J/A+A/642/A176 Chemical evolution of dSph galaxy Sextans (Theler+, 2020)
The chemical evolution of the dwarf spheroidal galaxy Sextans.
Theler R., Jablonka P., Lucchesi R., Lardo C., North P., Irwin M.,
Battaglia G., Hill V., Tolstoy E., Venn K., Helmi A., Kaufer A., Primas F.,
Shetrone M.
<Astron. Astrophys. 642, A176 (2020)>
=2020A&A...642A.176T 2020A&A...642A.176T (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Abundances ; Equivalent widths ;
Radial velocities ; Effective temperatures
Keywords: stars: abundances - galaxies: dwarf - galaxies: evolution
Abstract:
We present our analysis of the FLAMES dataset targeting the central
25' region of the Sextans dwarf spheroidal galaxy (dSph). This
dataset is the third major part of the high-resolution spectroscopic
section of the ESO large program 171.B-0588(A) obtained by the Dwarf
galaxy Abundances and Radial-velocities Team (DART). Our sample is
composed of red giant branch stars down to V∼20.5mag, the level of the
horizontal branch in Sextans, and allows users to address questions
related to both stellar nucleosynthesis and galaxy evolution.
We provide metallicities for 81 stars, which cover the wide
[Fe/H]=-3.2 to -1.5dex range. The abundances of ten other
elements are derived: Mg, Ca, Ti, Sc, Cr, Mn, Co, Ni, Ba, and Eu.
Despite its small mass, Sextans is a chemically evolved system,
showing evidence of a contribution from core-collapse and Type Ia
supernovae as well as low-metallicity asymptotic giant branch stars
(AGBs). This new FLAMES sample offers a sufficiently large number of
stars with chemical abundances derived with high accuracy to firmly
establish the existence of a plateau in [alpha/Fe] at ∼0.4dex followed
by a decrease above [Fe/H]~-2dex. These features reveal a close
similarity with the Fornax and Sculptor dSphs despite their very
different masses and star formation histories, suggesting that these
three galaxies had very similar star formation efficiencies in their
early formation phases, probably driven by the early accretion of
smaller galactic fragments, until the UV-background heating impacted
them in different ways. The parallel between the Sculptor and Sextans
dSph is also striking when considering Ba and Eu. The same chemical
trends can be seen in the metallicity region common to both galaxies,
implying similar fractions of SNeIa and low-metallicity AGBs. Finally,
as to the iron-peak elements, the decline of [Co/Fe] and [Ni/Fe] above
[Fe/H]~-2 implies that the production yields of Ni and Co in SNeIa are
lower than that of Fe. The decrease in [Ni/Fe] favours models of SNeIa
based on the explosion of double-degenerate sub-Chandrasekhar mass
white dwarfs.
Description:
Our targets are RGBs located in the central 250 field of the Sextans
dSph.
We gathered high-resolution (R∼20000) spectra of 101 stars in the HR10,
HR13, and H14 gratings of the multi-fibre spectrograph FLAMES/GIRAFFE
installed at the VLT (ESO Program 171.B-0588(A)). The observations
were conducted in three runs from March to December 2004.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 113 112 Position, photometry and radial velocities
of our targets
table3.dat 65 89 Parameters derived from photometry for the
probable members of our sample
table4.dat 66 110 The radial velocities measured by DAOSPEC in each
of the HR10, HR13, HR14 setups, and their average
table5.dat 44 205 Equivalent widths of the stars observed with UVES
table6.dat 33 89 Four stellar parameters for the probables members
of our sample
table9.dat 42 268 Complete line list used to derive all the atomic
abundances
table10.dat 86 87 *Atomic abundances for Fe, Mg, Ca and Sc
table11.dat 91 87 *Atomic abundances for TiI, TiII, Cr and Mn
table12.dat 81 87 *Atomic abundances for TiI, TiII, Cr and Mn
table13.dat 131 120 Equivalent widths of the GIRAFFE sample
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Note on table10.dat, table11.dat, table12.dat: The solar abundances are from
Grevesse & Sauval, 1998SSRv...85..161G 1998SSRv...85..161G.
