J/A+A/556/A20 Variable stars in globular NGC7492 (Figuera Jaimes+, 2013)
Variable stars in the globular cluster NGC 7492. New discoveries and physical parameter determination. Figuera Jaimes R., Arellano Ferro A., Bramich D.M., Giridhar S., Kuppuswamy K. <Astron. Astrophys. 556, A20 (2013)> =2013A&A...556A..20F
ADC_Keywords: Clusters, globular ; Stars, variable ; Photometry, VRI Keywords: stars: globular clusters: individual: NGC 7492 - stars: variables: RR Lyrae - blue stragglers - stars: abundances - stars: distances - stars: horizontal-branch Abstract: 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.). 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. 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. Description: table3.dat file contains the time-series V, R and I photometry for all the RR Lyrae, long-period, SX Phe variables and candidates in NGC 7492. 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. Observations were made from 2004/10/04 to 2012/06/29 with the 2.0m telescope of the Indian Astronomical Observatory (IAO) at Hanle, India, using the Johnson-Kron-Cousins V, R, and I filters. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table2.dat 91 7 *Celestial coordinates for all of the confirmed and candidate variables in our field of view table3.dat 80 1101 Time series V, R and I photometry for all the RR Lyrae, long-period, SX Phe variables and candidates in NGC 7492
Note on table2.dat: The coordinates correspond to the epoch of the V reference image, which is the heliocentric Julian date ∼2453284.26d.
See also: VII/151 : Structure Parameters of Galactic Globular Clusters (Webbink 1985) II/37 : UBV HR Diagrams of Globular Clusters (Philip+ 1976) J/MNRAS/419/342 : SX Phe stars in globular clusters (Cohen+, 2012) J/MNRAS/416/2265 : Variable stars in NGC 5024 (M53) (Arellano Ferro+, 2011) J/MNRAS/402/226 : NGC 5053 variables VrI light curves (Arellano Ferro+, 2010) J/MNRAS/396/1075 : Properties of Galactic globular clusters (Georgiev+, 2009) J/ApJ/682/1217 : Red giants abundances in 7 globular clusters (Kirby+, 2008) J/A+A/476/307 : Period variations in galactic RRab stars (Le Borgne+, 2007) J/AJ/129/1607 : Equivalent widths of 4 RGB in NGC 7492 (Cohen+, 2005) J/other/RMxAA/40.209 : VR light curves of RR Lyrae in NGC4147 (Arellano+, 2004) J/ApJ/590/797 : Parameters of galactic GCs (Van Den Bregh+, 2003) J/A+AS/67/327 : CCD photometry in NGC 7492 (Buonanno+, 1987) J/MNRAS/122/363 : Eggen PV photometry in NGC 7492 (Cuffey, 1961) Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 4 A4 --- Name Variable name (V1, V2, V4-V7, CSX1) 6- 12 A7 --- OType Variable type (RR0, RR1, LPV or SX Phe) 14- 15 I2 h RAh Hour of right ascension (J2000) 17- 18 I2 min RAm Minute of right ascension (J2000) 20- 24 F5.2 s RAs Second of right ascension (J2000) 26 A1 --- DE- Sign of declination (J2000) 27- 28 I2 deg DEd Degree of declination (J2000) 30- 31 I2 arcmin DEm Arcmin of declination (J2000) 33- 36 F4.1 arcsec DEs Arcsecond of declination (J2000) 38- 49 F12.4 d T0 ? JD epoch of maximum 51 A1 --- u_Per [~] Uncertainty flag on Per 52- 61 F10.7 d Per ? Period 62 A1 --- f_Per [a] Period change (1) 64- 69 F6.3 mag Vmag Mean V-band magnitude 70 A1 --- f_Vmag [bc] Intensity-weighted or mean magnitude (1) 72- 76 F5.3 mag V-R ? V-R color index 77 A1 --- f_V-R [bc] Intensity-weighted or mean color (1) 79 A1 --- l_Vamp [≳] Limit flag on VAmp 80- 84 F5.3 mag Vamp V-band full amplitude 86- 90 F5.3 mag Ramp ? R-band full amplitude 91 A1 --- u_Ramp [?] Uncertainty flag on Ramp
Note (1): Flag as follows: a = If we consider a secular period change, the period is P0=0.412119d at the epoch E=2453284.2652d and the period change rate is β∼47d/Myr. b = Intensity-weighted magnitude calculated from the light curve model. c = Mean magnitude from our data.
Byte-by-byte Description of file: table3.dat
Bytes Format Units Label Explanations
1- 4 A4 --- Name Variable star ID (V1, V2, V4-V7, CSX1) 6 A1 --- Filt [VRI] Observation filter (V, R or I) 8- 20 F13.5 d HJD Heliocentric Julian date at mid-exposure 22- 27 F6.3 mag magst [12.83/19.78] Standard magnitude 29- 34 F6.3 mag maginst [13.89/20.40]Instrumental magnitude 36- 40 F5.3 mag e_maginst [0.001/0.134] Magnitude uncertainty (standard or instrumental) 42- 50 F9.3 s-1 Fref [89.5/27399.2] Reference flux (in ADU/s unit) (1) 52- 56 F5.3 s-1 e_Fref Reference flux uncertainty (in ADU/s unit) 58- 66 F9.3 s-1 DFlux [-1939/348] Difference flux (in ADU/s unit) (1) 68- 73 F6.3 s-1 e_DFlux Difference flux uncertainty (in ADU/s unit) 75- 80 F6.4 --- p [0.14/1.021] Photometric scale factor (1)
Note (1): Light curves for each star were constructed by calculating the total flux ftot(t) in adu/s at each epoch t from ftot(t)=fref+fdiff(t)/p(t) where fref is the reference flux (adu/s), fdiff(t) is the differential flux (adu/s) and p(t) is the photometric scalefactor (the integral of the kernel solution) Conversion to instrumental magnitudes was achieved using mins(t)=25.0-2.5log(ftot(t)) where mins(t) is the instrumental magnitude of the star at time t. Uncertainties were propagated in the correct analytical fashion.
Acknowledgements: Roberto Figuera Jaimes, robertofiguera(at)gmail.com
(End) Roberto Figuera Jaimes [ESO], Emmanuelle Perret [CDS] 19-Jul-2013
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