UBVRIJH photometry of two new luminous δ Scuti stars and the discovery of δ Scuti pulsation in the most evolved Ap star known |
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| Authors: | C Koen DW Kurtz RO Gray D Kilkenny G Handler F Van Wyk F Marang H Winkler |
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| Institution: | 1South African Astronomical Observatory, PO Box 9, Observatory, 7935 Cape, South Africa;2Laboratoire d'Astrophysique de l'OMP, CNRS UMR 5572, Observatoire Midi-Pyrénées, 14 avenue Edouard Belin, F-31400 Toulouse, France;3Centre for Astrophysics, University of Central Lancashire, Preston PR1 2HE;4Department of Astronomy, University of Cape Town, 7701 Rondebosch, South Africa;5Department of Physics and Astronomy, Appalachian State University, Boone, NC 28608, USA;6Department of Physics, Soweto Campus, Vista University, Private Bag X09, 2013 Bertsham, South Africa |
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| Abstract: | Time-series photometry of the Hipparcos variable stars HD 199434 and 21190 is reported. Both stars are pulsators of the δ Scuti type. Reclassifications of the MK types of the stars, based on new spectrograms, are given. HD 21190 is found to be F2III SrEuSi:, making it the most evolved Ap star known. Its Strömgren photometric indices support the peculiar spectral type. It is also one of the most evolved δ Scuti stars known. Its combined Ap– δ Scuti nature makes it an important test of models of pulsation in peculiar stars recently developed by Turcotte et al., although it is more extreme than any model they examined. Physical parameters of both stars are estimated from Strömgren and H β photometry, and Hipparcos absolute magnitudes. We attempt mode identifications based on amplitude ratios and phase differences from our photometry. The dominant pulsation of HD 21190 may be an overtone radial mode. The model fits for HD 199434 are even less satisfactory, but favour an ?=2 mode. Given the good quality and wavelength coverage of our data, the poor results from the application of the photometric theory of mode identification may call into question the use of that technique. |
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| Keywords: | techniques: photometric stars: individual: HD 199434 stars: individual: HD 21190 stars: oscillations δ Scuti |
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