J/AJ/157/35 The population of pulsating variable stars in Sextans (Vivas+, 2019)
The population of pulsating variable stars in the Sextans dwarf spheroidal
galaxy.
Vivas A.K., Alonso-Garcia J., Mateo M., Walker A., Howard B.
<Astron. J., 157, 35 (2019)>
=2019AJ....157...35V 2019AJ....157...35V (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Populations, stellar ; Stars, variable ;
Stars, dwarfs ; Photometry, SDSS ; Stars, distances
Keywords: galaxies: dwarf - galaxies: individual (Sextans) -
galaxies: stellar content - stars: variables: general -
stars: variables: RR Lyrae
Abstract:
A large extension of the Sextans dwarf spheroidal galaxy, 7 deg2, has
been surveyed for variable stars using the Dark Energy Camera at the
Blanco Telescope at Cerro Tololo Inter-American Observatory, Chile. We
report seven anomalous Cepheids, 199 RR Lyrae stars, and 16 dwarf Cepheids
in the field. This is only the fifth extragalactic system in which
dwarf Cepheids have been systematically searched. Henceforth, the new
stars increase the census of stars coming from different environments
that can be used to asses the advantages and limitations of using dwarf
Cepheids as standard candles in populations for which the metallicity
is not necessarily known. The dwarf Cepheids found in Sextans have a mean
period of 0.066 day and a mean g amplitude of 0.87 mag. They are located
below the horizontal branch, spanning a range of 0.8 mag: 21.9<g<22.7.
The number of dwarf Cepheids in Sextans is low compared with other galaxies
such as Carina, which has a strong intermediate-age population. On the
other hand, the number and ratio of RR Lyrae stars to dwarf Cepheids are
quite similar to those of Sculptor, a galaxy which, as Sextans, is
dominated by an old stellar population. The dwarf Cepheid stars found
in Sextans follow a well-constrained period-luminosity relationship with
an rms=0.05 mag in the g band, which was set up by anchoring to the
distance modulus given by the RR Lyrae stars. Although the majority of
the variable stars in Sextans are located toward the center of the galaxy,
we have found two RR Lyrae stars and one anomalous Cepheid in the outskirts
of the galaxy that may be extratidal stars and suggest that this galaxy
may be undergoing tidal destruction. These possible extratidal variable
stars share the same proper motions as Sextans, as seen by recent Gaia
measurements. Two additional stars that we initially classified as
foreground RR Lyrae stars may actually be other examples of Sextans
extratidal anomalous Cepheids, although radial velocities are needed
to prove that scenario.
Description:
Observations were taken during two observing runs in 2014 and 2017.
Our strategy consisted of obtaining continuous observations of our field
in two bands (g and r) for several consecutive hours each night. In 2014,
we covered two fields at each side of the center of Sextans, placed along
the semimajor axis of the galaxy (fields A and B; see Figure 1). In each
of the first 2 nights of the 3 night run, we gave priority to a different
field in order to obtain a set of continuous g, r exposures during ∼6 hr
and secure the observation of at least one full pulsational period of
the DC stars. Nonetheless, a few observations of the other field were
inserted through the night. The observing sequence consisted of 300 and
500 s in g and r, respectively. The third night, we alternated between
the two fields continuously. In this observing run, we collected ∼36 epochs
per band per field. Although the cadence was designed for DC stars, having
observations during 3 nights made the data set suitable for longer-period
variables, such as RR Lyrae stars and anomalous Cepheids. For the 2017 run,
we had only 1 night available, so the observing strategy changed, and
we prioritized the number of epochs over multiband observations. The goal
for this run was to cover the central part of the galaxy (field C). We ran
sequences of 10x300 s in g and 1x500 s in r consecutively for 5.5 hr,
the time in which the galaxy was above an airmass of ∼1.8. In total,
we obtained 48 and four observations in g and r, respectively.
