J/MNRAS/442/2381 Variable stars in M4 primary field (Nascimbeni+, 2014)
The M 4 Core Project with HST.
III. Search for variable stars in the primary field.
Nascimbeni V., Bedin L.R., Heggie D.C., Van Den Berg M., Giersz M.,
Piotto G., Brogaard K., Bellini A., Milone A.P., Rich R.M., Pooley D.,
Anderson J., Ubeda L., Ortolani S., Malavolta L., Cunial A.,
Pietrinferni A.
<Mon. Not. R. Astron. Soc., 442, 2381-2391 (2014)>
=2014MNRAS.442.2381N 2014MNRAS.442.2381N
ADC_Keywords: Clusters, globular ; Stars, variable ; Photometry, HST
Keywords: techniques: photometric - binaries: general -
stars: variables: general - globular clusters: individual: NGC 6121
Abstract:
We present the results of a photometric search for variable stars in
the core of the Galactic globular cluster Messier 4 (M 4). The input
data are a large and unprecedented set of deep Hubble Space Telescope
WFC3 images (large programme GO-12911; 120 orbits allocated),
primarily aimed at probing binaries with massive companions by
detecting their astrometric wobbles. Though these data were not
optimized to carry out a time-resolved photometric survey, their
exquisite precision, spatial resolution and dynamic range enabled us
to firmly detect 38 variable stars, of which 20 were previously
unpublished. They include 19 cluster-member eclipsing binaries
(confirming the large binary fraction of M 4), RR Lyrae and objects
with known X-ray counterparts. We improved and revised the parameters
of some among published variables.
Description:
The full GO-12911 data set was gathered during 120 HST orbits,
arranged in 12 epochs made of 10 HST visits each, where each visit is
one orbit. Each orbit is filled with five 392-396s exposures in the
blue filter F467M (except for 11 isolated frames for which the F467M
exposure time was set to 366s), and one additional 20s exposure
through a red F775W filter at the beginning of the orbit.
The first visit occurred on 2012 Oct 9, followed by a 100 d gap and
then by 11 other visits regularly spaced at an ∼24d cadence. In
this work, we will focus on a homogeneous subset of 589 'deep'
(392-396s) F467M images, in order to take advantage of a denser
sampling and smaller flux contamination from giants.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 84 38 Variables found and their characteristics
table2.dat 59 17887 Light curves of the variables found
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See also:
J/ApJS/120/265 : HST photometry of M4 (Ibata+, 1999)
J/AJ/145/43 : CASE. V. Three eclipsing binaries in M4 (Kaluzny+, 2013)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Seq [1/38] Sequential number
4- 7 I4 --- ID [275/9050] ID code of the source according to
our catalogue
9- 17 F9.5 deg RAdeg Right ascension (J2000)
19- 27 F9.5 deg DEdeg Declination (J2000)
29- 34 F6.2 mag mag.i [-16.5/-6.8] Instrumental magnitude in F467M
36- 40 F5.2 mag Vmag [13.0/22.1] Standard Johnson V magnitude from
Sarajedini et al. (2007AJ....133.1658S 2007AJ....133.1658S)
42 A1 --- Mm [Y/N] Membership flag derived from the VPD
44- 48 A5 --- VType Variability class assigned by our study (5)
49 A1 --- l_Per Limit flag on Per
50- 57 F8.6 d Per [0.18/8.2]?=- Most probable photometric period
58- 59 A2 --- n_Per [*? ] Doubled or ambiguous period (1)
61- 67 A7 --- OName Other star name(s) (2)
68 A1 --- n_OName [+] Different variability class (3)
70- 84 A15 --- Note Individual notes (4)
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Note (1): A few periods of dEBs, marked with a *, have been doubled with
respect to the best-fitting periodogram solution, following astrophysical
arguments (see Section 3.1 for details). Two cases are ambiguous, and
marked with an additional question mark.
Note (2): The cross-references to the variable catalogues by Kaluzny et al.
(2013AcA....63..181K 2013AcA....63..181K, letter K, <Cl* NGC 6121 Saw VNN> in Simbad) and
Clement et al. (2001AJ....122.2587C 2001AJ....122.2587C, letter C).
Note (3): + = two variables, 6858 and 6955, were once classified as a single,
atypical RR Lyr, C40 (Clement et al., 2001AJ....122.2587C 2001AJ....122.2587C, and references
therein)
Note (4): Codes used in the notes:
MS = main-sequence star
BSEQ = binary sequence star (between fiducial MS and MS+0.75 mag)
HB = horizontal branch
BSS = blue straggler star
CX = X-ray source from the catalogue by Bassa et al. (2004ApJ...609..755B 2004ApJ...609..755B,
[BPH2004] CX NN in Simbad)
TO = turn-off star
NM = not a cluster member
Note (5): classes among EB (eclipsing binaries), cEB or dEB (contact or
detached eclipsing binaries), RRab or RRc (fundamental or first overtone
RR Lyr), or UNK=unknown.
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Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 --- ID [275/9050] ID code of the source according to
our catalogue
6- 19 F14.6 d BJD Mid-exposure time in the BJD-TDB time standard
21- 28 F8.4 mag mag.i [-17.1/-5.9] Instrumental magnitude in F467M
30- 35 F6.4 mag e_mag.i [0.0066/1] rms uncertainty on mag.i
37- 44 F8.3 pix Xpos X centroid position on the chip
46- 53 F8.3 pix Ypos Y centroid position on the chip
55- 59 F5.3 --- qfit [0/0.65] Quality parameter (lower is better)
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History:
From electronic version of the journal
References:
Bedin et al., Paper I 2013AN....334.1062B 2013AN....334.1062B
Milone et al., Paper II 2014MNRAS.439.1588M 2014MNRAS.439.1588M
(End) Patricia Vannier [CDS] 27-Feb-2015