J/ApJ/817/41 Abundances of 4 metal-poor red giants in BooII (Ji+, 2016)
High-resolution spectroscopy of extremely metal-poor stars in the least-evolved
galaxies: Bootes II.
Ji A.P., Frebel A., Simon J.D., Geha M.
<Astrophys. J., 817, 41 (2016)>
=2016ApJ...817...41J 2016ApJ...817...41J (SIMBAD/NED BibCode)
ADC_Keywords: Abundances ; Equivalent widths ; Stars, giant ; Galaxies, optical
Keywords: galaxies: dwarf ; galaxies: individual: Boo II;
Local Group; stars: abundances
Abstract:
We present high-resolution Magellan/MIKE spectra of the four brightest
confirmed red giant stars in the ultra-faint dwarf galaxy Bootes II
(Boo II). These stars all inhabit the metal-poor tail of the BooII
metallicity distribution function. The chemical abundance pattern of
all detectable elements in these stars is consistent with that of the
Galactic halo. However, all four stars have undetectable amounts of
neutron-capture elements Sr and Ba, with upper limits comparable to
the lowest ever detected in the halo or in other dwarf galaxies. One
star exhibits significant radial velocity variations over time,
suggesting it to be in a binary system. Its variable velocity has
likely increased past determinations of the Boo II velocity
dispersion. Our four stars span a limited metallicity range, but their
enhanced α-abundances and low neutron-capture abundances are
consistent with the interpretation that Boo II has been enriched by
very few generations of stars. The chemical abundance pattern in Boo
II confirms the emerging trend that the faintest dwarf galaxies have
neutron-capture abundances distinct from the halo, suggesting the
dominant source of neutron-capture elements in halo stars may be
different than in ultra-faint dwarfs.
Description:
A total of 16 Boo II member stars were identified with Keck/DEIMOS
observations (M. Geha et al. 2015, in preparation). We selected the
four brightest members on the red giant branch sample for
high-resolution follow-up (see Figure 1).
The four target stars were observed with the Magellan Inamori Kyocera
Echelle (MIKE) spectrograph on the Clay telescope in the full optical
wavelength range from 3500 to 9000Å in March 2010, 2011 and 2014
and in June 2015 (see table 1).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 104 4 Observing details
table2.dat 86 217 Equivalent Widths
table3.dat 49 4 Stellar parameters
table4.dat 40 65 Magellan/MIKE chemical abundances of Boo II stars
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See also:
V/139 : The SDSS Photometric Catalog, Release 9 (Adelman-McCarthy+, 2012)
J/ApJS/216/10 : DUSTiNGS. I. The Good Source Catalog (Boyer+, 2015)
J/MNRAS/440/2665 : SDSS J021933.13+200830.2 spectroscopy (Roederer+, 2014)
J/A+A/562/A146 : Chemical abundances of 8 metal-poor stars (Ishigaki+, 2014)
J/ApJ/779/102 : Metallicities of RGB stars in dwarf galaxies (Kirby+, 2013)
J/ApJ/769/57 : Equivalent widths of metal-poor stars (Frebel+, 2013)
J/ApJ/767/134 : Abundances of red giant stars in UFD galaxies (Vargas+, 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/AJ/144/4 : Dwarf galaxy data in the Local Group (McConnachie+, 2012)
J/ApJ/711/350 : Metal-poor giant Boo-1137 abundances (Norris+, 2010)
J/ApJ/655/492 : Equivalent widths of 26 metal-poor stars (Aoki+, 2007)
http://www.sdss.org/ : SDSS home page
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 A4 --- --- [SDSS]
6- 23 A18 --- Name SDSS truncated name (JHHMMSS.s+DDMMSS.s)
25- 26 I2 h RAh [13] Hour of right ascension (J2000)
28- 29 I2 min RAm [57/58] Minute of right ascension (J2000)
31- 34 F4.1 s RAs Second of right ascension (J2000)
36 A1 --- DE- [+] Sign of declination (J2000)
37- 38 I2 deg DEd [12] Degree of declination (J2000)
40- 41 I2 arcmin DEm [51/54] Arcminute of declination (J2000)
43- 46 F4.1 arcsec DEs Arcsecond of declination (J2000)
48- 77 A30 --- Date Observation date(s)
79- 81 F3.1 arcsec Slit [0.7/1] Slit width (1)
83- 86 F4.1 h Exp [5.8/12.2] Exposure time
88- 92 F5.2 mag gmag [19.2/19.6] g-band magnitude
94- 98 F5.2 mag Vmag [18.8/19.2] V-band magnitude (2)
100-101 I2 --- S/N [11/17] Signal to noise ratio at 5300Å (3)
103-104 I2 --- S/N6 [21/29] Signal to noise ratio at 6000Å (3)
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Note (1): A 1.0" slit leads to a spectral resolution of ∼22000 at red
wavelengths and ∼28000 at blue wavelengths. A 0.7" slit yields a
spectral resolution of ∼28000 and ∼35000 in the red and blue,
respectively.
