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Astron. Astrophys. 328, 158-166 (1997)

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A search for delta Scuti stars in northern open clusters

I. CCD photometry of NGC 7245, NGC 7062, NGC 7226 and NGC 7654

M. Viskum 1, M.M. Hernández 2, J.A. Belmonte 2 and S. Frandsen 1

1 Institute of Physics and Astronomy, University of Aarhus, DK-8000 Århus C, Denmark
2 Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain

Received 7 April 1997 / Accepted 21 July 1997

Abstract

In an effort to test stellar structure and evolution models, analysis of oscillations in A and F stars in open clusters is carried out by the STACC network (Frandsen 1992). In this paper we describe our effort to locate a suitable open cluster in the northern hemisphere for a future multi-site campaign. We present BV Johnson and time series CCD photometry of four poorly studied open clusters: NGC 7245, NGC 7062, NGC 7226 and NGC 7654. New improved colour-magnitude diagrams for these four northern hemisphere clusters, together with the results from the search for variable stars in the clusters are presented. The cluster reddening, distance and age are estimated from isochrone fitting.

In the four clusters, we discovered a total of two [FORMULA] Scuti stars, one eclipsing binary, one variable of unknown type and evidence for 3 potential variables all situated within the [FORMULA] Scuti instability strip. We find that the fraction of [FORMULA] Scuti stars in these four open clusters is much lower than among field stars and in other open clusters suggesting that some additional parameters control the pulsation, parameters that we do not understand at this moment.

Key words: open clusters – HR diagrams – stars: oscillations – stars: ffi Scuti – stars: evolution

Send offprint requests to: M. Viskum

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© European Southern Observatory (ESO) 1997

Online publication: March 24, 1998

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