Oscillation mode identifications and models for the δ Scuti star FG

We present new spectroscopic and photometric time series observations of the δ Scuti star FG Vir. We detect the oscillations via changes in the equivalent widths of hydrogen and metal absorption lines. From the ratios between spectroscopic and photometric amplitudes, we assign l values to the eight strongest oscillation modes. In particular, we identify two radial modes (l = 0) and find that the main pulsation mode (147 μHz) has l = 1. One of the radial modes (at 140μHz) is the fundamental, implying that two modes with lower frequencies are g-modes. For the radial modes, we compare frequencies with those calculated from a scaled δ Scuti star model and derive a density 0.1645± 0.0005 ρ⊙. We then obtain a distance of 84±3pc, in excellent agreement with the Hipparcos value. Finally, we suggest that a 3.5-day variability in all observables (equivalent widths and intensity) is caused by stellar rotation.