Whole earth telescope observations of am canum venaticorum-discoseismology at last

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.ˡ 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 μHz always on the high-frequency side. The set of harmonics has a fundamental frequency of 951 μHz. No modulation is detected at this frequency in the light curve. In addition, modulations with frequencies 972.5 and 988.9 μHz are detected with low amplitudes. The structure of the dominant 1903 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

Whole earth telescope observations of am canum venaticorum-discoseismology at last

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.ˡ 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 μHz always on the high-frequency side. The set of harmonics has a fundamental frequency of 951 μHz. No modulation is detected at this frequency in the light curve. In addition, modulations with frequencies 972.5 and 988.9 μHz are detected with low amplitudes. The structure of the dominant 1903 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 unusual helium variable AM Canum Venaticorum

The unusual variable star AM CVn has puzzled astronomers for over 40 years. This object, both a photometric and spectroscopic variable, is believed to contain a pair of hydrogen-deficient white dwarfs of extreme mass ratio, transferring material via an accretion disk. We examine the photometric properties of AM CVn, analyzing 289 hours of high-speed photometric data spanning 1976 to 1992. The power spectrum displays significant peaks at 988.7, 1248.8, 1902.5, 2853.8, 3805.2, 4756.5, and 5707.8 μHz (1011.4, 800.8, 525.6, 350.4, 262.8, 210.2, and 175.2 s). We find no detectable power at 951.3 μHz (1051 s), the previously reported main frequency. The 1902.5, 2853.9, and 3805.2 μHz peaks are multiplets, with frequency splitting in each case of 20.77 ± 0.05 μHz. The 1902.5 μHz seasonal pulse shapes are identical, within measurement noise, and maintain the same amplitude and phase as a function of color. We have determined the dominant frequency to be 1902.509802 ± 0.00001 μHz, with p = + 1.71 (±0.04) X 10-11 s s-ˡ. We discuss the implications of these findings on a model forAM CVn

The unusual helium variable AM Canum Venaticorum

The unusual variable star AM CVn has puzzled astronomers for over 40 years. This object, both a photometric and spectroscopic variable, is believed to contain a pair of hydrogen-deficient white dwarfs of extreme mass ratio, transferring material via an accretion disk. We examine the photometric properties of AM CVn, analyzing 289 hours of high-speed photometric data spanning 1976 to 1992. The power spectrum displays significant peaks at 988.7, 1248.8, 1902.5, 2853.8, 3805.2, 4756.5, and 5707.8 μHz (1011.4, 800.8, 525.6, 350.4, 262.8, 210.2, and 175.2 s). We find no detectable power at 951.3 μHz (1051 s), the previously reported main frequency. The 1902.5, 2853.9, and 3805.2 μHz peaks are multiplets, with frequency splitting in each case of 20.77 ± 0.05 μHz. The 1902.5 μHz seasonal pulse shapes are identical, within measurement noise, and maintain the same amplitude and phase as a function of color. We have determined the dominant frequency to be 1902.509802 ± 0.00001 μHz, with p = + 1.71 (±0.04) X 10-11 s s-ˡ. We discuss the implications of these findings on a model forAM CVn

A detection of the evolutionary time scale of the da white dwarf G117-B15A with the Whole Earth Telescope

We have detected the time rate of change for the main pulsation period of the 13,000 K DA white dwarf G117-B15A, using the Whole Earth Telescope (WET). The observed rate of period change, P = (12.0 ± 3.5) x 10- 15 s s - ', is somewhat larger than the published theoretical calculations of the rate of period change due to cooling, based on carbon core white dwarf models. We discuss other effects that could contribute to the observed rate of period change

A detection of the evolutionary time scale of the da white dwarf G117-B15A with the Whole Earth Telescope

We have detected the time rate of change for the main pulsation period of the 13,000 K DA white dwarf G117-B15A, using the Whole Earth Telescope (WET). The observed rate of period change, P = (12.0 ± 3.5) x 10- 15 s s - ', is somewhat larger than the published theoretical calculations of the rate of period change due to cooling, based on carbon core white dwarf models. We discuss other effects that could contribute to the observed rate of period change

Whole Earth Telescope observations of the DAV white dwarf G226-29

We observed G226-29 for 121 hr in 1992 February and confirm the presence of the three previously identified frequencies close to 109 s. We find no evidence of other pulsation periods down to our noise level of about 0.35 millimodulation amplitudes. The presence of only one triplet pulsation mode in G226-29 and its effective temperature near the blue edge of the instability strip identify the observed triplet of modes near 109 s as rotationally split components of the k = 1, l = 1 mode. With the mode identification, we derived a rotation period of 8.9 hr and an inclination of the pulsation axis of 70°-75° to our line of sight