Emission Features of Several Be Stars as Related to Their Luminosity Class and Spectral Type

1976 ◽  
pp. 33-36
Author(s):  
H. Hubert ◽  
M. Th. Chambon
Keyword(s):  
Spectral Type ◽  
Be Stars ◽  
Luminosity Class

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 Rotational Velocities of “Field” Be Stars

2004 ◽  
Vol 215 ◽  
pp. 89-90 ◽  
Author(s):  
J. Zorec ◽  
R. Levenhagen ◽  
J. Chauville ◽  
F. Royer ◽  
N. V. Leister ◽  
...  
Keyword(s):  
Spectral Type ◽  
Narrow Range ◽  
Be Stars ◽  
Class Groups ◽  
B Stars ◽  
Luminosity Class

Distributions of true rotational velocities as a function of spectral type for different luminosity class groups of B and Be Stars are compared. While the distributions for B stars differ clearly from one luminosity class to another, those of Be Stars differ less, which indicates that due to rotational effects many Be Stars are considered more evolved than they actually are. Be Stars ‘select’ a narrow range of true rotational velocities to display the Be phenomenon and those of latter spectral types rotate only marginally faster than the early ones.

scholarly journals Quantitative Spectral Classification of Be Stars on Low Dispersion Spectra

1979 ◽  
Vol 47 ◽  
pp. 247-258 ◽  
Author(s):  
Lucienne Divan
Keyword(s):  
Spectral Type ◽  
Central Star ◽  
Low Pressure ◽  
Be Stars ◽  
Spectral Classification ◽  
Luminosity Class ◽  
Low Dispersion ◽  
The Continuum

AbstractTwo separate Balmer jumps are observed in some Be stars. The first one, in absorption and unchanging, is attributed to the central star and gives its spectral type and luminosity class in the λ,D system. The second one, occuring at shorter wavelengths, either in absorption or in emission, originates in layers at a low pressure. It is shown that these layers modify the colors of the central star on both sides of the Balmer jump and that they are not optically thin even in the continuum.

scholarly journals Emission Features of Several Be Stars as Related to Their Luminosity Class and Spectral Type

1976 ◽  
Vol 70 ◽  
pp. 33-36
Author(s):  
H. Hubert ◽  
M. Th. Chambon
Keyword(s):  
Spectral Type ◽  
Be Stars ◽  
Luminosity Class

At the Haute Provence Observatory, a survey of the Be stars brighter than the seventh magnitude was initiated by Herman and her collaborators twenty years ago.

scholarly journals Shell Stars in the Geneva Photometric System

1987 ◽  
Vol 92 ◽  
pp. 523-525
Author(s):  
B. Hauck
Keyword(s):  
Spectral Type ◽  
Main Sequence ◽  
Photometric System ◽  
Be Stars ◽  
Main Sequence Stars ◽  
Class V ◽  
Luminosity Class ◽  
Be Star ◽  
Shell Star

L. Divan (1979) showed that the Balmer jump is greater in a Be-shell star than in a star of same spectral type and we will consider if this property is also present in A and F-shell stars by studying their data in the Geneva photometric system. Two photometric parameters in this system are correlated with the Balmer jump: d=(U-Bl) -1.430 (B1-B2) and Δ=(U-B2) -0.832 (B2-G). In addition to the Balmer jump, Δ is also sensitive to blanketing. Both parameters are reddening free. A study of the Be stars of luminosity class V or IV classified by Slettebak (1982) shows that, in a d vs Δ diagram, they are in the area of main sequence stars or a little above, while the majority of Be-shell stars are above the Be star sequence. Pleione is well known for presenting a Be phase followed by a shell phase.

scholarly journals Observed Relations Between Physical Properties and MK Classification as Functions of Metal Abundance for F5-K4 Stars

1976 ◽  
Vol 72 ◽  
pp. 75-78
Author(s):  
M. Grenon
Keyword(s):  
Physical Properties ◽  
Spectral Range ◽  
Spectral Type ◽  
Photometric System ◽  
Luminosity Class ◽  
Empirical Relations ◽  
Metal Abundance ◽  
Systematic Effects ◽  
The Absolute ◽  
Absolute Magnitudes

The Geneva photometric system has been calibrated in terms of [M/H], θeff, Mv in the spectral range F5 to K4. As the spectral type is a datum generally available, we derive empirical relations showing the coupling of θeff and [M/H] at given spectral type and luminosity class. Similar relations are offered for the absolute magnitudes and provide a more accurate means for deriving spectroscopic parallaxes. Systematic effects on the estimation of the luminosity class are also shown.

