A new method for the spectroscopic identification of stellar non-radial pulsation modes

II. Mode identification of the δ Scuti star FG Virginis

¹ Institut für Astronomie der Universität Wien, Türkenschanzstrasse 17, 1180 Vienna, Austria e-mail: zima@ster.kuleuven.be
² Dept. of Physics and Astronomy, Univ. of Canterbury, Private Bag 4800, Christchurch, New Zealand
³ Department of Astronomy and Space Physics, Uppsala University, Box 515, 75120 Uppsala, Sweden
⁴ Observatoire de la Cote d'Azur, Departement GEMINI – UMR 6203, 06304 Nice, France
⁵ INAF – Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate(LC), Italy
⁶ Thüringer Landessternwarte, 07778 Tautenburg, Germany
⁷ McDonald Observatory, University of Texas at Austin, 1 University Station, C1402 Austin, Texas, USA

Received: 18 January 2006
Accepted: 1 June 2006

Abstract

Aims.We present a mode identification based on new high-resolution time-series spectra of the non-radially pulsating δ Scuti star FG Vir (HD 106384, , A5V). From 2002 February to June a global Delta Scuti Network (DSN) campaign, utilizing high-resolution spectroscopy and simultaneous photometry has been conducted for FG Vir in order to provide a theoretical pulsation model. In this campaign we have acquired 969 Echelle spectra covering 147 h at six observatories.

Methods.The mode identification was carried out by analyzing line profile variations by means of the Fourier parameter fit method, where the observational Fourier parameters across the line are fitted with theoretical values. This method is especially well suited for determining the azimuthal order m of non-radial pulsation modes and thus complementary with the method of Daszynska-Daszkiewicz (2002) which does best at identifying the degree .

Results.15 frequencies between 9.2 and 33.5 d^-1 were detected spectroscopically. We determined the azimuthal order m of 12 modes and constrained their harmonic degree . Only modes of low degree () were detected, most of them having axisymmetric character mainly due to the relatively low projected rotational velocity of FG Vir. The detected non-axisymmetric modes have azimuthal orders between -2 and 1. We derived an inclination of 19°, which implies an equatorial rotational rate of 66 km s^-1.