Coherent Oscillations In UX Ursae Majoris

NSFMcDonald Observator

Time Resolved Spectroscopy Of Cataclysmic Variables - SS Cygni

NSF AST76-23882, AST 79-06340McDonald Observator

Whole Earth Telescope Observations of the Helium Interacting Binary PG 1346+082 (CR Bootis)

We present our analysis of 240 hr of white-light, high-speed photometry of the dwarf nova-like helium variable PG 1346+082 (CR Boo). We identify two frequencies in the low-state power spectrum, at 679.670 ± 0.004 μHz and 669.887 ± 0.008 μHz. The 679.670 μHz variation is coherent over at least a 2 week time span, the first demonstration of a phase-coherent photometric variation in any dwarf nova-like interacting binary white dwarf system. The high-state power spectrum contains a complex fundamental with a frequency similar, but not identical, to the low-state spectrum, and a series of harmonics not detected in low state. We also uncover an unexpected dependence of the high-frequency power\u27s amplitude and frequency structure on overall system magnitude. We discuss these findings in light of the general AM CVn system model, particularly the implications of the high-order harmonics on future studies of disk structure, mass transfer, and disk viscosity

The light curve of the ZZ ceti star G226-29

G226-29 is a pulsating DA white dwarf, or ZZ Ceti star. Using 65 hr of high-speed photometry accumulated from 1980 to 1982, we have decomposed the light curve of G226-29 into its component pulsations. There are three pulsations in the light curve, ali of which have periods dose to 109.3 s. Their fractional semiamplitudes and periods are 0.0031 and 109.08684 s, 0.0011 and 109.27929 s, and 0.0031 and 109.47242 s. The pulsations are evenly spaced in frequency, and those with the longest and shortest periods have nearly equal amplitudes. We propose that the pulsations are g-mode pulsations with the same values of I and k, but with different values of m, whose periods have been split by slow rotation of the white dwarf. Depending on the specific value of I we assign to the pulsations, the equatorial rotational velocity of G226-29 is between I and 2 km s-ˡ

The light curve of the ZZ ceti star G226-29

G226-29 is a pulsating DA white dwarf, or ZZ Ceti star. Using 65 hr of high-speed photometry accumulated from 1980 to 1982, we have decomposed the light curve of G226-29 into its component pulsations. There are three pulsations in the light curve, ali of which have periods dose to 109.3 s. Their fractional semiamplitudes and periods are 0.0031 and 109.08684 s, 0.0011 and 109.27929 s, and 0.0031 and 109.47242 s. The pulsations are evenly spaced in frequency, and those with the longest and shortest periods have nearly equal amplitudes. We propose that the pulsations are g-mode pulsations with the same values of I and k, but with different values of m, whose periods have been split by slow rotation of the white dwarf. Depending on the specific value of I we assign to the pulsations, the equatorial rotational velocity of G226-29 is between I and 2 km s-ˡ

Mode identification of pulsating white dwarfs using the Hubble Space Telescope

We have obtained time-resolved ultraviolet spectroscopy for the pulsating DAV stars G226-29 and G185-32 and for the pulsating DBV star PG 1351+489 with the Hubble Space Telescope Faint Object Spectrograph to compare the ultraviolet to the optical pulsation amplitude and determine the pulsation indices. We find that for essentially all observed pulsation modes, the amplitude rises to the ultraviolet as the theoretical models predict for l=1 nonradial g-modes. We do not find any pulsation mode visible only in the ultraviolet, nor any modes whose phase flips by 180° in the ultraviolet, as would be expected if high l pulsations were excited. We find one periodicity in the light curve of G185-32, at 141 s, which does not Ðt theoretical models for the change of amplitude with wavelength of g-mode pulsations

The 1051 s period of the interacting binary white dwarf amcvn

The close binary system AM CVn consists of two white dwarfs; the lower mass white dwarf, a helium white dwarf, is transferring mass to its higher mass companion. The light curve of AM CVn has a double humped variation with a period of 1051 s that previously was identified with the orbital period of the system. An earlier measurement of the 1051 s period seemed to show that it was increasing rapidly, too rapidly to be easily understood. We have, therefore, remeasured the rate of change of the 1051 s period. We find that the period is changing two orders of magnitude more slowly than previously thought: dP/dt= (–3.2±0.6) 10ˉ¹² s sˉ¹• Since the mass losing star in AM CVn is a white dwarf, the orbital period of the system must be increasing. We have found that the 1051 s period is decreasing, and, therefore, it cannot be caused by orbital motion. We reinterpret the 1051 s period as the rotation period of the accreting white dwarf, which must then be magnetized. We have also found a 1011.4 s period in the light curve that may be related to the orbital period, but cannot itself be the orbital period. Finally, we show that the double humped light curve may really be a single humped light curve with a period of 525.5s

The 1051 s period of the interacting binary white dwarf amcvn

The close binary system AM CVn consists of two white dwarfs; the lower mass white dwarf, a helium white dwarf, is transferring mass to its higher mass companion. The light curve of AM CVn has a double humped variation with a period of 1051 s that previously was identified with the orbital period of the system. An earlier measurement of the 1051 s period seemed to show that it was increasing rapidly, too rapidly to be easily understood. We have, therefore, remeasured the rate of change of the 1051 s period. We find that the period is changing two orders of magnitude more slowly than previously thought: dP/dt= (–3.2±0.6) 10ˉ¹² s sˉ¹• Since the mass losing star in AM CVn is a white dwarf, the orbital period of the system must be increasing. We have found that the 1051 s period is decreasing, and, therefore, it cannot be caused by orbital motion. We reinterpret the 1051 s period as the rotation period of the accreting white dwarf, which must then be magnetized. We have also found a 1011.4 s period in the light curve that may be related to the orbital period, but cannot itself be the orbital period. Finally, we show that the double humped light curve may really be a single humped light curve with a period of 525.5s

Evolutionary timescale of the pulsating white dwarf G117-B15A : the most stable optical clock known

We observe G117-B15A, the most precise optical clock known, to measure the rate of change of the main pulsation period of this blue-edge DAV white dwarf. Even though the obtained value is only within 1 σ, P = (2.3±1.4) x 10 -15 s s-ˡ, it is already constraining the evolutionary timescale of this cooling white dwarf star