J/ApJ/830/93 Abundances of the Ret II brightest red giant members (Ji+, 2016)
Complete element abundances of nine stars in the r-process galaxy Reticulum II.
Ji A.P., Frebel A., Simon J.D., Chiti A.
<Astrophys. J., 830, 93-93 (2016)>
=2016ApJ...830...93J 2016ApJ...830...93J (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Spectroscopy ; Stars, giant ; Abundances ;
Radial velocities ; Equivalent widths
Keywords: galaxies: dwarf; galaxies: individual: Ret II; Local Group;
nuclear reactions, nucleosynthesis, abundances; stars: abundances
Abstract:
We present chemical abundances derived from high-resolution
Magellan/Magellan Inamori Kyocera Echelle spectra of the nine
brightest known red giant members of the ultra-faint dwarf galaxy
Reticulum II (Ret II). These stars span the full metallicity range of
Ret II (-3.5<[Fe/H]< -2). Seven of the nine stars have extremely high
levels of r-process material ([Eu/Fe]∼1.7), in contrast to the
extremely low neutron-capture element abundances found in every other
ultra-faint dwarf galaxy studied to date. The other two stars are the
most metal-poor stars in the system ([Fe/H]< -3), and they have
neutron-capture element abundance limits similar to those in other
ultra-faint dwarf galaxies. We confirm that the relative abundances of
Sr, Y, and Zr in these stars are similar to those found in r-process
halo stars, but they are ∼0.5dex lower than the solar r-process
pattern. If the universal r-process pattern extends to those elements,
the stars in Ret II display the least contaminated known r-process
pattern. The abundances of lighter elements up to the iron peak are
otherwise similar to abundances of stars in the halo and in other
ultra-faint dwarf galaxies. However, the scatter in abundance ratios
is large enough to suggest that inhomogeneous metal mixing is required
to explain the chemical evolution of this galaxy. The presence of low
amounts of neutron-capture elements in other ultra-faint dwarf
galaxies may imply the existence of additional r-process sites besides
the source of r-process elements in Ret II. Galaxies like Ret II may
be the original birth sites of r-process enhanced stars now found in
the halo.
Description:
On 2015 October 1-4 we obtained high-resolution spectra of the
brightest nine confirmed members in Reticulum II. We used the Magellan
Inamori Kyocera Echelle (MIKE) spectrograph on the Magellan-Clay
telescope with a 1.0" slit, which provides a spectral resolution of
∼22000 and ∼28000 at red and blue wavelengths, respectively.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 80 9 *Observed stars and stellar parameters
table2.dat 161 396 Equivalent widths
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Note on table1.dat: All stars were observed with a 1.0" slit. Stars are
ordered by brightness.
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See also:
J/ApJ/808/108 : M2FS stellar spectroscopy of Reticulum 2 (Walker+, 2015)
J/ApJ/808/95 : Spectroscopy of Reticulum II (Simon+, 2015)
J/ApJ/807/171 : SkyMapper Survey metal-poor star spectrosc. (Jacobson+, 2015)
J/A+A/571/A47 : Linelist of CH in stellar atmospheres (Masseron+, 2014)
J/AJ/147/136 : Stars of very low metal abundance. VI. (Roederer+, 2014)
J/ApJ/779/102 : Metallicities of RGB stars in dwarf galaxies (Kirby+, 2013)
J/ApJ/767/134 : Abundances of red giant stars in UFD galaxies (Vargas+, 2013)
J/AJ/144/4 : Dwarf galaxies in the Local Group (McConnachie+, 2012)
J/ApJS/182/80 : Rare earth abundances (Sneden+, 2009)
J/ApJS/162/227 : Transition probabilities for SmII (Lawler+, 2006)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- --- [DES]
5- 18 A14 --- DES Star identifier (JHHMMSS+DDMMSS)
20- 22 I3 min Exp [58/220] Exposure time
24- 28 F5.2 mag Vmag [16/18.7] V-band magnitude (1)
30- 31 I2 --- S/N4 [7/22] Signal to noise ratio per pixel
at 4250Å
33- 34 I2 --- S/N6 [13/47] Signal to noise ratio per pixel
at 6000Å
36- 39 F4.1 km/s HRV [60.9/71.6] Heliocentric velocity
41- 43 F3.1 km/s e_HRV [0.1/0.3] HRV uncertainty (2)
45- 48 I4 K Teff [4608/5395] Effective temperature
50- 52 I3 K e_Teff [157/258] Teff uncertainty (3)
54- 57 F4.2 [cm/s2] logg [1/3.1] Log of surface gravity
59- 62 F4.2 [cm/s2] e_logg [0.3/0.4] logg uncertainty (3)
64- 67 F4.2 km/s Vt [1.3/2.4] Microturbulence velocity
69- 72 F4.2 km/s e_Vt [0.2/0.5] Vt uncertainty (3)
74- 78 F5.2 [Sun] [Fe/H] [-3.6/-2] Metallicity
80 A1 --- ID Letter used as identifier in table 2;
column added by CDS
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Note (1): V magnitudes were found with the conversion in
Bechtol+ (2015ApJ...807...50B 2015ApJ...807...50B).
