Periodic Variability of Be Stars: Nonradial Pulsation or Rotational Modulation?

1994 ◽  
pp. 311-324 ◽  
Author(s):  
D. Baade ◽  
L. A. Balona
Keyword(s):  
Be Stars ◽  
Rotational Modulation ◽  
Nonradial Pulsation

scholarly journals Periodic Variability of Be Stars: Nonradial Pulsation or Rotational Modulation?

1994 ◽  
Vol 162 ◽  
pp. 311-324 ◽  
Author(s):  
D. Baade ◽  
L.A. Balona
Keyword(s):  
Line Profile ◽  
Large Fraction ◽  
Be Stars ◽  
Rotational Modulation ◽  
Subsequent Discussion ◽  
Points Of View ◽  
Nonradial Pulsation

A large fraction of Be stars show periodic light and line profile variations with a timescale of about one day. The mechanism which causes these periodic variations has been attributed to nonradial pulsation (NRP) or rotational modulation (RM). The authors present arguments supporting the two opposing points of view with the purpose of stimulating subsequent discussion by the Symposium participants.

scholarly journals Apparent Variation of v sin i and Rotational Modulation in Be Stars

2004 ◽  
Vol 215 ◽  
pp. 93-94
Author(s):  
C. Neiner ◽  
S. Jankov ◽  
M. Floquet ◽  
A. M. Hubert
Keyword(s):  
Fourier Transform ◽  
Magnetic Dipole ◽  
Be Stars ◽  
Line Profiles ◽  
Transform Method ◽  
Rotational Modulation ◽  
Be Star ◽  
Apparent Variation ◽  
The Fourier Transform ◽  
First Time

v sin i was determined by applying the Fourier transform method to the line profiles of two classical Be Stars. A variation is observed in the apparent v sin i which corresponds to the main frequencies associated to nrp modes. Rotational modulation is observed in wind sensitive UV lines of the Be star ω Ori and is associated with an oblique magnetic dipole which is discovered for the first time in a classical Be star.

scholarly journals Pulsations of Ob-Stars: New Observations

1998 ◽  
Vol 185 ◽  
pp. 347-354 ◽  
Author(s):  
Dietrich Baade
Keyword(s):  
Main Sequence ◽  
Physical Parameters ◽  
Be Stars ◽  
Instability Strip ◽  
Ob Stars ◽  
Analysis Strategies ◽  
The Galaxy ◽  
Order Line ◽  
Nonradial Pulsation ◽  
Radial Pulsations

Improved observing and data analysis strategies have initiated a considerable expansion of the empirical knowledge about the pulsations of OB stars. Possible correlations between physical parameters and associated pulsation characteristics are becoming more clearly perceivable. This starts to include the asteroseismologically fundamental areas of g-modes and rapid rotation. The β Cephei instability strip continues to be the only locus where radial pulsations occur (but apparently not in all stars located in that strip). Except for spectral types B8/B9 near the main sequence, where pulsations are hardly detected even at low amplitudes, any major group of stars in the Galaxy that are obviously not candidate pulsators still remains to be identified. However, the incidence and amplitudes of OB star pulsations decrease steeply with metallicity. The behaviour of high-luminosity stars is less often dominated by very few modes. In broad-lined stars the moving-bump phenomenon is more common than low-order line-profile variability. But its relation to nonradial pulsation is not clear. The beating of low-ℓ nonradial pulsation modes that have identical angular mode indices may be the clockwork of the outbursts of at least some Be stars. The physics of this episodic mass loss process remains to be identified.

scholarly journals Multiperiodicity in light variations of 53 Persei: results from optical photometry in 1990 October–1991 January

1994 ◽  
Vol 162 ◽  
pp. 33-36
Author(s):  
L. Huang ◽  
Z. Guo ◽  
J. Hao ◽  
J.R. Percy ◽  
M.S. Fieldus ◽  
...  
Keyword(s):  
Line Profile ◽  
Separate Group ◽  
Single Site ◽  
Optical Observations ◽  
Optical Photometry ◽  
Period Analysis ◽  
Preliminary Results ◽  
Rotational Modulation ◽  
Uv Photometry ◽  
Nonradial Pulsation

The B type star 53 Persei was discovered in 1977 by Smith (1977) as the prototype of a separate group of B-type variables showing light and line profile variability. The physical cause of the variability was thought to be nonradial pulsation (NRP) (see, e.g. Smith et al. 1984). However, the NRP model for this star has been questioned by Balona (1986) who suggested the rotational modulation (RM) model to explain the variability. In order to resolve the long lasting debate about 53 Persei, a campaign was initiated to organize coordinated optical photometry and spectroscopy from the ground, and Far-UV photometry from Voyager in 1991 January. This paper presents the results of period analysis on the groundbased UBV data. In another paper, Smith & Huang (1994) report the new identification of pulsation modes using Voyager Far-UV photometry combined with the results from optical observations. Some preliminary results from APT uvby observations taken at a single site are also cited for comparison.

