J/MNRAS/490/4121 DECam colour-magnitude diagram of Crater II (Walker+, 2019)
A DECam view of the diffuse dwarf galaxy Crater II:
the colour-magnitude diagram.
Walker A.R., Martinez-Vazquez C.E., Monelli M., Vivas A.K., Bono G.,
Gallart C., Cassisi S., Andreuzzi G., Bernard E.J., Dall'Ora M.,
Fiorentino G., Nidever D.L., Olsen K., Pietrinferni A., Stetson P.B.
<Mon. Not. R. Astron. Soc., 490, 4121-4132 (2019)>
=2019MNRAS.490.4121W 2019MNRAS.490.4121W (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Populations, stellar ; Photometry ; Optical
Keywords: methods: data analysis - techniques: photometric - galaxies: dwarf -
galaxies: individual: Crater II - Local Group
Abstract:
We present a deep Blanco/DECam colour-magnitude diagram (CMD) for the
large but very diffuse Milky Way satellite dwarf galaxy Crater II. The
CMD shows only old stars with a clearly bifurcated subgiant branch
(SGB) that feeds a narrow red giant branch. The horizontal branch (HB)
shows many RR Lyrae and red HB stars. Comparing the CMD with
[Fe/H]=-2.0 and [α/Fe]=+0.3 alpha-enhanced BaSTI isochrones
indicates a mean age of 12.5Gyr for the main event and a mean age of
10.5Gyr for the brighter SGB. With such multiple star formation events
Crater II shows similarity to more massive dwarfs that have
intermediate age populations, however for Crater II there was early
quenching of the star formation and no intermediate age or younger
stars are present. The spatial distribution of Crater II stars overall
is elliptical in the plane of the sky, the detailed distribution shows
a lack of strong central concentration, and some inhomogeneities. The
10.5Gyr subgiant and upper main-sequence stars show a slightly higher
central concentration when compared to the 12.5Gyr population.
Matching to Gaia DR2 we find the proper motion of Crater II:
µαcosδ=-0.14±0.07,
µδ=-0.10±0.04mas/yr, approximately perpendicular to the
semimajor axis of Crater II. Our results provide constraints on the
star formation and chemical enrichment history of Crater II, but
cannot definitively determine whether or not substantial mass has been
lost over its lifetime.
Description:
The Crater II observations presented here derive from an allocation of
three nights awarded by NOAO (P.I. A.R. Walker, prop-id 2017A-0210)
with DECam on the Blanco 4m telescope at Cerro Tololo Inter-American
Observatory (CTIO). From these observations we have produced a deep
CMD and high-quality light curves for the Crater II variable stars,
with main science goals to study the star formation history and the
spatial distribution of the galaxy's stellar populations. When the
Moon was down we took exposures of 180s in a u, g, i sequence, centred
on the Crater II position as given by Torrealba et al.
(2016MNRAS.459.2370T 2016MNRAS.459.2370T) with small dithers to fill in the CCD gaps. If
the Moon was up only g, i exposures were taken. In photometric
conditions SDSS standard star fields were observed, mostly equatorial.
Objects:
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RA (ICRS) DE Designation(s)
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11 49 14.40 -18 24 46.8 NAME Crater II Dwarf Galaxy
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 71 74541 Crater II stellar photometry catalogue
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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- 5 I5 --- ID [1/74541] Internal object identifier
7- 15 F9.5 deg RAdeg Right ascension (J2000)
17- 26 F10.6 deg DEdeg Declination (J2000)
28- 34 F7.4 mag gmag DECam g-band magnitude
36- 40 F5.3 mag e_gmag Error on gmag
42- 48 F7.4 mag imag DECam i-band magnitude
50- 54 F5.3 mag e_imag Error on imag
56- 63 F8.6 mag E(B-V) Reddening (1)
65 I1 --- funi [0/1] Flag denoting whether the object is in
the uniform selection (44294/74541)
67 I1 --- fphot [0/1] Flag denoting whether the object is a
variable star (1166/74541)
69 I1 --- fspec [0/1] Flag denoting whether the object is
identified as a probable member on
spectroscopic grounds (70/74541)
71 I1 --- fvar [0/1] Flag denoting whether the object is
identified as a probable member on
photometric grounds (106/74541)
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Note (1): We obtain E(B-V) from the Schlegel, Finkbeiner & Davis
(1998ApJ...500..525S 1998ApJ...500..525S) interstellar dust maps using the python task
dustmaps (Green 2018JOSS....3..695G 2018JOSS....3..695G)
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History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 02-Feb-2023