J/ApJ/767/134 Abundances of red giant stars in UFD galaxies (Vargas+, 2013)
The distribution of alpha elements in ultra-faint dwarf galaxies.
Vargas L.C., Geha M., Kirby E.N., Simon J.D.
<Astrophys. J., 767, 134 (2013)>
=2013ApJ...767..134V 2013ApJ...767..134V
ADC_Keywords: Abundances ; Stars, giant ; Galaxies, nearby ; Radial velocities
Keywords: galaxies: abundances; galaxies: dwarf; galaxies: evolution;
Local Group
Abstract:
The Milky Way ultra-faint dwarf (UFD) galaxies contain some of the
oldest, most metal-poor stars in the universe. We present [Mg/Fe],
[Si/Fe], [Ca/Fe], [Ti/Fe], and mean [α/Fe] abundance ratios for
61 individual red giant branch stars across eight UFDs. This is the
largest sample of alpha abundances published to date in galaxies with
absolute magnitudes MV>-8, including the first measurements for
Segue 1, Canes Venatici II, Ursa Major I, and Leo T. Abundances were
determined via medium-resolution Keck/DEIMOS spectroscopy and spectral
synthesis. The sample spans the metallicity range -3.4<[Fe/H]←1.1.
With the possible exception of Segue 1 and Ursa Major II, the
individual UFDs show on average lower [α/Fe] at higher
metallicities, consistent with enrichment from Type Ia supernovae.
Thus, even the faintest galaxies have undergone at least a limited
level of chemical self-enrichment. Together with recent photometric
studies, this suggests that star formation in the UFDs was not a
single burst, but instead lasted at least as much as the minimum time
delay of the onset of Type Ia supernovae (∼100Myr) and less than
∼2Gyr. We further show that the combined population of UFDs has an
[α/Fe] abundance pattern that is inconsistent with a flat,
Galactic halo-like alpha abundance trend, and is also qualitatively
different from that of the more luminous CVn I dSph, which does show a
hint of a plateau at very low [Fe/H].
Description:
The sample was observed with the Keck/DEIMOS spectrograph between 6300
and 9100Å with a resolution of ∼1.3Å FWHM. We analyze only stars
identified as ultra-faint dwarf (UFD) members by Simon & Geha
(2007ApJ...670..313S 2007ApJ...670..313S) and Simon et al. (2011, J/ApJ/733/46).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 76 9 Ultra-faint dwarf (UFD) galaxies studied
table2.dat 142 143 *Abundance results
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Note on table2.dat: We include the reanalyzed abundance measurements for CVn I
(referenced to the Asplund et al. 2009ARA&A..47..481A 2009ARA&A..47..481A solar abundance scale)
at the bottom of Table 2. We use the CVn I sample from Kirby et al. (2010,
J/ApJS/191/352), reanalyzed to reflect our updated uncertainty analysis, which
does not assume symmetric uncertainties (Section 3.4).
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See also:
J/A+A/570/A61 : PM-selected stars of Hercules UFD (Fabrizio+, 2014)
J/ApJ/763/61 : Abundances of 7 red giant members of BootesI (Gilmore+, 2013)
J/ApJ/756/108 : HST VI phot. of variable stars in Leo T (Clementini+, 2012)
J/ApJ/756/79 : Optical phot. in 3 Local Group dwarf galaxies (Sand+, 2012)
J/ApJ/752/42 : BV time series in Ursa Major II (Dall'Ora+, 2012)
J/ApJ/733/46 : Velocity measurements in Segue 1 (Simon+, 2011)
J/AJ/141/90 : SEGUE stellar parameter pipeline. V. (Lee+, 2011)
J/A+A/511/L10 : Abundances and space velocities of 94 stars (Nissen+, 2010)
J/ApJ/723/1632 : Abundance spreads in Bootes I and Segue 1 (Norris+, 2010)
J/ApJ/719/931 : Chemical evolution of the UMi dSph (Cohen+, 2010)
J/ApJ/711/350 : Metal-poor giant Boo-1137 abundances (Norris+, 2010)
J/ApJ/708/560 : Spectroscopy of UMa II and Coma Ber (Frebel+, 2010)
J/ApJS/191/352 : Abundances in stars of MW dwarf satellites (Kirby+, 2010)
