scholarly journals The Onset of Quasi-Periodic Variations in Be Stars

1993 ◽  
Vol 134 ◽  
pp. 223-225
Author(s):  
T. Kogure ◽  
M. Mon ◽  
M. Suzuki
Keyword(s):  
Sudden Onset ◽  
Radial Velocities ◽  
Emission Lines ◽  
Absorption Lines ◽  
Close Binaries ◽  
Be Stars ◽  
Early Type ◽  
Stable Period ◽  
Long Term Variations

We present some evidence of the quasi-periodic long-term variations (QPLV) in the violet-to-red ratio of double-peaked emission lines (V/R variation) and/or in the radial velocities of shell absorption lines for some Be stars. Although the V/R variations are rather prevailing phenomena among Be stars, the QPLV is remarkable by the following characteristics: (1)The QPLV appears as a sudden onset of repeated V/R variations after a long (10 years), almost stable period, and it persists for a few or several periods in ten or more years.(2)The period and amplitude of V/R variations change from cycle to cycle and from star to star. The variations of radial velocities (RV) of shell absorption lines are usually nearly parallel with the V/R variations.(3)The QPLV appears usually in early type Be stars with large rotational velocities, regardless whether the stars are normal Be or shell stars, and whether they are close-binaries or single stars.

scholarly journals The Connection with B[e] stars

2000 ◽  
Vol 175 ◽  
pp. 26-36 ◽  
Author(s):  
Franz-Josef Zickgraf
Keyword(s):  
Common Property ◽  
Main Sequence ◽  
Emission Lines ◽  
Circumstellar Dust ◽  
Evolutionary Status ◽  
Be Stars ◽  
Early Type ◽  
Circumstellar Envelopes ◽  
Early Type Stars ◽  
Uniform Group

AbstractThe characteristics of the various types of B[e] stars are discussed and compared with those of classical Be stars. Both groups of stars are characterized by the presence of emission lines in their spectra, in particular of hydrogen. However, there are also significant differences between these classes. Classical Be stars lack hot circumstellar dust and strong forbidden low-excitation emission lines, which are typical characteristics produced by B[e]-type stars. While classical Be stars are a rather uniform group of early-type stars, B[e]-type stars form a quite heterogeneous group, very often of poorly known evolutionary status, comprising such diverse types of objects as near main-sequence objects, evolved lowmass proto-planetray nebulae and massive evolved hot supergiants. Even pre-main sequence Herbig Ae/Be stars sometimes find their way into the group of B[e] stars. However, despite these dissimilarities classical Be stars and B[e]-type stars, share a common property, namely the nonsphericity of their circumstellar envelopes.

scholarly journals An Unusually Stable and Short Spectroscopic Period of the Be Star 28 CMa

1982 ◽  
Vol 98 ◽  
pp. 167-170
Author(s):  
D. Baade
Keyword(s):  
Time Scale ◽  
Emission Lines ◽  
Be Stars ◽  
Stable Period ◽  
Be Star ◽  
First Time ◽  
Calar Alto

Spectroscopic (1970: ESO, 12 Å/mm, 6 spectra kindly put at my disposal by Prof. A. Van Hoof; 1976: ESO, 12 Å/mm; 1977: Calar Alto Observatory, 42 Å/mm; 1979: ESO, 12 Å/mm) and photometric (1976: ESO and Cerro Tololo, Hβ, uvby) observations of 28 CMa (B2-3 IV-Ve; 3.52 < mV < 4.18, irregular variations on the time scale of months or years reported; vrot = 80 km/s) revealed a very complex variability. All observed individual types of variations are known from at least a few other Be stars. In 28 CMa, however, for the first time a highly significant correlation between the various variations is established by a stable common period. The period is 1.365 days which seems to be the shortest stable period presently known of any Be star. There is no indication that the star's behaviour changed between 1970 and 1979. Only the equivalent widths of the emission lines increased noticeably.

scholarly journals O and Of Stars

1973 ◽  
Vol 49 ◽  
pp. 93-107
Author(s):  
Peter S. Conti
Keyword(s):  
Visible Spectrum ◽  
Emission Lines ◽  
Absorption Lines ◽  
Evolutionary Status ◽  
Be Stars ◽  
Type B ◽  
No Emission ◽  
Hot Stars ◽  
Hydrogen Lines ◽  
The Continuum

