Variable stars in the globular cluster NGC 7492

Abstract

Aims. We have performed a photometric V, R, I CCD time-series analysis with a baseline of about eight years of the outer-halo globular cluster NGC 7492 with the aim of searching for new variables and using these (and the previously known variables) to determine the physical parameters of interest for the cluster (e.g. metallicity, absolute magnitude of the horizontal branch, distance, etc.). Methods. We used difference image analysis to extract precise light curves in the relatively crowded star field, especially towards the densely populated central region. Several different approaches were used for variability detection that recover the known variables and lead to new discoveries. We determined the physical parameters of the only RR0 star using a light-curve Fourier decomposition analysis. Results. We found one new long-period variable and two SX Phe stars in the blue straggler region. We also present one candidate SX Phe star that requires follow-up observations. Assuming that the SX Phe stars are cluster members and using the period-luminosity relation for these stars, we estimate their distances as ∼25.2 ± 1.8 and 26.8 ± 1.8 kpc, and identify their possible modes of oscillation. We refined the periods of the two RR Lyrae stars in our field of view. We found that the RR1 star V2 is undergoing a period change and possibly exhibits the Blazhko effect. A Fourier decomposition of the light curve of the RR0 star V1 allowed us to estimate a metallicity of [Fe/H] ZW ∼ −1.68 ± 0.10 or [Fe/H] UVES ∼ −1.64 ± 0.13, a log-luminosity log(L/L ) ∼ 1.76 ± 0.02, an absolute magnitude M V ∼ 0.38 ± 0.04 mag, and a true distance modulus of μ 0 ∼ 16.93 ± 0.04 mag, which is equivalent to a distance of ∼24.3 ± 0.5 kpc. All of these values are consistent with previous estimates in the literature.

The Catalina Surveys Periodic Variable Star Catalog

“…The abrupt period change for CSSJ172304.0+290810 appears to have occurred within a 120-day window suggesting a rate of change of at least 2 d/Myr. This is consistent with some more extreme period changes observed by Kunder et al (2011) andFiguera Jaimes et al (2013). 6.5. δ Scutis δ Scuti variables can exhibit brightness variations from 0.003 to 0.9 mags in V and have periods of a few hours.…”

New variable stars towards the Galactic Bulge. I. The bright regime★†

“…We performed photometry on the VIMOS images using the difference image analysis (DIA) pipeline DanDIA Bramich & Freudling 2012;Bramich 2008), which works particularly well in crowded fields such as the cores of globular clusters (e.g. Kains et al 2015Kains et al , 2013bKains et al , 2012bFiguera Jaimes et al 2013;Bramich et al 2011) and the Galactic Bulge (e.g. Kains et al 2013a).…”

A census of variability in globular cluster M 68 (NGC 4590)

“…We used the DIA software DanDIA 1 Bramich 2008) following the recipes devised in our previous publications of time-series globular cluster observations (Kains et al 2012(Kains et al , 2013Figuera Jaimes et al 2013;Arellano Ferro et al 2013b) to reduce our observations. DIA is particularly adept at dealing with crowded fields like the cores of globular clusters, as described in detail in our previous papers (e.g.…”

“…Increasingly precise photometry has allowed for detailed study of pulsation properties of these stars, both from an observational point of view (e.g. Kains et al 2012Kains et al , 2013Arellano Ferro et al 2013a;Figuera Jaimes et al 2013;Kunder et al 2013a) and from a theoretical point of view using stellar evolution (e.g. Dotter et al 2007) and pulsation models (e.g.…”