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

N. Kains, D. M. Bramich, A. Arellano Ferro, R. Figuera Jaimes, U. G. Jørgensen, S. Giridhar, M. T. Penny, Khalid Al-Subai, J. M. Andersen, V. Bozza, P. Browne, M. Burgdorf, S. Calchi Novati, Y. Damerdji, C. Diehl, P. Dodds, M. Dominik, A. Elyiv, X. S. Fang, E. GianniniS. H. Gu, S. Hardis, K. Harpsøe, T. C. Hinse, A. Hornstrup, M. 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

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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.

Original languageEnglish
Article numberA36
JournalAstronomy and Astrophysics
Volume555
DOIs
Publication statusPublished - 5 Jul 2013

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Keywords

  • Globular clusters: individual: M 30 (NGC 7099)
  • Stars: variables: general
  • Stars: variables: RR Lyrae

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Kains, N., Bramich, D. M., Arellano Ferro, A., Figuera Jaimes, R., Jørgensen, U. G., Giridhar, S., Penny, M. T., Al-Subai, K., 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., ... Williams, A. (2013). Estimating the parameters of globular cluster M 30 (NGC 7099) from time-series photometry. Astronomy and Astrophysics, 555, [A36]. https://doi.org/10.1051/0004-6361/201321819