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See also:
J/AJ/126/2840 : BVI CCD photometry of Sextans dSph galaxy (Lee+, 2003)
J/MNRAS/411/1013 : CaII triplet in Sextans dSph galaxy (Battaglia+, 2011)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 7 A7 --- ID Star ID
9- 10 I2 h RAh Right ascension (J2000)
12- 13 I2 min RAm Right ascension (J2000)
15- 18 F4.1 s RAs Right ascension (J2000)
20 A1 ---- DE- Declination sign (J2000)
21- 22 I2 deg DEd Declination (J2000)
24- 25 I2 arcmin DEm Declination (J2000)
27- 30 F4.1 arcsec DEs Declination (J2000)
32- 36 F5.2 mag Vmag ESO/WFI V magnitude
38- 42 F5.2 mag Imag ESO/WFI I magnitude
44- 48 F5.2 mag Jmag UKIRT/WFCAM J magnitude
50- 54 F5.2 mag Hmag UKIRT/WFCAM H magnitude
56- 60 F5.2 mag Kmag ?=0 UKIRT/WFCAM K magnitude
62 A1 --- l_RV [~] Limit flag on RV, for probable binaries (1)
63- 68 F6.2 km/s RV Mean radial velocity (1)
70- 73 F4.2 km/s e_RV rms uncertainty on mean radial velocity
75-113 A39 --- Com Comments (2)
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Note (1): The radial velocities were determined using cross-correlation with an
input line list thanks to the program DAOSPEC Stetson & Pancino
(2008PASP..120.1332S 2008PASP..120.1332S). The radial velocities given here are the average
between the three values obtained in each grating, therefore we add a tilde
in the case of probable binaries.
Note (2): We comment on particularities noticed for some stars of our sample :
non-member, binary, polluted spectra (by a calibration lamp), carbon star,
or incomplete spectra.
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Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- ID Star ID
9- 12 I4 K T(V-I) [4011/5116] Effective temperature from V-I
14- 17 I4 K T(V-J) [4179/5428] Effective temperature from V-J
19- 22 I4 K T(V-H) [4026/5244] Effective temperature from V-H
24- 27 I4 K T(V-K) [4199/5725]?=0 Effective temperature from V-H
29- 33 F5.2 mag BCV Bolometric correction
35- 39 F5.2 mag Mbol Bolometric magnitude
41- 45 F5.2 [-] [Fe/H](CaT) Initial metallicity estimate from CaT
47- 50 F4.2 [-] e_[Fe/H](CaT) ? rms uncertainty on [Fe/H](CaT)
52- 53 I2 --- S/NHR10 [0/96] SNR in HR10 grism
55- 57 I3 --- S/NHR13 [0/141] SNR in HR13
59- 61 I3 --- S/NHR14 [0/144] SNR in HR14
63- 65 I3 --- S/Nav [5/117] Average Signal-to-noise ratio
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- ID Star ID
10- 15 F6.2 km/s RVHR10 ?=0 Radial velocity in HR10
17- 20 F4.2 km/s e_RVHR10 ?=0 rms uncertainty on RVHR10
22- 23 I2 --- o_RVHR10 ?=0 Number of used lines in HR10
25- 30 F6.2 km/s RVHR13 ?=0 Radial velocity in HR13
32- 35 F4.2 km/s e_RVHR13 ?=0 rms uncertainty on RVHR13
37- 38 I2 --- o_RVHR13 ?=0 Number of used lines in HR13
40- 45 F6.2 km/s RVHR14 ?=0 Radial velocity in HR14
47- 50 F4.2 km/s e_RVHR14 ?=0 rms uncertainty on RVHR14
52- 53 I2 --- o_RVHR14 ?=0 Number of used lines in HR14
55 A1 --- l_RVmean [~] Limit flag on RVmean (1)
56- 61 F6.2 km/s RVmean Mean radial velocity in HR10
63- 66 F4.2 km/s e_RVmean rms uncertainty on RVHR10
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Note (1): Probable binaries are indicated by a tilde symbol.
