A SURVEY FOR RAPID VARIABILITY AMONG EARLY MAIN-SEQUENCE A STARS

Abstract

ABSTRACT This is a survey of non-peculiar early (A0-A5) main-sequence A stars for rapid (4-30 minutes), low-amplitude (<10 millimagnitudes) variability. Peculiar stars (roAp stars) are presently the only objects known to exhibit this behavior on or near the main sequence. There are reasons for suspecting variability in 'non-peculiar' stars however; survey objects are in close proximity, in an HR diagram, to the Cepheid instability strip where many pulsation variables are found (e.g., the delta Scuti and roAp stars), and there is evidence of pulsational variability (at slightly longer periods) in the non-peculiar delta Scuti stars. The survey also is an independent test of the main-sequence mass-sequence mass-loss theory proposed by Willson et al. (1986). Finally, surveys of this type may produce objects of asteroseismological interest. All observations were gathered with the University of Wisconsin Two-Star Photometer. This instrument coupled with a computerized high-speed data collection system was used with small (0.41m-0.61m) telescopes Pine Bluff Observatory and Table Mountain Observatory. Several period-searching methods were used to analyze time series of differential-photometric data. This instrument and data reduction technique allow millimagnitude light variations to be detected. The survey did produce a few stars that are suspected of rapid variability and should be monitored with time. However, there is apparently no evidence for large scale rapid variablitiy among the non-peculiar early main sequence A stars observed. The survey also discovered several low-amplitude delta Scuti stars, all of which are in or blueward of the recognized instability strip. These stars support rpedicted that delta Scuti stars exist at lower amplitudes, and may also they earlier spectral types.