scholarly journals Long-Term V/R Variations of be Stars Due to Global One-Armed Oscillations of Equatorial Disks

1993 ◽  
Vol 134 ◽  
pp. 369-370
Author(s):  
Atsuo T. Okazaki
Keyword(s):  
Nonlinear Oscillations ◽  
Balmer Line ◽  
Density Gradients ◽  
Be Stars ◽  
Line Profiles ◽  
Be Star ◽  
On Line ◽  
The One ◽  
Long Term Variations

AbstractWe study the long-term variations of Balmer line profiles due to global one-armed oscillations in Be-star disks. In order to examine the qualitative effects of oscillations on line profiles, we assume that the eigenfunctions of one-armed nonlinear oscillations are similar to those of linear oscillations. Computing the line profiles for various values of disk parameters, we find that in small disks or in disks with steep density gradients the one-armed fundamental modes cause remarkable variabilities similar to the observed V/R variations.

scholarly journals Short-Term Spectroscopic Variations of the Be Star 11 Cam

1987 ◽  
Vol 92 ◽  
pp. 93-94
Author(s):  
J. Chauville ◽  
M. Alvarez ◽  
J.P. Sareyan ◽  
L. Ballereau ◽  
R. Michel
Keyword(s):  
Spectral Type ◽  
Balmer Line ◽  
Line Profiles ◽  
Short Term ◽  
Visual Magnitude ◽  
Be Star ◽  
Long Term Variations

11 Cam (HD 32343 = HR 1622) is a so-called “pole-on” Be star known for its long term variations, already noted by Merrill and Burwell (1943). Recent determinations of visual magnitude and spectral type are V = 5.222 and B2.5Ve (Rufener, 1981). The Balmer line profiles, especially Hα, have been frequently studied; Briot (1971), for instance, measured 40 and 4.9 Å equivalent widths for Hα and Hβ respectively; the Hα/Hβ peak to continuum ratio is 6.43/2.02 according to Gray and Marlborough (1974) who give v sin i = 131 km s-1, close to the value of 140 km s-1 adopted by Kogure (1968).

scholarly journals Some observational appearances of m=1 density waves in Be star disks

1994 ◽  
Vol 162 ◽  
pp. 380-381
Author(s):  
Atsuo T. Okazaki
Keyword(s):  
Angular Frequency ◽  
Be Stars ◽  
Line Profiles ◽  
Density Waves ◽  
Disk Rotation ◽  
Be Star

One-armed (i.e., m = 1) density waves are the only global waves in nearly Keplerian disks (Kato 1983). Their frequencies are much smaller than the angular frequency of disk rotation. Based on this theory, Okazaki (1991) proposed that the long-term V/R variations of Be stars are phenomena caused by the global m = 1 oscillations in the equatorial disks. Hummel and Hanuschik (1993) showed that line profiles of disks with m = 1 perturbation patterns are in agreement with the observed V/R variability.

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.

Aspects of the Evolution of the Romanian Tourists’ Preferences Concerning the Domestic Tourist Destinations

2019 ◽  
Vol 10 (1) ◽  
pp. 21-28
Author(s):  
Aniela Bălăcescu ◽  
Radu Șerban Zaharia
Keyword(s):  
Logistic Model ◽  
Local Level ◽  
Medium Term ◽  
Tourist Destinations ◽  
Tourism Management ◽  
Production And Consumption ◽  
On Line ◽  
The One ◽  
Long Term Studies

Abstract Tourist services represent a category of services in which the inseparability of production and consumption, the inability to be storable, the immateriality, and last but not least non-durability, induces in tourism management a number of peculiarities and difficulties. Under these circumstances the development of medium-term strategies involves long-term studies regarding on the one hand the developments and characteristics of the demand, and on the other hand the tourist potential analysis at regional and local level. Although in the past 20 years there has been tremendous growth of on-line booking made by household users, the tour operators agencies as well as those with sales activity continue to offer the specific services for a large number of tourists, that number, in the case of domestic tourism, increased by 1.6 times in case of the tour operators and by 4.44 times in case of the agencies with sales activity. At the same time, there have been changes in the preferences of tourists regarding their holiday destinations in Romania. Started on these considerations, paper based on a logistic model, examines the evolution of the probabilities and scores corresponding to the way the Romanian tourists spend their holidays on the types of tourism agencies, actions and tourist areas in Romania.

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 Ubiquitous C IV 1550 Variability in B and Be Stars

1987 ◽  
Vol 92 ◽  
pp. 286-288 ◽  
Author(s):  
G. Sonneborn ◽  
M.P. Garhart ◽  
C.A. Grady
Keyword(s):  
Time Scale ◽  
High Dispersion ◽  
Be Stars ◽  
Line Profiles ◽  
Standard Star ◽  
B Stars ◽  
Short And Long Term ◽  
Resonance Transitions ◽  
Long Term Behavior

Studies of line profile variability of the ultraviolet 1550 Angstrom resonance transitions of C IV in Be stars (Sonneborn et al. 1986; Grady, et al. 1986a,b) have prompted an investigation into the short- and long-term behavior of the C IV lines in other types of B stars. We present examples of two well-studied Be stars, Omega Orionis and 66 Ophiuchi, and two non-Be stars, Beta Cephei and the standard star Zeta Cassiopeiae. Zeta Cas is also known to be a 53 Per variable (see Cox 1983). The IUE SWP high-dispersion spectra of Beta Cep and Zeta Cas have been obtained from the IUE archives. It has been known for some years that the C IV line profiles in Beta Cep vary in a time scale of several days (Fishel and Sparks, 1980). However, it came as a surprise to discover C IV variability in Zeta Cas. Available data allow us to set an upper limit of several months for the time scale of Zeta Cas C IV variability. The principal difference between the C IV variability in Be and non-Be stars appears to be the magnitude and velocity range of the effect.

