J/A+A/588/A128 Variable stars in globular clusters (Figuera Jaimes+, 2016)
Exploring the crowded central region of ten Galactic globular clusters using
EMCCDs. Variable star searches and new discoveries.
Figuera Jaimes R., Bramich D.M., Skottfelt J., Kains N., Jorgensen U.G.,
Horne K., Dominik M., Alsubai K.A., Bozza V., Calchi Novati S., Ciceri S.,
D'Ago G., Galianni P., Gu S.-H., W Harpsoe K.B., Haugbolle T., Hinse T.C.,
Hundertmark M., Juncher D., Korhonen H., Mancini L., Popovas A., Rabus M.,
Rahvar S., Scarpetta G., Schmidt R.W., Snodgrass C., Southworth J.,
Starkey D., Street R.A., Surdej J., Wang X.-B., Wertz O.
(The MiNDSTEp Consortium)
<Astron. Astrophys. 588, A128 (2016)>
=2016A&A...588A.128F 2016A&A...588A.128F (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular ; Stars, variable ; Photometry
Keywords: blue stragglers - galaxies: star clusters: general -
globular clusters: general - stars: variables: RR Lyrae -
novae, cataclysmic variables -
instrumentation: high angular resolution
Abstract:
To obtain time-series photometry of the very crowded central regions
of Galactic globular clusters. To obtain better angular resolution
than has been previously achieved with conventional CCDs on
ground-based telescopes. To complete, or improve, the census of the
variable star population in those stellar systems.
Images were taken using the Danish 1.54-m Telescope at the ESO
observatory at La Silla in Chile. The telescope was equipped with an
electron-multiplying CCD, and the short-exposure-time images obtained
(ten images per second) were stacked using the shift-and-add technique
to produce the normal-exposure-time images (minutes). Photometry was
performed via difference image analysis. Automatic detection of
variable stars in the field was attempted.
The light curves of 12541 stars in the cores of ten globular clusters
were statistically analysed to automatically extract the variable
stars. We obtained light curves for 31 previously known variable stars
(3 long-period irregular, 2 semi-regular, 20 RR Lyrae, 1 SX Phoenicis,
3 cataclysmic variables, 1 W Ursae Majoris-type and 1 unclassified)
and we discovered 30 new variables (16 long-period irregular, 7
semi-regular, 4 RR Lyrae, 1 SX Phoenicis and 2 unclassified).
Description:
Observations were taken during 2013 and 2014 as part of an ongoing
program at the 1.54m Danish telescope at the ESO observatory at La
Silla in Chile that was implemented from April to September each year.
table1.dat file contains the time-series I photometry for all the
variables in the globular clusters studied in this work. 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:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
stars.dat 98 61 Ephemerides and main characteristics of the
variable stars in the field of globular
clusters (tables 4-12)
table1.dat 103 4697 Time series I photometry for all the variables
studied in this work
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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- 7 A7 --- Cluster Globular cluster name
9- 15 A7 --- Star Variable star ID
18- 19 I2 h RAh Right ascension (J2000)
21- 22 I2 min RAm Right ascension (J2000)
24- 29 F6.3 s RAs Right ascension (J2000)
31 A1 --- DE- Declination sign (J2000)
32- 33 I2 deg DEd Declination (J2000)
35- 36 I2 arcmin DEm Declination (J2000)
38- 42 F5.2 arcsec DEs Declination (J2000)
44- 55 F12.4 d Epoch ? Epoch used (HJD)
57- 66 F10.6 d Per ? Period
68- 75 F8.6 d e_Per ? rms uncertainty on Per
77- 81 F5.2 mag Imed ? Median I magnitude
83- 86 F4.2 mag Amp ? Peak-to-peak amplitude in the light curve,
A(i'+z')
88- 90 I3 --- Nep Number of epoch
92- 98 A7 --- Type Classification of the variable
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 7 A7 --- Cluster Globular cluster name
9- 15 A7 --- Star Variable star ID
17 A1 --- Filt [I] Observation filter
19- 31 F13.5 d HJD Heliocentric Julian date at mid-exposure
33- 38 F6.3 mag magst Standard magnitude
40- 44 F5.3 mag maginst Instrumental magnitude
46- 50 F5.3 mag e_maginst Magnitude uncertainty (standard or
instrumental)
52- 62 F11.3 s-1 Fref Reference flux (in ADU/s unit) (1)
64- 74 F11.3 s-1 e_Fref Reference flux uncertainty (in ADU/s unit)
76- 87 F12.3 s-1 DFlux Difference flux (in ADU/s unit) (1)
89- 96 F8.3 s-1 e_DFlux Difference flux uncertainty (in ADU/s unit)
98-103 F6.4 --- p Photometric scale factor (1)
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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)=17.5-2.5log(ftot(t))
where mins(t) is the instrumental magnitude of the star at time t.
Uncertainties were propagated in the correct analytical fashion.
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Acknowledgements:
Roberto Figuera, robertofiguera(at)gmail.com
History:
* 30-Mar-2016: First on-line version
* 13-Apr-2016: Error of period of NGC5286 V63 corrected
(End) Patricia Vannier [CDS] 01-Feb-2016