J/A+A/631/A171 Neutron-capture elements in dwarf galaxies (Skuladottir+, 2019)
Neutron-capture elements in dwarf galaxies.
I. Chemical clocks and the short timescale of the r-process.
Skuladottir A., Hansen C.J, Salvadori S., Choplin A.
<Astron. Astrophys. 631, A171 (2019)>
=2019A&A...631A.171S 2019A&A...631A.171S
ADC_Keywords: Galaxies, nearby ; Abundances
Keywords: stars: abundances - Galaxy: abundances - galaxies: abundances -
galaxies: groups: individual: Sculptor - galaxies: dwarf -
galaxies: evolution
Abstract:
The heavy elements (Z>30) are created in neutron (n)-capture
processes which are predicted to happen at vastly different
nucleosynthetic sites. To study these processes in an environment
different from the Milky Way, we target the n-capture elements in red
giant branch stars in the Sculptor dwarf spheroidal galaxy. Using ESO
VLT/FLAMES spectra, we measure the chemical abundances of Y, Ba, La,
Nd, and Eu, in 98 stars covering the metalliticy range
-2.4<[Fe/H]←0.9. This is the first paper in a series about the
n-capture elements in dwarf galaxies, and here we focus on the
relative and absolute timescales of the slow (s)- and rapid (r)-
processes in Sculptor. From the abundances of the s-process element Ba
and the r-process element Eu, it is clear that the r-process
enrichment occurred throughout the entire chemical evolution history
of Sculptor. Furthermore, there is no evidence for the r-process to
have a significant time delay relative to core-collapse supernovae.
Neutron star mergers are therefore unlikely the dominant (or only)
nucleosynthetic site of the r-process. However, the products of the
s-process only become apparent at [Fe/H]~=-2 in Sculptor, and the
s-process becomes the dominant source of Ba at [Fe/H]≳-2. We test
the use of [Y/Mg] and [Ba/Mg] as chemical clocks in Sculptor.
Similarly to what is observed in the Milky Way, [Y/Mg] and [Ba/Mg]
increase towards younger ages. However, there is an offset in the
trends, where the abundance ratios of [Y/Mg] in Sculptor are
significantly lower than those of the Milky Way at any given age. This
is most likely caused by metallicity dependence of yields from the
s-process, as well as different relative contribution of the s-process
to core-collapse supernovae in these galaxies. Comparisons of our data
with that of the Milky Way and the Fornax dwarf spheroidal galaxy
furthermore show that these chemical clocks are both metallicity and
environment dependent.
Description:
Positions, atmospheric parameters and chemical abundances for 98 stars
in the Sculptor dwarf spheoridal, as determined by VLT/FLAMES high-res
spectra.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tableb1.dat 135 98 Atmospheric parameters and chem. abundances
tableb2.dat 34 76 Linelist
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See also:
J/MNRAS/383/183 : CaII triplet of RGB from VLT/FLAMES obs. (Battaglia+, 2008)
J/A+A/574/A129 : The First CEMP star in the Sculptor dSph (Skuladottir+, 2015)
J/A+A/580/A129 : Sulphur in the Sculptor dSph (Skuladottir+, 2015)
J/A+A/606/A71 : dSph RGB abundance and velocities (Skuladottir+, 2017)
Byte-by-byte Description of file: tableb1.dat
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Bytes Format Units Label Explanations
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1- 7 A7 --- Star Name of star
9 I1 h RAh Right ascension (J2000.0)
11- 12 I2 min RAm Right ascension (J2000.0)
14- 18 F5.2 s RAs Right ascension (J2000.0)
20 A1 --- DE- Declination sign (J2000.0)
21- 22 I2 deg DEd Declination (J2000.0)
24- 25 I2 arcmin DEm Declination (J2000.0)
27- 31 F5.2 arcsec DEs Declination (J2000.0)
33- 36 I4 K Teff Effective Temperature
38- 40 F3.1 [cm/s2] log(g) Surface gravity
42- 44 F3.1 km/s vt Microturbulence velocity
46- 50 F5.2 --- [Fe/H] Abundance [Fe/H]
52- 55 F4.2 --- e_[Fe/H] Error on [Fe/H]
57 I1 --- o_Mg Number of measured Mg lines
59- 63 F5.2 --- [Mg/Fe] ?=- Abundance [Mg/Fe]
65- 68 F4.2 --- e_[Mg/Fe] ?=- Error on [Mg/Fe]
70 I1 --- o_Y Number of measured Y lines
72- 76 F5.2 --- [Y/Fe] ?=- Abundance [Y/Fe]
78- 81 F4.2 --- e_[Y/Fe] ?=- Error on [Y/Fe]
83 I1 --- o_Ba Number of measured Ba lines
85- 89 F5.2 --- [Ba/Fe] Abundance [Ba/Fe]
91- 94 F4.2 --- e_[Ba/Fe] Error on [Ba/Fe]
96- 97 I2 --- o_La Number of measured La lines
99-103 F5.2 --- [La/Fe] ?=- Abundance [La/Fe]
105-108 F4.2 --- e_[La/Fe] ?=- Error on [La/Fe]
110-111 I2 --- o_Nd Number of measured Nd lines
113-117 F5.2 --- [Nd/Fe] ?=- Abundance [Nd/Fe]
119-122 F4.2 --- e_[Nd/Fe] ?=- Error on [Nd/Fe]
124 I1 --- o_Eu Number of measured Eu lines
126-130 F5.2 --- [Eu/Fe] ?=- Abundance [Eu/Fe]
132-135 F4.2 --- e_[Eu/Fe] ?=- Error on [Eu/Fe]
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Byte-by-byte Description of file: tableb2.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- Ion Elemental ion
9- 16 F8.3 0.1nm lambda Wavelength
18- 22 F5.3 --- Chiex Excitation potential
24- 29 F6.3 [-] log(gf) Oscillator strength
32- 34 A3 --- Inst [G/U] GIRAFFE/UVES
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Acknowledgements:
Asa Skuladottir, skuladottir(at)mpia.de>
(End) Asa Skuladottir [MPIA, Germany], Patricia Vannier [CDS] 02-Oct-2019