Bibcode
Deras, D.; Arellano Ferro, A.; Lázaro, C.; Bustos Fierro, I. H.; Calderón, J. H.; Muneer, S.; Giridhar, Sunetra
Bibliographical reference
Monthly Notices of the Royal Astronomical Society, Volume 486, Issue 2, p.2791-2808
Advertised on:
6
2019
Citations
27
Refereed citations
25
Description
We present the results from VI CCD time-series photometry of the
globular cluster M13 (NGC 6205). From the Fourier decomposition of the
light curves of RRab and RRc stars we found an average metallicity of
[Fe/H]zw = -1.58 ± 0.09. The distance to the cluster was
estimated as 7.1 ± 0.1 kpc from independent methods related to
the variable star families RR Lyrae, SX Phe and W Virginis, from the
luminosity of the theoretical ZAHB and from the orbit solution of a
newly discovered contact binary star. The RR Lyrae pulsation modes are
segregated by the red edge of the first overtone instability strip in
this OoII-type cluster. A membership analysis of 52 800 stars in the
field of the cluster is presented based on Gaia-DR2 proper motions which
enabled the recognition of 23 070 likely cluster members, for 7630 of
which we possess VI photometry. The identification of member stars
allowed the construction of a clean CMD and a proper ZAHB and isochrone
fitting, consistent with a reddening, age and distance of 0.02 mag, 12.6
Gyr and 7.1 kpc, respectively. We report seven new variables: one RRc,
two SX Phe stars, three SR and one contact binary. V31 presents
double-mode nature and we confirm V36 as RRd. 15 variable star
candidates are also reported. The analysis of 18 stars in the field of
the cluster, reported as RR Lyrae from the Gaia-DR2 data base, reveals
that at least seven are not variable. We noted the presence of a
high-velocity star in the field of the cluster.
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