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J/MNRAS/413/1275    VrI light curves of NGC6981 variables    (Bramich+, 2011)

CCD time-series photometry of the globular cluster NGC 6981: variable star census and physical parameter estimates. Bramich D.M., Figuera Jaimes R., Giridhar S., Arellano Ferro A. <Mon. Not. R. Astron. Soc., 413, 1275-1294 (2011)> =2011MNRAS.413.1275B
ADC_Keywords: Clusters, globular ; Stars, variable ; Photometry, CCD Keywords: stars: variables: general - stars: variables: RR Lyrae - globular clusters: individual: NGC6981 - Galaxy: stellar content Abstract: We present the results from 10 nights of observations of the globular cluster NGC 6981 (M72) in the V, R and I Johnson wavebands. We employed the technique of difference image analysis to perform precision differential photometry on the time-series images, which enabled us to carry out a census of the understudied variable star population of the cluster. We show that 20 suspected variables in the literature are actually non-variable, and we confirm the variable nature of another 29 variables while refining their ephemerides. We also detect 11 new RR Lyrae variables and three new SX Phe variables, bringing the total confirmed variable star count in NGC 6981 to 43. We performed Fourier decomposition of the light curves for a subset of RR Lyrae stars and used the Fourier parameters to estimate the fundamental physical parameters of the stars using relations available in the literature. Mean values of these physical parameters have allowed us to estimate the physical parameters of the parent cluster. We derive a metallicity of [Fe/H]ZW~-1.48±0.03 on the Zinn & West scale (or [Fe/H]UVES~-1.38±0.03 on the new Carretta et al. scale) for NGC 6981, and distances of ∼16.73±0.36 and ∼16.68±0.36kpc from analysis of the RR0 and RR1 stars separately. We also confirm the Oosterhoff type I classification for the cluster, and show that our colour-magnitude data are consistent with the age of ∼12.75±0.75Gyr derived by Dotter et al. Description: Time-series V, R, and I photometry for all the confirmed variables in our field of view, except V27 and V35 which lie outside of our field of view. We list standard and instrumental magnitudes and their uncertainties corresponding to the variable star identification, filter, and epoch of mid-exposure. For completeness, we also list the reference flux, difference flux, and photometric scale factor, along with the uncertainties on the reference and difference fluxes. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table23.dat 117 43 Celestial coordinates for all the confirmed variables in our field of view, except V27 and V35 which lie outside of our field of view and details of all confirmed variables in NGC 6981 table4.dat 77 8114 CCD time-series V, R, and I photometry of 41 variables in NGC6981
Byte-by-byte Description of file: table23.dat
Bytes Format Units Label Explanations
1- 3 A3 --- VName Variable Star ID (VN or VNN, NN≤56) 5- 6 I2 h RAh ? Right ascension (J2000.0) (1) 8- 9 I2 min RAm ? Right ascension (J2000.0) (1) 11- 15 F5.2 s RAs ? Right ascension (J2000.0) (1) 17 A1 --- DE- Declination sign (J2000.0) (1) 18- 19 I2 deg DEd ? Declination (J2000.0) (1) 21- 22 I2 arcmin DEm ? Declination (J2000.0) (1) 24- 27 F4.1 arcsec DEs ? Declination (J2000.0) (1) 29- 30 A2 --- K95 Kadla et al. (1995A&A...302..723K) candidate variables ID, <Cl* NGC 6981 KBP AN> in Simbad 32- 38 A7 --- VType Variable Type (RR0, RR0/RR1, RR1 or SX Phe) 39 A1 --- u_VType [abc] Uncertain variable type (2) 41- 45 A5 --- Blend Blend Guide: Inner or Outer (3) 47- 48 I2 --- Nmax ? Number of observed maxima (4) 49 A1 --- --- [,] 50- 51 I2 --- Nmin ? Number of observed minima (4) 53- 63 F11.3 d Tmax ? HJD epoch of maximum light 64 A1 --- n_Tmax [d] Uncertainty flag on Tmax (5) 66- 74 F9.7 d Per ? Period 75 A1 --- n_Per [efg] Note on Per (6) 77- 83 F7.5 d PerS ? Period from Shapley & Ritchie, 1920ApJ....52..232S (7) 84 A1 --- n_PerS [h] PerS does not match our data (8) 86- 94 F9.7 d PerR ? Period from Rosino (1953, Pub. Oss. Bologna, 6, 49 (No.2)) (7) 95 A1 --- n_PerR [h] PerR does not match our data (8) 97-104 F8.6 d PerN ? Period from Nobili (1957MmSAI..28..141N) (7) 105 A1 --- n_PerN [h] PerN does not match our data (8) 107-116 F10.8 d PerD ? Period from Dickens & Flinn (1972MNRAS.158...99D) (7) 117 A1 --- n_PerD [h] PerD does not match our data (8)
Note (1): The coordinates are from the V reference image, which is the heliocentric Julian date ∼2453284.11d (J2004.7614) Note (2): Note on VType as follows: a = These variables are RR Lyrae stars, and we believe that they are of the RR0 type, but we cannot confirm this (see Section 3.6) b = the classification for this variable is most likely RR0 (see Section 3.5) c = these variables are RR Lyrae stars, but we have been unable to distinguish their subtype (see Section 3.6) Note (3): A guide to the level of blending of the variable star PSF in the reference images is provided, where "Inner" and "Outer" indicate that the variable is inside or outside, respectively, of the highly crowded central area of the cluster (the dividing line is placed at r=50"), and where "Blend" indicates that the variable is blended with a star of similar or greater brightness. Note (4): Number Nmax and Nmin of light-curve maxima and minima, respectively, that were observed in full during our observation runs. Note (5): d: the epoch of maximum light is uncertain because we have not observed the light-curve peak. The epoch reported here is that of the data point closest to the suspected peak. Note (6): Note as follows: e = the period listed for V29 is the period P0 in equation (6). We detect a secular period change for this star of β≈-1.38x10-8d/d (see Section 3.5) f = due to the poor phase coverage of our observations for this variable, we have been unable to determine a reliable period (see Section 3.5) g = the periods listed for the SX Phe variables are the periods associated with the largest amplitude oscillation Note (7): Note that most of the period estimates from previous authors fail to phase our light curves properly, which highlights the importance of the longer temporal baseline and much better photometric precision of our data. Note (8): h: our photometric data are not well phased by these periods.
Byte-by-byte Description of file: table4.dat
Bytes Format Units Label Explanations
1- 3 A3 --- VName Variable star ID, as in table4 5 A1 --- Filter [VRI] Observation filter 7- 19 F13.5 d HJD Heliocentric Julian date at mid-exposure 21- 26 F6.3 mag magst ?=0.000 Standard magnitude 28- 33 F6.3 mag maginst Instrumental magnitude 35- 39 F5.3 mag e_mag Magnitude uncertainty (standard or instrumental) 41- 48 F8.3 s-1 Fref Reference flux (in ADU/s unit) 50- 54 F5.3 s-1 e_Fref Reference flux uncertainty (in ADU/s unit) 56- 63 F8.3 s-1 DFlux Difference flux (in ADU/s unit) 65- 70 F6.3 s-1 e_DFlux Difference flux uncertainty (in ADU/s unit) 72- 77 F6.4 --- p Photometric scale factor
Acknowledgements: Daniel Bramich, dbramich(at)
(End) Daniel Bramich [ESO, Germany], Patricia Vannier [CDS] 30-Mar-2012
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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