My intention here is to discuss the ‘high temperature’ portion of this symposium and call attention to those stars that are called Of. There are some similarities in spectral appearance to WR stars, e.g. emission lines. I should first like to define what I think are the essential differences among four groups of hot stars;O stars: Stars that have only absorption lines in the visible spectrum. Type O is distinguished from type B by the presence of He ii 4541 at MK dispersion. It may be that some (supergiants) O stars will have emission lines in the rocket UV region but this description will be primarily concerned with ground based observations.Of stars: These are O type stars that also have λλ 4634,40 N iii in emission above the continuum. In addition to normal O star absorption lines and N iii emission, they may also have other lines in emission. I will discuss this further below.Oe stars: These are O type stars that have emission in the hydrogen lines (or at least at Hα), but with no emission in N iii or in other lines. I personally think that this small class of objects is related to the Be stars in their evolutionary status and in their emission mechanism.WR stars: These stars are primarily characterized by emission lines. The only absorption lines seen are violet shifted (P Cyg type). Although in some cases emission lines appear which are similar to those found in some Of stars, the latter types always have some unshifted absorption lines present. Several Of stars have P Cyg profiles in some lines.

scholarly journals Singly-Ionized Iron Emission Lines in the Spectra of Early Type Stars

1976 ◽  
Vol 70 ◽  
pp. 99-103
Author(s):  
R. Viotti ◽  
P. Koubský
Keyword(s):  
Spectroscopic Investigation ◽  
Emission Lines ◽  
Be Stars ◽  
Early Type ◽  
Atomic Processes ◽  
Early Type Stars ◽  
Stellar Envelopes ◽  
Two Parameter

The appearance of singly ionized iron emission lines in the spectra of early type stars is studied, and the results of a spectroscopic investigation of EW Lac and other Be stars are given. We also discuss the atomic processes of excitation of Fe ii in the stellar envelopes using a two-parameter diagram W, NeT−1/2e.

scholarly journals Precise Radial Velocities of F, G, K Dwarfs

1988 ◽  
Vol 132 ◽  
pp. 79-81
Author(s):  
Bruce Campbell ◽  
Gordon A. H. Walker
Keyword(s):  
Radial Velocities ◽  
Absorption Lines ◽  
Spectroscopic Binaries ◽  
Brown Dwarf ◽  
Dwarf Stars ◽  
Low Level ◽  
The Past ◽  
Velocity Variations

We have monitored changes in the radial velocities of 24 bright F, G and K dwarf stars (known spectroscopic binaries excluded) for the past six years at CFHT by imposing the absorption lines of HF gas in the spectra to act as wavelength fiducials. The average external error in the δ(velocities) which are based on some 16 stellar lines is 13 m/s corresponds to 0.6 micron in the spectrum or 0.04 of a diode spacing per line. Reductions are complete for 16 stars. There is no evidence for brown dwarf companions in the sample. Two previously unknown spectroscopic binaries were found, and seven stars show indications of significant, long-term, low-level velocity variations which could be interpreted as purturbations by companions of a few Jupiter masses with periods greater than 12 years except for γ Cep, which may have a period of 2.7 years, and ε Eri. Observing time has been guaranteed for at least two more years at CFHT.

scholarly journals Observations of stellar winds in early type stars

1981 ◽  
Vol 59 ◽  
pp. 1-18
Author(s):  
Peter S. Conti
Keyword(s):  
Resonance Line ◽  
Optical Spectrum ◽  
Main Sequence ◽  
Emission Lines ◽  
Stellar Winds ◽  
Be Stars ◽  
Early Type ◽  
Main Sequence Stars ◽  
Early Type Stars ◽  
Line P

I have been asked to review the “observations” of winds in “early-type” stars. This normally means stars of spectral type OB and those of the Wolf-Rayet (WR) class. In this paper I will concentrate on the massive population I stars of these types, and primarily the O and WR classes on which most of the recent work has been done. The early B type supergiants share many of the wind properties of the O stars but the later supergiant types, Be stars, and main sequence stars may not. Stellar winds are a ubiquitous phenomenon among these early type stars (Snow and Morton 1976). We see evidence of their winds in the resonance line P Cygni profiles in the UV region, in the emission lines of Hα and λ4686 He II in the optical spectrum, and in the free-free emission from the ionized plasma as observed in the IR and radio regions of the spectrum.

scholarly journals Global oscillations in Be star envelopes: observational evidence

1994 ◽  
Vol 162 ◽  
pp. 384-385
Author(s):  
R. W. Hanuschik ◽  
W. Hummel ◽  
O. Dietle ◽  
J. Dachs ◽  
E. Sutorius
Keyword(s):  
Full Range ◽  
Observational Evidence ◽  
Spectral Lines ◽  
Emission Lines ◽  
Be Stars ◽  
Intrinsic Structure ◽  
Be Star

