J/AJ/155/183 Properties of variables in the NGC 1846 field (Salinas+, 2018)
Stellar variability at the main-sequence turnoff of the intermediate-age LMC
cluster NGC 1846.
Salinas R., Pajkos M.A., Vivas A.K., Strader J., Contreras Ramos R.
<Astron. J., 155, 183 (2018)>
=2018AJ....155..183S 2018AJ....155..183S (SIMBAD/NED BibCode)
ADC_Keywords: Magellanic Clouds ; Clusters, globular ; Stars, variable ;
Photometry, SDSS ; Cross identifications
Keywords: globular clusters: individual (NGC 1846) - Magellanic Clouds -
stars: variables: delta Scuti
Abstract:
Intermediate-age (IA) star clusters in the Large Magellanic Cloud
(LMC) present extended main-sequence turn-offs (MSTO) that have been
attributed to either multiple stellar populations or an effect of
stellar rotation. Recently it has been proposed that these extended
main sequences can also be produced by ill-characterized stellar
variability. Here we present Gemini-S/Gemini Multi-Object Spectrometer
(GMOS) time series observations of the IA cluster NGC 1846. Using
differential image analysis, we identified 73 new variable stars, with
55 of those being of the Delta Scuti type, that is, pulsating
variables close the MSTO for the cluster age. Considering completeness
and background contamination effects, we estimate the number of
δ Sct belonging to the cluster between 40 and 60 members, although
this number is based on the detection of a single δ Sct within
the cluster half-light radius. This amount of variable stars at the
MSTO level will not produce significant broadening of the MSTO, albeit
higher-resolution imaging will be needed to rule out variable stars as
a major contributor to the extended MSTO phenomenon. Though modest, this
amount of δ Sct makes NGC 1846 the star cluster with the highest
number of these variables ever discovered. Lastly, our results present
a cautionary tale about the adequacy of shallow variability surveys in
the LMC (like OGLE) to derive properties of its δ Sct population.
Description:
Observations of NGC 1846 were conducted using the 8.1 m Gemini South
telescope, located at Cerro Pachon, Chile, on the night of 2015 December 30
under the Gemini Fast Turnaround mode (Gemini program GS-2015B-FT-7).
The imaging mode of the Gemini Multi-Object Spectrometer (GMOS; Hook et al.
2004PASP..116..425H 2004PASP..116..425H) provided us a 5.5 square arcminute field of view (fov).
The SDSS filter system was used to yield 6, 66, and 6 images, in g, r,
and i, each having exposure times of 120 s, 120 s, and 90 s, respectively.
The total time span of observations was 0.136 days (3.26 hr), adequate
for detection of δ Sct, which will have periods of less than ∼6 hr.
The GMOS-S array detector consists of three 2048x4176 pixels Hamamatsu
detectors. Observations were obtained with 2x2 binning, resulting in a pixel
scale of 0.16"/pixel.
Objects:
--------------------------------------------------
RA (ICRS) DE Designation(s)
--------------------------------------------------
05 23 34.6 -69 45 22 LMC = NAME LMC
05 07 34.90 -67 27 32.5 NGC 1846 = ESO 56-67
--------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 81 76 Positions, mean magnitudes, r amplitudes, periods
and classification for all of the variables
discovered in the NGC 1846 field
appen.dat 79 54 Notes on Some Individual Variables
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See also:
J/AcA/53/93 : OGLE RR Lyrae in LMC (Soszynski+, 2003)
J/AcA/59/1 : VI light curves of LMC RR Lyrae stars (Soszynski+, 2009)
J/AcA/59/239 : VI light curves of LMC long-period variables
(Soszynski+, 2009)
J/AcA/60/1 : VI light curves of LMC delta Scuti stars (Poleski+, 2010)
J/AJ/145/160 : Variables in LMC globular clusters. III. Reticulum
(Kuehn+, 2013)
J/MNRAS/430/676 : Massive clusters in the LMC (Baumgardt+, 2013)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- ID Variable star identifier in NGC 1846 field
(VNN)
5- 6 I2 h RAh Hour of Right Ascension (J2000)
8- 9 I2 min RAm Minute of Right Ascension (J2000)
11- 16 F6.3 s RAs Second of Right Ascension (J2000)
18- 18 A1 --- DE- Sign of the Declination (J2000)
19- 20 I2 deg DEd Degree of Declination (J2000)
22- 23 I2 arcmin DEm Arcminute of Declination (J2000)
25- 29 F5.2 arcsec DEs Arcsecond of Declination (J2000)
31- 35 F5.2 mag gmagmean [18.78/24.58]? Mean g band magnitude
37- 41 F5.2 mag rmagmean [18.86/24.44]? Mean r band magnitude
43- 46 F4.2 mag rAmp [0.01/0.8]? r band amplitude
47 A1 --- u_rAmp [:] Uncertainty flag on rAmp
49 A1 --- l_Per [>] Lower limit flag on Per
50- 54 F5.3 d Per [0.038/0.2] Period
56- 58 A3 --- Type Classification (1)
60- 79 A20 --- CI Cross identification with OGLE
81 A1 --- n_ID [*] Denotes a note on the individual source
in the Appendix of this paper (see appen.dat
file)
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Note (1): Classification as follows:
D = delta Scuti;
RRL = RR Lyrae;
E = Eclipsing binary;
U = Variable with unknown classification.
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Byte-by-byte Description of file: appen.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- ID Variable star identifier in NGC 1846 field (VNN)
5- 79 A75 --- Note Text of the note
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History:
From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 21-Nov-2018