scholarly journals Pulsations of Be stars: time series analysis of He I λ4921

1994 ◽  
Vol 162 ◽  
pp. 100-101
Author(s):  
M. E. Hahula ◽  
D. R. Gies
Keyword(s):  
Time Series ◽  
Time Series Analysis ◽  
Mass Loss ◽  
Power Spectra ◽  
Phase Content ◽  
Be Stars ◽  
Optical Photometry ◽  
Multi Wavelength ◽  
Spectroscopy Optical ◽  
Nonradial Pulsation

We present the results of time series observations of He I λ4921 in the spectra of 10 Be stars. The spectra were obtained during multi-wavelength campaigns of IUE spectroscopy, optical photometry and polarimetry, and spectroscopy undertaken to study the connection (if any) between nonradial pulsation (NRP) and mass loss in Be stars. Power spectra have been calculated for the time series of intensity variations within the profiles. These were used to determine periodic variability and phase content to analyze the variations in the context of the NRP model. The observations were made at three observatories (Table 1). All the spectra record at least Hβ and He I λ4921 with a S/N > 200 per pixel and a resolution of ≈ 0.2 Å. We have concentrated the analysis on He I λ4921 as a probe of photospheric variability. This line is generally free of emission (unlike He I λ6678), but in some cases an Fe II λ4924 shell component appears in the red wing.

scholarly journals Fiber Fed Spectrograph for Line Variability Studies

1988 ◽  
Vol 132 ◽  
pp. 31-34 ◽  
Author(s):  
P. Felenbok ◽  
J. Guérin
Keyword(s):  
Line Profile ◽  
Main Sequence ◽  
Single Site ◽  
Be Stars ◽  
Correlated Observations ◽  
Rotational Modulation ◽  
High Flexibility ◽  
Gain Access ◽  
Star Rotation

In our studies of activity in pre-main sequence Herbig Ae/Be stars we are mainly interested in searching rotational modulation of line profile. If the period of star rotation is of the order of one or two days, the data collected from a single site is insufficient. This led us to start correlated observations from two or three sites spread as much as possible in longitude. Our first bi-site observations started in 1982 on AB Aur from two observatories located 11 hours apart.: CFHT in Hawaï and OHP in France. To achieve a high flexibility and to gain access to telescopes without attached spectrographs. We built an instrument that is mobile and specially designed for line profile studies.

scholarly journals HR 4074: an Emission-Free NRP Twin of the Be Star 28 CMa

2002 ◽  
Vol 185 ◽  
pp. 248-249
Author(s):  
S. Štefl ◽  
Th. Rivinius ◽  
D. Baade
Keyword(s):  
Time Series ◽  
Line Profile ◽  
Rotational Velocity ◽  
Be Stars ◽  
Narrow Component ◽  
Rotational Modulation ◽  
Line Core ◽  
Emission Activity ◽  
History Of ◽  
Be Star

In spite of considerable progress in the investigation of rapid line-profile variations (lpv) of Be stars, at least two models still compete in the literature: the rotational modulation, assuming mostly corotating circumstellar structures (Balona, 2000), and nonradial pulsations (Maintz et al. and Rivinius et al., these proceedings). Attempts to explain the lpv of Be stars were often connected with the proto-typical star 28 (ω) CMa (HR 2749 = HD 56139, B2IV-Ve, v sin i = 80 km/s). Štefl et al. (1998) described variability in three line-profile components: in the narrow component of the line core, in the line core itself and in the wings. The Balmer emission of 28 CMa is variable and has always been observed to be at least moderate, mostly strong.HR 4074 (HD 89890, B3 III, v sin i = 70 km/s) has a different history of its emission activity. From a single spectrogram taken in 1893, Pickering (1898) reported an emission in Hβ. Subsequent observations never confirmed this. If it was not mis-identified by Pickering, HR 4074 would be in the probably longest B-star phase known of any Be star. HR 4074 is very probably not an SPB star - the spectral type is too early, the rotational velocity too high and light variations too low for this classification. Baade (1984) detected rapid lpv with a period P ≈ 2.25 d. Our time series analysis of radial velocity (RV) variations, measured as line modes, and that of full profiles give P = (2.3179 ± 0.0008) d.

scholarly journals Search for Rotational Modulation in Pre-Main Sequence Herbig Ae/Be Stars

1988 ◽  
Vol 132 ◽  
pp. 105-108
Author(s):  
C. Catala ◽  
J. Czarny ◽  
P. Felenbok
Keyword(s):  
Main Sequence ◽  
Stellar Winds ◽  
Be Stars ◽  
Main Sequence Stars ◽  
Intermediate Mass ◽  
The Past ◽  
Rotational Modulation

The Herbig Ae/Be stars (Herbig, 1960; Finkenzeller and Hundt, 1984) are widely believed to be intermediate mass (2-5 M⊙) pre-main sequence stars. In the past few years, a big effort has been made to model their outer layers, and it has been shown that they possess stellar winds and extended chromospheres (Catala et al., 1984; Catala et al., 1986a; Catala and Kunasz, 1987).

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