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J/A+A/578/A128      VI light curves of NGC4590 variables     (Kains+, 2015)

A census of variability in globular cluster M68 (NGC 4590). Kains N., Arellano Ferro A., Figuera Jaimes R., Bramich D. M., Skottfelt J., Jorgensen U.G., Tsapras Y., Street R.A., Browne P., Dominik M., Horne K., Hundertmark M., Ipatov S., Snodgrass C., Steele I.A., Alsubai K.A., Bozza V., Calchi Novati S., Ciceri S., D'Ago G., Galianni P., Gu S.-H., Harpsoe K., Hinse T.C., Juncher D., Korhonen H., Mancini L., Popovas A., Rabus M., Rahvar S., Southworth J., Surdej J., Vilela C., Wang X.-B., Wertz O. <Astron. Astrophys. 578, A128 (2015)> =2015A&A...578A.128K
ADC_Keywords: Clusters, globular ; Photometry, CCD Keywords: stars: variables: RR Lyrae - stars: variables: general - globular clusters: individual: M68 Abstract: We analyse 20 nights of CCD observations in the V and I bands of the globular cluster M68 (NGC 4590), using these 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. We reduced our data using difference image analysis, in order to achieve the best possible photometry in the crowded field of the cluster. In doing so, we showed 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 M68 through Fourier decomposition and empirical relations. The variable star properties then allowed us to derive the cluster's metallicity and distance. M68 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 an additional 4 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 in order to derive period changes for some of the single-mode RRL stars, and analyse the significant number of double-mode RRL stars in M68. 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 15.00 ± 0.11 mag (using RR0 stars), 15.00±0.05mag (using RR1 stars), 14.97±0.11mag (using SX Phe stars), and 15.00±0.07mag (using the MV-[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±0.30kpc, respectively. Thanks to the first use of difference image analysis on time-series observations of M68, we are now confident that we have a complete census of the RRL stars in this cluster. Description: V and I time-series photometry and difference imaging parameters for all confirmed variables in NGC 4590. Objects: ------------------------------------------- RA (2000) DE Designation(s) ------------------------------------------- 12 39 27.98 -26 44 38.6 M68 = NGC 4590 ------------------------------------------- File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table43.dat 97 50 Data for all confirmed variable stars in NGC4590 ngc4590.dat 82 21747 *V and I light curves for 49 variables
Note on ngc4590.dat: No light curve data for V32.
See also: J/MNRAS/413/1275 : VrI light curves of NGC6981 variables (Bramich+, 2011) J/A+A/548/A92 : VrI light curves of NGC1904 variables (Kains+, 2012) J/A+A/555/A36 : VrI light curves of NGC7099 variables (Kains+, 2013) Byte-by-byte Description of file: table43.dat
Bytes Format Units Label Explanations
1- 3 A3 --- VName Variable ID (V1 to V53, V40-V42 missing) 5- 6 I2 h RAh Right ascension (J2000) 8- 9 I2 min RAm Right ascension (J2000) 11- 16 F6.3 s RAs Right ascension (J2000) 18 A1 --- DE- Declination sign (J2000) 19- 20 I2 deg DEd Declination (J2000) 22- 23 I2 arcmin DEm Declination (J2000) 25- 29 F5.2 arcsec DEs Declination (J2000) 31- 39 F9.4 d Ep [2697/6434]?=- Epoch (HJD-2450000) 41- 51 F11.7 d Per [0.03/323]?=- Variability period 53- 58 F6.3 d/Myr beta [-1.1/1.6]?=- Period-change rate parameter β,where relevant (in 2.738x10-9) 60- 64 F5.2 mag <Vmag> [9.8/18.1]?=- Intensity-weighted mean V magnitude (1) 66- 70 F5.2 mag <Imag> [15/17.68]?=- Intensity-weighted mean I magnitude (1) 72- 73 A2 --- l_Vamp [∼ ≥] Limit flag on Vamp 74- 77 F4.2 mag Vamp [0.1/4.1]?=- Amplitude in V band 79 A1 --- u_Iamp [~] Uncertainty flag on Iamp 80- 83 F4.2 mag Iamp [0.1/0.8]?=- Amplitude in I band 85- 94 A10 --- VType Variable type: RR0/1, SX Phe, or Mira 96- 97 A2 --- n_VType [bd+? ] Note on VType (2)
Note (1): calculated from Fourier fits for all RRL stars, as the mean magnitude is stable even for unsatisfactory fits. For stars without good Fourier fits, amplitudes are calculated from the data. For V27, the data are taken from the ASAS catalogue Pojmanski (2002AcA....52..397P, Cat. II/264). The data for V32 are taken from Clement et al. (1993ApJ...412..183C, Cat. J/ApJ/412/183), as that star is outside of our field of view. Note (2): Notes as follows: b = star which exhibit Blazhko modulation in their light curve d = double-mode pulsation + = this star is FI Hydra ? = uncertainty flag
Byte-by-byte Description of file: ngc4590.dat
Bytes Format Units Label Explanations
1- 3 A3 --- VName Variable ID (VNN) 5 A1 --- Filter [VI] Filter (V or I) 7- 19 F13.5 d JD Julian date 21- 26 F6.3 mag mag.s [12.7/18.5] Standard magnitude 28- 33 F6.3 mag mag.i [14.8/21.3] Instrumental magnitude 35- 39 F5.3 mag e_mag.i [0.001/0.2] Error on the magnitude 41- 49 F9.3 s-1 Fref [44/5832] Reference flux (in ADU/s) 51- 56 F6.3 s-1 e_Fref [0.9/1.6]Error on the reference flux (in ADU/s) 58- 67 F10.3 s-1 DFlux [-11069/11018] Differential flux (in ADU/s) 69- 75 F7.3 s-1 e_DFlux [2/56] Error on the differential flux (in ADU/s) 77- 82 F6.4 --- p [0.5/3.1] Photometric scale factor
Acknowledgements: Noe Kains, noekains(at)gmail.com
(End) Noe Kains [STScI], Patricia Vannier [CDS] 27-Feb-2015
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