J/A+A/573/A103 Light curves for variables in 5 clusters (Skottfelt+, 2015)
Searching for variable stars in the cores of five metal rich globular clusters using EMCCD observations. Skottfelt J., Bramich D.M., Figuera Jaimes R., Jorgensen U.G., Kains N., Arrellano Ferro A., Alsubai K.A., Bozza V., Calchi Novati S., Ciceri S., D'Ago G., Dominik M., Galianni P., Gu S.H., Harpsoe K.B.W., Haugboelle T., Hinse T.C., Hundertmark M., Juncher D., Korhonen H., Liebig C., Mancini L., Popovas A., Rabus M., Rahvar S., Scarpetta G., Schmidt R.W., Southworth J., Snodgrass C., Starkey D., Street R.A., Surdej J., Wang X.-B., Wertz O. (The MiNDSTEp consortium) <Astron. Astrophys. 573, A103 (2015)> =2015A&A...573A.103S
ADC_Keywords: Clusters, globular ; Stars, variable ; Photometry, CCD Keywords: globular clusters: individual: (NGC 6388, NGC 6441, NGC 6528, NGC 6638, NGC 6652) - stars: variables: RR Lyrae - stars: variables: general - instrumentation: high angular resolution Abstract: In this paper, we present the analysis of time-series observations from 2013 and 2014 of five metal rich ([Fe/H]>-1) globular clusters: NGC6388, NGC6441, NGC6528, NGC6638, and NGC6652. The data have been used to perform a census of the variable stars in the central parts of these clusters. The observations were made with the electron multiplying CCD (EMCCD) camera at the Danish 1.54m Telescope at La Silla, Chile, and they were analysed using difference image analysis (DIA) to obtain high-precision light curves of the variable stars. It was possible to identify and classify all of the previously known or suspected variable stars in the central regions of the five clusters. Furthermore, we were able to identify, and in most cases classify 48, 49, 7, 8, and 2 previously unknown variables in NGC 6388, NGC 6441, NGC 6528, NGC 6638, and NGC 6652, respectively. Especially interesting is the case of NGC 6441, for which the variable star population of about 150 stars has been thoroughly examined by previous studies, including a Hubble Space Telescope study. In this paper we are able to present 49 new variable stars for this cluster, of which one (possibly two) are RR Lyrae stars, two are W Virginis stars, and the rest are long period semi-regular or irregular variables on the red giant branch. We have also detected the first double mode RR Lyrae in the cluster. Description: The observations were carried out with the EMCCD instrument at the Danish 1.54m telescope at La Silla, Chile. EMCCD time-series i+z photometry for all confirmed variables in our field of view in NGC 6388, NGC 6441, NGC 6528, NGC 6638, and NGC 6652. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 59 5 Coordinates and physical parameters of the clusters stars.dat 112 172 Details of the variables in our field of view (tables 4-11 of the paper) photom.dat 98 4958 Electron Multiplying CCD (EMCCD) time-series i+z photometry for all confirmed variable stars
See also: J/A+AS/127/167 : Variable stars in NGC6638 (Rutily+ 1997) J/AJ/122/2600 : Variable stars in NGC6441 (Pritzl+ 2001) J/AJ/124/949 : Variable stars in NGC6388 (Pritzl+ 2002) J/AJ/126/1381 : HST snaphost study of NGC6441 (Pritzl+ 2003) J/AJ/132/1014 : Image-subtraction photom of NGC6388, NGC6441 (Corwin+ 2006) J/MNRAS/413/1275 : VrI light curves of NGC6981 variables (Bramich+, 2011) J/A+A/553/A111 : Two new variables in NGC6981 (Skottfelt+, 2013) Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 3 A3 --- --- [NGC] 4- 7 I4 --- NGC Cluster NGC number 9- 10 I2 h RAh Right ascension (J2000.0) 12- 13 I2 min RAm Right ascension (J2000.0) 15- 19 F5.2 s RAs Right ascension (J2000.0) 21 A1 --- DE- Declination sign (J2000.0) 22- 23 I2 deg DEd Declination (J2000.0) 25- 26 I2 arcmin DEm Declination (J2000.0) 28- 31 F4.1 arcsec DEs Declination (J2000.0) 33- 37 F5.2 [Sun] [Fe/H] [-1/-0.1] Metallicity of the cluster (1) 39- 42 F4.2 [Sun] e_[Fe/H] rms uncertainty on [Fe/H] 44- 47 F4.2 [-] c [1.3/1.8] Central concentration (2) 50- 59 F10.2 d Epoch Epoch of the reference image (JD)
Note (1): from Roediger et al., 2014ApJS..210...10R. Note (2): Central concentration c=log10(rt/rc), where rt and rc are the tidal and core radii, respectively (from Harris 1996AJ....112.1487H, Cat. VII/195, (2010 edition)).
