Whole Earth Telescope observations of AM Canum Venaticorum - discoseismology at last

Details Whole Earth Telescope observations of AM Canum Venaticorum - discoseismology at last Whole Earth Telescope observations of AM Canum Venaticorum - discoseismology at last

Apr 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998a%26a...332..939s&link_type=abstract

Astronomy and Astrophysics, v.332, p.939-957 (1998)

Astronomy and Astrophysics

Astrophysics

28

Stars: Individual: Am Canum Venaticorum, Novae, Cataclysmic Variables, Stars: Oscillations, White Dwarfs, Accretion, Accretion Disks

Scientific paper

We report the results of 143.2 hours of time-series photometry over a 12 day period for AM CVn (= HZ 29) as part of the Whole Earth Telescope (WET) project. This star is believed to be an ultra-short period cataclysmic binary. In the temporal spectrum of the light curve we find a series of 5 harmonically related frequency mo dulations, some with sidebands with a constant frequency spacing of 20.8 mu Hz always on the high-frequency side. The set of harmonics has a fundamental frequency of 951 mu Hz. No modulation is detected at this frequency in the light curve. In addition, modulations with frequencies 972.5 and 988.9 mu Hz are detected with low amplitudes. The structure of the dominant 1903 mu Hz modulation explains part of the "phase jitter" observed earlier. The amplitude of this peak is modulated with a period of 13.32 +/- 0.05 hrs. The same period is detected in absorption line shape modulations, most likely arising from variable aspects of the outer parts of the disk (Patterson et al. 1993). The observed periodic light modulations can be explained as a combination of aspect variations of disk modifications due to tidally induced shocks as described by Savonie et al. (1994), which leads to a two-armed spiral structure, and the mode coupling model of Lubow (1991), which leads to a three-fold azimuthal symmetry in the outer parts of the disk and a prograde precessing wave. The two- and three-fold azimuthal structures are stationary in the binary frame and explain the higher harmonics of the orbital period we observe in the light curve. This may be the first example of a successful disco-seismological interpretation. In addition we propose that the variable amplitude modulation at 989 mu Hz may be explained as a g-mode pulsation, which indicates that the central white dwarf may be a DO with a hot envelope. Based on data obtained in observing time allocated by Mc Donald Observatory, Texas; Mauna Kea Observatory, Hawaii; Vainu Bappu Observatory, India; Wise Observatory, Israel; Haute-Provence Observatory, France; The Nordic Optical Telescope and the Isaac Newton Telescope at Roque de Los Muchachos Observatory, La Palma, Spain.

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