Line-profile variations due to adiabatic non-radial pulsations in rotating stars. I. Observable characteristics of spheroidal modes
TL;DR: In this paper, the surface-velocity field of a rotating, adiabatically pulsating star, which accounts for the effects of the Coriolis force, is considered.
Abstract: We present a useful formulation of the surface-velocity field of a rotating, adiabatically pulsating star, which accounts for the effects of the Coriolis force. We use this model to investigate the observable spectroscopic characteristics of non-radial pulsations. We calculate time series of absorption line profiles in a carefully chosen domain of parameter space. Only mono-periodic spheroidal modes are investigated; atmospheric changes due to the pulsation are neglected. The line-profile variations, as well as their behavior inferred from two well-defined diagnostics, are presented in two-dimensional parameter grids. We show that the intensity variations in time series of theoretical spectra, at each position in the line profile, cannot be described by a single sinusoid: at least one harmonic sinusoid needs to be included. Across the line profile the relative amplitudes and phases of these sinusoids vary independently. The blue-to-red phase difference found at the main pulsation frequency turns out to be an indicator of the degree , rather than the azimuthal order ; the phase difference of the variations with the first harmonic frequency is an indicator of . Hence, the evaluation of the variability at the harmonic frequency can improve the results derived from an analysis of observed line profiles. We find, that if line-profile variations at the line center dominate over the variations in the line wings, this does not give conclusive information on the ratio of the horizontal to the vertical pulsational surface motions. Tesseral modes, when observed at not too high inclinations, are as much capable of producing considerable line-profile variations as sectoral modes. We find that, within the limits of our model, the effects of rotation on the appearance of the line-profile variations are important for low-degree sectoral modes, and for the sub-class of the tesseral modes with an even number.
Citations
More filters
01 Jan 2020
TL;DR: Based on a photometric and preliminary asteroseismic analysis, this paper showed that the mid B-type giant 18 Peg is one of the most evolved members of the rare class of slowly pulsating B-stars and thus bears tremendous potential to derive a tight lower limit for the width of the upper main sequence.
Abstract: The predicted width of the upper main sequence in stellar evolution models depends on the empirical calibration of the convective overshooting parameter. Despite decades of discussions, its precise value is still unknown and further observational constraints are required to gauge it. Based on a photometric and preliminary asteroseismic analysis, we show that the mid B-type giant 18 Peg is one of the most evolved members of the rare class of slowly pulsating B-stars and, thus, bears tremendous potential to derive a tight lower limit for the width of the upper main sequence. In addition, 18 Peg turns out to be part of a single-lined spectroscopic binary system with an eccentric orbit that is greater than 6 years. Further spectroscopic and photometric monitoring and a sophisticated asteroseismic investigation are required to exploit the full potential of this star as a benchmark object for stellar evolution theory.
9 citations
TL;DR: In this paper, Johnson and Stromgren photometric and medium-resolution spectroscopic observations of the delta Scuti type variable star V784 Cassiopeae were obtained in three consecutive years between 1999 and 2001.
Abstract: We present an analysis of new Johnson and Stromgren photometric and medium-resolution spectroscopic observations of the delta Scuti type variable star V784 Cassiopeae. The data were obtained in three consecutive years between 1999 and 2001. The period analysis of the light curve resulted in the detection of four frequencies ranging from 9.15 c/d to 15.90 c/d, while there is a suggestion for more, unresolved frequency components, too. The mean Stromgren indices and Hipparcos parallax were combined to calculate the following physical parameters: =7100+-100 K, log g=3.8+-0.1, M_bol=1.50+-0.15 mag. The position of the star in the HR diagram was used to derive evolutionary mass and age yielding to a consistent picture of an evolved delta Scuti star with a mixture of radial plus non-radial modes.
9 citations
TL;DR: In this article, Johnson and Stromgren photometric and medium-resolution spectroscopic observa- tions of the δ Scuti type variable star V784 Cassiopeae were obtained in three consecutive years between 1999 and 2001.
