Astron. Astrophys. 323, 429-441 (1997)

A spectroscopic search for high azimuthal-order pulsation in broad-lined late F- and early G-stars ^*

D. Baade ¹ and H. Kjeldsen <sup>2

1</sup> European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching b. München, Germany (dbaade@eso.org)
² Theoretical Astrophysics Center, Institute of Physics and Astronomy, Bygning 520 , Århus Universitet, DK-8000 Århus C, Denmark (hans@obs.aau.dk)

Received 5 December 1996 / Accepted 14 January 1997

Abstract

During 3 consecutive nights, 13 southern F- and G-type dwarfs and giants outside the conventional Scuti instability strip were observed at high spectral (3 km/s) and medium temporal (10-15 min) resolution. The stars were selected for their reported broad spectral lines (v sin 40 km/s) so that pulsation in higher azimuthal-order nonradial harmonics could, via the rotational Doppler effect, reveal itself by line profile variability. Two stars turned out to have very narrow lines, one was confirmed as a short-period double-lined binary. Line profile ondulations typical of pulsation with azimuthal order 8 14 were detected in Aql and Ara. In addition, Ara displayed line profile distortions at a larger scale as they would result from a mode with 4. The observational sampling of all three variabilities constrains possible periods only poorly. However, if the variations are periodic, they may well be too slow for p -mode oscillations. This would suggest a relation to the new class of Dor variables in which g -modes seem to be excited. If so, the two stars could be the first Dor stars with detected higher nonradial-harmonic pulsation. While uvby photometry places Aql still just within the Scuti strip, Ara would be the reddest candidate Dor star to date. For the remaining 8 stars, upper amplitude limits between 2 and 6 km/s were derived for nonradial mode orders 6 16 and p -modes with periods 20 minutes. In 3 stars narrow absorption lines were detected which probably are due to a cool companion.

Key words: stars: oscillations stars: ffi Sct Sun: oscillations stars ffi Aql; ffl2 Ara

* Based on observations obtained at the European Southern Observatory on La Silla, Chile

Send offprint requests to: D. Baade

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Contents

• 1. Introduction
• 2. Observations and their reduction
• 3. The sample observed
• 4. Results
  • 4.1. Non-detections
    • 4.1.1. Model computations
    • 4.1.2. Detection limits
  • 4.2. Probable detections
    • 4.2.1. Ara
    • 4.2.2. Aql
  • 4.3. Narrow-lined secondary spectra
• 5. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1997

Online publication: June 5, 1998

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