Objects:
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RA (ICRS) DE Designation(s)
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10 13 02.9 -01 36 53 Sextans = NAME Dwarf Elliptical Galaxy in Sex
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 75 16 Dwarf Cepheid (DC) stars
table3.dat 146 199 RR Lyrae stars
table4.dat 75 7 Anomalous Cepheids
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See also:
B/gcvs : General Catalogue of Variable Stars (Samus+, 2007-2017)
II/349 : The Pan-STARRS release 1 (PS1) Survey - DR1 (Chambers+, 2016)
J/AJ/110/2166 : Variables in Sextans dSph galaxy (Mateo+ 1995)
J/AJ/126/2840 : BVI CCD photometry of Sextans dSph galaxy (Lee+, 2003)
J/AJ/137/3100 : Radial velocities of 4 dSph galaxies (Walker+, 2009)
J/ApJ/708/717 : Light curve templates of RR Lyrae stars (Sesar+, 2010)
J/MNRAS/411/1013 : CaII triplet in Sextans dSph galaxy (Battaglia+, 2011)
J/MNRAS/460/30 : gi photometry of Sextans dSph galaxy stars (Roderick+, 2016)
J/A+A/609/A53 : Tracing stars of MW dwarf galaxies: Sextans
(Cicuendez+, 2018)
J/A+A/616/A12 : Gaia DR2 sources in GC and dSph (Gaia Collaboration+, 2018)
J/ApJ/855/43 : Distant RR Lyrae stars discovered with HiTS (Medina+, 2018)
Byte-by-byte Description of file: table2.dat table4.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 A4 --- ID Identification number (DCNN or ACN)
6- 14 F9.5 deg RAdeg Right Ascension in decimal degrees (J2000.0)
16- 23 F8.5 deg DEdeg Declination in decimal degrees (J2000.0)
25- 26 I2 --- o_gmag [32/48] Number of gmag observations
28- 29 I2 --- o_rmag [4/38] Number of rmag observations
31- 35 F5.2 mag gmagmean [18.64/22.79] Mean magnitude in g-band
37- 41 F5.2 mag rmagmean [18.55/22.8] Mean magnitude in r-band
43- 48 F6.4 d Per [0.0509/0.9198] Period
50- 53 F4.2 mag gamp [0.08/1.14] The g-band amplitude
55- 58 F4.2 mag ramp [0.37/0.84]? The r-band amplitude
60- 63 F4.1 arcmin DSex [3.1/60.5]? Distance to the center of Sextans
(only in Table 2)
65- 71 A7 --- Com Comment on membership (only in Table 2) (G1)
73- 75 A3 --- OName Other name (only in Table 4)
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 5 A5 --- ID Identification number (RRNNN)
7- 15 F9.5 deg RAdeg Right Ascension in decimal degrees (J2000.0)
17- 24 F8.5 deg DEdeg Declination in decimal degrees (J2000.0)
26- 27 A2 --- Type [ab c d] Type of variable
29- 34 F6.4 d Per [0.2799/0.7801]? Period
36- 46 F11.5 d MJD0 [56723.9974/57848.33177]? Modified Julian Date
at maximum light
48- 49 I2 --- o_gmag [28/48] Number of gmag observations
51- 54 F4.2 mag gamp [0.14/1.49]? The g-band amplitude
56- 60 F5.2 mag gmagmean [18.05/20.83] Mean magnitude in g-band
62- 66 F5.2 mag gmagmax [17.43/20.47]? Maximum magnitude in g-band
68- 71 F4.2 mag gsigfit [0.01/0.09]? rms of the template fit in g-band
73- 80 A8 --- gtemp Best template fitted in g-band from
Sesar et al. (2010, J/ApJ/708/717) library
82- 83 I2 --- o_rmag [2/38] Number of rmag observations
85- 88 F4.2 mag ramp [0.1/0.95]? The r-band amplitude
90- 94 F5.2 mag rmagmean [17.91/20.61] Mean magnitude in r-band
96-100 F5.2 mag rmagmax [17.54/20.26]? Maximum magnitude in r-band
102-105 F4.2 mag rsigfit [0.01/0.06]? rms of the template fit in r-band
107-114 A8 --- rtemp Best template fitted in r-band from
Sesar et al. (2010, J/ApJ/708/717) library
116-138 A23 --- OName Other name(s)
140-146 A7 --- Com Comment on membership (G1)
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Global notes:
Note (G1): "Sextans" member or "Field" star.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 15-May-2019