J/ApJ/954/55 Abundances of member stars of the Sextans dSph (Roederer+, 2023)
Abundance analysis of stars at large radius in the Sextans dwarf spheroidal
galaxy.
Roederer I.U., Pace A.B., Placco V.M., Caldwell N., Koposov S.E., Mateo M.,
Olszewski E.W., Walker M.G.
<Astrophys. J. 954, 55 (2023)>
=2023ApJ...954...55R 2023ApJ...954...55R (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, dwarf; Spectra, optical; Abundances; Equivalent widths;
Reddening
Keywords: Dwarf spheroidal galaxies; Nucleosynthesis; Stellar abundances
Abstract:
We present the stellar parameters and chemical abundances of
30 elements for five stars located at large radii (3.5-10.7 times the
half-light radius) in the Sextans dwarf spheroidal galaxy. We selected
these stars using proper motions, radial velocities, and
metallicities, and we confirm them as metal-poor members of Sextans
with -3.34≤[Fe/H]≤-2.64 using high-resolution optical spectra
collected with the Magellan Inamori Kyocera Echelle spectrograph. Four
of the five stars exhibit normal abundances of C (-0.34≤[C/Fe]≤+0.36),
mild enhancement of the α elements Mg, Si, Ca, and Ti
([α/Fe]=+0.12±0.03), and unremarkable abundances of Na, Al, K,
Sc, V, Cr, Mn, Co, Ni, and Zn. We identify three chemical signatures
previously unknown among stars in Sextans. One star exhibits large
overabundances ([X/Fe]>+1.2) of C, N, O, Na, Mg, Si, and K, and large
deficiencies of heavy elements ([Sr/Fe]=-2.37±0.25,
[Ba/Fe]=-1.45±0.20, [Eu/Fe]<+0.05), establishing it as a member of
the class of carbon-enhanced metal-poor stars with no enhancement of
neutron-capture elements. Three stars exhibit moderate enhancements of
Eu (+0.17≤[Eu/Fe]≤+0.70), and the abundance ratios among
12 neutron-capture elements are indicative of r-process
nucleosynthesis. Another star is highly enhanced in Sr relative to
heavier elements ([Sr/Ba]=+1.21±0.25). These chemical signatures can
all be attributed to massive, low-metallicity stars or their end
states. Our results, the first for stars at large radius in Sextans,
demonstrate that these stars were formed in chemically inhomogeneous
regions, such as those found in ultra- faint dwarf galaxies.
Description:
Our targets were selected as confirmed members in radial velocity
surveys (Pace+ 2023, in preparation) or from a proper-motion-based
selection (Pace+ 2022ApJ...940..136P 2022ApJ...940..136P) using Gaia's EDR3.
See Section 2.1.
We used the Magellan Inamori Kyocera Echelle (MIKE) spectrograph on
the Landon Clay (Magellan II) Telescope at Las Campanas Observatory,
Chile, to collect high-resolution spectra of seven stars in Sextans.
These spectra were obtained on several nights in 2021 and 2022, with a
spectral resolving power of R∼41000 on the blue spectrograph
(3350<λ<5000Å) and R∼36000 on the red spectrograph
(5000<λ<9150Å).
