J/ApJ/723/1632 Abundance spreads in Bootes I and Segue 1 (Norris+, 2010)
Chemical enrichment in the faintest galaxies: the carbon and iron abundance
spreads in the Bootes I dwarf spheroidal galaxy and the Segue 1 system.
Norris J.E., Wyse R.F.G., Gilmore G., Yong D., Frebel A., Wilkinson M.I.,
Belokurov V., Zucker D.B.
<Astrophys. J., 723, 1632-1650 (2010)>
=2010ApJ...723.1632N 2010ApJ...723.1632N
ADC_Keywords: Abundances ; Galaxies, nearby ; Photometry, SDSS ; Stars, giant ;
Radial velocities
Keywords: galaxies: abundances - galaxies: dwarf - stars: abundances -
galaxies: individual (Bootes I, Segue 1) - Galaxy: abundances -
Abstract:
We present an AAOmega spectroscopic study of red giants in the
ultra-faint dwarf galaxy Bootes I (MV~-6) and the Segue 1 system
(MV~-1.5), either an extremely low luminosity dwarf galaxy or an
unusually extended globular cluster. Both Bootes I and Segue 1 have
significant abundance dispersions in iron and carbon. Bootes I has a
mean abundance of [Fe/H]=-2.55±0.11 with an [Fe/H] dispersion of
σ=0.37±0.08, and abundance spreads of Δ[Fe/H]=1.7 and
Δ[C/H]=1.5. Segue 1 has a mean of [Fe/H]=-2.7±0.4 with [Fe/H]
dispersion of σ=0.7±0.3, and abundances spreads of
Δ[Fe/H]=1.6 and Δ[C/H]=1.2. Moreover, Segue 1 has a
radial-velocity member at four half-light radii that is extremely
metal-poor and carbon-rich, with [Fe/H]=-3.5, and [C/Fe]=+2.3. Modulo
an unlikely non-member contamination, the [Fe/H] abundance dispersion
confirms Segue 1 as the least-luminous ultra-faint dwarf galaxy known.
Description:
Candidate red giant members of Bootes I and Segue 1 were observed with
the Anglo-Australian Telescope/AAOmega fiber-fed spectrograph
combination during 2007 April 18-20 and 2006 May 23-29. Only the blue
spectra from the 2007 data set are discussed in this paper. These
spectra have resolution R=5000 and cover the wavelength range
3850-4540Å.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 64 122 Observational data and derived heliocentric
velocities for stars in the Bootes I field
table2.dat 64 134 Observational data and derived heliocentric
velocities for stars in the Segue 1 field
table3.dat 68 16 Observational data and derived atmospheric
parameters for candidate member stars of Bootes I
table4.dat 67 6 Observational data and derived atmospheric
parameters for candidate member stars of Segue 1
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See also:
II/306 : The SDSS Photometric Catalog, Release 8 (Adelman-McCarthy+, 2011)
J/ApJ/711/350 : Metal-poor giant Boo-1137 abundances (Norris+, 2010)
J/ApJ/692/1464 : Spectroscopy of Segue 1 (Geha+, 2009)
J/MNRAS/380/281 : Faint Galactic satellites survey (Martin+, 2007)
J/AJ/117/981 : Estimation of stellar metal abundance. II. (Beers+, 1999)
Byte-by-byte Description of file: table[12].dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- Seq Identification number
6- 7 I2 h RAh Hour of Right Ascension (J2000)
9- 10 I2 min RAm Minute of Right Ascension (J2000)
12- 16 F5.2 s RAs Second of Right Ascension (J2000)
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- 28 F4.1 arcsec DEs Arcsecond of Declination (J2000)
30- 34 F5.2 mag gmag [17.25/21.49] SDSS-DR4 g band magnitude
36- 40 F5.2 mag imag SDSS-DR4 i band magnitude
42- 46 F5.1 arcmin Xpix X pixel location
48- 52 F5.1 arcmin Ypix Y pixel location
54- 57 F4.1 arcmin Rad [2.1/60] Radius from center
59- 62 I4 km/s HRV [-207/327] Heliocentric radial velocity
64 A1 --- Mem? [y/n] Candidate member? (1)
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Note (1): Candidate radial-velocity members in Bootes I (table 1) lying within
the range 85-130km/s (N=36 for "y").
Candidate radial-velocity members in Segue 1 (table 2) lying within
the range 185-230km/s (N=9 for "y").
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Byte-by-byte Description of file: table3.dat table4.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 I7 --- Seq Star number
8 A1 --- f_Seq [cde] Question about membership (1)
10- 13 F4.1 arcmin Rad [2.1/48.8] Radius from center
15- 17 I3 km/s HRV [94/216] Heliocentric radial velocity
19- 23 F5.2 mag gmag [17.52/19.3] SDSS-DR4 g-band magnitude
25- 29 F5.3 mag (g-r)0 Corrected (g-r) color index
31- 35 F5.3 mag (r-z)0 ? Corrected (r-z) color index
37- 40 F4.2 0.1nm K' ? CaII K line-strength index (K') defined by
Beers et al. (1999, Cat. J/AJ/117/981)
42- 45 I4 K Teff Effective temperature
47- 49 F3.1 [cm/s2] logg Surface gravity
51- 55 F5.2 [Sun] [Fe/H] ? Abundance of [Fe/H]
56 A1 --- f_[Fe/H] [abcgh] Origin of [Fe/H] (1)
58- 62 F5.2 [Sun] [C/H] ? Abundance of [C/H]
64- 68 F5.2 [Sun] [C/Fe] ? Abundance of [C/Fe]
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Note (1): Flag as follows:
a = From the new VLT/UVES high-resolution, high-S/N, data mentioned in the
text. The abundance coincides with the value obtained from AAOmega
moderate-resolution CaII K' data.
b = From this work, based on AAOmega moderate-resolution CaII K' data.
c = Likely non-member, though velocity matches systemic. See the text for
discussion.
d = Inconsistent blue and red abundances. See the text for discussion.
e = RGB member from Geha et al. (2009, Cat. J/ApJ/692/1464), not observed by
us.
g = From G. Gilmore et al. (2010, in preparation), based on VLT/Flames/UVES
data.
h = From Norris et al. (2010, Cat. J/ApJ/711/350).
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 26-Jul-2012