Astron. Astrophys. 335, 549-560 (1998)

Oscillation mode identifications and models for the  Scuti star FG Virginis

M. Viskum ¹, H. Kjeldsen ^{1, 2}, T.R. Bedding ³, T.H. Dall ¹, I.K. Baldry ³, H. Bruntt ¹ and S. Frandsen <sup>1

1</sup> Institute of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C, Denmark
² Theoretical Astrophysics Center, Danmarks Grundforskningsfond, Aarhus University, DK-8000 Aarhus C, Denmark
³ Chatterton Astronomy Department, School of Physics, University of Sydney, 2006, Australia

Received 30 January 1998 / Accepted 22 April 1998

Abstract

We present new spectroscopic and photometric time series observations of the 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 values to the eight strongest oscillation modes. In particular, we identify two radial modes () and find that the main pulsation mode (147 µHz) has . 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  Scuti star model and derive a density . We then obtain a distance of pc, 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.

Key words: ffi Scuti stars: oscillations stars: individual: HD106384=FG Vir

Send offprint requests to: M. Viskum

SIMBAD Objects

Contents

• 1. Introduction
• 2. Observations and basic data reduction
  • 2.1. Spectroscopy
  • 2.2. Photometry
• 3. Determination of equivalent widths
  • 3.1. Equivalent-width variations of the Balmer lines
  • 3.2. Equivalent-width variations of metal lines
• 4. Frequency analysis
• 5. Mode identification
• 6. Comparison with a pulsation model
  • 6.1. Density of FG Vir
  • 6.2. Distance and mass of FG Vir
• 7. Rotation period of FG Vir
• 8. Summary of results
• Acknowledgements
• References

© European Southern Observatory (ESO) 1998

Online publication: June 18, 1998
helpdesk@link.springer.de