J/ApJ/803/63 gr photometry of stars in Kim 2 (Kim+, 2015)
Discovery of a faint outer halo Milky Way star cluster in the southern sky.
Kim D., Jerjen H., Milone A.P., Mackey D., Da Costa G.S.
<Astrophys. J., 803, 63 (2015)>
=2015ApJ...803...63K 2015ApJ...803...63K
ADC_Keywords: Clusters, globular ; Milky Way ; Photometry, ugriz
Keywords: Galaxy: formation; Galaxy: halo; galaxies: dwarf;
globular clusters: general; Local Group
Abstract:
We report the discovery of a new, low-luminosity star cluster in the
outer halo of the Milky Way. High-quality gr photometry is presented,
from which a color-magnitude diagram is constructed, and estimates of
age, [Fe/H], [α/Fe], and distance are derived. The star cluster,
which we designate as Kim 2, lies at a heliocentric distance of
∼105kpc. With a half-light radius of ∼12.8pc and ellipticity of
ε∼0.12, it shares the properties of outer halo globular
clusters, except for at higher metallicity ([Fe/H]~-1.0) and lower
luminosity (Mv~-1.5). These parameters are similar to those for the
globular cluster AM 4, which is considered to be associated with the
Sagittarius dwarf spheroidal galaxy. We find evidence of dynamical
mass segregation and the presence of extra-tidal stars that suggests
that Kim 2 is most likely a star cluster. Spectroscopic observations
for radial-velocity membership and chemical abundance measurements are
needed to further understand the nature of the object.
Description:
To investigate the nature of Kim 2, deep follow-up observations were
obtained with the Gemini Multi-Object Spectrograph (GMOS) in imaging
mode at the 8.1m Gemini-South telescope through director's time
(GS-2014B-DD-3) on 2014 September 20, 21, 22, and 30 and October 29 in
g and r bands. These g' and r' filters are similar, but not identical,
to the g and r filters used by the SDSS. We chose the nine best images
in each band for our photometric analysis.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 42 134 GMOS photometry for stars within 3rh from
the center of Kim 2
table4.dat 158 1 Properties of Kim 2
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See also:
B/eso : ESO Science Archive Catalog (ESO, 1991-2015)
VII/202 : Globular Clusters in the Milky Way (Harris, 1997)
J/MNRAS/435/1928 : Dwarf galaxy planes in Local Group (Pawlowski+, 2013)
J/ApJ/527/199 : HST observations of old clusters in the LMC (Johnson+, 1999)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 2 I2 h RAh Hour of right ascension (J2000)
4- 5 I2 min RAm Minute of right ascension (J2000)
7- 11 F5.2 s RAs Second of right ascension (J2000)
13 A1 --- DE- Sign of declination (J2000)
14- 15 I2 deg DEd Degree of declination (J2000)
17- 18 I2 arcmin DEm Arcminute of declination (J2000)
20- 24 F5.2 arcsec DEs Arcsecond of declination (J2000)
26- 30 F5.3 arcmin Dist [0.04/1.3] Radial distance
32- 36 F5.2 mag rmag [20.4/26.5] GMOS r-band magnitude
38- 42 F5.2 mag g-r [-0.2/1.9] GMOS g-r color index
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 5 A5 --- Name Cluster name
7- 8 I2 h RAh Hour of right ascension (J2000)
10- 11 I2 min RAm Minute of right ascension (J2000)
13- 17 F5.2 s RAs Second of right ascension (J2000)
19 A1 --- DE- Sign of declination (J2000)
20- 21 I2 deg DEd Degree of declination (J2000)
23- 24 I2 arcmin DEm Arcminute of declination (J2000)
26- 30 F5.2 arcsec DEs Arcsecond of declination (J2000)
32- 38 F7.3 deg GLON Galactic longitude
40- 46 F7.3 deg GLAT Galactic latitude
48- 52 F5.2 mag (m-M)0 Distance modulus
54- 57 F4.2 mag e_(m-M)0 Distance modulus uncertainty
59- 63 F5.1 kpc Dist [104.7] Heliocentric distance
65- 67 F3.1 kpc e_Dist Heliocentric distance uncertainty
69- 72 F4.1 kpc Dgc [99.4] Galactocentric distance
74- 76 F3.1 kpc e_Dgc Galactocentric distance uncertainty
78- 81 F4.1 [Sun] [Fe/H] [-1] Metallicity
83- 86 F4.2 [Sun] E_[Fe/H] Positive error on [Fe/H]
88- 91 F4.2 [Sun] e_[Fe/H] Negative error on [Fe/H]
93- 95 F3.1 [Sun] [a/Fe] [0.2] Abundance [α/Fe]
97- 100 F4.1 Gyr Age [11.5] Age
102- 104 F3.1 Gyr E_Age Positive error on Age
106- 108 F3.1 Gyr e_Age Negative error on Age
110- 113 F4.1 pc rh [12.8] Half-light radius (Plummer profile) (1)
115- 117 F3.1 pc e_rh rh uncertainty
119- 121 F3.1 pc rc [8.5] Core radius (King profile) (1)
123- 125 F3.1 pc e_rc rc uncertainty
127- 130 F4.1 pc rt Tidal radius (King profile) (1)
132- 134 F3.1 pc e_rt [64] rt uncertainty
136- 139 F4.2 --- ell [0.12] Ellipticity
141- 144 F4.2 --- e_ell ell uncertainty
146- 147 I2 deg PA [35] Position Angle (θ)
149- 149 I1 deg e_PA PA uncertainty
151- 154 F4.1 mag Mv [-1.5] Total V-band luminosity
156- 158 F3.1 mag e_Mv MV uncertainty
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Note (1): Adopting a distance of 104.7kpc.
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History:
From electronic version of the journal
(End) Emmanuelle Perret [CDS] 03-Aug-2015