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Byte-by-byte Description of file: table5.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 F7.2 0.1nm lambda Wavelength
9- 12 A4 --- El Element
14- 17 F4.2 eV chiex Excitation potential
19- 23 F5.2 [-] log(gf) Oscillator strength
25- 27 I3 0.1nm EW1 ? S05-5 equivalent width
29- 32 F4.1 0.1nm e_EW1 ? rms uncertainty on EW1
33 A1 --- n_EW1 [*] Note on EW1 (1)
36- 38 I3 0.1nm EW2 ? S08-229 equivalent width
40- 43 F4.1 0.1nm e_EW2 ? rms uncertainty on EW2
44 A1 --- n_EW2 [*] Note on EW2 (1)
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Note (1): The asterisk indicates lines with equivalent widths >180Å which
were not considered in the analysis.
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- ID Star ID
9- 12 I4 K Teff Effective temperature
14- 17 F4.2 [cm/s2] logg Surface gravity
19- 22 F4.2 km/s vturb Micro-turbulence velocity
24- 28 F5.2 [-] [Fe/H] Metallicity
30- 33 F4.2 [-] e_[Fe/H] ? rms uncertainty on [Fe/H]
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Byte-by-byte Description of file: table9.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 F8.3 0.1nm lambda Wavelength
10- 13 A4 --- El Element
15- 20 A6 --- n_El Note on El (1)
22- 26 F5.3 eV chiex Excitation potential
28- 33 F6.3 [-] log(gf) Oscillator strength
35- 42 E8.3 --- C6 C6 constant
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Note (1): The hyperfine components are indicated with * and their corresponding
equivalent lines are followed by (equi).
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Byte-by-byte Description of file: table10.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- ID Star ID
8 A1 --- n_ID [*] Note (1)
10- 14 F5.2 [-] [Fe/H] Metallicity with solar abundance
logε(X)☉=7.50
16- 19 F4.2 [-] e_[Fe/H] Systematic error on [Fe/H]
21- 24 F4.2 [-] er_[Fe/H] Random error on [Fe/H]
26 A1 --- --- [(]
27- 28 I2 --- o_[Fe/H] Number of lines used to determined [Fe/H]
abundance
29 A1 --- --- [)]
31- 35 F5.2 [-] [Mg/Fe] ? Abundance [Mg/Fe] with solar abundance
logε(X)☉=7.58
37- 40 F4.2 [-] e_[Mg/Fe] ? Systematic error on [Mg/Fe]
42- 45 F4.2 [-] er_[Mg/Fe] ? Random error on [Mg/Fe]
47- 51 F5.2 [-] [Ca/Fe] ? Abundance [Ca/Fe] with solar abundance
logε(X)☉=6.36
53- 56 F4.2 [-] e_[Ca/Fe] ? Systematic error on [Ca/Fe]
58- 61 F4.2 [-] er_[Ca/Fe] ? Random error on [Ca/Fe]
63 A1 --- --- [(]
64- 65 I2 --- o_[Ca/Fe] ? Number of lines used to determined [Ca/Fe]
abundance
66 A1 --- --- [)]
68- 72 F5.2 [-] [Sc/Fe] ? Abundance [Sc/Fe] with solar abundance
logε(X)☉=3.17
74- 77 F4.2 [-] e_[Sc/Fe] ? Systematic error on [Sc/Fe]
79- 82 F4.2 [-] er_[Sc/Fe] ? Random error on [Sc/Fe]
84 A1 --- --- [(]
85 I1 --- o_[Sc/Fe] ? Number of lines used to determined [Sc/Fe]
abundance
86 A1 --- --- [)]
--------------------------------------------------------------------------------
Note (1): The asterisks indicate stars with spectra at signal-to-noise ≤ 10.