Objects:
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RA (ICRS) DE Designation(s)
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10 13 02.89 -01 36 53.0 Sextans = NAME Sextans Dwarf Spheroidal
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File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 127 7 Star names, coordinates, photometry, and reddening
table4.dat 133 351 Line atomic data and derived abundances
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See also:
I/350 : Gaia EDR3 (Gaia Collaboration, 2020)
V/154 : Sloan Digital Sky Surveys (SDSS), Release 16 (DR16) (Ahumada+, 2020)
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
J/AJ/90/2221 : UMi dwarf galaxy BV photometry (Olszewski+, 1985)
J/A+A/416/1117 : Abundances in the early Galaxy (Cayrel+, 2004)
J/A+A/435/373 : Broadening of Fe II lines by H collisions (Barklem+, 2005)
J/AJ/131/375 : Phot. and velocities of Sculptor dSph giants (Westfall+, 2006)
J/ApJS/162/227 : Transition probabilities for SmII (Lawler+, 2006)
J/ApJ/667/1267 : CrI transition probabilities (Sobeck+, 2007)
J/ApJ/681/1524 : Detailed abundances for 28 metal-poor stars (Lai+, 2008)
J/AJ/137/3100 : Radial velocities of 4 dSph galaxies (Walker+, 2009)
J/ApJS/182/51 : Transition prob. of rare earth elements (Lawler+, 2009)
J/ApJS/182/80 : Rare earth abundances (Sneden+, 2009)
J/A+A/503/541 : Li in late-type stars non-LTE calculations (Lind+, 2009)
J/A+A/522/A26 : Fe Abundances in metal-poor stars (Sbordone+ 2010)
J/ApJ/724/341 : Nucleosynthesis of massive metal-free stars (Heger+, 2010)
J/ApJ/724/975 : Heavy elements abund. of metal-poor stars (Roederer+, 2010)
J/MNRAS/411/1013 : CaII triplet in Sextans dSph galaxy (Battaglia+, 2011)
J/ApJS/194/35 : Atomic transition probabilities of Mn (Den Hartog+, 2011)
J/ApJ/750/76 : r-process peaks elements in HD 160617 (Roederer+, 2012)
J/ApJ/769/57 : Equivalent widths of metal-poor stars (Frebel+, 2013)
J/ApJS/211/20 : NiI transition probability measurements (Wood+, 2014)
J/AJ/147/136 : Stars of very low metal abundance. VI. (Roederer+, 2014)
J/MNRAS/441/3127 : FeI oscillator strengths for Gaia-ESO (Ruffoni+, 2014)
J/ApJS/215/20 : Vanadium log(gf) and transition probabilities (Lawler+, 2014)
J/ApJS/220/13 : Co I transition probabilities (Lawler+, 2015)
J/MNRAS/460/30 : gi photometry of Sextans dSph galaxy stars (Roderick+, 2016)
J/ApJS/228/10 : Transition prob. for 183 lines of Cr II (Lawler+, 2017)
J/A+A/609/A53 : Tracing stars of MW dwarf galaxies: Sextans (Cicuendez+, 2018)
J/ApJ/860/125 : Six warm metal-poor stars iron abundances (Roederer+, 2018)
J/A+A/616/A12 : Gaia DR2 sources in GC and dSph (Gaia Collaboration+, 2018)
J/ApJS/249/30 : R-Process Alliance: metal-poor star sp. (Holmbeck+, 2020)
J/A+A/641/A127 : 13 dsph and ultra-faint galaxies analysis (Reichert+, 2020)
J/A+A/642/A176 : Chemical evolution of dSph galaxy Sextans (Theler+, 2020)
J/ApJ/953/31 : Abund. in warm VMP stars from Keck/HIRES sp. (Sneden+, 2023)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 A4 --- SNR Signal-to-noise ratio (1)
6- 24 I19 --- GaiaEDR3 Gaia EDR3 identifier
26- 44 A19 --- SDSS SDSS DR13 name (JHHMMSS.ss+DDMMSS.s)
46- 55 A10 --- OID Other identifier (abbreviated name)
57- 58 I2 h RAh Hour of right ascension (J2000)
60- 61 I2 min RAm Minute of right ascension (J2000)
63- 67 F5.2 s RAs Second of right ascension (J2000)
69 A1 --- DE- Sign of declination (J2000)
70- 71 I2 deg DEd Degree of declination (J2000)
73- 74 I2 arcmin DEm Arcminute of declination (J2000)
76- 79 F4.1 arcsec DEs Arcsecond of declination (J2000)
81- 85 F5.2 --- Re/Rh [3.04/10.68] Re to Rh ratio (2)
87- 91 F5.2 mag Gmag [16.75/18.49] Gaia G-band magnitude
93- 97 F5.2 mag gmag [17.86/18.8] SDSS g-band magnitude
99- 103 F5.2 mag Bmag [18.48/19.38] B magnitude (3)
105- 109 F5.2 mag Vmag [17.27/18.27] V magnitude (3)
111- 115 F5.3 mag E(B-V)SF [0.027/0.043] Reddening from dust maps in
Schlafly & Finkbeiner (2011ApJ...737..103S 2011ApJ...737..103S)
117 A1 --- l_E(B-V)Na Limit flag on E(B-V)Na
118- 122 F5.3 mag E(B-V)Na [0.01/0.07]? Reddening from the interstellar
NaI D absorption
124- 127 F4.2 mag E(B-V) [0.02/0.05]? Adopted reddening
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Note (1): Star sample as follows:
High = Stars with high-S/N observations
Low = Stars with low-S/N observations
Note (2): We focused on bright and distant (Re/Rh≳3) stars, where
Re=(x2+y2/q2)0.5 is the deprojected elliptical radius, and Rh
is the Sextans half-light radius.
