FG Vir 2002 (DSN 22)

From 2002 February to June, a global Delta Scuti Network (DSN) campaign, utilizing high-resolution spectroscopy as well as photometry, has been carried out for the Delta Scuti star FG Vir (HD 106384, V = 6.57, A5V). This star is nonradially pulsating with at least 24 modes and the possible presence of g-modes provides the possibility to probe its deep interior. In this campaign we have acquired 940 echelle spectra covering 150 hours at six observatories. Mode identification will be performed by the pixel-by-pixel method (Mantegazza 2000), the moment method and the Amplitude-Phase-method, proposed by Telting&Schrijvers.;

FG Vir is one of the best studied Delta Scuti stars and has been a target of extensive photometric (Breger et al. 1995, 1998), as well as spectroscopic campaigns (Mantegazza et al. 1994, Viskum et al. 1998). 24 independent pulsation modes between 9.2 and 34.1 c/d have been detected so far, but a reliable mode identification and thus definite pulsational models are still lacking. Mode typing is especially important for decreasing the degrees of freedom of theoretical models. With it's moderate vsini of 21 km/s, FG Vir is an ideal candidate for the spectroscopic detection of the low-degree modes, which have been already found photometrically.

The 2002 Campaign

During 2002 February 28 and June 2, 2002 we have obtained 31 nights of high-resolution echelle-spectroscopy at the following six observatories:
  • SAAO (42h)
  • McDonald Obs. (33h)
  • Tautenburg Obs./Jena (15h)
  • Mt. John Obs. (20h)
  • Obs. Haut Provence (24h)
  • ESO (15h).
Weather conditions were spectroscopic during approximately 50 % of the run.

Integration times were between 7 and 10 minutes and resulted in a Signal to Noise ratio (SNR) of 50 to 200. In order to combine the information of several absorption lines and thus increase the SNR, the measured wavelength range covers 4400 to 6000 A at a resolving power between 50000 and 60000.
From a spectroscopic point of view, we were able to detect 14 modes, which also have been photometrically confirmed. Mode identification showed that all are of low order with l<4 and 7 oscillation modes have axisymmetric character.
Multi-color photometry has been taken at five observatories in order to enable the application of the pixel-by-pixel method and to increase the number of detected frequencies. More than 60 frequencies were revealed from the photometric data, taken during this campaign. The results have been published in A&A; (download PS file).

Representation of the temperature variations on the surface of FG Vir due to 10 nonradial pulsation modes. This is only a crude model of the observations for an inclination of 15.