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

A. Arellano Ferro, P. E. Mancera Piña, D. M. Bramich, Sunetra Giridhar, J. A. Ahumada, N. Kains, K. Kuppuswamy

Research output: Contribution to journalArticle

12 Citations (Scopus)

Abstract

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]<inf>UVES</inf> = -1.31 ± 0.01(statistical) ± 0.12(systematic) ([Fe/H]<inf>ZW</inf> = -1.42) and a distance of 30.0 ± 1.5 kpc, and from the RRc stars we found [Fe/H]<inf>UVES</inf> = -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.

Original languageEnglish
Pages (from-to)727-746
Number of pages20
JournalMonthly Notices of the Royal Astronomical Society
Volume452
Issue number1
DOIs
Publication statusPublished - 28 Apr 2015

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variable stars
stars
light curve
time series
decomposition
harmonics
estimates
globular clusters
borders
photometry
charge coupled devices
strip
luminosity
radii
distribution
analysis
border
parameter

Keywords

  • Globular clusters: individual: NGC 6229
  • Stars: horizontal branch
  • Stars: variables: RR Lyrae

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Revisiting the variable star population in NGC 6229 and the structure of the horizontal branch. / Arellano Ferro, A.; Mancera Piña, P. E.; Bramich, D. M.; Giridhar, Sunetra; Ahumada, J. A.; Kains, N.; Kuppuswamy, K.

In: Monthly Notices of the Royal Astronomical Society, Vol. 452, No. 1, 28.04.2015, p. 727-746.

Research output: Contribution to journalArticle

Arellano Ferro, A, Mancera Piña, PE, Bramich, DM, Giridhar, S, Ahumada, JA, Kains, N & Kuppuswamy, K 2015, 'Revisiting the variable star population in NGC 6229 and the structure of the horizontal branch', Monthly Notices of the Royal Astronomical Society, vol. 452, no. 1, pp. 727-746. https://doi.org/10.1093/mnras/stv1299
Arellano Ferro, A. ; Mancera Piña, P. E. ; Bramich, D. M. ; Giridhar, Sunetra ; Ahumada, J. A. ; Kains, N. ; Kuppuswamy, K. / Revisiting the variable star population in NGC 6229 and the structure of the horizontal branch. In: Monthly Notices of the Royal Astronomical Society. 2015 ; Vol. 452, No. 1. pp. 727-746.
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AU - Arellano Ferro, A.

AU - Mancera Piña, P. E.

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AU - Giridhar, Sunetra

AU - Ahumada, J. A.

AU - Kains, N.

AU - Kuppuswamy, K.

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N2 - 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.

AB - 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.

KW - Globular clusters: individual: NGC 6229

KW - Stars: horizontal branch

KW - Stars: variables: RR Lyrae

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