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.
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TL;DR: In this paper, a numerical simulation of the line profile variation beyond a single-surface approximation was carried out by taking account of the finite thickness of the spectral line-forming layer, and the simulation was compared with the observed line profiles.
Abstract: Prior to the last decade, most observations of roAp stars have concerned light variations. Recently some new, striking results of spectroscopic observations with high time resolution, high spectral dispersion, and a high signal-tonoise ratio became available. Since the oscillations found in roAp stars are high overtones, the vertical wavelengths of the oscillations are so short that the amplitude and phase of the variation of each spectroscopic line are highly dependent on the level of the line profile. Hence, analyses of the variation of the spectroscopic lines of roAp stars potentially provide us with new information about the vertical structure of the atmosphere of these stars. In order to extract such information, a numerical simulation of the line-profile variation beyond a single-surface approximation is necessary. We carried out a numerical simulation of line-profile variation by taking account of the finite thickness of the line-forming layer. We demonstrated how effective this treatment is, by comparing the simulation with the observed line profiles.
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TL;DR: In this article , it was shown that the bright B-type star γ Columbae is the stripped pulsating core of a previously much more massive star of roughly 12 M⊙ that just finished central hydrogen fusion.
Abstract: Stellar cores, that is, the central regions where densities and temperatures are high enough for nuclear fusion processes to take place, are usually covered by an opaque envelope. Only in very rare cases, stars may expose their cores, for example, when a tiny fraction of them evolve into Wolf–Rayet or helium hot subdwarf stars. However, for the vast majority of stars, namely unevolved stars that burn hydrogen into helium in their centres, direct observational clues on the cores are still missing. On the basis of a spectroscopic and photometric analyses, here we show that the bright B-type-star γ Columbae is the stripped pulsating core (with a mass of 4–5 M⊙, where M⊙ is the mass of the Sun) of a previously much more massive star of roughly 12 M⊙ that just finished central hydrogen fusion. The discovery of this star, which is still in a short-lived post-stripping structural re-adjustment phase, paves the way to obtain invaluable insights into the physics of both single and binary stars with respect to nuclear astrophysics and common-envelope evolution. In particular, it provides observational constraints on the structure and evolution of stripped-envelope stars.
2 citations
01 Jan 2021
TL;DR: In this paper, the authors investigate the diverse variability observed in the massive O+B eclipsing binary HD 165246 and make use of space-based photometry assembled with the K2 mission as well as ground-based spectroscopy to characterise the pulsational variability observed.
Abstract: The physics that drive the evolution of O-type stars are not well understood. These stars experience a plethora of different phenomena which alter their evolution, including pulsations, chemical transport, wind mass-loss, rapid rotation, multiplicity, etc. In this chapter, we investigate the diverse variability observed in the massive O+B eclipsing binary HD 165246. We make use of space-based photometry assembled with the K2 mission as well as ground-based spectroscopy to characterise the pulsational variability observed in HD 165246.
2 citations
TL;DR: In this paper, a numerical simulation of the line profile variation beyond a single-surface approximation was carried out by taking account of the finite thickness of a line forming layer, and the simulation was compared with the observed line profiles.
Abstract: Prior to the last decade, most observations of roAp stars have concerned the light variations. Recently some new, striking results of spectroscopic observations with high time resolution, high spectral dispersion, and a high signal-to-noise ratio became available. Since the oscillations found in roAp stars are high overtones, the vertical wavelengths of the oscillations are so short that the amplitude and phase of the variation of each spectroscopic line are highly dependent on the level of the line profile. Hence, analyses of the variation of the spectroscopic lines of roAp stars potentially provide us with new information about the vertical structure of the atmosphere of these stars. In order to extract such information, a numerical simulation of the line-profile variation beyond a single-surface approximation is necessary. We carried out a numerical simulation of line-profile variation by taking account of the finite thickness of the line forming layer. We demonstrated how effective this treatment is, by comparing the simulation with the observed line profiles.
2 citations
Cites background from "Line-profile variations due to adia..."
...…stars, ζ Ophiuchi variables, which are nonradial pulsators oscillating with low order p-, or g-modes (Osaki 1971; Stamford & Watson 1976, 1977; Smith 1977; Kubiak 1978; Vogt & Penrod 1983; Balona 1986a, 1986b, 1987; Kambe & Osaki 1988; Aerts & Waelkens 1993; Schrijvers et al. 1997; Townsend 1997)....
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01 Jan 2000
TL;DR: In this article, the authors apply the surface imaging technique to high-resolution spectra of the rapidly rotating β Cep-type star ω 1 Sco. Assuming only temperature fluctuations due to pulsations, they obtain a map of the surface corotating with the dominant pulsation mode.
Abstract: We apply the surface imaging technique to high-resolution spectra of the rapidly rotating β Cep-type star ω 1 Sco. Assuming only temperature fluctuations due to pulsations, we obtain a map of the surface corotating with the dominant pulsation mode. Prom the map we identify the dominant mode and find traces of a second pulsation mode. We conclude that the traditional surface imaging technique can be successfully used for mapping stellar non-radial pulsations.
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References
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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....
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...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....
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...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)....
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