Note (3): The B and V magnitudes are calculated from the SDSS g magnitude using
the Population II star transformations of Jordi+ (2006A&A...460..339J 2006A&A...460..339J).
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 A4 --- Ion Species
6- 12 F7.2 0.1nm lambda [3907/8807] Wavelength in Angstroms
14- 17 F4.2 eV ExPot [0/6.21] Excitation potential
19- 24 F6.2 [-] loggf [-10.3/0.7] Log of degeneracy times
oscillator strength
26- 29 F4.2 [-] e_loggf [0.01/0.3] Mean error on log of
degeneracy times oscillator strength
31- 32 I2 --- r_loggf [1/36] Reference for log of degeneracy
times oscillator strength (1)
34- 38 F5.1 0.1pm EWJ1008+0001 ? Equivalent width in milli Angstroms
for star J1008+0001
40 A1 --- l_logeJ1008+0001 ? Limit on log epsilon abundance for
star J1008+0001
42- 46 F5.2 [-] logeJ1008+0001 [-2.5/8.1]? Log epsilon abundance
for star J1008+0001
48- 52 F5.2 --- NLTEcJ1008+0001 ? NLTE correction to log epsilon
abundance for star J1008+0001
54- 58 F5.1 0.1pm EWJ1010-0220 ? Equivalent width in milli Angstroms
for star J1010-0220
60 A1 --- l_logeJ1010-0220 ? Limit on log epsilon abundance for
star J1010-0220
62- 66 F5.2 [-] logeJ1010-0220 [-2.3/6.7]? Log epsilon abundance for
star J1010-0220
68- 72 F5.2 --- NLTEcJ1010-0220 ? NLTE correction to log epsilon
abundance for star J1010-0220
74- 78 F5.1 0.1pm EWJ1015-0238 ? Equivalent width in milli Angstroms
for star JJ1015-0238
80 A1 --- l_logeJ1015-0238 ? Limit on log epsilon abundance for
star JJ1015-0238
82- 86 F5.2 [-] logeJ1015-0238 [-2.7/6.7]? Log epsilon abundance for
star JJ1015-0238
88- 92 F5.2 --- NLTEcJ1015-0238 ? NLTE correction to log epsilon
abundance for star JJ1015-0238
94- 98 F5.1 0.1pm EWJ1018-0155 ? Equivalent width in milli Angstroms
for star J1018-0155
100 A1 --- l_logeJ1018-0155 ? Limit on log epsilon abundance for
star J1018-0155
102- 106 F5.2 [-] logeJ1018-0155 [-2.01/6.8]? Log epsilon abundance for
star J1018-0155
108- 112 F5.2 --- NLTEcJ1018-0155 ? NLTE correction to log epsilon
abundance for star J1018-0155
114- 118 F5.1 0.1pm EWJ1018-0209 ? Equivalent width in milli Angstroms
for star J1018-0209
120 A1 --- l_logeJ1018-0209 ? Limit on log epsilon abundance for
star J1018-0209
122- 126 F5.2 [-] logeJ1018-0209 [-2.14/6.9]? Log epsilon abundance for
star J1018-0209
128- 133 F6.3 --- NLTEcJ1018-0209 ? NLTE correction to log epsilon
abundance for star J1018-0209
--------------------------------------------------------------------------------
Note (1): References for log of degeneracy times oscillator strength --
1 = Smith+ 1998ApJ...506..405S 1998ApJ...506..405S, using HFS from Kurucz 2011CaJPh..89..417K 2011CaJPh..89..417K
2 = Kramida+ 2020, Version 5.9; http://physics.nist.gov/asd
3 = Pehlivan Rhodin+ 2017A&A...598A.102P 2017A&A...598A.102P
