EDP Sciences
Free access
Volume 371, Number 2, May IV 2001
Page(s) 614 - 625
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20010369

A&A 371, 614-625 (2001)
DOI: 10.1051/0004-6361:20010369

SX Phoenicis stars in the core of 47 Tucanae

H. Bruntt1, S. Frandsen1, R. L. Gilliland2, J. Christensen-Dalsgaard1, 3, J. O. Petersen4, P. Guhathakurta5, P. D. Edmonds6 and G. Bono7, 8

1  Institut for Fysik og Astronomi, Aarhus Universitet, 8000 Aarhus C, Denmark
2  Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, Maryland 21218, USA
3  Teoretisk Astrofysik Center, Danmarks Grundforskningsfond, Aarhus Universitet, 8000 Aarhus C, Denmark
4  Astronomisk Observatorium, Niels Bohr Institutet for Astronomi, Fysik og Geofysik, Juliane Maries Vej 30, 2100 København Ø, Denmark
5  UCO/Lick Observatory, University of California, 1156 High Street, Santa Cruz, California 95064, USA
6  Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
7  Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monte Porzio Catone, Italy
8  European Southern Observatory, Casilla 19001, Santiago, Chile

(Received 7 December 2000 / Accepted 9 March 2001)

We present new results on five of six known SX Phoenicis stars in the core of the globular cluster 47 Tucanae. We give interpretations of the light curves in the V and I bands from 8.3 days of observations with the Hubble Space Telescope near the core of 47 Tuc. The most evolved SX Phe star in the cluster is a double-mode pulsator (V2) and we determine its mass to be $(1.54\pm0.05) M_\odot$ from its position in the Hertzsprung-Russell diagram and by comparing observed periods with current theoretical pulsation models. For V14 we do not detect any pulsation signal. For the double-mode pulsators V3, V15, and V16 we cannot give a safe identification of the modes. We also describe the photometric techniques we have used to extract the light curves of stars in the crowded core. Some of the SX Phoenicis are saturated and we demonstrate that even for stars that show signs of a bleeding signal we can obtain a point-to-point accuracy of 1-3% .

Key words: techniques: photometric -- stars: blue stragglers -- stars: variable: $\delta$ set -- stars: individual: 47 Tuc

Offprint request: H. Bruntt, bruntt@ifa.au.dk

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