J/A+A/507/803VI photometry of new M53 variables (Dekany+, 2009)

Study of globular cluster M53: new variables, distance, metallicity. Dekany I., Kovacs G. <Astron. Astrophys. 507, 803 (2009)> =2009A&A...507..803DADC_Keywords: Clusters, globular ; Stars, variable ; Photometry, VRIKeywords: globular clusters: individual: M53 - methods: data analysis - stars: variables: general - stars: variables: RR Lyr - stars: oscillations - stars: abundancesAbstract: We study the variable star content of the globular cluster M53 to compute the physical parameters of the constituting stars and the distance of the cluster. Covering two adjacent seasons in 2007 and 2008, new photometric data are gathered for 3048 objects in the field of M53. By using the OIS (optimal image subtraction) method and subsequently TFA (trend filtering algorithm), we search for variables in the full sample by using discrete Fourier transformation and box-fitting least squares method. We select variables based on the statistics related to these methods combined with visual inspection. We identified 12 new variables (2 RR Lyrae stars, 7 short periodic stars - 3 of them are SX Phe stars - and 3 long-period variables). No eclipsing binaries were found in the present sample. Except for the 3 (hitherto unknown) Blazhko RR Lyrae (two RRab and an RRc) stars, no multiperiodic variables were found. We showed that after proper period shift, the PLC (period-luminosity-color) relation for the first overtone RR Lyrae sample tightly follows the one spanned by the fundamental stars. Furthermore, the slope is in agreement with that derived from other clusters. Based on the earlier Baade-Wesselink calibration of the PLC relations, the derived reddening-free distance modulus of M53 is 16.31±0.04mag, corresponding to a distance modulus of 18.5mag for the Large Magellanic Cloud. From the Fourier parameters of the RRab stars we obtained an average iron abundance of -1.58±0.03 (error of the mean). This is ∼0.5dex higher than the overall abundance of the giants as given in the literature and derived in this paper from the three-color photometry of giants. We suspect that the source of this discrepancy (observable also in other, low-metallicity clusters) is the lack of a sufficient number of low-metallicity objects in the calibrating sample of the Fourier method.Description: Johnson V and Kron-Cousins I photometric time series of the variables detected in our work and the Fourier decompositions of cluster RR Lyrae stars with magnitude-transformed light curves in V band are presented. The file 'rrlvcoe.dat' contains the Fourier decompositions of the TFA-filtered standard V light curves of 11 fundamental-mode and 13 first overtone mode RR Lyrae stars for which flux-to-magnitude transformation was performed. Fourier parameters refer to a sine decomposition defined by the following expression: V(t) = A0 + A1*sin[2*{pi]*(t-t0)*1*f0+φ1] + A2*sin[2*{pi]*(t-t0)*2*f0+φ2] + ... ID type period epoch A0 N sigma A M A_1 phi_1 ... A_M phi_M Here 'ID' is the identification number of a star according to the Catalog of Variable Stars in Globular Clusters (CVSGC, Clement et al. 2001AJ....122.2587C); 'type' has a value of 'RR0' or 'RR1' for fundamental and first overtone pulsators, respectively; 'N' is the number of the data points used in the calculation of the Fourier decomposition; 'sigma' is the standard deviation of the residuals of the fit; 'A' is the total amplitude of the light variation calculated from the fitted Fourier sum; and 'M' is the order of the Fourier fit. For RR0 stars, M=10, while M=3 for RR1 stars. In the case of RR1 stars table cells corresponding to Fourier terms higher than 3 are filled with zero values. Photometric time series of the M53 variable stars are given in the following files: 'vXX.YZ.ext' where 'XX' is a two-digit integer number corresponding to the variable's name in the CVSGC (e.g., for variable V6, 'XX'='06'); the value of 'Y' is 'v' or 'i', for V or I band data, respectively; the value of 'Z' is 'r' or 'f', for raw (i.e., non-TFA) or TFA-filtered data, respectively; and the value of 'ext' is either 'flx' or 'mag', for data in differential flux units or standard magnitude units, respectively. Note that TFA post-processing was done for the V data only.File Summary:

FileName Lrecl Records Explanations

ReadMe 80 . This file stars.dat 82 68 Properties of the RR Lyrae stars rrlvcoe.dat 196 24 Fourier decompositions of cluster RR Lyrae stars with magnitude-transformed light curves in V color flux/* 24 136 Individual raw differential flux curves fluxtfa/* 24 68 Individual TFA-processed differential flux curves mag/* 21 56 Individual V and I light curves

See also: J/AJ/109/269 : Photometry of NGC 5053 (Sarajedini+ 1995) J/PAZh/23/454 : Identification and coordinates in M 53 (Evstigneeva+, 1997) J/AJ/116/1775 : BV photometry of M53 (Rey+, 1998) J/A+A/358/547 : M53 variable stars V light curves (Kopacki, 2000)Byte-by-byte Description of file: stars.dat

