Population I pulsating stars

Tsvetkov, Ts.

doi:10.1007/bf00641730

Cited by 12 publications

(3 citation statements)

References 25 publications

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“…where P is the pulsational period. The empirically calibrated "period-gravity" relation of Tsvetkov (1988) can be used to estimate the mean gravity, and this can be taken as a first approximation to derive stellar parameters. According to Andrievsky et al (2002b) (their Fig.…”

Section: Grid Of 1d Lhd Modelsmentioning

confidence: 99%

Spectroscopic properties of a two-dimensional time-dependent Cepheid model

Vasilyev

Ludwig

Freytag

et al. 2017

A&A

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Context. Standard spectroscopic analyses of Cepheid variables are based on hydrostatic one-dimensional model atmospheres, with convection treated using various formulations of mixing-length theory. Aims. This paper aims to carry out an investigation of the validity of the quasi-static approximation in the context of pulsating stars. We check the adequacy of a two-dimensional time-dependent model of a Cepheid-like variable with focus on its spectroscopic properties. Methods. With the radiation-hydrodynamics code CO5BOLD, we construct a two-dimensional time-dependent envelope model of a Cepheid with T eff = 5600 K, log g = 2.0, solar metallicity, and a 2.8-day pulsation period. Subsequently, we perform extensive spectral syntheses of a set of artificial iron lines in local thermodynamic equilibrium. The set of lines allows us to systematically study effects of line strength, ionization stage, and excitation potential. Results. We evaluate the microturbulent velocity, line asymmetry, projection factor, and Doppler shifts. The microturbulent velocity, averaged over all lines, depends on the pulsational phase and varies between 1.5 and 2.7 km s −1 . The derived projection factor lies between 1.23 and 1.27, which agrees with observational results. The mean Doppler shift is non-zero and negative, -1 km s −1 , after averaging over several full periods and lines. This residual line-of-sight velocity (related to the "K-term") is primarily caused by horizontal inhomogeneities, and consequently we interpret it as the familiar convective blueshift ubiquitously present in non-pulsating late-type stars. Limited statistics prevent firm conclusions on the line asymmetries. Conclusions. Our two-dimensional model provides a reasonably accurate representation of the spectroscopic properties of a shortperiod Cepheid-like variable star. Some properties are primarily controlled by convective inhomogeneities rather than by the Cepheiddefining pulsations. Extended multi-dimensional modelling offers new insight into the nature of pulsating stars.

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Section: Grid Of 1d Lhd Modelsmentioning

confidence: 99%

Spectroscopic properties of a two-dimensional time-dependent Cepheid model

Vasilyev

Ludwig

Freytag

et al. 2017

A&A

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“…Using these parameters, the radius of the star was derived as 2.85(23) R ⊙ . The surface gravity (logg = 3.887(159)) was obtained from the relation given by Tsvetkov [11] and the mass (M/M ⊙ = 2.28( 9)) was computed by means of the equation taken from Cox and Pilachowski [12].…”

Section: Resultsmentioning

confidence: 99%

STEREO observations of HD90386 (RX Sex): a δ-Scuti or a hybrid star?

Özuyar

Stevens

Whittaker

et al. 2016

J. Phys.: Conf. Ser.

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HD 90386 is a rarely studied bright A2V type Delta Scuti star (V = 6.66 mag). It displays short-term light curve variations which are originated due to either a beating phenomenon or a non-periodic variation. In this paper, we presented high-precision photometric data of HD 90386 taken by the STEREO satellite between 2007 and 2011 to shed light on its internal structure and evolution stage. From the frequency analysis of the four-year data, we detected that HD 90386 had at least six different frequencies between 1 and 15 c d −1 . The most dominant frequencies were found at around 10.25258 c d −1 (A ∼ 1.92 mmag) and 12.40076 c d −1 (A ∼ 0.61 mmag). Based on the ratio between these frequencies, the star was considered as an overtone pulsator. The variation in pulsation period over 35 years was calculated to be dP/Pdt = 5.39(2) x 10 −3 yr −1 . Other variabilities at around 1.0 c d −1 in the amplitude spectrum of HD90386 were also discussed. In order to explain these variabilities, possible rotational effects and Gamma Dor type variations were focused. Consequently, depending on the rotation velocity of HD 90386, we speculated that these changes might be related to Gamma Dor type high-order g-modes shifted to the higher frequencies and that HD 90386 might be a hybrid star. *

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Section: Grid Of 1d Lhd Modelsmentioning

confidence: 99%

Spectroscopic properties of a two-dimensional time-dependent Cepheid model

Vasilyev

Ludwig

Freytag

et al. 2018

A&A

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Context. Standard spectroscopic analyses of variable stars are based on hydrostatic 1D model atmospheres. This quasi-static approach has not been theoretically validated. Aim. We aim at investigating the validity of the quasi-static approximation for Cepheid variables. We focus on the spectroscopic determination of the effective temperature Teff, surface gravity log g, microturbulent velocity ξt, and a generic metal abundance log A, here taken as iron.Methods. We calculated a grid of 1D hydrostatic plane-parallel models covering the ranges in effective temperature and gravity that are encountered during the evolution of a 2D time-dependent envelope model of a Cepheid computed with the radiation-hydrodynamics code CO5BOLD. We performed 1D spectral syntheses for artificial iron lines in local thermodynamic equilibrium by varying the microturbulent velocity and abundance. We fit the resulting equivalent widths to corresponding values obtained from our dynamical model for 150 instances in time, covering six pulsational cycles. In addition, we considered 99 instances during the initial non-pulsating stage of the temporal evolution of the 2D model. In the most general case, we treated Teff, log g, ξt, and log A as free parameters, and in two more limited cases, we fixed Teff and log g by independent constraints. We argue analytically that our approach of fitting equivalent widths is closely related to current standard procedures focusing on line-by-line abundances.Results. For the four-parametric case, the stellar parameters are typically underestimated and exhibit a bias in the iron abundance of ≈−0.2 dex. To avoid biases of this type, it is favorable to restrict the spectroscopic analysis to photometric phases ϕph ≈ 0.3…0.65 using additional information to fix the effective temperature and surface gravity.Conclusions. Hydrostatic 1D model atmospheres can provide unbiased estimates of stellar parameters and abundances of Cepheid variables for particular phases of their pulsations. We identified convective inhomogeneities as the main driver behind potential biases. To obtain a complete view on the effects when determining stellar parameters with 1D models, multidimensional Cepheid atmosphere models are necessary for variables of longer period than investigated here.

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Population I pulsating stars

Cited by 12 publications

References 25 publications

Spectroscopic properties of a two-dimensional time-dependent Cepheid model

Spectroscopic properties of a two-dimensional time-dependent Cepheid model

STEREO observations of HD90386 (RX Sex): a δ-Scuti or a hybrid star?

Spectroscopic properties of a two-dimensional time-dependent Cepheid model

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