A1 Refereed original research article in a scientific journal
Estimating the parameters of globular cluster M 30 (NGC 7099) from time-series photometry
Authors: Kains N, Bramich D M, Arellano Ferro A, Figuera Jaimes R, Jørgensen 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, Harpsøe K, Hinse T C, Hornstrup A, Hundertmark M, 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
Publisher: EDP Sciences
Publication year: 2013
Journal: Astronomy and Astrophysics
Journal acronym: A&A
Article number: A36
Volume: 555
Number of pages: 15
ISSN: 0004-6361
DOI: https://doi.org/10.1051/0004-6361/201321819
Web address : http://dx.doi.org/10.1051/0004-6361/201321819
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.
