Hydrodynamical Survey of First‐Overtone Cepheids

Abstract

A hydrodynamical survey of the pulsational properties of first overtone Galactic Cepheids is presented. The goal of this study is to reproduce their observed light-and radial velocity curves. The comparison between the models and the observations is made in a quantitative manner on the level of the Fourier coefficients. Purely radiative models fail to reproduce the observed features, but convective models give good agreement. It is found that the sharp features in the Fourier coefficients are indeed caused by the P 1 /P 4 = 2 resonance, despite the very large damping of the 4th overtone. For the adopted mass-luminosity relation the resonance center lies near a period of 4. d 2 ± 0.2 as indicated by the observed radial velocity data, rather than near 3. d 2 as the light-curves suggest.

Strange Cepheids and RR Lyrae Stars

“…In particular, the turbulent eddy viscosity has a large e †ect. (We recall that our convective a parameters were calibrated to give good agreement with the observations of classical Cepheids ; Feuchtinger et al 2000).…”

“…While, at least near the blue edge, this is not a large e †ect for the fundamental mode, it becomes critically important for the strange modes, which get all their driving from the hydrogen partial ionization region. To study its e †ects on the strange modes and to ascertain that they survive convection, we have used the Florida code Kollath Kollath, & Buchler 2001) with a deÐned as in Feuchtinger, Buchler, & Kollath (2000), with values that are very similar to those used in our study of Ðrst overtone Cepheids, viz., a d \ 2.177, a c \ 0.4, a s \ 0.433, a l \ 0.12, a t \ 0.001, a r \ 0.4, a p \ 0, and We use the OPAL opacities of Iglesias & a l \ 1.5. Rogers (1996) and Alexander & Ferguson (1994).…”

Variable stars in nearby galaxies

“…When these resonances observed in Cepheids of the Galaxy and Magellanic Clouds are used to constrain purely radiative models, one obtains stellar masses that are too small to be in agreement with stellar evolution calculations. According to Buchler et al (1999), it is clear that some form of convective transport and of turbulent dissipation is needed to make progress; this has been proved for example for the first overtone mode Cepheids in the Galaxy (Feuchtinger et al 2000).…”

Pulsation in Cool Hydrogen Deficient Stars

“…Additionaly we used Alexander opacities for low temperatures, but for a slightly different composition. The linear analysis we employ (see Feuchtinger, 2000) is simple. By perturbing the equations of motion and energy and the grid equation, we end up with a linear non-adiabtic radial pulsation code.…”

“…The model is described in Wuchterl &Feuchtinger (1998) andFeuchtinger (1999a,b). The influence of the parameters on pulsation was investigated by Feuchtinger et al (2000). We neglected overshooting, the flux limiter, radiative cooling, turbulent viscosity and pressure.…”