scholarly journals Short-term variability and mass loss in Be stars

2018 ◽  
Vol 620 ◽  
pp. A145 ◽  
Author(s):  
D. Baade ◽  
A. Pigulski ◽  
Th. Rivinius ◽  
L. Wang ◽  
Ch. Martayan ◽  
...  
Keyword(s):  
Be Stars ◽  
Frequency Pattern ◽  
Similar Frequency ◽  
Good Target ◽  
Variability Pattern ◽  
Be Star ◽  
Shell Star ◽  
Mass Ejection ◽  
Combination Frequencies

Context. In early-type Be stars, groups of nonradial pulsation (NRP) modes with numerically related frequencies may be instrumental for the release of excess angular momentum through mass-ejection events. Difference and sum/harmonic frequencies often form additional groups. Aims. The purpose of this study is to find out whether a similar frequency pattern occurs in the cooler third-magnitude B7-8 IIIe shell star ν Pup. Methods. Time-series analyses were performed of space photometry with BRITE-Constellation (2015, 2016/17, and 2017/18), SMEI (2003–2011), and HIPPARCOS (1989–1993). Two IUE SWP and 27 optical echelle spectra spanning 20 years were retrieved from various archives. Results. The optical spectra exhibit no anomalies or well-defined variabilities. A magnetic field was not detected. All three photometry satellites recorded variability near 0.656 c/d which is resolved into three features separated by ∼0.0021 c/d. Their first harmonics and two combination frequencies form a second group, whose features are similarly spaced by 0.0021 c/d. The frequency spacing is very nearly but not exactly equidistant. Variability near 0.0021 c/d was not detected. The long-term frequency stability could be used to derive meaningful constraints on the properties of a putative companion star. The IUE spectra do not reveal the presence of a hot subluminous secondary. Conclusions. ν Pup is another Be star exhibiting an NRP variability pattern with long-term constancy and underlining the importance of combination frequencies and frequency groups. This star is a good target for efforts to identify an effectively single Be star.

scholarly journals Photometric studies of Be star variability

1994 ◽  
Vol 162 ◽  
pp. 299-300
Author(s):  
John R. Percy
Keyword(s):  
Time Scales ◽  
Balmer Line ◽  
Radial Pulsation ◽  
Be Stars ◽  
Photometric Study ◽  
Short Term ◽  
Hot Stars ◽  
Be Star ◽  
Short Term Variability

Be stars are hot stars which have shown emission in at least one Balmer line on at least one occasion. As the definition implies, the Be phenomenon can be variable with time: on time scales of days to decades as the circumstellar disc develops and disperses; on time scales of days to months in a few Be stars which are interacting binaries; on time scales of 0.2 to 2 days due to non-radial pulsation or possibly rotation. The Be stars are worthy of photometric study because they are bright and numerous; the nature of the short-term variability is not yet agreed upon; the cause of the development of the disc - and its relationship to the short-term variability - is also not yet known.

scholarly journals The Spheroidal/Ellipsoidal, Variable Mass-Loss, Decelerated Be Star Model (Review Paper)

1987 ◽  
Vol 92 ◽  
pp. 384-410 ◽  
Author(s):  
V. Doazan
Keyword(s):  
Variable Mass ◽  
Thermodynamic Characteristics ◽  
Be Stars ◽  
Star Model ◽  
B Stars ◽  
Proposed Model ◽  
Mass Outflow ◽  
Be Star ◽  
Model Review ◽  
The One

The proposed model is empirical; it is based on analysis of the available data on Be stars obtained in all the observable spectral regions, and it is required to be thermodynamically self-consistent. Rather than trying to answer the question: “What is the origin of the Be-phenomenon?” We ask: First. “What phenomena characterize empirically Be stars?” Second, “What thermodynamic characteristics are implied by the existence of such phenomena?” Third. “What inferences may be made an the atmospheric structure of a Be star from these empirical and thermodynamical characteristics?” The observed phenomena, their thermodynamical implications and the resulting model have each two aspects. On the one hand, the observational evidence for a nonradiatively heated, expanding chromosphere-corona implies the existence of both a nonradiative energy flux and a mass outflow from the photosphere. This first aspect is common to both Be and normal B stars, at least for the earliest subtypes.

scholarly journals A Transient Shock-Wave in the Shell of the Be Star HD 184279

1987 ◽  
Vol 92 ◽  
pp. 95-98
Author(s):  
D. Ballereau ◽  
J. Chauville
Keyword(s):  
Shock Wave ◽  
Radial Velocity ◽  
Emission Spectrum ◽  
Short Term ◽  
Balmer Series ◽  
Spectroscopic Observations ◽  
The Past ◽  
Be Star ◽  
Long Term Variations

HD 184279 (V1294 Aql) has presented in the past an emission spectrum on the first terms of the Balmer series, and shell absorptions on the hydrogen and neutral helium lines. Their variations have been reported by Merrill (1952), Merrill and Lowen (1953) and Svolopoulos (1975). Ballereau and Hubert-Delplace (1982) evidenced long-term V/R variations with an amplitude of ∼100 km s-1. Short-term photometric variations are irregular (Tempesti and Patriarca, 1976), while long-term variations are correlated with radial velocity (RV) of shell lines (Horn et al., 1982). Ballereau and Chauville (in preparation) extended the spectroscopic observations until 1984 and confirmed the pseudo-periodic variations, the last half-period ranging over 3.4 years (April 1, 1980-August 1, 1983).

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