4 = Kramida+ 2020, Version 5.9; http://physics.nist.gov/asd,
using HFS from VALD3 (Piskunov+ 1995A&AS..112..525P 1995A&AS..112..525P,
Pakhomov+ 2019ARep...63.1010P 2019ARep...63.1010P)
5 = Den Hartog+ 2023ApJS..265...42D 2023ApJS..265...42D
6 = Den Hartog+ 2021ApJS..255...27D 2021ApJS..255...27D
7 = Lawler & Dakin 1989JOSAB...6.1457L 1989JOSAB...6.1457L,
using HFS from Kurucz 2011CaJPh..89..417K 2011CaJPh..89..417K
8 = Lawler+ 2013ApJS..205...11L 2013ApJS..205...11L
9 = Pickering+ 2001ApJS..132..403P 2001ApJS..132..403P,
using corrections given in Pickering+ 2002ApJS..138..247P 2002ApJS..138..247P
10 = Wood+ 2013ApJS..208...27W 2013ApJS..208...27W
11 = Lawler+ 2014ApJS..215...20L 2014ApJS..215...20L, including HFS
12 = Wood+ 2014ApJS..214...18W 2014ApJS..214...18W, including HFS
13 = Sobeck+ 2007ApJ...667.1267S 2007ApJ...667.1267S
14 = Lawler+ 2017ApJS..228...10L 2017ApJS..228...10L
15 = Den Hartog+ 2011ApJS..194...35D 2011ApJS..194...35D, including HFS
16 = O'Brian+ 1991JOSAB...8.1185O 1991JOSAB...8.1185O
17 = Den Hartog+ 2014ApJS..215...23D 2014ApJS..215...23D
18 = Ruffoni+ 2014MNRAS.441.3127R 2014MNRAS.441.3127R
19 = Belmonte+ 2017ApJ...848..125B 2017ApJ...848..125B
20 = Blackwell+ 1982MNRAS.199...43B 1982MNRAS.199...43B
21 = Melendez & Barbuy 2009A&A...497..611M 2009A&A...497..611M
22 = Den Hartog+ 2019ApJS..243...33D 2019ApJS..243...33D
23 = Lawler+ 2015ApJS..220...13L 2015ApJS..220...13L, including HFS
24 = Wood+ 2014ApJS..211...20W 2014ApJS..211...20W
25 = Roederer & Lawler 2012ApJ...750...76R 2012ApJ...750...76R
26 = Biemont+ 2011MNRAS.414.3350B 2011MNRAS.414.3350B
27 = Ljung+ 2006A&A...456.1181L 2006A&A...456.1181L
28 = Kramida+ Version 5.9; http://physics.nist.gov/asd,
using HFS/IS from McWilliam 1998AJ....115.1640M 1998AJ....115.1640M
or other sources when available
29 = Lawler+ 2001ApJ...556..452L 2001ApJ...556..452L,
using HFS from Ivans+ 2006ApJ...645..613I 2006ApJ...645..613I when available
30 = Lawler+ 2009ApJS..182...51L 2009ApJS..182...51L
31 = Li+ 2007PhyS...76..577L 2007PhyS...76..577L,
using HFS from Sneden+ 2009ApJS..182...80S 2009ApJS..182...80S
32 = Den Hartog+ 2003ApJS..148..543D 2003ApJS..148..543D
33 = Lawler+ 2006ApJS..162..227L 2006ApJS..162..227L,
using HFS/IS from Roederer+ 2008ApJ...675..723R 2008ApJ...675..723R
34 = Lawler+ 2001ApJ...563.1075L 2001ApJ...563.1075L,
using HFS/IS from Ivans+ 2006ApJ...645..613I 2006ApJ...645..613I
35 = Wickliffe+ 2000JQSRT..66..363W 2000JQSRT..66..363W
36 = Biemont+ 2000MNRAS.312..116B 2000MNRAS.312..116B,
using HFS/IS from Roederer+ 2012ApJS..203...27R 2012ApJS..203...27R
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History:
From electronic version of the journal
License: cc-by
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 04-Nov-2025