Short-Period Variability of b, a, and F Stars.IV. Variability in the Lower Hertzsprung Gap
Abstract
The lower instability strip extends from the main sequence upward to the RR Lyrae region. Hot and cool borders were established which intersect the main sequence at A4 and F2. In the instability strip, more than 20 percent of the stars show regular variability larger than 0.010 mag. These variables have normal masses and show a wide range in metal abundances and rotational velocities. Metal abundance and binan characteristics appear to have no isifluence on the incidence of variability. Pulsation is found to be strongly related to rotational velocity, v sin i. The variables of small amplitudes share the high rotational velocity of the nonvariables, while the incidence of larger amplitudes depends critically on low rotational velocity. The mean rotational velocity of the variables 2 magnitudes above the main sequence is less than 0.3 that of similar nonvariables. This effect decreases as the main sequence is approached. A period-luminosity-color relation is established, with an average deviation of less than 0.3 mag in M . The observed coefficients of log P and log (T /T o) agree adequately with the predicted relation = -2.5 log P - 10 log (T / ) - 1.25 log + constant which assumes a variable Q-value. Metal abundance and rotation have no effect on the period. The pulsation constant Q is found to vary slightly along the instability strip, and a preliminary value of Q = 0.029 i 0.007 is derived, indicating that the variables pulsate in the fundamental and/or first overtone. It is proposed that the period differences among classical Cepheids, Sct stars, RR Lyrae stars, and dwarf Cepheids are caused not only by luminosity differences but also by large mass differences.
- Publication:
-
The Astrophysical Journal Supplement Series
- Pub Date:
- December 1969
- DOI:
- 10.1086/190200
- Bibcode:
- 1969ApJS...19...99B