Previous
abstract 
Next
abstract
Until recently, no stars on the cool side of the Cepheid instability strip in the HR diagram (with the possible exception of the Sun) have been suspected of exhibiting non-radial gravity modes. For example, 53 Persei (Sp = B4 IV) has $T_{eff} \approx 16,000$\ K and the DOV star PG 1159-035 has $T_{eff} \approx 123,000$\ K. The papers listed below (and references therein) present a dozen stars which are typically early F stars of luminosity class V or IV-V and which are photometrically variable up to 0.1 magnitude, with periods ranging from 0.3 to 1.8 days (an order of magnitude slower than one would expect of stars of this spectral type and luminosity class undergoing simple radial pulsations). 9 Aurigae (Sp = F0 V, $T_{eff} \approx 7200$\ K, per = 1.277 days) has shown evidence of radial velocity variations of order 6 km/sec and possible line profile variations. $\gamma$ Doradus, which has two periods near 0.75 days, has definitely shown line profile variations. For HD 96008 the notion of rotational modulation is ruled out because its photometric period would imply an equatorial rotational speed of 330 km/sec -- incompatible with its having sharp spectral lines. 9 Aurigae and HD 224638 (Sp $\approx$ F0, per = 1.47 days) have both shown sudden phase shifts in their light curves. Having eliminated a number of possibilities for individual stars, I conclude that these stars are either exhibiting non-radial g -modes, or we are confronted with a completely new physical mechanism for producing light variations in stars. We present preliminary results of ongoing observations of some of these stars.
\refs
Antonello, E., and Mantegazza, L.\ 1986, Astron. Astrophys. 164 , 40.
Balona, L. A. et al. 199[3], Monthly Not. R. A. S. , in press.
Krisciunas, K. et al. \ 1993, Monthly Not. R. A. S. \ 263 , 781.
Krisciunas, K.\ 1993, Comments on Astrophys. \ 17 , no. 4, in press.
Mantegazza, L. et al. \ 1991, IBVS 3612.
Mantegazza, L., and Poretti, E.\ 1991, IBVS 3690.
Mantegazza, L. et al. \ 1993, in Inside the Stars , ASP Conf. Series 40 , 651.
\unrefs