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Byte-by-byte Description of file: table11.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- ID Star ID
8 A1 --- n_ID [*] Note (1)
10- 14 F5.2 [-] [TiI/Fe] ? Abundance [TiI/Fe] with solar abundance
logε(X)☉=5.02
16- 19 F4.2 [-] e_[TiI/Fe] ? Systematic error on [TiI/Fe]
21- 24 F4.2 [-] er_[TiI/Fe] ? Random error on [TiI/Fe]
26 A1 --- --- [(]
27 I1 --- o_[TiI/Fe] ? Number of lines used to determined [TiI/Fe]
abundance
28 A1 --- --- [)]
31- 35 F5.2 [-] [TiII/Fe] ? Abundance [TiII/Fe] with solar abundance
logε(X)☉=5.02
37- 40 F4.2 [-] e_[TiII/Fe] ? Systematic error on [TiII/Fe]
42- 45 F4.2 [-] er_[TiII/Fe] ? Random error on [TiII/Fe]
47 A1 --- --- [(]
48 I1 --- o_[TiII/Fe] ? Number of lines used to determined
[TiII/Fe] abundance
49 A1 --- --- [)]
52- 56 F5.2 [-] [Cr/Fe] ? Abundance [Cr/Fe] with solar abundance
logε(X)☉=5.67
58- 61 F4.2 [-] e_[Cr/Fe] ? Systematic error on [Cr/Fe]
63- 66 F4.2 [-] er_[Cr/Fe] ? Random error on [Cr/Fe]
68 A1 --- --- [(]
69 I1 --- o_[Cr/Fe] ? Number of lines used to determined [Cr/Fe]
abundance
70 A1 --- --- [)]
73- 77 F5.2 [-] [Mn/Fe] ? Abundance [Mn/Fe] with solar abundance
logε(X)☉=5.39
79- 82 F4.2 [-] e_[Mn/Fe] ? Systematic error on [Mn/Fe]
84- 87 F4.2 [-] er_[Mn/Fe] ? Random error on [Mn/Fe]
89 A1 --- --- [(]
90 I1 --- o_[Mn/Fe] ? Number of lines used to determined [Mn/Fe]
abundance
91 A1 --- --- [)]
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Note (1): The asterisks indicate stars with spectra at signal-to-noise ≤10.
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Byte-by-byte Description of file: table12.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- ID Star ID
8 A1 --- n_ID [*] Note (1)
11- 15 F5.2 [-] [Co/Fe] ? Abundance [Co/Fe] with solar abundance
logε(X)☉=4.92
17- 20 F4.2 [-] e_[Co/Fe] ? Systematic error on [Co/Fe]
22- 25 F4.2 [-] er_[Co/Fe] ? Random error on [Co/Fe]
27- 31 F5.2 [-] [NI/Fe] ? Abundance [TiII/Fe] with solar abundance
logε(X)☉=6.25
33- 36 F4.2 [-] e_[NI/Fe] ? Systematic error on [NI/Fe]
38- 41 F4.2 [-] er_[NI/Fe] ? Random error on [NI/Fe]
43 A1 --- --- [(]
44 I1 --- o_[NI/Fe] ? Number of lines used to determined [NI/Fe]
abundance
45 A1 --- --- [)]
47- 51 F5.2 [-] [Ba/Fe] ? Abundance [Ba/Fe] with solar abundance
logε(X)☉=2.13
53- 56 F4.2 [-] e_[Ba/Fe] ? Systematic error on [Ba/Fe]
58- 61 F4.2 [-] er_[Ba/Fe] ? Random error on [Ba/Fe]
63 A1 --- --- [(]
64 I1 --- o_[Ba/Fe] ? Number of lines used to determined [Ba/Fe]
abundance
65 A1 --- --- [)]
67- 71 F5.2 [-] [Eu/Fe] ? Abundance [Eu/Fe] with solar abundance
logε(X)☉=5.39
73- 76 F4.2 [-] e_[Eu/Fe] ? Systematic error on [Eu/Fe]
78- 81 F4.2 [-] er_[Eu/Fe] ? Random error on [Eu/Fe]
--------------------------------------------------------------------------------
Note (1): The asterisks indicate stars with spectra at signal-to-noise ≤10.
