SIMBAD references

An analysis of Hp photometry of DK Virginis is carried out. The analysis reveals two frequencies, f₁=9.2095 and f₂=7.5764 cycles.day^–1. These values turn out to be good enough to bridge the gap between the two available series of ground-based data, obtained in 1973 and 1980, so that the frequencies can be refined. The refined 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 JD_☉ 2,441,715.0294±0.0008 and 2,441,715.1205±0.0007. The synthetic light curve, computed with these 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 effective 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 M_☉ or somewhat smaller. Finally, an examination of linear nonadiabatic pulsation frequencies of modes with l≤2 indicates that the two observed modes cannot both be radial, and that the f₁ mode must be nonradial if the star is still on the main sequence.

The properties of the Hipparcos spectral window are examined in the Appendix.