J/A+A/591/A11 SMC BV photometry of 9 star cluster fields (Dias+, 2016)
SMC west halo: a slice of the galaxy that is being tidally stripped?
Star clusters trace age and metallicity gradients.
Dias B., Kerber L., Barbuy B., Bica E., Ortolani S.
<Astron. Astrophys. 591, A11 (2016)>
=2016A&A...591A..11D 2016A&A...591A..11D (SIMBAD/NED BibCode)
ADC_Keywords: Magellanic Clouds ; Clusters, open ; Clusters, globular ;
Photometry, CCD ; Photometry, UBV
Keywords: galaxies: star clusters - Magellanic Clouds - galaxies: structure -
Hertzsprung-Russell (HR) and C-M diagrams - galaxies: stellar content
Abstract:
The evolution and structure of the Magellanic Clouds is currently
under debate. The classical scenario in which both the Large and Small
Magellanic Clouds (LMC, SMC) are orbiting the Milky Way has been
challenged by an alternative in which the LMC and SMC are in their
first close passage to our Galaxy. The clouds are close enough to us
to allow spatially resolved observation of their stars, and detailed
studies of stellar populations in the galaxies are expected to be able
to constrain the proposed scenarios. In particular, the west halo (WH)
of the SMC was recently characterized with radial trends in age and
metallicity that indicate tidal disruption.
We intend to increase the sample of star clusters in the west halo of
the SMC with homogeneous age, metallicity, and distance derivations to
allow a better determination of age and metallicity gradients in this
region. Distances and positions are compared with the orbital plane of
the SMC depending on the scenario adopted.
Comparisons of observed and synthetic V(B-V) colour-magnitude diagrams
were used to derive age, metallicity, distance, and reddening for star
clusters in the SMC west halo. Observations were carried out using the
4.1m SOAR telescope. Photometric completeness was determined through
artificial star tests, and the members were selected by statistical
comparison with a control field. We derived an age of 1.23±0.07Gyr
and [Fe/H]=-0.87±0.07 for the reference cluster NGC 152,
compatible with literature parameters. Age and metallicity gradients
are confirmed in the WH: 2.6±0.6Gyr/° and
-0.19±0.09dex/°, respectively. The age-metallicity relation for
the WH has a low dispersion in metallicity and is compatible with a
burst model of chemical enrichment. All WH clusters seem to follow the
same stellar distribution predicted by dynamical models, with the
exception of AM-3, which should belong to the counter-bridge. Bruck 6
is the youngest cluster in our sample. It is only 130±40Myr old and
may have been formed during the tidal interaction of SMC-LMC that
created the WH and the Magellanic bridge.
We suggest that it is crucial to split the SMC cluster population into
groups: main body, wing and bridge, counter-bridge, and WH. This is
the way to analyse the complex star formation and dynamical history of
our neighbour. In particular, we show that the WH has clear age and
metallicity gradients and an age-metallicity relation that is also
compatible with the dynamical model that claims a tidal influence of
the LMC on the SMC.
Description:
Photometric magnitudes from SOAR Optical Imager for individual stars
in nine stellar clusters in the Small Magellanic Cloud are presented.
The following clusters are presented: Bruck2, Bruck4, Bruck6, HW5,
HW6, Kron8, Kron11, Lindsay14, and NGC152. For each star equatorial
coordinates and B, V (Bessel) magnitudes with their errors are given.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 90 9 *Observation log
bruck2.dat 56 852 Star coordinates, magnitudes for Bruck 2
bruck4.dat 56 1810 Star coordinates, magnitudes for Bruck 4
bruck6.dat 56 1659 Star coordinates, magnitudes for Bruck 6
hw5.dat 56 2561 Star coordinates, magnitudes for HW 5
hw6.dat 56 2942 Star coordinates, magnitudes for HW 6
kron11.dat 56 1210 Star coordinates, magnitudes for Kron 8
kron8.dat 56 3744 Star coordinates, magnitudes for Kron 11
lind14.dat 56 2762 Star coordinates, magnitudes for Lindsay 14
ngc152.dat 56 2999 Star coordinates, magnitudes for NGC 152
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Note on table2.dat: The CCDs were displaced by ∼20" from the cluster centre to
avoid the gap between the set of two E2V CCDs in SOI, as shown in Fig. 2.
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See also:
J/MNRAS/389/678 : Magellanic Clouds catalogue of extended objects (Bica+, 2008)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- Name Cluster name
12- 13 I2 h RAh Right ascension (J2000) (1)
15- 16 I2 min RAm Right ascension (J2000) (1)
18- 19 I2 s RAs Right ascension (J2000) (1)
21 A1 --- DE- Declination sign (J2000) (1)
22- 23 I2 deg DEd Declination (J2000) (1)
25- 26 I2 arcmin DEm Declination (J2000) (1)
28- 29 I2 arcsec DEs Declination (J2000) (1)
31- 34 F4.2 arcmin D Diameter (1)
36- 45 A10 "date" Obs.date Observation date
47 A1 --- B [B] Filter
49- 53 A5 s ExpTimeB Exposure time in B band
55- 58 F4.2 --- AirMassB Airmass in B band
60- 62 F3.1 arcsec SeeingB Seeing in B band
64 A1 --- V [V] Filter
66- 70 A5 s ExpTimeV Exposure time in V band
72- 75 F4.2 --- AirMassV Airmass in V band
77- 79 F3.1 arcsec SeeingV Seeing in V band
81- 90 A10 --- FileName Name of the table with BV photometry
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Note (1): from Bica et al. (2008, Cat. J/MNRAS/389/678).
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Byte-by-byte Description of file: b*.dat h*.dat k*.dat lind14.dat ngc152.dat
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Bytes Format Units Label Explanations
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2- 3 I2 h RAh Right ascension (J2000.0)
5- 6 I2 min RAm Right ascension (J2000.0)
8- 11 F4.1 s RAs Right ascension (J2000.0)
14 A1 --- DE- Declination sign (J2000.0)
15- 16 I2 deg DEd Declination (J2000.0)
18- 19 I2 arcmin DEm Declination (J2000.0)
21- 24 F4.1 arcsec DEs Declination (J2000.0)
27- 32 F6.3 mag Bmag B magnitude
36- 40 F5.3 mag e_Bmag B magnitude error
43- 48 F6.3 mag Vmag V magnitude
52- 56 F5.3 mag e_Vmag V magnitude error
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Acknowledgements:
Luciano Fraga, lfraga(at)lna.br
References:
Dias et al., 2014A&A...561A.106D 2014A&A...561A.106D
Self-consistent physical parameters for 5 intermediate-age SMC stellar
clusters from CMD modelling.
(End) Bruno Dias [ESO, Chile], Patricia Vannier [CDS] 17-May-2016