J/AJ/137/272 : Space velocities orbits in the Milky Way halo (Roederer+ 2009)
J/ApJ/705/328 : Abundance measurements in Sculptor dSph (Kirby+, 2009)
J/ApJ/692/1464 : Spectroscopy of Segue 1 (Geha+, 2009)
J/ApJ/682/1217 : Abundances in red giants in 7 globular clusters (Kirby+, 2008)
J/AJ/128/1177 : Galactic stellar abundances (Venn+, 2004)
J/A+A/416/1117 : Abundances in the early Galaxy (Cayrel+, 2004)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 17 A17 --- Name UFD galaxy name
19- 21 I3 kpc Dist [23/417] Heliocentric distance (Rhelio) (1)
23 A1 --- f_Dist [*] UFD added at CDS (2)
25- 28 I4 km/s RV [-128/208]? Radial velocity (3)
30- 32 F3.1 km/s e_RV [0.9/2]? RV uncertainty
34- 36 F3.1 km/s Sig [3.3/7.6]? ∼3σ of the systemic UFD
velocity (σV) (3)
38- 40 F3.1 km/s e_Sig [0.8/1.7]? Sig uncertainty
42- 45 F4.1 mag VMag [-7.1/-1.5]? Absolute V-band magnitude (4)
47 I1 --- NMg [0/3]? Number of Mg measurements
49 I1 --- NSi [2/7]? Number of Si measurements
51- 52 I2 --- NCa [1/13]? Number of Ca measurements
54 I1 --- NTi [3/8]? Number of Ti measurements
56- 57 I2 --- Na [4/13]? Number of [α/Fe]avg measurements
59- 63 F5.2 [Sun] <[Fe/H]> [-2.9/-1.9]? Mean metallicity (5)
65- 68 F4.2 [Sun] e_<[Fe/H]> [0.05/0.2]? <[Fe/H]> uncertainty
70- 76 A7 --- UFD Abbreviated name as in table 2 (column added
by CDS)
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Note (1): Rhelio from Martin et al. (2008ApJ...684.1075M 2008ApJ...684.1075M);
see references therein for each UFD.
Note (2): CVn I was added by CDS with distance from Kirby et al. 2010,
(J/ApJS/191/352); see also the Note on table2.dat.
Note (3): RV and σV taken from Simon & Geha (2007ApJ...670..313S 2007ApJ...670..313S)
except for Segue1, taken from Simon et al. (2011, Cat. J/ApJ/733/46).
Note (4): VMag from Martin et al. (2008ApJ...684.1075M 2008ApJ...684.1075M) except for Leo T,
taken from Irwin et al. (2007ApJ...656L..13I 2007ApJ...656L..13I).
Note (5): <[Fe/H]> is the mean metallicity for each UFD using only the
stars with good [α/Fe]avg measurements (see Section 3.4.).
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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- 7 A7 --- UFD Name of UFD Galaxy
10- 11 I2 h RAh Hour of Right Ascension (J2000)
13- 14 I2 min RAm Minute of Right Ascension (J2000)
16- 20 F5.2 s RAs Second of Right Ascension (J2000)
22 A1 --- DE- Sign of the Declination (J2000)
23- 24 I2 deg DEd Degree of Declination (J2000)
26- 27 I2 arcmin DEm Arcminute of Declination (J2000)
29- 32 F4.1 arcsec DEs Arcsecond of Declination (J2000)
35- 39 F5.2 [Sun] [Fe/H] [-3.5/-0.8] Iron abundance relative to the Sun
42- 45 F4.2 [Sun] e_[Fe/H] Uncertainty in [Fe/H]
48- 52 F5.2 [Sun] [a/Fe] α-elements abundance [α/Fe]
55- 58 F4.2 [Sun] E_[a/Fe] Upper limit uncertainty in [a/Fe]
61- 64 F4.2 [Sun] e_[a/Fe] Lower limit uncertainty in [a/Fe]
67- 71 F5.2 [Sun] [Mg/Fe] ? Magnesium-to-iron abundance ratio
74- 77 F4.2 [Sun] E_[Mg/Fe] ? Upper limit uncertainty in [Mg/Fe]
80- 83 F4.2 [Sun] e_[Mg/Fe] ? Lower limit uncertainty in [Mg/Fe]
86- 90 F5.2 [Sun] [Si/Fe] ? Silicon-to-iron abundance ratio
93- 96 F4.2 [Sun] E_[Si/Fe] ? Upper limit uncertainty in [Si/Fe]
99-102 F4.2 [Sun] e_[Si/Fe] ? Lower limit uncertainty in [Si/Fe]
105-109 F5.2 [Sun] [Ca/Fe] ? Calcium-to-iron abundance ratio
112-115 F4.2 [Sun] E_[Ca/Fe] ? Upper limit uncertainty in [Ca/Fe]
118-121 F4.2 [Sun] e_[Ca/Fe] ? Lower limit uncertainty in [Ca/Fe]
124-128 F5.2 [Sun] [Ti/Fe] ? Titanium-to-iron abundance ratio
131-134 F4.2 [Sun] E_[Ti/Fe] ? Upper limit uncertainty in [Ti/Fe]
137-140 F4.2 [Sun] e_[Ti/Fe] ? Lower limit uncertainty in [Ti/Fe]
142 A1 --- A [a] Flag for possibly anomalous abundance
ratio (see Section 5.3)
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 20-Nov-2014