Up to now, planet search programs have concentrated on main sequence stars later than spectral type F5. However, identifying planets of early type stars would be interesting. For example, the mass loss of planets orbiting early and late type stars is
different because of the differences of the EUV and X-ray radiation of the host stars. As an initial step, we carried out a program to identify suitable A-stars in the CoRoT fields using spectra taken with the AAOmega spectrograph. In total we identified 562 A-stars in IRa01, LRa01, and LRa02.
In 2007, a companion with planetary mass was found around the pulsating subdwarf B star V391 Pegasi with the timing method, indicating that a previously undiscovered population of substellar companions to apparently single subdwarf B stars might exis
t. Following this serendipitous discovery, the EXOTIME (http://www.na.astro.it/~silvotti/exotime/) monitoring program has been set up to follow the pulsations of a number of selected rapidly pulsating subdwarf B stars on time-scales of several years with two immediate observational goals: 1) determine Pdot of the pulsational periods P 2) search for signatures of substellar companions in O-C residuals due to periodic light travel time variations, which would be tracking the central stars companion-induced wobble around the center of mass. These sets of data should therefore at the same time: on the one hand be useful to provide extra constraints for classical asteroseismological exercises from the Pdot (comparison with local evolutionary models), and on the other hand allow to investigate the preceding evolution of a target in terms of possible binary evolution by extending the otherwise unsuccessful search for companions to potentially very low masses. While timing pulsations may be an observationally expensive method to search for companions, it samples a different range of orbital parameters, inaccessible through orbital photometric effects or the radial velocity method: the latter favours massive close-in companions, whereas the timing method becomes increasingly more sensitive towards wider separations. In this paper we report on the status of the on-going observations and coherence analysis for two of the currently five targets, revealing very well-behaved pulsational characteristics in HS 0444+0458, while showing HS 0702+6043 to be more complex than previously thought.
Methods to measure masses of PG1159 stars in order to test evolutionary scenarios are currently based on spectroscopic masses or asteroseismological mass determinations. One recently discovered PG1159 star in a close binary system may finally allow t
he first dynamical mass determination, which has so far been analysed on the basis of one SDSS spectrum and photometric monitoring. In order to be able to phase future radial velocity measurements of the system SDSSJ212531.92-010745.9, we follow up on the photometric monitoring of this system to provide a solid observational basis for an improved orbital ephemeris determination. New white-light time series of the brightness variation of SDSSJ212531.92-010745.9 with the Tuebingen 80cm and Goettingen 50cm telescopes extend the monitoring into a second season (2006), tripling the length of overall observational data available, and significantly increasing the time base covered. We give the ephemeris for the orbital motion of the system, based on a sine fit which now results in a period of 6.95573(5)h, and discuss the associated new amplitude determination in the context of the phased light curve variation profile. The accuracy of the ephemeris has been improved by more than one order of magnitude compared to that previously published for 2005 alone.
