EDP Sciences
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Volume 376, Number 1, September II 2001
Page(s) 175 - 187
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20010950

A&A 376, 175-187 (2001)
DOI: 10.1051/0004-6361:20010950

$\delta$ Scuti stars in Praesepe

I. The STACC 1998 campaign -the photometry
S. Frandsen1, A. Pigulski2, J. Nuspl3, M. Breger4, J. A. Belmonte5, T. H. Dall1, T. Arentoft6, C. Sterken6, T. Medupe7, S. K. Gupta8, F. J. G. Pinheiro9, M. J. P. F. G. Monteiro9, C. Barban10, M. Chevreton11, E. Michel10, J. M. Benko3, Sz. Barcza3, R. Szabó3, Z. Kolaczkowski2, G. Kopacki2 and S. N. Udovichenko12

1  Institute for Physics and Astronomy, University of Aarhus, Universitetsparken, Bygn. 520, 8000 Aarhus C, Denmark
2  Institute of Astronomy, Wroclaw University, Kopernika 11, 51-622 Wroclaw, Poland
3  Konkoly Observatory, 1525 Budapest XII, PO Box 67, Hungary
4  Institut für Astronomie, Türkenschanzstrasse 17, 1180 Wien, Austria
5  Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain
6  Astronomy Group, University of Brussels (VUB), Pleinlaan 2, 1050 Brussels, Belgium
7  South African Astronomical Observatory, PO Box 9, Observatory 7935, Cape, South Africa
8  UP State Observatory, Manora Peak, Nainital -263 129, India
9  Centro de Astrofísica da Universidade do Porto, rua das Estrelas, 4150-762 Porto, Portugal
10  Observatoire de Paris, DASGAL, UMR 8633, 92195 Meudon, France (Present address of C.B.: National Solar Observatory, 950 N. Cherry Ave., Tucson, AZ 85719, USA.)
11  Observatoire de Paris, DAEC, UMR 8632, 92195 Meudon, France
12  Odessa Astronomical Observatory, Park Shevchenko, Odessa 270014, Ukraine

(Received 20 April 2001 / Accepted 27 June 2001)

We present the results of the multisite differential CCD photometry for the two $\delta$ Scuti stars, BN and BV Cnc, in the open cluster Praesepe. The main objective was to identify the character of the pulsation modes in BN Cnc deriving their accurate periods, amplitudes and phases. These parameters are essential for the mode identification which uses combined photometric and spectroscopic data and is presented in the second article. For BN Cnc, six pulsation modes with amplitudes above the detection limit (~0.5 mmag) were detected. Using the same CCD frames it was possible to verify the presence of the four pulsation modes in BV Cnc, the faintest of $\delta$ Scuti stars in Praesepe. It is shown that in this very low-amplitude pulsator, substantial amplitude variations are seen between 1997 and 1998.

Key words: stars: oscillations -- stars: variable: $\delta$ Scuti -- open clusters and associations: individual: Praesepe

Offprint request: S. Frandsen, srf@ifa.au.dk

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© ESO 2001