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 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:
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FileName Lrecl Records Explanations
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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
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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
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Bytes Format Units Label Explanations
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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)
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Note (1): from Roediger et al., 2014ApJS..210...10R 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 1996AJ....112.1487H,
Cat. VII/195, (2010 edition)).
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Byte-by-byte Description of file: stars.dat
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Bytes Format Units Label Explanations
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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 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 2006AJ....132.1014C)
112 A1 --- n_Per2 [af] unusual period (1)
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Note (1): Notes as follows:
a = Period from Pritzl et al. (2002AJ....124..949P 2002AJ....124..949P)
b = Denoted SV1 in Corwin et al. (2006AJ....132.1014C 2006AJ....132.1014C), Cl* NGC 6441 CSP V1
c = Denoted SV2 in Corwin et al. (2006AJ....132.1014C 2006AJ....132.1014C), Cl* NGC 6441 CSP V2
d = Denoted SV4 in Corwin et al. (2006AJ....132.1014C 2006AJ....132.1014C), Cl* NGC 6441 CSP V4
e = Denoted SV5 in Corwin et al. (2006AJ....132.1014C 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 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).
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Byte-by-byte Description of file: photom.dat
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Bytes Format Units Label Explanations
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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)
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Note (1): Instrumental magnitudes are related to the other quantities via
mag.i=17.5-2.5*log10(Fref+DFlux/p).
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Acknowledgements:
Jesper Skottfelt, skottfelt(at)nbi.dk
(End) Jesper Skottfelt [NBI], Patricia Vannier [CDS] 05-Jan-2015