scholarly journals Interacting Binaries as Be Stars

1987 ◽  
Vol 92 ◽  
pp. 451-455
Author(s):  
Mirek J. Plavec
Keyword(s):  
Spectral Type ◽  
Binary Stars ◽  
Emission Lines ◽  
Close Binary ◽  
High Electron ◽  
Be Stars ◽  
Close Binary Stars ◽  
High Ionization ◽  
Mass Outflow ◽  
Balmer Lines

AbstractSemidetached close binary stars of the Algol type often have primary components of spectral type A0 or earlier and display emission at Hα (sometimes also at higher Balmer lines). They are therefore Be stars. Many binaries of this type are not eclipsing and must look like “ordinary” Be stars. We have discovered high-ionization emission lines of N V, C IV, Si IV, Fe III, etc. in the ultraviolet spectra of totally eclipsing Algols. They probably originate in circumstellar turbulent regions at fairly high electron temperatures, of the order of 100 000 K. They are not detectable in most non-eclipsing systems, but may be there and may play an important role in the dynamics of accretion and mass outflow from the systems.

scholarly journals The number of Be stars compared with the number of B stars, taking into account the specific physical characteristics of Be stars

1994 ◽  
Vol 162 ◽  
pp. 356-357
Author(s):  
D. Briot ◽  
J. Zorec
Keyword(s):  
Spectral Type ◽  
Bright Star ◽  
Physical Parameters ◽  
Emission Characteristics ◽  
Be Stars ◽  
Constant Mass ◽  
B Stars ◽  
The Past ◽  
Star Catalogue

It is very important for the understanding of the Be phenomenon, and particularly for locating a possible Be phase in the evolutionary track of B stars, to accurately determine the proportion of Be stars among all B stars. This type of study was already made several times in the past. Results obtained generally show a maximum Be frequency around spectral type B2 then a decrease towards late spectral types. Actually Be stars do not have the same characteristics as “normal” B stars and we have to take this into account in the determination of the ratio : number of Be stars / number of B stars. We use the Bright Star Catalogue (Hoffleit & Jaschek 1982) and the Supplement to the Bright Star Catalogue (Hoffleit, Saladyga & Wlasuk 1983) containing stars V= 7.10 and brighter. This study needed to be made separately for the different spectral types because:- Physical parameters of B stars are very different from B0 to B9;- Emission characteristics of Be stars vary very much, with a decrease from B0e to B9e.We successively consider three effects which can influence the frequency of Be stars:- The over-luminosity of Be stars as compared with B stars;- Spectral type changes during constant mass evolution;- Spectral type changes due to the fast rotation of Be stars.

Lithium in Cool Stars Detected in EUV Surveys

2000 ◽  
Vol 198 ◽  
pp. 366-367 ◽  
Author(s):  
G. Tagliaferri ◽  
L. Pastori ◽  
G. Cutispoto ◽  
R. Pallavicini
Keyword(s):  
Spectral Line ◽  
Spectral Type ◽  
Rotational Velocity ◽  
Luminosity Class ◽  
Photometric Observations ◽  
Cool Stars ◽  
Active Cool

We selected a sample of active cool stars detected in the EUV band by the ROSAT WFC and performed spectroscopic and photometric observations. We inferred spectral type, luminosity class, distance, binary status, rotational velocity. Here we show the results of the Li abundances determination from the Li I 6707.8 Å spectral line.

scholarly journals Optical Spectroscopy of Six Carbon-Rich Proto-Planetary Nebulae

1993 ◽  
Vol 155 ◽  
pp. 339-339
Author(s):  
B.J. Hrivnak
Keyword(s):  
Optical Spectroscopy ◽  
Spectral Type ◽  
Planetary Nebulae ◽  
Luminosity Class ◽  
Dust Temperature ◽  
Medium Resolution

We are engaged in a program of optical spectroscopy of proto–planetary nebulae (PPN). The objects were initially selected from the IRAS database on the basis of their strong infrared excesses, indicating dust temperature of 150–250 K. Spectra have been obtrained at medium resolution for the purpose of obtaining the spectral type, luminosity class, and to search for chemical peculiarities resulting from the post–AGB nature of the objects. We found our PPN candidates to typically display F–G supergiant spectra.

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