FG Vir (=HD 106384) is a Scuti variable near the end of its main-sequence evolution. 435 hours of photometric measurements by the Delta Scuti Network determined 24 statistically significant frequencies from 9.20 to 34.12 c/d (106 to 395 µHz). Details of this campaign as well as references to earlier measurements and results can be found in Breger et al. (1998). The large number of detected pulsation modes makes this star an excellent candidate for asteroseismological investigations. This requires the identifications of the observed pulsation frequencies with specific pulsation modes. While the problem is rather complex, considerable progress has been achieved, as shown by Breger et al. (1995), Guzik et al. (1998) and Viskum et al. (1998).
The pulsation mode indentification from observed frequencies requires accurate determinations of the basic parameters of the star. From the available photometry, Mantegazza et al. (1994) derived K and . A correction for a misprint in the literature leads to a correction of to 3.9. We can now improve these values further by including the accurate Hipparcos parallax which predicts mag. This is slightly fainter than the value of mag predicted by photometry. This leads to a corresponding shift in to 4.00. These values are in exact agreement with those derived by Viskum et al. (1998). We estimate the uncertainties to be K in temperature and in .
The values of the pulsation constants Q can be estimated from the following empiric equation:
The constant, -6.456, in the above formula is based on solar values of mag, mag, K and . If the Q values are calculated from photometry, the observational uncertainties in observing these parameters lead to an uncertainty in Q of about 18%.
The corresponding Q values are shown in Table 1.
Table 1. Pulsation frequencies of FG Vir
© European Southern Observatory (ESO) 1999
Online publication: November 26, 1998