Estimating the parameters of globular cluster M 30 (NGC 7099) from time-series photometry^{⋆,⋆⋆,⋆⋆⋆}

¹ European Southern Observatory, Karl-Schwarzschild Straße 2, 85748 Garching bei München, Germany
e-mail: nkains@eso.org
² Instituto de Astronomía, Universidad Nacional Autónoma de Mexico, 04510 Ciudad de Mexico, Mexico
³ SUPA School of Physics & Astronomy, University of St Andrews, North Haugh, St. Andrews, KY16 9SS, UK
⁴ Niels Bohr Institute, University of Copenhagen, Juliane Maries vej 30, 2100 Copenhagen, Denmark
⁵ Centre for Star and Planet Formation, Geological Museum, Øster Voldgade 5, 1350 Copenhagen, Denmark
⁶ Indian Institute of Astrophysics, Koramangala, 560034 Bangalore, India
⁷ Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210, USA
⁸ Qatar Foundation, PO Box, 5825 Doha, Qatar
⁹ Department of Astronomy, Boston University, 725 Commonwealth Ave, Boston, MA 02215, USA
¹⁰ Dipartimento di Fisica “E.R Caianiello”, Universit di Salerno, via Ponte Don Melillo, 84084 Fisciano, Italy
¹¹ Istituto Nazionale di Fisica Nucleare, Sezione di Napoli, Italy
¹² HE Space Operations GmbH, Flughafenallee 24, 28199 Bremen, Germany
¹³ Istituto Internazionale per gli Alti Studi Scientifici (IIASS), 84019 Vietri Sul Mare ( SA), Italy
¹⁴ Institut d’Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août 17, Sart Tilman, Bât. B5c, 4000 Liège, Belgium
¹⁵ Astronomisches Rechen – Institut, Zentrum für Astronomie der Universität Heidelberg (ZAH), Mönchhofstr. 12−14, 69120 Heidelberg, Germany
¹⁶ Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
¹⁷ Main Astronomical Observatory, Academy of Sciences of Ukraine, vul. Akademika Zabolotnoho 27, 03680 Kyiv, Ukraine
¹⁸ National Astronomical Observatories/Yunnan Observatory, Chinese Academy of Sciences, 650011 Kunming, PR China
¹⁹ Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, 650011 Kunming, PR China
²⁰ Korea Astronomy and Space Science Institute, 305-348 Daejeon, Korea
²¹ Institut for Rumforskning og -teknologi, Danmarks Tekniske Universitet, Juliane Maries 30, 2100 København Ø, Denmark
²² Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark
²³ Jodrell Bank Centre for Astrophysics, University of Manchester, Oxford Road, Manchester, M13 9PL, UK
²⁴ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
²⁵ Perth Observatory, Walnut Road, Bickley, 6076 Perth, Australia
²⁶ Departamento de Astronomía y Astrofísica, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 7820436 Macul, Santiago, Chile
²⁷ Department of Physics, Sharif University of Technology, PO Box, 11155–9161 Tehran, Iran
²⁸ Perimeter Institute for Theoretical Physics, 31 Caroline St. N., Waterloo ON, N2L 2Y5, Canada
²⁹ Instituto de Astronomía – UNAM, Km 103 Carretera Tijuana Ensenada, 422860 Ensenada ( Baja Cfa), Mexico
³⁰ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
³¹ INFN, Gruppo Collegato di Salerno, Sezione di Napoli, Italy
³² Max Planck Institute for Solar System Research, Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany
³³ Astrophysics Group, Keele University, Staffordshire, ST5 5BG, UK

Received: 2 May 2013
Accepted: 15 May 2013

Abstract

Aims. We present the analysis of 26 nights of V and I time-series observations from 2011 and 2012 of the globular cluster M 30 (NGC 7099). We used our data to search for variable stars in this cluster and refine the periods of known variables; we then used our variable star light curves to derive values for the cluster’s parameters.

Methods. We used difference image analysis to reduce our data to obtain high-precision light curves of variable stars. We then estimated the cluster parameters by performing a Fourier decomposition of the light curves of RR Lyrae stars for which a good period estimate was possible. We also derived an estimate for the age of the cluster by fitting theoretical isochrones to our colour-magnitude diagram (CMD).

Results. Out of 13 stars previously catalogued as variables, we find that only 4 are bona fide variables. We detect two new RR Lyrae variables, and confirm two additional RR Lyrae candidates from the literature. We also detect four other new variables, including an eclipsing blue straggler system, and an SX Phoenicis star. This amounts to a total number of confirmed variable stars in M 30 of 12. We perform Fourier decomposition of the light curves of the RR Lyrae stars to derive cluster parameters using empirical relations. We find a cluster metallicity [Fe/H]_ZW = −2.01 ± 0.04, or [Fe/H]_UVES = −2.11 ± 0.06, and a distance of 8.32 ± 0.20 kpc (using RR0 variables), 8.10 kpc (using one RR1 variable), and 8.35 ± 0.42 kpc (using our SX Phoenicis star detection in M 30). Fitting isochrones to the CMD, we estimate an age of 13.0 ± 1.0 Gyr for M 30.