Abstract: We present an analysis of new Johnson and Stromgren photometric and medium-resolution spectroscopic observa- tions of the δ Scuti type variable star V784 Cassiopeae. The data were obtained in three consecutive years between 1999 and 2001. The period analysis of the light curve resulted in the detection of four frequencies ranging from 9.15 d −1 to 15.90 d −1 , while there is a suggestion for more, unresolved frequency components, too. The mean Stromgren indices and Hipparcos par- allax were combined to calculate the following physical parameters: � Teff� = 7100 ± 100 K, log g = 3.8 ± 0.1, Mbol = 1. m 50 ± 0. m 15. The position of the star in the HR diagram was used to derive evolutionary mass and age yielding to a consistent picture of an evolved δ Scuti star with a mixture of radial plus non-radial modes.
9 citations
TL;DR: In this article, high-resolution spectroscopic observations of the rapidly rotating Scuti star γ Bootis have been carried out in 2005, over six consecutive nights, in order to search for line-profile variability.
Abstract: High-resolution spectroscopic observations of the rapidly rotating δ Scuti star γ Bootis have been carried out in 2005, over six consecutive nights, in order to search for line-profile variability. Time-series, consisting of flux measurements at each wavelength bin across the Ti II 4571.917 A line profile as a function of time, have been Fourier analysed. The results confirm the early detection reported by Kennelly et al. of a dominant periodic component at frequency 21.28 cycles d −1 in the observer’s frame, probably due to a high-azimuthal-order sectorial mode. Moreover, we found other periodicities at 5.06, 12.02 cycles d −1 , probably present but not secure, and at 11.70 and 18.09 cycles d −1 , uncertain. The latter frequency, if present, should be identifiable as another high-azimuthal-order sectorial mode and the three additional terms as low-l modes as proved by the analysis of the first three moments of the line. Owing to the short time baseline and the one-site temporal sampling we consider our results only preliminary but encouraging for a more extensive multisite campaign. A refinement of the atmospheric physical parameters of the star has been obtained from our spectroscopic data and adopted for preliminary computations of evolutionary models of
8 citations
Cites background from "Line-profile variations due to adia..."
...Other interpretations are obviously possible since it has been demonstrated that tesseral modes with l − |m| small, observed at an inclination angle of about 50 degrees, might produce similar moving patterns as sectorial modes observed equator-on (i.e. Schrijvers et al. 1997)....
[...]
...…width and the first three moments (which describe the centre-of-mass velocity of the line, the line width, and the line skewness, respectively) of the Tiii 4571.917Å line profile, as a function of time, following the prescriptions given by Balona et al. (1996) and Schrijvers et al. (1997)....
[...]
TL;DR: In this paper, the authors present the results of a large international spectroscopic campaign on the Scuti star BN Cnc. Combining observations from ve observatories taken over more than two weeks, they calculate line indices of the H line.
Abstract: We present the results of a large international spectroscopic campaign on the Scuti star BN Cnc. Combining observations from ve observatories taken over more than two weeks, we calculate line indices of the H line. A line index is the integrated line flux in a software lter divided by the continuum flux. We demonstrate that this can be used in combination with simultaneous photometry to classify the oscillation modes. We recover all the frequencies also found from photometry and assign likely mode identications, which dier slightly from previously published values, but are found to be consistent with simple models. The dierence in identication is found to have very little eect on the derived luminosity and temperature.
7 citations
Cites background from "Line-profile variations due to adia..."
...None of them has ever been applied to δ Scuti stars as faint as BN Cnc. Detailed studies of line profile variations have been carried out for β Cephei stars (e.g. Telting & Schrijvers 1997 or Schrijvers et al. 1997)....
[...]
References
More filters
Book•
01 Jan 1986
15 citations
"Line-profile variations due to adia..." refers background in this paper
...Many authors (e.g. Smith 1986; Gies & Kullavanijaya 1988; Kambe & Osaki 1988; Yang et al. 1988; Kambe et al. 1990) have used the number of visible bumps or, equivalently, the blue-to-red phase difference ∆Ψ0 to identify |m| according to ∆Ψ0 = |m|π....
[...]
...In his discussion of the so called k-problem, Smith (1986) mentioned that for high k(0)-values, the toroidal term(s) caused by rotation might be able to mimic the amplitude-distribution characteristics of a low-k(0) mode....
[...]
...The difficulty to derive k-values from amplitude diagrams The determination of the k-value from observed lineprofiles has been discussed by several authors (e.g. Smith 1986; Kambe et al. 1990; Lee & Saio 1990)....
[...]