The δ Scuti Star DK Virginis (HR 5005) Revisited1

Abstract

ABSTRACT. An analysis of Hp photometry of DK Virginis is carried out. The analysis reveals two frequencies, and cycles day~1. These values turn out to be good enough to bridge the f 1 \ 9.2095 f 2 \ 7.5764 gap between the two available series of ground-based data, obtained in 1973 and 1980, so that the frequencies can be reÐned. The reÐned values are equal to 9.20945 and 7.57641 cycles day~1. The corresponding V amplitudes amount to 8.6^0.4 and 11.1^0.4 mmag, and the epochs of maximum light are equal to 2,441,715.0294^0.0008 and 2,441,715.1205^0.0007. The synthetic light curve, computed with these JD _ parameters, correctly reproduces the large light range on JD 2,439,177, the night in 1966 when the star was discovered to be variable, and the small range on JD 2,440,682, when the light variation was not detected. In this way, all photometric observations of DK Vir are accounted for, indicating that the two frequencies have not changed appreciably since 1965, and that the V amplitudes were constant over the interval from 1965 to 1980.Using a photometric e †ective temperature and Hipparcos parallax, we plot the star in the H-R diagram. Comparison with evolutionary tracks then shows that DK Vir is at the end of the main-sequence stage of its evolution or slightly beyond, with a mass of 2.1 or somewhat smaller. Finally, an examination of linear M _ nonadiabatic pulsation frequencies of modes with l ¹ 2 indicates that the two observed modes cannot both be radial, and that the mode must be nonradial if the star is still on the main sequence. f 1 The properties of the Hipparcos spectral window are examined in the Appendix.

The multimode pulsation of theδScuti star V784 Cassiopeae

“…5, where a close-up to the main peaks is presented. As Hipparcos has good spectral window (in sense of having only weak and asymmetric sidelobes), the very good agreement of the main peaks supports our frequency analysis (see Jerzykiewicz & Pamyatnykh 2000 for a recent discussion on the use of Hipparcos photometric data).…”

β Cephei stars in the ASAS-3 data

“…It can be seen from Table 7 that frequencies for most of them range between 10 and 12 d −1 . As already explained by Jerzykiewicz & Pamyatnykh (2000) and Koen & Eyer (2002), these spurious frequencies are due to aliasing originating from the convolution of the low-frequency changes and the spectral window dominated by the rotation frequency of the satellite (11.25 d −1 ). For five of the seven β Cephei stars in Table 7, the agreement between frequencies derived from the Hipparcos and ASAS-3 data is very good.…”

Properties and nature of Be stars

“…It appears to us that this precious data set seems to be overinterpreted by some investigators. While the set is basically free from the usual one-day aliases occurring for observations from the Earth, it has its own, very selective time distribution as was pointed out byŠtefl et al (1998) and recently discussed by Percy et al (2002aPercy et al ( , 2002b and Jerzykiewicz & Pamyatnykh (2000). Besides, it usually represents something like 100 data points per one object.…”