J/ApJ/837/54 Variable stars in the globular cluster DDO 216-A1 (Cole+, 2017)
DDO 216-A1: a central globular cluster in a low-luminosity transition-type
galaxy.
Cole A.A., Weisz D.R., Skillman E.D., Leaman R., Williams B.F.,
Dolphin A.E., Johnson L.C., McConnachie A.W., Boylan-Kolchin M.,
Dalcanton J., Governato F., Madau P., Shen S., Vogelsberger M.
<Astrophys. J., 837, 54-54 (2017)>
=2017ApJ...837...54C 2017ApJ...837...54C (SIMBAD/NED BibCode)
ADC_Keywords: Photometry, HST ; Stars, variable ; Clusters, globular
Keywords: galaxies: dwarf; galaxies: individual: DDO 216;
galaxies: star clusters: general; Local Group
Abstract:
We confirm that the object DDO 216-A1 is a substantial globular
cluster at the center of Local Group galaxy DDO 216 (the Pegasus dwarf
irregular), using Hubble Space Telescope ACS imaging. By fitting
isochrones, we find the cluster metallicity [M/H]=-1.6±0.2, for
reddening E(B-V)=0.16±0.02; the best-fit age is 12.3±0.8Gyr. There
are ∼30 RR Lyrae variables in the cluster; the magnitude of the
fundamental mode pulsators gives a distance modulus of 24.77±0.08
--identical to the host galaxy. The ratio of overtone to fundamental
mode variables and their mean periods make DDO 216-A1 an Oosterhoff
Type I cluster. We find a central surface brightness of 20.85±0.17
F814W mag/arcsec2, a half-light radius of 3.1" (13.4pc), and an
absolute magnitude M814=-7.90±0.16 (M/M☉∼105). King models
fit to the cluster give the core radius and concentration index,
rc=2.1"±0.9" and c=1.24±0.39. The cluster is an "extended"
cluster somewhat typical of some dwarf galaxies and the outer halo of
the Milky Way. The cluster is projected ≲30pc south of the center of
DDO 216, unusually central compared to most dwarf galaxy globular
clusters. Analytical models of dynamical friction and tidal
destruction suggest that it probably formed at a larger distance, up
to ∼1kpc, and migrated inward. DDO 216 has an unexceptional specific
cluster frequency, SN=10. DDO 216 is the lowest-luminosity Local
Group galaxy to host a 105M☉ globular cluster and the only
transition-type (dSph/dIrr) galaxy in the Local Group with a globular
cluster.
Description:
We observed the Pegasus dwarf irregular (PegDIG; DDO216) using the
Advanced Camera for Surveys Wide Field Camera (ACS/WFC) as part of the
Cycle 22 program GO-13768. The observations, which comprise 34.3 and
37.4ks in the F814W (Broad I band) and F475W (Sloan g band) filters,
respectively, were made between 2015 July 23 and 26 using HST.
Parallel observations at a distance of ∼6' were obtained
simultaneously through the equivalent filters on the Wide Field Camera 3.
Objects:
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RA (ICRS) DE Designation(s)
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23 28 26.30 +14 44 25.2 DDO216-A1 = [HM82] A1
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 118 36 Variable stars in DDO216-A1
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See also:
B/hst : HST Archived Exposures Catalog (STScI, 2007)
VII/195 : Globular Clusters in the Milky Way (Harris, 1996)
J/MNRAS/345/747 : RR Lyrae in 4 Fornax globular clusters (Mackey+, 2003)
J/ApJS/161/304 : Star clusters in the MW and satellites (McLaughlin+, 2005)
J/A+A/442/85 : GC candidates in Low SB Galaxies (Sharina+, 2005)
J/ApJ/699/1742 : LCID project. I. Cetus and Tucana variables (Bernard+, 2009)
J/ApJ/697/1993 : Spitzer study of AGB stars. III. (Boyer+, 2009)
J/MNRAS/396/1075 : GC in nearby dwarf galaxies. II (Georgiev+, 2009)
J/MNRAS/392/879 : Globular clusters in nearby dwarf galaxies (Georgiev+, 2009)
J/MNRAS/406/329 : Variable stars in M54 (Sollima+, 2010)
J/AJ/142/187 : HST obs. of 7 Pop.II variable stars (Benedict+, 2011)
J/AJ/142/199 : Sizes and luminosities of stellar systems (Brodie+, 2011)
J/MNRAS/411/1536 : Spectroscopy of of IC4499 red giants (Hankey+, 2011)
J/AJ/144/4 : Dwarf galaxies in the Local Group (McConnachie+, 2012)
J/ApJ/779/102 : Metallicities of RGB stars in dwarf galaxies (Kirby+, 2013)
J/MNRAS/441/3570 : Nuclear star clusters in 228 spiral gal. (Georgiev+, 2014)
J/MNRAS/439/1015 : Velocities of red giants in 7 LG dwarf gal. (Kirby+, 2014)
J/ApJ/789/147 : Star formation histories of LG dwarf galaxies (Weisz+, 2014)
J/ApJ/812/158 : Leo P RR Lyrae candidates & cumulative SFH (McQuinn+, 2015)
J/ApJ/829/26 : Variable stars in Andromeda XXV field. III. (Cusano+, 2016)
J/MNRAS/457/2122 : Nuclear star clusters photometric masses (Georgiev+, 2016)
J/ApJ/827/33 : PHAT. XVI. Star cluster masses and ages (Johnson+, 2016)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 2 I2 h RAh [23] Hour of right ascension (J2000)
4- 5 I2 min RAm [28] Minute of right ascension (J2000)
7- 12 F6.3 s RAs [35.9/36.9] Second of right ascension (J2000)
17 A1 --- DE- [+] Sign of declination (J2000)
18- 19 I2 deg DEd [14] Degree of declination (J2000)
21- 22 I2 arcmin DEm [44] Arcminute of declination (J2000)
24- 28 F5.2 arcsec DEs [18.5/30.8] Arcsecond of declination (J2000)
33- 37 I5 --- ID [16415/40802] Index number (1)
41- 47 F7.2 pix Xpix X pixel coordinate
49- 55 F7.2 pix Ypix Y pixel coordinate
57- 62 F6.3 mag gmag [25.3/26.4] Mean HST/ACS F475W (g) band magnitude
65- 69 F5.3 mag e_gmag [0.02/0.1] Uncertainty in F475Wmag
73- 78 F6.3 mag Imag [24.4/25.3] Mean HST/ACS F814W (I) band magnitude
81- 85 F5.3 mag e_Imag [0.02/0.05] Uncertainty in F814Wmag
89- 93 F5.3 d Per [0.3/1] Period
97-101 F5.3 d e_Per [0.01/0.2]? Uncertainty in Per
105-118 A14 --- Type Variable type
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Note (1): Variables within 8" of the cluster center.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 16-Oct-2017