Note (2): Velocity error is from FWHM of cross-correlation.
Note (3): See Ji+ (2016Natur.531..610J 2016Natur.531..610J) for stellar parameter uncertainty
breakdown.
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Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- Ion Molecule or Ion identifier
7- 13 F7.2 0.1nm lambda [3743.3/6678] Wavelength in 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- 30 F5.1 10-13m EW-A [17/179]? DES J033523-540407 equivalent width
in milli-Angstroms
32 A1 --- f_EW-A s=abundance determined with spectrum synthesis
34- 38 F5.2 [-] loge-A [-1.1/6.1]? DES J033523-540407 log abundance
40- 44 F5.1 10-13m EW-B [14/188]? DES J033607-540235 equivalent width
in milli-Angstroms
46 A1 --- f_EW-B s=abundance determined with spectrum synthesis
48- 52 F5.2 [-] loge-B [-0.9/5.9]? DES J033607-540235 log abundance
54- 58 F5.1 10-13m EW-C [19/236]? DES J033447-540525 equivalent width
in milli-Angstroms
60 A1 --- f_EW-C s=abundance determined with spectrum synthesis
62- 66 F5.2 [-] loge-C [-0.8/5.8]? DES J033447-540525 log abundance
68- 72 F5.1 10-13m EW-D [17/200]? DES J033531-540148 equivalent width
in milli-Angstroms
74 A1 --- f_EW-D s=abundance determined with spectrum synthesis
76 A1 --- l_loge-D Limit flag on loge-D
77- 81 F5.2 [-] loge-D [-2/5.4]? DES J033531-540148 log abundance
83 A1 --- l_EW-E Limit flag on EW-E
84- 88 F5.1 10-13m EW-E [20/218]? DES J033548-540349 equivalent width
in milli-Angstroms
90 A1 --- f_EW-E s=abundance determined with spectrum synthesis
92 A1 --- l_loge-E Limit flag on loge-E
93- 97 F5.2 [-] loge-E [-0.9/6.8]? DES J033548-540349 log abundance
99 A1 --- l_EW-F Limit flag on EW-F
100-104 F5.1 10-13m EW-F [36/193]? DES J033537-540401 equivalent width
in milli-Angstroms
106 A1 --- f_EW-F s=abundance determined with spectrum synthesis
108 A1 --- l_loge-F Limit flag on loge-F
109-113 F5.2 [-] loge-F [-0.6/6]? DES J033537-540401 log abundance
115 A1 --- l_EW-G Limit flag on EW-G
116-120 F5.1 10-13m EW-G [16/187]? DES J033556-540316 equivalent width
in milli-Angstroms
122 A1 --- f_EW-G s=abundance determined with spectrum synthesis
124 A1 --- l_loge-G Limit flag on loge-G
125-129 F5.2 [-] loge-G [-1.3/6.1]? DES J033556-540316 log abundance
131 A1 --- l_EW-H Limit flag on EW-H
132-136 F5.1 10-13m EW-H [32/194]? DES J033457-540531 equivalent width
in milli-Angstroms
138 A1 --- f_EW-H s=abundance determined with spectrum synthesis
140 A1 --- l_loge-H Limit flag on loge-H
141-145 F5.2 [-] loge-H [-0.06/6.7]? DES J033457-540531 log abundance
147 A1 --- l_EW-I Limit flag on EW-I
148-152 F5.1 10-13m EW-I [40/203]? DES J033454-540558 equivalent width
in milli-Angstroms
154 A1 --- f_EW-I s=abundance determined with spectrum synthesis
156 A1 --- l_loge-I Limit flag on loge-I
157-161 F5.2 [-] loge-I [-0.2/7.3]? DES J033454-540558 log abundance
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 18-Jan-2017