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

• Verfasst von: Vasilyev, Valeriy [VerfasserIn]
• Verfasst von: Ludwig, Hans-Günter [VerfasserIn]
• Verfasst von: Lemasle, Bertrand [VerfasserIn]
• Titel: Spectroscopic properties of a two-dimensional time-dependent Cepheid model
• Titelzusatz: I. Description and validation of the model
• Verf.angabe: V. Vasilyev, H.-G. Ludwig, B. Freytag, B. Lemasle, and M. Marconi
• E-Jahr: 2017
• Jahr: 25 October 2017
• Umfang: 13 S.
• Fussnoten: Gesehen am 12.01.2021
• Titel Quelle: Enthalten in: Astronomy and astrophysics
• Ort Quelle: Les Ulis : EDP Sciences, 1969
• Jahr Quelle: 2017
• Band/Heft Quelle: 606(2017) Artikel-Nummer A140, 13 Seiten
• ISSN Quelle: 1432-0746
• DOI: doi:10.1051/0004-6361/201731422
• Datenträger: Online-Ressource
• Sprache: eng
• K10plus-PPN: 1571413545

Abstract

Standard spectroscopic analyses of Cepheid variables are based on hydrostatic one-dimensional model atmospheres, with convection treated using various formulations of mixing-length theory.<i>Aims. <i/>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. <i>Methods. <i/>With the radiation-hydrodynamics code CO5BOLD, we construct a two-dimensional time-dependent envelope model of a Cepheid with <i>T<i/><sub>eff<sub/> = 5600 K, log <i>g<i/> = 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.<i>Results. <i/>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<sup>-1<sup/>. 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<sup>-1<sup/>, 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.<i>Conclusions. <i/>Our two-dimensional model provides a reasonably accurate representation of the spectroscopic properties of a short-period Cepheid-like variable star. Some properties are primarily controlled by convective inhomogeneities rather than by the Cepheid-defining pulsations. Extended multi-dimensional modelling offers new insight into the nature of pulsating stars.