circumstellar Envelope ◽  
Be Stars ◽  
Uv Astronomy ◽  
B Stars ◽  
Stellar Radiation ◽  
Wide Range

One of the interesting results of ultraviolet (UV) astronomy was the discovery of ions from unexpected stages of ionization in spectra of O,B stars. The most common ions concerned are O VI and N V, but also C IV and Si IV in B stars. The presence of these ions is anomalous because generally their abundance is expected to be negligible if they are produced by photoionization by stellar radiation, either in the photosphere or in a cool circumstellar envelope (CE). The same ions are observed in the UV spectra of Be stars. Previous investigations, largely with Copernicus spectra, have reported O VI and N V in late Oe and early Be stars and Si IV in stars as cool as B5 (Marlborough, 1981 and references therein). In this paper we present the results of a preliminary survey of IUE spectra of Be stars covering a wide range of spectral type.

scholarly journals Spectrophotometric and Photometric Behaviours of Be Stars: the Circumstellar Envelope Formation Mechanisms

2000 ◽  
Vol 175 ◽  
pp. 448-451 ◽  
Author(s):  
J. Zorec ◽  
A.M. Hubert ◽  
A. Moujtahid
Keyword(s):  
Formation Mechanisms ◽  
Circumstellar Envelope ◽  
Be Stars ◽  
Circumstellar Envelopes ◽  
Discrete Mass

AbstractA mechanism to create circumstellar envelopes in Be stars is proposed. The mechanism assumes a mass-loaded wind produced by ablated discrete stellar ejecta. The discrete mass ejections are suggested by the long-term spectrophotometric behaviours of Be stars and by their short and long-lived light outbursts discovered recently.

scholarly journals Paschen and Brackett Lines in Be stars

2000 ◽  
Vol 175 ◽  
pp. 472-475
Author(s):  
L. Cidale ◽  
J. Zorec ◽  
J.P. Maillard ◽  
N. Morrell
Keyword(s):  
Emission Line ◽  
Stellar Atmosphere ◽  
Velocity Fields ◽  
Circumstellar Envelope ◽  
Be Stars ◽  
Line Profiles ◽  
Circumstellar Envelopes ◽  
Hydrogen Line ◽  
Stellar Activity ◽  
Central Stars

AbstractThe activities detected in Be stars indicate that the formation of the circumstellar envelope and its structure cannot be studied independently of the phenomena taking place in the outermost layers of the central stars. Assuming that related to the stellar activity there is an expanding atmospheric region with temperatures Te > Teff followed by an envelope with a decreasing temperature, we calculated hydrogen line profiles for different velocity fields and different positions of temperature maxima relative to the underlying photosphere. Results show that the Hα line is not very sensitive to changes introduced to the stellar atmosphere and to the nearby circumstellar layers. Moreover, the Hα emission line profiles look like those produced by disc-like circumstellar envelopes seen pole-on, although the model for the circumstellar envelope is spherical. However, the first members of the Paschen and Brackett series are strongly sensitive to any changes introduced in the photospheric and exophotospheric layers. We conclude that the study of these lines may then be valuable to obtain new insight on the activity of central stars and on the phenomena involved in circumstellar envelope formation in Be stars.

scholarly journals Infrared properties of active OB stars in the Magellanic Clouds from the Spitzer SAGE survey

2010 ◽  
Vol 6 (S272) ◽  
pp. 254-259
Author(s):  
Alceste Z. Bonanos ◽  
Danny J. Lennon ◽  
Derck L. Massa ◽  
Marta Sewilo ◽  
Fabian Köhlinger ◽  
...  
Keyword(s):  
Magellanic Clouds ◽  
Spectral Energy ◽  
Be Stars ◽  
Energy Distributions ◽  
Photometric Variability ◽  
B Stars ◽  
Ob Stars ◽  
Luminous Blue Variables ◽  
Red Supergiants ◽  
Be Star

AbstractWe present a study of the infrared properties of 4922 spectroscopically confirmed massive stars in the Large and Small Magellanic Clouds, focusing on the active OB star population. Besides OB stars, our sample includes yellow and red supergiants, Wolf-Rayet stars, Luminous Blue Variables (LBVs) and supergiant B[e] stars. We detect a distinct Be star sequence, displaced to the red, and find a higher fraction of Oe and Be stars among O and early-B stars in the SMC, respectively, when compared to the LMC, and that the SMC Be stars occur at higher luminosities. We also find photometric variability among the active OB population and evidence for transitions of Be stars to B stars and vice versa. We furthermore confirm the presence of dust around all the supergiant B[e] stars in our sample, finding the shape of their spectral energy distributions (SEDs) to be very similar, in contrast to the variety of SED shapes among the spectrally variable LBVs.

scholarly journals Continuum Flux Excess in Be Stars Determined from Spectral Lines

2000 ◽  
Vol 175 ◽  
pp. 502-505 ◽  
Author(s):  
J. Zorec ◽  
D. Ballereau ◽  
J. Chauville
Keyword(s):  
Central Star ◽  
Spectral Lines ◽  
Circumstellar Envelope ◽  
Be Stars ◽  
Line Profiles ◽  
Aspect Angle ◽  
The Continuum

AbstractWe study the continuum flux excess at λ4471 by comparing the observed He I λ4471 line profiles with non-LTE model line profiles. Assuming that emission of the Hγ line is formed nearly in the same regions of the circumstellar envelope as those where the visible continuum flux excess rises, we estimate the continuum opacity needed to account for the veiling of the He I λ4471 line. The flux excess so derived is then studied as a function of the stellar aspect angle in an attempt to determine the degree of incidence of the envelope geometry near the central star on the continuum flux of Be stars.

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