J/ApJ/826/110 Boo-127 and Boo-980 high-resolution spectra (Frebel+, 2016)
The chemical evolution of the Bootes I ultra-faint dwarf galaxy.
Frebel A., Norris J.E., Gilmore G., Wyse R.F.G.
<Astrophys. J., 826, 110-110 (2016)>
=2016ApJ...826..110F 2016ApJ...826..110F (SIMBAD/NED BibCode)
ADC_Keywords: Equivalent widths ; Stars, metal-deficient ; Stars, giant
Keywords: early universe; galaxies: dwarf; Galaxy: halo; Local Group;
stars: abundances; stars: Population II
Abstract:
We present chemical abundance measurements of two metal-poor red giant
stars in the ultra-faint dwarf galaxy Bootes I, based on Magellan/MIKE
high-resolution spectra. For Boo-980, with [Fe/H]=-3.1 , we present
the first elemental abundance measurements, while Boo-127, with
[Fe/H]=-2.0 , shows abundances in good agreement with previous
measurements. Light and iron-peak element abundance ratios in the two
Bootes I stars, as well as those of most other Bootes I members,
collected from the literature, closely resemble those of regular
metal-poor halo stars. Neutron-capture element abundances Sr and Ba
are systematically lower than the main halo trend and also show a
significant abundance spread. Overall, this is similar to what has
been found for other ultra-faint dwarf galaxies. We apply corrections
to the carbon abundances (commensurate with stellar evolutionary
status) of the entire sample and find 21% of stars to be
carbon-enhanced metal-poor (CEMP) stars, compared to 13% without using
the carbon correction. We reassess the metallicity distribution
functions for the CEMP stars and non-CEMP stars, and confirm earlier
claims that CEMP stars might belong to a different, earlier
population. Applying a set of abundance criteria to test to what
extent Bootes I could be a surviving first galaxy suggests that it is
one of the earliest assembled systems that perhaps received gas from
accretion from other clouds in the system, or from swallowing a first
galaxy or building block type object. This resulted in the two stellar
populations observable today.
Description:
We observed Boo-980 and Boo-127 stars with the MIKE spectrograph on
the Magellan-Clay telescope in 2010 March and 2011 March. Details of
the MIKE observations and photometry taken from Norris et al.
(2008ApJ...689L.113N 2008ApJ...689L.113N) are given in Table 1. MIKE spectra have nearly
full optical wavelength coverage over the range ∼3500-9000Å
(R∼22000 in the red and ∼28000 in the blue wavelength regime).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 77 2 Observing details of Bootes I stars
table2.dat 57 444 Equivalent width measurements of the Bootes I stars
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See also:
J/ApJ/817/41 : Abundances of 4 metal-poor red giants in BooII (Ji+, 2016)
J/MNRAS/439/788 : Stromgren and Washington photometry in Boo I (Hughes+, 2014)
J/A+A/562/A146 : Chemical abundances of 8 metal-poor stars (Ishigaki+, 2014)
J/ApJ/769/57 : Equivalent widths of metal-poor stars (Frebel+, 2013)
J/ApJ/763/61 : Abundances of 7 red giant members of BootesI (Gilmore+, 2013)
J/ApJ/762/26 : Most metal-poor stars. II. Galactic halo stars (Yong+, 2013)
J/ApJ/742/54 : CASH project II. Extremely metal-poor stars (Hollek+, 2011)
J/ApJ/736/146 : Radial velocities of stars in Bootes I (Koposov+, 2011)
J/ApJ/723/1632 : Abundance spreads in Bootes I and Segue 1 (Norris+, 2010)
J/AN/331/474 : Abundances of metal-poor stars (Frebel, 2010)
J/ApJ/711/350 : Metal-poor giant Boo-1137 abundances (Norris+, 2010)
J/AJ/136/2321 : Washington photometry of Bootes I stars (Hughes+, 2008)
J/MNRAS/380/281 : Faint galactic satellites spectrosc. survey (Martin+, 2007)
J/ApJ/655/492 : Equivalent widths of 26 metal-poor stars (Aoki+, 2007)
J/A+A/439/129 : HERES II. Spectroscopic analysis (Barklem+, 2005)
J/A+A/416/1117 : Abundances in the early Galaxy (Cayrel+, 2004)
J/AJ/120/1841 : Abundances & Kinematics of Halo & Disk Stars (Fulbright 2000)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 4 A4 --- --- [Boo-]
5- 7 I3 --- [NGW2008] Star name
9- 10 I2 h RAh Hour of right ascension (J2000)
12- 13 I2 min RAm Minute of right ascension (J2000)
15- 19 F5.2 s RAs Second of right ascension (J2000)
21 A1 --- DE- Sign of declination (J2000)
22- 23 I2 deg DEd Degree of declination (J2000)
25- 26 I2 arcmin DEm Arcminute of declination (J2000)
28- 31 F4.1 arcsec DEs Arcsecond of declination (J2000)
33- 43 A11 "Y/M/D" Date First UT date of observation
44 A1 --- --- [,]
45- 52 A8 --- Date2 Other day(s) of observation
54- 56 F3.1 arcsec Slit Slit
58- 60 F3.1 h Exp Exposure time
62- 66 F5.2 mag g0 Corrected g-band magnitude from Norris+,
2008ApJ...689L.113N 2008ApJ...689L.113N
68- 71 F4.2 mag (g-r)0 Corrected (g-r) color index
73- 74 I2 --- S/N 5300Å signal-to-noise ratio
76- 77 I2 --- S/N2 6000Å signal-to-noise ratio
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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- 4 A4 --- Sp Species identifier
6- 13 F8.3 0.1nm lambda [3423.7/6978.9] Wavelength; Angstroms
15- 18 F4.2 eV ExPot [0/4.6]? Excitation potential
20 A1 --- f_ExPot [H] H:Flag indicating a hyperfine-structure
line
22- 27 F6.3 [-] log(gf) [-5.7/0.7]? Log oscillator strength
29- 33 F5.1 10-13m EW-980 [15.9/199.2]? Equivalent width of Boo-980;
milli-Angstroms
35 A1 --- f_EW-980 [s] s: Flag indicating spectrum synthesis used
37- 41 F5.2 [Sun] loge-980 [-2.2/5]? Log abundance in Boo-980
43 A1 --- l_loge-980 Limit flag on loge-980
44- 48 F5.1 10-13m EW-127 [15.4/394.2]? Equivalent width of Boo-127;
milli-Angstroms
50 A1 --- f_EW-127 [s] s: Flag indicating spectrum synthesis used
52 A1 --- l_loge-127 Limit flag on loge-127
53- 57 F5.2 [Sun] loge-127 [-0.7/6.4]? Log abundance in Boo-127
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 26-Sep-2016