CCD time-series photometry of the globular cluster NGC 5053: RR Lyrae, Blue Stragglers and SX Phoenicis stars revisited★

et al. 2012

A&A

Self Cite

Aims. We present the analysis of 11 nights of V and I time-series observations of the globular cluster NGC 1904 (M 79). Using this we searched for variable stars in this cluster and attempted to refine the periods of known variables, making use of a time baseline spanning almost 8 years. We use our data to derive the metallicity and distance of NGC 1904. Methods. We used difference imaging 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.Results. Out of 13 stars previously classified as variables, we confirm that 10 are bona fide variables. We cannot detect variability in one other within the precision of our data, while there are two which are saturated in our data frames, but we do not find sufficient evidence in the literature to confirm their variability. We also detect a new RR Lyrae variable, giving a total number of confirmed variable stars in NGC 1904 of 11. Using the Fourier parameters, we find a cluster metallicity [Fe/H] ZW = −1.63 ± 0.14, or [Fe/H] UVES = −1.57 ± 0.18, and a distance of 13.3 ± 0.4 kpc (using RR0 variables) or 12.9 kpc (using the one RR1 variable in our sample for which Fourier decomposition was possible).

Section: Effective Temperaturecontrasting

confidence: 34%

Section: Discussionmentioning

confidence: 50%

See 1 more Smart Citation

Constraining the parameters of globular cluster NGC 1904 from its variable star population

Kains

Bramich

et al. 2012

A&A

Self Cite

“…4.2 in Nemec et al (1995) and also Sect. 5.2 in Arellano Ferro et al (2010). SX Phe stars are well known as distance indicators through their P-L relation (e.g.…”

Section: Sx Phoenicis Stars and Candidatesmentioning

confidence: 99%

Variable stars in the globular cluster NGC 7492

Ferro

Bramich

et al. 2013

A&A

Self Cite

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.

“…Here, however, we adopt a slightly different value of K 0 = 0.41 ± 0.02 mag, as in several of our previous studies (e.g. Arellano Ferro et al 2010), in order to maintain consistency with a true distance modulus of μ 0 = 18.5 mag for the LMC (Freedman et al 2001). A nominal error of 0.02 mag on K 0 was adopted in the absence of uncertainties on K 0 in the literature.…”

Section: Absolute Magnitudementioning

confidence: 99%

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

Kains

Ferro

et al. 2015

A&A

Self Cite

Aims. We analyse 20 nights of CCD observations in the V and I bands of the globular cluster M 68 (NGC 4590) and use them to detect variable objects. We also obtained electron-multiplying CCD (EMCCD) observations for this cluster in order to explore its core with unprecedented spatial resolution from the ground. Methods. We reduced our data using difference image analysis to achieve the best possible photometry in the crowded field of the cluster. In doing so, we show that when dealing with identical networked telescopes, a reference image from any telescope may be used to reduce data from any other telescope, which facilitates the analysis significantly. We then used our light curves to estimate the properties of the RR Lyrae (RRL) stars in M 68 through Fourier decomposition and empirical relations. The variable star properties then allowed us to derive the cluster's metallicity and distance. Results. M 68 had 45 previously confirmed variables, including 42 RRL and 2 SX Phoenicis (SX Phe) stars. In this paper we determine new periods and search for new variables, especially in the core of the cluster where our method performs particularly well. We detect 4 additional SX Phe stars and confirm the variability of another star, bringing the total number of confirmed variable stars in this cluster to 50. We also used archival data stretching back to 1951 to derive period changes for some of the single-mode RRL stars, and analyse the significant number of double-mode RRL stars in M 68. Furthermore, we find evidence for double-mode pulsation in one of the SX Phe stars in this cluster. Using the different classes of variables, we derived values for the metallicity of the cluster of [Fe/H] = −2.07 ± 0.06 on the ZW scale, or −2.20 ± 0.10 on the UVES scale, and found true distance moduli μ 0 = 15.00 ± 0.11 mag (using RR0 stars), 15.00 ± 0.05 mag (using RR1 stars), 14.97 ± 0.11 mag (using SX Phe stars), and 15.00 ± 0.07 mag (using the M V −[Fe/H] relation for RRL stars), corresponding to physical distances of 10.00 ± 0.49, 9.99 ± 0.21, 9.84 ± 0.50, and 10.00 ± 0.30 kpc, respectively. Thanks to the first use of difference image analysis on time-series observations of M 68, we are now confident that we have a complete census of the RRL stars in this cluster.