Estimating the parameters of globular cluster M 30 (NGC 7099) from time-series photometry

N. Kains*, D. M. Bramich, A. Arellano Ferro, Roberto Jose Figuera Jaimes, U. G. Jorgensen, S. Giridhar, M. T. Penny, K. A. Alsubai, J. M. Andersen, V. Bozza, Paul Browne, M. Burgdorf, S. Calchi Novati, Y. Damerdji, C. Diehl, Peter Dodds, Martin Dominik, A. Elyiv, X. -S. Fang, E. GianniniS. -H. Gu, S. Hardis, K. Harpsoe, T. C. Hinse, A. Hornstrup, Markus Peter Gerhard Hundertmark, J. Jessen-Hansen, D. Juncher, E. Kerins, H. Kjeldsen, H. Korhonen, C. Liebig, M. N. Lund, M. Lundkvist, L. Mancini, R. Martin, M. Mathiasen, M. Rabus, S. Rahvar, D. Ricci, K. Sahu, G. Scarpetta, J. Skottfelt, C. Snodgrass, J. Southworth, J. Surdej, J. Tregloan-Reed, C. Vilela, O. Wertz, A. Williams

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

21 Citations (Scopus)

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 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.

Original languageEnglish
Article numberA36
Number of pages15
JournalAstronomy & Astrophysics
Volume555
Early online date25 Jun 2013
DOIs
Publication statusPublished - Jul 2013

Keywords

  • Stars: variables: general
  • Stars: variables: RR Lyrae
  • Globular clusters: individual: M 30 (NGC 7099)
  • RR-lyrae variables
  • Difference image-analysis
  • Large-magellanic-cloud
  • Deep CCD photometry
  • SX phoenicis stars
  • Metal abundances
  • Luminosity function
  • Dwarf novae
  • M30
  • NGC-7099

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