Bytes Format Units Label Explanations

1- 3 A3 --- ID Identification name, VNN 4 A1 --- n_ID [*] * for new detections 6- 10 A5 --- Type Variability type (1) 12- 13 I2 h RAh Right ascension (J2000) 15- 16 I2 min RAm Right ascension (J2000) 18- 21 F4.1 s RAs Right ascension (J2000) 23 A1 --- DE- Declination sign (J2000) 24- 25 I2 deg DEd Declination (J2000) 27- 28 I2 arcmin DEm Declination (J2000) 30- 33 F4.1 arcsec DEs Declination (J2000) 35- 39 F5.1 arcsec d Radial distance (2) 41- 50 F10.7 d Per ? Period 52- 53 I2 10-7d e_Per ? rms uncertainty on Per 55- 58 F4.1 --- SNR Signal-to-noise ratio (3) 60 A1 --- l_Vmag [~] Limit flag on Vmag 61- 66 F6.3 mag Vmag ? Average Johnson V magnitude (4) 68- 72 F5.3 mag V-Ic ? Average Johnson-Cousins V-I colour index (4) (5) 74- 81 F8.5 d-1 Freq ? Frequency

Note (1): Types as follows: RRab = fundamental overtone RRc = first overtone RRabB = Blazhko variable RRcB = Blazhko variable sp = short period star lp = long period variableNote (2): The radial distance d is measured from the nominal cluster center defined in Stetson's catalog of photometric standards (Stetson, 2000PASP..112..925S; RA=13:12:55.26; DE=+18:10:09.8 [2000.0])Note (3): Signal-to-noise ratio calculated in the [0.0,20]d^{-1}frequency range for RR Lyrae (No V1-V72), [0.0,50]d^{-1}frequency range for short period stars (No V73-V83)Note (4): The V and V-I magnitude averages (i.e., the zero frequency constant in their Fourier decompositions) are given in those cases in which the flux-to-magnitude conversion was reliable.Note (5): For variable V75, only instrumental V magnitude average is shown because the star was saturated in the I band.

Byte-by-byte Description of file: rrlvcoe.dat

Bytes Format Units Label Explanations

1- 3 A3 --- ID Star identification in CVSGC, VNN, Cl* NGC 5024 GOR VNN in Simbad 5- 7 A3 --- Type RR Lyrae type (RR0 or RR1) 9- 17 F9.7 d Per Period 19- 27 F9.1 --- t0 Epoch of Fourier decomposition (1) 29- 35 F7.4 mag A0 Zero-frequency constant (magnitude average) (1) 37- 39 I3 --- N Number of data points 41- 46 F6.4 mag sigma Residual standard deviation 48- 53 F6.4 mag A Total amplitude 55- 56 I2 --- M Order of the Fourier decomposition 58- 63 F6.4 mag A1 A1 Fourier amplitude (1) 65- 70 F6.4 rad phi1 φ1 Fourier phase (1) 72- 77 F6.4 mag A2 A2 Fourier amplitude (1) 79- 84 F6.4 rad phi2 φ2 Fourier phase (1) 86- 91 F6.4 mag A3 A3 Fourier amplitude (1) 93- 98 F6.4 rad phi3 φ3 Fourier phase (1) 100-105 F6.4 mag A4 A4 Fourier amplitude (1) 107-112 F6.4 rad phi4 φ4 Fourier phase (1) 114-119 F6.4 mag A5 A5 Fourier amplitude (1) 121-126 F6.4 rad phi5 φ5 Fourier phase (1) 128-133 F6.4 mag A6 A6 Fourier amplitude (1) 135-140 F6.4 rad phi6 φ6 Fourier phase (1) 142-147 F6.4 mag A7 A7 Fourier amplitude (1) 149-154 F6.4 rad phi7 φ7 Fourier phase (1) 156-161 F6.4 mag A8 A8 Fourier amplitude (1) 163-168 F6.4 rad phi8 φ8 Fourier phase (1) 170-175 F6.4 mag A9 A9 Fourier amplitude (1) 177-182 F6.4 rad phi9 φ9 Fourier phase (1) 184-189 F6.4 mag A10 A10 Fourier amplitude (1) 191-196 F6.4 rad phi10 φ10 Fourier phase (1)

Note (1): in Fourier decomposition (f0=1/Per): V(t) = A0 + A1*sin[2*{pi]*(t-t0)*1*f0+φ1] + A2*sin[2*{pi]*(t-t0)*2*f0+φ2] + ...

Byte-by-byte Description of file: flux/*

Bytes Format Units Label Explanations

1- 13 F13.5 d HJD Heliocentric Julian Date 15- 24 F10.3 --- Flux Johnson V or Cousins I-band raw differential flux (in ADU units)

Byte-by-byte Description of file: fluxtfa/*

Bytes Format Units Label Explanations

1- 13 F13.5 d HJD Heliocentric Julian Date 15- 24 F10.3 --- Flux Johnson V TFA-processed differential flux (in ADU units)

Byte-by-byte Description of file: mag/*

Bytes Format Units Label Explanations

1- 13 F13.5 d HJD Heliocentric Julian Date 15- 21 F7.4 mag mag Johnson V or Cousins I-band standard magnitude

Acknowledgements: Istvan Dekany, dekany(at)konkoly.hu(End)Istvan Dekany [Konkoly Obs., Hungary], Patricia Vannier [CDS] 24-Sep-2009

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