CCD photometry of the globular cluster M2: RR Lyrae physical parameters and new variables

Lázaro, C.; Ferro, A. Arellano; Arévalo, M. J.; Bramich, D. M.; Giridhar, Sunetra; Poretti, E.

doi:10.1111/j.1365-2966.2006.10742.x

Cited by 22 publications

(34 citation statements)

References 41 publications

(75 reference statements)

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“…The problem of the Jurcsik & Kovács (1996) calibration of giving values of [Fe/H] too large by ∼0.2–0.3 dex for very metal poor stars has been discussed particularly for the RRab stars in NGC 5053 by Nemec (2004), whose result [Fe/H]=−1.73 is very similar to ours (−1.76). This issue has also been pointed out by Jurcsik & Kovács (1996) themselves, Kovács (2002) and for other clusters by Cacciari, Corwin & Carney (2005) (M3), Lázaro et al (2006) (M2), Arellano Ferro et al (2008a) (NGC 5466) and Arellano Ferro et al (2008b) (NGC 6366). It is also interesting to note that a good agreement between the Fourier and spectroscopic [Fe/H] values for the Large Magellanic Cloud (LMC) RR Lyrae stars was found by Gratton et al (2004) and Di Fabrizio et al (2005) after a systematic correction of ∼−0.2 dex was applied to the Fourier values.…”

Section: Fourier Decomposition Approach To the Physical Parameters supporting

confidence: 58%

“…Recent numerical methods in the analysis of stellar CCD images have proven to be very powerful in isolating faint stars and performing accurate photometry even in very crowded fields, such as in the central regions of globular clusters (Alard & Lupton 1998; Alard 2000; Bramich et al 2005; Bramich 2008). In a series of papers, we have taken advantage of these mathematical techniques to study the known variable stars and to search for new ones in several globular clusters of assorted metallicities (Arellano Ferro et al 2004; Arellano Ferro et al 2008a,b; Lázaro et al 2006). In particular, we used the Fourier decomposition technique to estimate fundamental physical parameters of the RR Lyrae stars, and we searched for eclipsing binaries and variability among the blue stragglers (BS).…”

Section: Introductionmentioning

confidence: 99%

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

Ferro

Giridhar

Bramich

2009

Monthly Notices of the Royal Astronomical Society

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We report the results of CCD V, r and I time‐series photometry of the globular cluster NGC 5053. New times of maximum light are given for the eight known RR Lyrae stars in the field of our images, and their periods are revised. Their V light curves were Fourier decomposed to estimate their physical parameters. A discussion on the accuracy of the Fourier‐based iron abundances, temperatures, masses and radii is given. New periods are found for the five known SX Phe stars, and a critical discussion of their secular period changes is offered. The mean iron abundance for the RR Lyrae stars is found to be [Fe/H]∼−1.97 ± 0.16 and lower values are not supported by the present analysis. The absolute magnitude calibrations of the RR Lyrae stars yield an average true distance modulus of 16.12 ± 0.04 or a distance of 16.7 ± 0.3 kpc. Comparison of the observational colour magnitude diagram (CMD) with theoretical isochrones indicates an age of 12.5 ± 2.0 Gyr for the cluster. A careful identification of all reported blue stragglers (BS) and their V, I magnitudes leads to the conclusion that BS12, BS22, BS23 and BS24 are not BS. On the other hand, three new BS are reported. Variability was found in seven BS, very likely of the SX Phe type in five of them, and in one red giant star. The new SX Phe stars follow established Period–Luminosity relationships and indicate a distance in agreement with the distance from the RR Lyrae stars.

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Section: Fourier Decomposition Approach To the Physical Parameters supporting

confidence: 58%

Section: Introductionmentioning

confidence: 99%

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

Ferro

Giridhar

Bramich

2009

Monthly Notices of the Royal Astronomical Society

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“…Following Lázaro et al (2006), we have calculated the luminosities of SMC RRc stars from as well as from . The results are plotted in Fig.…”

Section: Physical Parameter Extractionmentioning

confidence: 99%

“…Luminosities calculated using SC93 relation () are larger than those estimated by the K98 relation () and the difference may be attributed to different scalings (zero points) of the two relations. The zero point of the luminosity scale of RRc stars is still a matter of controversy (Nemec 2004; Cacciari et al 2005; Lázaro et al 2006). Some problems with the Simon's calibration for the RRc stars were also noted by Catelan (2004) who concluded that SC93's relations for L and M cannot both be simultaneously valid.…”

Section: Physical Parameter Extractionmentioning

confidence: 99%

Physical parameters of the Small Magellanic Cloud RR Lyrae stars and the distance scale

Deb¹,

Singh²

2009

Monthly Notices of the Royal Astronomical Society

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We present a careful and detailed light curve analysis of RR Lyrae stars in the Small Magellanic Cloud (SMC) discovered by the Optical Gravitational Lensing Experiment (OGLE) project. Out of 536 single‐mode RR Lyrae stars selected from the data base, we have investigated the physical properties of 335 ‘normal‐looking’ RRab stars and 17 RRc stars that have good quality photometric light curves. We have also been able to estimate the distance modulus of the cloud which is in good agreement with those determined from other independent methods. The Fourier decomposition method has been used to study the basic properties of these variables. Accurate Fourier decomposition parameters of 536 RR Lyrae stars in the OGLE‐II data base are computed. Empirical relations between the Fourier parameters and some physical parameters of these variables have been used to estimate the physical parameters for the stars from the Fourier analysis. Further, the Fourier decomposition of the light curves of the SMC RR Lyrae stars yields their mean physical parameters as and MV= 0.78 ± 0.02 for 335 RRab variables and and MV= 0.76 ± 0.05 for 17 RRc stars. Using the absolute magnitude together with the mean magnitude, intensity‐weighted mean magnitude and the phase‐weighted mean magnitude of the RR Lyrae stars, the mean distance modulus to the SMC is estimated to be 18.86 ± 0.01, 18.83 ± 0.01 and 18.84 ± 0.01 mag, respectively, from the RRab stars. From the RRc stars, the corresponding distance modulus values are found to be 18.92 ± 0.04, 18.89 ± 0.04 and 18.89 ± 0.04 mag, respectively. Since the Fourier analysis is a very powerful tool for the study of the physical properties of the RR Lyrae stars, we emphasize the importance of exploring the reliability of the calculation of Fourier parameters together with the uncertainty estimates keeping in view the large collections of photometric light curves that will become available from variable star projects of the future.

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“…We use Fourier decomposition to constrain the properties of the cluster itself, following previous papers on other clusters (Arellano Ferro et al 2004, 2008a,b, 2010Lázaro et al 2006;Bramich et al 2011). This cluster has been poorly studied with no major published long-baseline time-series CCD observations, although it contains 13 stars classified as variables, including 5 detected in a recent study by Amigo et al (2011).…”

Section: Introductionmentioning

confidence: 99%

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

Kains

Bramich

Jaimes

et al. 2012

A&A

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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).

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CCD photometry of the globular cluster M2: RR Lyrae physical parameters and new variables

Cited by 22 publications

References 41 publications

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

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

Physical parameters of the Small Magellanic Cloud RR Lyrae stars and the distance scale

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

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