The Physics of Pulsating White Dwarf Stars

in Leaflet - Astronomical Society of the Pacific (2012, September), 462

We present a summary of the properties of white dwarf stars, beginning with a brief reminder of their basic characteristics. We continue with a discussion of the spectral types, evolution, and other ... [more ▼]

We present a summary of the properties of white dwarf stars, beginning with a brief reminder of their basic characteristics. We continue with a discussion of the spectral types, evolution, and other properties of cooling white dwarfs, with an emphasis on the internal physics. We then introduce the pulsating white dwarfs and provide an updated view of their status. We finally discuss the impact (real and potential) of asteroseismology on our knowledge of degenerate stars. [less ▲]

Asteroseismic Solutions for the Two Fast Subdwarf B Pulsators Balloon 090100001 and PG 1336-018

in Leaflet - Astronomical Society of the Pacific (2008, January), 392

We present two new asteroseismic studies of the rapid sdB pulsator PG 1336-018 and the hybrid sdB pulsator Balloon (BAL) 090100001. For PG 1336-018, the analysis is based on 25 periods extracted from the ... [more ▼]

We present two new asteroseismic studies of the rapid sdB pulsator PG 1336-018 and the hybrid sdB pulsator Balloon (BAL) 090100001. For PG 1336-018, the analysis is based on 25 periods extracted from the white-light photometry of the Xcov17 Whole Earth Telescope campaign (Kilkenny et al. 2003). For BAL 090100001, we use 10 periods of high amplitudes for which constraints on the ℓ-index have been derived from high S/N multicolour photometry. From asteroseismology, we estimate important structural parameters for these two stars, including the stellar mass and the H-rich envelope thickness. The analyses presented here are of particular interest since the asteroseismic results can be tested using independent constraints, which confirm the robustness of the solutions in both cases. [less ▲]

An Asteroseismological Analysis of the Pulsating B Subdwarf Feige 48 Taking into Account Rotation

in Leaflet - Astronomical Society of the Pacific (2008, January), 392

We present a new analysis of the short period pulsating sdB star Feige 48 using the same observations as done in our previous work, but exploiting, this time, our new period-matching codes that include ... [more ▼]

We present a new analysis of the short period pulsating sdB star Feige 48 using the same observations as done in our previous work, but exploiting, this time, our new period-matching codes that include the rotation of the star. The pulsation spectrum of Feige 48 shows the signature of rotational splitting with a mean frequency spacing of about 28 μHz between the components of three different frequency multiplets. In addition, Feige 48 has been shown to be a member of a close binary system with an invisible (most likely a white dwarf) companion. Assuming various internal rotation laws, we are now able to fit all nine observed frequencies simultaneously, and not only the four m = 0 components that we identified a priori in our previous effort. For solid body rotation, our optimal model shows slightly different structural parameters than those obtained previously on the basis of purely spherical models. Interestingly, that optimal model is also characterized by a rotation period of 9.028 h, which falls exactly on the value of the orbital period found independently from spectroscopy, namely, 9.024 ± 0.072 h. This very strongly implies that Feige 48 is tidally locked, a suggestion quite consistent with theoretical expectations for such a close binary system. In the same vein, our investigations also demonstrate explicitly that the idea of a fast rotating core can be eliminated for Feige 48. [less ▲]

Constraints on Seismic Models of Balloon 090100001 through High-Sensitivity Multicolour Photometry

in Leaflet - Astronomical Society of the Pacific (2008, January), 392

We report on an analysis of high S/N ratio UBV multicolour photometry of the bright pulsating sdB star Balloon 090100001 gathered at the Canada-France-Hawaii Telescope with the help of the Montreal 3 ... [more ▼]

We report on an analysis of high S/N ratio UBV multicolour photometry of the bright pulsating sdB star Balloon 090100001 gathered at the Canada-France-Hawaii Telescope with the help of the Montreal 3-channel photometer LAPOUNE. Through an application of the color-amplitude method described in Randall et al. (2005), we were able to identify the degree index ℓ of several individual pulsation modes. These identifications provide extremely useful constraints on possible seismic models for Balloon 090100001. [less ▲]

Astrophysics: 1951

in Leaflet - Astronomical Society of the Pacific (1952), 6(273), 178-188