The M 4 Core Project with HST – III. Search for variable stars in the primary field★
- V. Nascimbeni1,†,
- L. R. Bedin1,
- D. C. Heggie2,
- M. van den Berg3,4,
- M. Giersz5,
- G. Piotto1,6,
- K. Brogaard7,8,
- A. Bellini9,
- A. P. Milone10,
- R. M. Rich11,
- D. Pooley12,13,
- J. Anderson9,
- L. Ubeda9,
- S. Ortolani1,6,
- L. Malavolta1,6,
- A. Cunial1,6 and
- A. Pietrinferni14
- 1INAF – Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, I-35122 Padova, Italy
- 2School of Mathematics and Maxwell Institute for Mathematical Sciences, University of Edinburgh, Kings Buildings, Edinburgh EH9 3JZ, UK
- 3Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, the Netherlands
- 4Harvard–Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
- 5Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, ul. Bartycka 18, 00-716 Warsaw, Poland
- 6Dipartimento di Fisica e Astronomia ‘Galileo Galilei’, Università di Padova, Vicolo dell'Osservatorio 3, I-35122 Padova, Italy
- 7Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade, 8000 Aarhus C, Denmark
- 8Department of Physics and Astronomy, University of Victoria, PO Box 3055, Victoria, BC V8W 3P6, Canada
- 9Space Telescope Science Institute, 3800 San Martin Drive, Baltimore, MD 21218, USA
- 10Research School of Astronomy and Astrophysics, The Australian National University, Cotter Road, Weston, ACT 2611, Australia
- 11Department of Physics and Astronomy, University of California, Los Angeles, CA 90095, USA
- 12Department of Physics, Sam Houston State University, Huntsville, TX 77341, USA
- 13Eureka Scientific, Inc., 2452 Delmer Street, Suite 100, Oakland, CA 94602, USA
- 14INAF – Osservatorio Astronomico di Teramo, Via M. Maggini, I-64100 Teramo, Italy
- ↵†E-mail: valerio.nascimbeni{at}unipd.it
- Accepted 2014 May 6.
- Received 2014 May 6.
- In original form 2014 April 5.
- First published online June 20, 2014.
Abstract
We present the results of a photometric search for variable stars in the core of the Galactic globular cluster Messier 4 (M 4). The input data are a large and unprecedented set of deep Hubble Space Telescope WFC3 images (large programme GO-12911; 120 orbits allocated), primarily aimed at probing binaries with massive companions by detecting their astrometric wobbles. Though these data were not optimized to carry out a time-resolved photometric survey, their exquisite precision, spatial resolution and dynamic range enabled us to firmly detect 38 variable stars, of which 20 were previously unpublished. They include 19 cluster-member eclipsing binaries (confirming the large binary fraction of M 4), RR Lyrae and objects with known X-ray counterparts. We improved and revised the parameters of some among published variables.
Key words
- techniques: photometric
- binaries: general
- stars: variables: general
- globular clusters: individual: NGC 6121
- © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
