Estimating the parameters of globular cluster M 30 (NGC 7099) from time-series photometry
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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 derive 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.
Kains , N , Bramich , D M , Arellano Ferro , A , Figuera Jaimes , R J , Jorgensen , U G , Giridhar , S , Penny , M T , Alsubai , K A , Andersen , J M , Bozza , V , Browne , P , Burgdorf , M , Calchi Novati , S , Damerdji , Y , Diehl , C , Dodds , P , Dominik , M , Elyiv , A , Fang , X -S , Giannini , E , Gu , S -H , Hardis , S , Harpsoe , K , Hinse , T C , Hornstrup , A , Hundertmark , M P G , Jessen-Hansen , J , Juncher , D , Kerins , E , Kjeldsen , H , Korhonen , H , Liebig , C , Lund , M N , Lundkvist , M , Mancini , L , Martin , R , Mathiasen , M , Rabus , M , Rahvar , S , Ricci , D , Sahu , K , Scarpetta , G , Skottfelt , J , Snodgrass , C , Southworth , J , Surdej , J , Tregloan-Reed , J , Vilela , C , Wertz , O & Williams , A 2013 , ' Estimating the parameters of globular cluster M 30 (NGC 7099) from time-series photometry ' Astronomy & Astrophysics , vol 555 , A36 . DOI: 10.1051/0004-6361/201321819
Astronomy & Astrophysics
Reproduced with permission from Astronomy & Astrophysics, © 2013 ESO.
N.K. acknowledges an ESO Fellowship. The research leading to these results has received funding from the European Community’s Seventh Framework Programme (/FP7/2007-2013/) under grant agreement No. 229517. A.A.F. acknowledges the support of DGAPA-UNAM through project IN104612. A.A.F. and S.G. are thankful to the CONACyT (México) and the Department of Science and Technology (India) for financial support under the Indo-Mexican collaborative project DST/INT/MEXICO/RP001/2008. O.W. (aspirant FRS – FNRS), A.E. (post-doc PRODEX), Y.D. (post-doc PRODEX) and J. Surdej acknowledge support from the Communauté française de Belgique – Actions de recherche concertées – Académie universitaire Wallonie-Europe. T.C.H. gratefully acknowledges financial support from the Korea Research Council for Fundamental Science and Technology (KRCF) through the Young Research Scientist Fellowship Program. T.C.H. acknowledges financial support from KASI (Korea Astronomy and Space Science Institute) grant number 2012-1-410-02. K.A., D.B., M.D., M.H., and C.L. are supported by NPRP grant NPRP-09-476-1-78 from the Qatar National Research Fund (a member of Qatar Foundation). The Danish 1.54 m telescope is operated based on a grant from the Danish Natural Science Foundation (FNU). Funding for the Stellar Astrophysics Centre at Aarhus University is provided by The Danish National Research Foundation. This research was supported in part by the project ASTERoseismic Investigations with SONG and Kepler (ASTERISK), funded by the European Research Council (grant agreement No.: 267864). C.S. received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement No. 268421. C.H.G. and X.S.F. acknowledge support from National Natural Science Foundation of China (grants Nos. 10373023 and 10773027). H.K. acknowledges support from a Marie-Curie Intra-European Fellowship.
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