Note (2): Converted from SDSS photometry using Schlafly & Finkbeiner
(2011ApJ...737..103S 2011ApJ...737..103S) and Jordi et al. (2006A&A...460..339J 2006A&A...460..339J).
Note (3): Signal-to-noise is per pixel.
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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 A5 --- Ion Element/Ion/Molecule designation
7- 13 F7.2 0.1nm lambda [3783.5/6678]? Wavelength; Angstroms
15- 18 F4.2 eV ExPot [0/4.4]? Excitation potential
20- 24 F5.2 [-] log(gf) [-5.7/0.7]? Log oscillator strength
26 A1 --- l_EW1 Limit flag on EW1
27- 31 F5.1 10-13m EW1 [15/197.2]? SDSS J135751.2+125137.0
equivalent width (in milli-Angstroms)
33 A1 --- f_EW1 [s] Flag on EW1 (1)
35 A1 --- l_loge1 Limit flag on loge1
36- 40 F5.2 [-] loge1 [-2.2/6]? SDSS J135751.2+125137.0 log abundance
42- 46 F5.1 10-13m EW2 [26/253]? SDSS J135759.7+125426.4
equivalent width (in milli-Angstroms)
48 A1 --- f_EW2 [s] Flag on EW2 (1)
50 A1 --- l_loge2 Limit flag on loge2
51- 55 F5.2 [-] loge2 [-2.2/6.2]? SDSS J135759.7+125426.4
log abundance
57- 61 F5.1 10-13m EW3 [19.5/194]? SDSS J135756.2+125207.7
equivalent width (in milli-Angstroms)
63 A1 --- f_EW3 [s] Flag on EW3 (1)
65 A1 --- l_loge3 Limit flag on loge3
66- 70 F5.2 [-] loge3 [-2.2/6]? SDSS J135756.2+125207.7 log abundance
72 A1 --- l_EW4 Limit flag on EW4
73- 77 F5.1 10-13m EW4 [21.6/160]? SDSS J135801.4+125105.2
equivalent width (in milli-Angstroms)
79 A1 --- f_EW4 [s] Flag on EW4 (1)
81 A1 --- l_loge4 Limit flag on loge4
82- 86 F5.2 [-] loge4 [-2/6.1]? SDSS J135801.4+125105.2 log abundance
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Note (1):
s = abundance determined with spectrum synthesis.
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 4 A4 --- --- [SDSS]
6- 23 A18 --- Name SDSS truncated name (JHHMMSS.s+DDMMSS.s)
25- 28 I4 K Teff [4936/5192] Effective temperature
30- 33 F4.2 [cm/s2] logg [1.8/2.6] Lof of surface gravity
35- 38 F4.2 km/s xi [1.6/2.1] Microturbulent velocity
40- 44 F5.2 [Sun] [Fe/H] [-3/-2.6] Metallicity [Fe/H]
46- 49 I4 K Tphot [5005/5217] Photometric temperature (4)
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Note (4): Using converted SDSS magnitudes and B-V calibration from
Alonso et al. (1999A&AS..140..261A 1999A&AS..140..261A).
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1 I1 --- Seq Stellar identifier code (1)
3- 7 A5 --- Ion Element/Ion/Molecule designation
9- 11 I3 --- N [1/109] Number of lines used in analysis
13 A1 --- l_loge Limit flag on loge
14- 18 F5.2 [-] loge [-2.3/6.2] Log number abundance
19 A1 --- u_loge [:] Uncertainty flag on loge; see text
21- 24 F4.2 [-] e_loge [0.1/0.5]? The 1σ uncertainty in loge
26 A1 --- l_[X/H] Limit flag on [X/H]
27- 31 F5.2 [-] [X/H] [-5.1/-1.1] Log abundance relative to hydrogen
32 A1 --- u_[X/H] [:] Uncertainty flag on [X/H]; see text
34 A1 --- l_[X/Fe] Limit flag on [X/Fe]
35- 39 F5.2 [-] [X/Fe] [-2.4/1.7] Log abundance relative to iron
40 A1 --- u_[X/Fe] [:] Uncertainty flag on [X/Fe]; see text
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Note (1): Code as follows:
1 = SDSS J135751.2+125137.0;
2 = SDSS J135759.7+125426.4;
3 = SDSS J135756.2+125207.7;
4 = SDSS J135801.4+125105.2.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 06-Apr-2016