Byte-by-byte Description of file: stars.dat
Bytes Format Units Label Explanations
1- 3 A3 --- --- [NGC] 4- 7 I4 --- NGC Cluster NGC number 9- 12 A4 --- VName Variable name, VNNN 13 A1 --- n_VName [b-e] Alternative variable number (1) 15- 16 I2 h RAh Right ascension (J2000.0) (2) 18- 19 I2 min RAm Right ascension (J2000.0) (2) 21- 26 F6.3 s RAs Right ascension (J2000.0) (2) 28 A1 --- DE- Declination sign (J2000.0) (2) 29- 30 I2 deg DEd Declination (J2000.0) (2) 32- 33 I2 arcmin DEm Declination (J2000.0) (2) 35- 39 F5.2 arcsec DEs Declination (J2000.0) (2) 41- 49 F9.4 d Epoch ?=- Epoch of maximum light (HJD-2450000) 51- 60 F10.6 d Per [0.1/250]?=- Period (2) 61 A1 --- n_Per [h] Per is not the fundamental period (1) 63- 67 F5.2 mag <Imag> [11.7/19.6]?=- Mean I magnitude 69- 72 F4.2 mag Amp ?=- Amplitude found in our special i'+z' filter (3) 74- 76 A3 --- Bl [i -] Blend (4) 78- 89 A12 --- Class Variability classification 91 A1 --- n_Per1 [g] Period from 2002 paper (1) 93-101 F9.5 d Per1 ? Period from Pritzl et al. (2003AJ....126.1381P) 105 A1 --- l_Per2 [~] Limit flag on Per2 106-111 F6.3 d Per2 ? Period from Corwin et al. (2006AJ....132.1014C) 112 A1 --- n_Per2 [af] unusual period (1)
Note (1): Notes as follows: a = Period from Pritzl et al. (2002AJ....124..949P) b = Denoted SV1 in Corwin et al. (2006AJ....132.1014C), Cl* NGC 6441 CSP V1 c = Denoted SV2 in Corwin et al. (2006AJ....132.1014C), Cl* NGC 6441 CSP V2 d = Denoted SV4 in Corwin et al. (2006AJ....132.1014C), Cl* NGC 6441 CSP V4 e = Denoted SV5 in Corwin et al. (2006AJ....132.1014C), Cl* NGC 6441 CSP V5 f = These stars have shorter periods than expected for stars of the SR class, but it is not clear how to otherwise classify them according to the GCVS schema given their position on the RGB. g = Period from Pritzl et al. (2001AJ....122.2600P) h = First-overtone period; fundamental period is found to be 0.72082d. Note (2): The celestial coordinates correspond to the epoch of the reference image, which is given in table1. Note (3): The filter i'+z' represents the EMCCD imager passband which roughly corresponds to the combination of the SDSS i' and z' filters. Note (4): The blend column describes whether the star is blended with i = brighter star(s), ii = star(s) of similar magnitude, or iii = fainter/no star(s).
Byte-by-byte Description of file: photom.dat
Bytes Format Units Label Explanations
1- 3 A3 --- --- [NGC] 4- 7 I4 --- NGC Cluster NGC number 9- 12 A4 --- VName Variable name, VNNN 14 A1 --- Filter [I] Observation filter 16- 28 F13.5 d HJD Heliocentric Julian date of observation 30- 35 F6.3 mag mag.s ?=0 Standard magnitude 37- 42 F6.3 mag mag.i ?=0 Instrumental magnitude (1) 44- 48 F5.3 mag e_mag.i ?=0 Error on the magnitude 50- 60 F11.3 1/s Fref Reference flux (in ADU/s) (1) 62- 69 F8.3 1/s e_Fref Error on the reference flux (in ADU/s) 71- 82 F12.3 1/s DFlux Differential flux (in ADU/s) 84- 91 F8.3 1/s e_DFlux Error on the differential flux (in ADU/s) 93- 98 F6.4 --- p Photometric scale factor (1)
Note (1): Instrumental magnitudes are related to the other quantities via mag.i=17.5-2.5*log10(Fref+DFlux/p).
Acknowledgements: Jesper Skottfelt, skottfelt(at)nbi.dk
(End) Jesper Skottfelt [NBI], Patricia Vannier [CDS] 05-Jan-2015
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