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Byte-by-byte Description of file: table13.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 F7.2 0.1nm lambda Wavelength
9- 12 A4 --- El Element
14- 17 F4.2 eV chiex Excitation potential
19- 23 F5.2 [-] log(gf) Oscillator strength
25- 27 I3 0.1nm EW1 ? S08-3 equivalent width
29- 32 F4.1 0.1nm e_EW1 ? S08-3 equivalent width error
33 A1 --- n_EW1 [*] Note on EW1 (1)
35- 37 I3 0.1nm EW2 ? S08-6 equivalent width
39- 42 F4.1 0.1nm e_EW2 ? S08-6 equivalent width error
43 A1 --- n_EW2 [*] Note on EW1 (1)
44- 46 I3 0.1nm EW3 ? S05-10 equivalent width
48- 51 F4.1 0.1nm e_EW3 ? S05-10 equivalent width error
52 A1 --- n_EW3 [*] Note on EW1 (1)
53- 55 I3 0.1nm EW4 ? S08-38 equivalent width
57- 60 F4.1 0.1nm e_EW4 ? S08-38 equivalent width error
61 A1 --- n_EW4 [*] Note on EW1 (1)
62- 64 I3 0.1nm EW5 ? S08-239 equivalent width
66- 69 F4.1 0.1nm e_EW5 ? S08-239 equivalent width error
70 A1 --- n_EW5 [*] Note on EW1 (1)
71- 73 I3 0.1nm EW6 ? S08-241 equivalent width
75- 77 F3.1 0.1nm e_EW6 ? s08-241 equivalent width error
78 A1 --- n_EW6 [*] Note on EW1 (1)
79- 81 I3 0.1nm EW7 ? S08-242 equivalent width
83- 86 F4.1 0.1nm e_EW7 ? S08-242 equivalent width error
87 A1 --- n_EW7 [*] Note on EW1 (1)
88- 90 I3 0.1nm EW8 ? S07-69 equivalent width
92- 95 F4.1 0.1nm e_EW8 ? S07-69 equivalent width error
96 A1 --- n_EW8 [*] Note on EW1 (1)
97- 99 I3 0.1nm EW9 ? S08-59 equivalent width
101-104 F4.1 0.1nm e_EW9 ? S08-59 equivalent width error
105 A1 --- n_EW9 [*] Note on EW1 (1)
106-108 I3 0.1nm EW10 ? S05-60 equivalent width
110-112 F3.1 0.1nm e_EW10 ? S05-60 equivalent width error
114-116 I3 0.1nm EW11 ? S08-246 equivalent width
118-121 F4.1 0.1nm e_EW11 ? S08-246 equivalent width error
122 A1 --- n_EW11 [*] Note on EW1 (1)
123-125 I3 0.1nm EW12 ? S08-183 equivalent width
127-130 F4.1 0.1nm e_EW12 ? S08-183 equivalent width error
131 A1 --- n_EW12 [*] Note on EW12 (1)
--------------------------------------------------------------------------------
Note (1): the asterisks indicate lines with equivalent widths >180Å,
which were not considered in the analysis (see Section 6.1).
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Acknowledgements:
Pascale Jablonka, pascale.jablonka(at)epfl.ch
(End) Patricia Vannier [CDS] 09-Jun-2020