THE DELTA-SCUTI STAR PG VIRGINIS .1. MULTIPLE PULSATION FREQUENCIES DETERMINED WITH A COMBINED DSN WET CAMPAIGN/

A coordinated photometric campaign of FG Vir at nine observatories cov ering 170 hours was undertaken by DSN (Delta Scuti Network) and WET (W hole Earth Telescope). Two different observing techniques were adopted for the two telescope networks in order to optimize different frequen cy ranges. Ten pulsation frequencies between 9.19 and 34.12 c/d (112 a nd 395 mu Hz) were detected with amplitudes ranging from 0.8 to 22 mma g. Pulsational instability is observed only in specific frequency regi ons. Additional frequencies of pulsation within these regions probably exist, but do not reach the significance criterion of amplitude signa l/noise adopted by us, Comparisons with previously obtained data show that the amplitudes of the main frequencies are stable over a year or longer. A preliminary identification of the ten dominant frequencies i s proposed in a stellar model with 1.8M. in advanced main-sequence pha se of evolution. The frequencies correspond to low order p and g modes with l less than or equal to 2 and radial order 1 to 6. According to the linear nonadiabatic calculations, the identified modes are driven by the opacity mechanism along with many other modes. For asteroseismo logy of delta Scuti stars, FG Vir is an extremely important candidate, especially because of the probable presence of g modes.