J/MNRAS/492/1061 A DECam view of Crater II - Variable stars (Vivas+, 2020)
A DECam view of the diffuse dwarf galaxy Crater II - Variable stars.
Vivas A.K., Walker A.R., Martinez-Vazquez C.E., Monelli M., Bono G.,
Dorta A., Nidever D.L., Fiorentino G., Gallart C., Andreuzzi G.,
Braga V.F., Dall'Ora M., Olsen K., Stetson P.B.
<Mon. Not. R. Astron. Soc., 492, 1061-1077 (2020)>
=2020MNRAS.492.1061V 2020MNRAS.492.1061V (SIMBAD/NED BibCode)
ADC_Keywords: Stars, variable ; Galaxies, dwarf ; Galaxies, nearby ;
Photometry ; Optical
Keywords: stars: variables: general - stars: variables: RR Lyrae -
galaxies: dwarf - galaxies: individual: Crater II - Local Group -
galaxies: stellar content
Abstract:
Time series observations of a single dithered field centred on the
diffuse dwarf satellite galaxy Crater II were obtained with the Dark
Energy Camera (DECam) at the 4m Blanco Telescope at Cerro Tololo
Inter-American Observatory, Chile, uniformly covering up to two
half-light radii. Analysis of the g and i time series results in the
identification and characterization of 130 periodic variable stars,
including 98 RR Lyrae stars, 7 anomalous Cepheids, and 1 SX Phoenicis
star belonging to the Crater II population, and 24 foreground
variables of different types. Using the large number of ab-type RR
Lyrae stars present in the galaxy, we obtained a distance modulus to
Crater II of (m-M)0=20.333±0.004 (stat) ±0.07 (sys). The
distribution of the RR Lyrae stars suggests an elliptical shape for
Crater II, with an ellipticity of 0.24 and a position angle of
153°. From the RR Lyrae stars, we infer a small metallicity
dispersion for the old population of Crater II of only 0.17dex. There
are hints that the most metal-poor stars in that narrow distribution
have a wider distribution across the galaxy, while the slightly more
metal-rich part of the population is more centrally concentrated.
Given the features in the colour-magnitude diagram of Crater II, the
anomalous Cepheids in this galaxy must have formed through a binary
evolution channel of an old population.
Description:
Observations were carried out using the Dark Energy Camera (DECam;
Flaugher et al. 2015AJ....150..150F 2015AJ....150..150F) on the 4m Blanco Telescope at
Cerro Tololo Inter-American Observatory, Chile. With a field of view
of 3 square degrees, a single DECam field allows us to cover an area
extending to about twice the rh of the galaxy, which was measured to
be 31.2arcmin by Torrealba et al. (2016MNRAS.459.2370T 2016MNRAS.459.2370T). The
observations were carried out during three consecutive nights, from
2017 March 19 to 2017 March 21, with a few additional exposures taken
two weeks later, on the night of 2017 April 4. Crater II culminated
near the middle of the night during the March nights, allowing
continuous observation of the galaxy for about 9h during each of the
three nights. Our strategy consisted of observing a single field in
filters g and i, with the galaxy centred on CCD N4 (one of the central
CCDs in the camera). Exposure times were 180s in both filters. In
total, we gathered 160 and 158 observations in g and i, respectively.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 74 130 Periodic variable stars in Crater II
table2.dat 34 34578 Time series photometry of variable stars in the
field of view of Crater II
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 A4 --- ID Object identifier (VNNN) (for V1-V97 as
[JKY2018] VNNN in Simbad and for V97-V134 as
[MWM2018] VNNN in Simbad)
6- 14 F9.5 deg RAdeg Right ascension (J2000)
16- 24 F9.5 deg DEdeg Declination (J2000)
26- 32 F7.5 d Period Variability period
34- 36 I3 --- o_gmag Number of observations in the g-band
38- 41 F4.2 mag Ampg Variability amplitude in the g-band
43- 47 F5.2 mag gmag Mean magnitude in the g-band
49- 51 I3 --- o_imag Number of observations in the i-band
53- 56 F4.2 mag Ampi Variability amplitude in the i-band
58- 62 F5.2 mag imag Mean magnitude in the i-band
64- 68 F5.3 mag E(B-V) Colour excess from Schlegel et al.
(1998ApJ...500..525S 1998ApJ...500..525S)
70- 74 A5 --- Type Variability type (1)
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Note (1): Variability type as follows:
ab = type ab RR Lyrae star (83/130)
c = type-c RR Lyrae star (5/130)
d = type-d RR Lyrae star (10/130)
AC = anomalous Cepheid (7/130)
DC = dwarf Cepheid star (1/130)
FDC = Field dwarf Cepheid star (5/130)
Fab = Field type-ab RR Lyrae star (4/130)
Fc = Field type-c RR Lyrae star (1/130)
Eclip = eclipsing binary star (14/130)
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 4 A4 --- ID Object identifier (VNNN) (for V1-V97 as
[JKY2018] VNNN in Simbad and for V97-V134 as
[MWM2018] VNNN in Simbad)
6- 19 F14.6 d MJD Modified Julian Date
21- 26 F6.3 mag gimag Apparent magnitude in g or i band
28- 32 F5.3 mag e_gimag Error on gimag
34 A1 --- Filter [gi] Filter used for the observation
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History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 13-Mar-2023