Multi-Site Observations of the DAV White Dwarf R 548

The pulsating DA white dwarf R 548 was observed for 46 h in October 1993 in an eight-site campaign. New peaks near the known doublets in the Fourier transform are found

ESO & NOT photometric monitoring of the Cloverleaf quasar

The Cloverleaf quasar, H1413+117, has been photometrically monitored at ESO (La Silla, Chile) and with the NOT (La Palma, Spain) during the period 1987--1994. All good quality CCD frames have been successfully analysed using two independent methods (i.e. an automatic image decomposition technique and an interactive CLEAN algorithm). The photometric results from the two methods are found to be very similar, and they show that the four lensed QSO images vary significantly in brightness (by up to 0.45 mag), nearly in parallel. The lightcurve of the $D$ component presents some slight departures from the general trend which are very likely caused by micro-lensing effects. Upper limits, at the 99% confidence level, of 150 days on the absolute value for the time delays between the photometric lightcurves of this quadruply imaged variable QSO, are derived. This is unfortunately too large to constrain the lens model but there is little doubt that a better sampling of the lightcurves should allow to accurately derive these time delays. Pending a direct detection of the lensing galaxy (position and redshift), this system thus constitutes another good candidate for a direct and independent determination of the Hubble parameter. Based on observations collected at the European Southern Observatory (La Silla, Chile) and with the Nordic Optical Telescope (La Palma, Spain). Table 1. Logbook for the ESO and NOT observations together with photometric results for the Cloverleaf quasar. This long table can be accessed on the WWW at the URL address: http://vela.astro.ulg.ac.be/grav_lens/glp_homepage.html

quasar

ESO & NOT photometric monitoring of the Cloverlea

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