Since 1982, we are performing a long-term spectroscopic observing programme of emission-lines in Be stars (Hanuschik 1987, Hanuschik et al. 1988, Dachs et al. 1992, Sutorius 1992, Dietle 1993). We are using ESO's 1.4m CAT, at resolution R ≥ 50 000 and S/N = 100–1000. Spectral lines chosen are the optically thick Hα, Hβ lines and the optically thin Fe ii λ5317 line. The latter line is an extremely sharp tracer (Δvth = 2 km s−1) for the kinematics in the disks. We believe that our atlas shows the full range of intrinsic structure of these emission lines.

scholarly journals Optical Spectra of Nuclei of Early Type Galaxies

1980 ◽  
Vol 5 ◽  
pp. 193-193
Author(s):  
Gerhard F. O. Schnur ◽  
W. A. Sherwood
Keyword(s):  
Spectral Resolution ◽  
Strong Absorption ◽  
Emission Lines ◽  
Absorption Lines ◽  
Nuclear Region ◽  
Early Type ◽  
Ionized Gas ◽  
Balmer Series ◽  
Weak Absorption ◽  
Normal Galaxies

Early type galaxies classified as SO by Sandage or lenticulars and SO/a appearing in RCBG have been observed with the IDS on the ESO 3.6 m telescope. The slit was 1” × 4” and the spectral resolution was 9 Å from 3900 Å to 7000 Å. Statistics for the first 50 galaxies observed are given.18% of the sample show the [OIII] doublet stronger than Hß; 32% have spectra dominated by the Balmer series progressing from mainly emission through strong absorption series to weak absorption; 20% have only [NII] or [SII] in emission while 30% show absorption lines and bands. That is, 70% show emission lines toward the nuclear region. Among the 50 galaxies, HI at 21 cm has been detected in 21 galaxies: 16 of these show ionized gas to be present. NGC5273 has Seyfert characteristics with strong [OIII]; Hß has a width of ˜1000 kms-1. The low luminosity end of the Seyfert distribution may be found among normal galaxies.

scholarly journals The binary orbit of HD 92740

1979 ◽  
Vol 83 ◽  
pp. 291-295
Author(s):  
Virpi S. Niemelä
Keyword(s):  
Observational Data ◽  
Orbital Motion ◽  
Radial Velocities ◽  
Emission Lines ◽  
Absorption Lines ◽  
Balmer Series ◽  
Absorption And Emission ◽  
Carina Nebula ◽  
Binary Orbit

HD 92740 is a star located in the Carina nebula showing a Wolf-Rayet spectrum of type WN7. Faint absorption lines of the upper Balmer series of hydrogen, and also of the Pickering series of Hell are present in the spectrum, in addition to the WN emissions. Although absorption lines present in a Wolf-Rayet spectrum are generally assumed to arise in a companion OB star, a previous study (Niemelä 1973) of the radial velocities of HD 92740 showed that the absorption and emission lines followed the same orbital motion. Subsequent spectral observations of this star have been carried out at the Cerro Tololo Inter-American Observatory, Chile, and at the Córdoba Observatory, Argentina, during four years; the observational data are listed in Conti, Niemelä and Walborn (1978). These observations showed that the true period is 8 times longer than the initially derived period of 10 days, and that doubtlessly the absorption lines belong to the WN star.

scholarly journals Radial Velocity Variations of the Be Shell Star V923 AQL /HD 183556/ in the Past Sixty Years

1989 ◽  
Vol 107 ◽  
pp. 377-377
Author(s):  
P. Koubsky ◽  
A.F. Gulliver ◽  
P. Harmanec ◽  
D. Ballereau ◽  
J. Chauville ◽  
...  
Keyword(s):  
Cycle Length ◽  
Be Stars ◽  
Binary Model ◽  
Be Star ◽  
Low Mass ◽  
Velocity Variations ◽  
Shell Star ◽  
Low Mass Ratio ◽  
Long Term Variations

The analysis of 149 radial velocities of V923 Aql from 1927 to 1987 revealed that the observed RV variations arise from a superpositon of cyclic long-term velocity variations of variable amplitude and cycle length / 20≦2K≦65 km.s-1, 1800d≦P≦2400d/ and an orbital motion with a period of 214.75 days and an amplitude 2K=12.4 km.s-1. The binary system consists of a B5-7 e primary and low-mass /about 0.5 M⊙/ secondary separated some 250 R⊙. Both, the long orbital period and low mass ratio are typical of /interacting/ binaries containing a Be star. The observed cycle length of the long-term changes are very similar to those observed for ɽTau, the only Be binary with the long-term variations known to date. V923 Aql thus becomes the second representative of binary Be stars, for which it is conceivable to interpret the long-term variations by an elongated envelope, revolving due to the attractive force of the secondary, and'formed by the process of mass transfer from the secondary to primary, as predicted by the binary model of the Be phenomenon.

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