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Issue A&A
Volume 386, Number 3, May II 2002
Page(s) 964 - 970
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20020357



A&A 386, 964-970 (2002)
DOI: 10.1051/0004-6361:20020357

Mode characterisation in $\delta$ Scuti stars

I. Pup , GN And , V1208 Aql and AV Cet
T. H. Dall1, 2 and S. Frandsen1

1  Institute for Physics and Astronomy, University of Aarhus, Universitetsparken, Bygn. 520, 8000 Aarhus C, Denmark
2  Nordic Optical Telescope, Apartado 474, 38700 Santa Cruz de La Palma, Spain

(Received 1 May 2001 / Accepted 5 March 2002 )

Abstract
We present new spectroscopic observations of four bright $\delta$ Scuti pulsators. Line indices of the Balmer lines can be used to establish mode identifications using the ratio R between such line index amplitudes and photometric amplitudes. For the well known radial pulsator  Pup an absolute value of the amplitude ratio of the radial mode was found to R=0.43, consistent with earlier values of $R \sim 0.5$ reported for other $\delta$ Scuti stars. In GN And we recover the recently reported newly excited mode, while the former dominant mode was not recovered. We confirm that V1208 Aql is a non-radial pulsator, containing two modes of different degree. In V1208 Aql we report a previously unseen mode behavior: the phases of both modes are reversed between the core and wings of the H $\beta$ line, suggesting the presence of more undetected modes. For AV Cet we find that the dominant mode is a previously undetected one. We suggest the undertaking of new photometric observations of $\rho$ Pup, GN And, V1208 Aql and AV Cet to determine the frequencies and amplitudes of the pulsations.


Key words: stars: oscillations -- stars: variables: $\delta$ Sct -- stars: individual: GN And -- stars: individual: V1208 Aql   -- stars: individual: AV Cet -- stars: individual: Pup

Offprint request: T. H. Dall, tdall@ifa.au.dk

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