Revisiting the variable star population in NGC 6229 and the structure of the horizontal branch

We report an analysis of new V and I CCD time series photometry of the distant globular cluster NGC 6229. The principal aims were to explore the field of the cluster in search of new variables, and to Fourier decompose the RR Lyrae light curves in pursuit of physical parameters. We found 25 new vari...

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Bibliographic Details
Published in:Monthly notices of the Royal Astronomical Society 2015-09, Vol.452 (1), p.727-746
Main Authors: Arellano Ferro, A., Mancera Piña, P. E., Bramich, D. M., Giridhar, Sunetra, Ahumada, J. A., Kains, N., Kuppuswamy, K.
Format: Article
Language:English
Subjects:
Clusters
Decomposition
Estimates
Fourier analysis
Giant stars
Horizontal
Luminosity
Photometry
Red giant stars
Scientific imaging
Searching
Time series
Variables
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Summary:We report an analysis of new V and I CCD time series photometry of the distant globular cluster NGC 6229. The principal aims were to explore the field of the cluster in search of new variables, and to Fourier decompose the RR Lyrae light curves in pursuit of physical parameters. We found 25 new variables: 10 RRab, 5 RRc, 6 SR, 1 CW, 1 SX Phe, and 2 that we were unable to classify. Secular period changes were detected and measured in some favourable cases. The classifications of some of the known variables were rectified. The Fourier decomposition of RRab and RRc light curves was used to independently estimate the mean cluster value of [Fe/H] and distance. From the RRab stars we found [Fe/H]UVES = −1.31 ± 0.01(statistical) ± 0.12(systematic) ([Fe/H]ZW = −1.42) and a distance of 30.0 ± 1.5 kpc, and from the RRc stars we found [Fe/H]UVES = −1.29 ± 0.12 and a distance of 30.7 ± 1.1 kpc, respectively. Absolute magnitudes, radii and masses are also reported for individual RR Lyrae stars. Also discussed are the independent estimates of the cluster distance from the tip of the red giant branch, 34.9 ± 2.4 kpc and from the period–luminosity relation of SX Phe stars, 28.9 ± 2.2 kpc. The distribution of RR Lyrae stars in the horizontal branch shows a clear empirical border between stable fundamental and first overtone pulsators which has been noted in several other clusters; we interpret it as the red edge of the first overtone instability strip.
ISSN:0035-8711
1365-2966
DOI:10.1093/mnras/stv1299