J/ApJ/855/83 Abundances of very metal-poor stars in Sagittarius (Hansen+, 2018)
Ages and heavy element abundances from very metal-poor stars in the Sagittarius
dwarf galaxy.
Hansen C.J., El-Souri M., Monaco L., Villanova S., Bonifacio P., Caffau E.,
Sbordone L.
<Astrophys. J., 855, 83 (2018)>
=2018ApJ...855...83H 2018ApJ...855...83H
ADC_Keywords: Galaxies, spectra; Stars, metal-deficient; Abundances;
Radial velocities; Optical
Keywords: galaxies: dwarf ; galaxies: evolution ; Galaxy: halo ;
nuclear reactions, nucleosynthesis, abundances ; stars: abundances ;
stars: chemically peculiar
Abstract:
Sagittarius (Sgr) is a massive disrupted dwarf spheroidal galaxy in
the Milky Way halo that has undergone several stripping events.
Previous chemical studies were restricted mainly to a few, metal-rich
([Fe/H]≳-1) stars that suggested a top-light initial mass function
(IMF). Here we present the first high-resolution, very metal-poor
([Fe/H]=-1 to -3) sample of 13 giant stars in the main body of Sgr. We
derive abundances of 13 elements, namely C, Ca, Co, Fe, Sr, Ba, La,
Ce, Nd, Eu, Dy, Pb, and Th, that challenge the interpretation based on
previous studies. Our abundances from Sgr mimic those of the
metal-poor halo, and our most metal-poor star ([Fe/H]~-3) indicates a
pure r-process pollution. Abundances of Sr, Pb, and Th are presented
for the first time in Sgr, allowing for age determination using
nuclear cosmochronology. We calculate ages of 9±2.5Gyr. Most of the
sample stars have been enriched by a range of asymptotic giant branch
(AGB) stars with masses between 1.3 and 5M☉.
SgrJ190651.47-320147.23 shows a large overabundance of Pb (2.05dex)
and a peculiar abundance pattern best fit by a 3M☉ AGB star.
Based on star-to-star scatter and observed abundance patterns, a
mixture of low- and high-mass AGB stars and supernovae (15-25M☉)
is necessary to explain these patterns. The high level (0.29±0.05dex)
of Ca indicates that massive supernovae must have existed and polluted
the early ISM of Sgr before it lost its gas. This result is in
contrast with a top-light IMF with no massive stars polluting Sgr.
Description:
Observations were obtained using the high-resolution, cross-dispersed
UV-Visual Echelle Spectrograph (UVES) mounted at the unit 2 telescope
(UT2/Keueyen) of the ESO Very Large Telescope (VLT) in Cerro Paranal,
Chile.
Out of 13 stars, 12 were observed with central wavelengths of 390nm
and 580nm, for the blue and red arms, respectively. We adopted a 1.4"
wide slit and 2x2 on-chip binning. All the stars were observed for
∼2400-13000s at an airmass between 1.0 and 1.3 in 2009 April and July.
The very metal-poor star Sgr 2300225 was observed using a slightly
different setup in an earlier run (in 2005 August).
Objects:
------------------------------------------------------------------------
RA (ICRS) DE Designation(s) (HRV)
------------------------------------------------------------------------
18 55 03.1 -30 28 42 Sagittarius= NAME Sgr dSph (HRV∼141km/s)
------------------------------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 69 13 Observations of our Sgr sample
table2.dat 45 13 Stellar parameters
table6.dat 37 68 Line list for region around Th
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See also:
J/AJ/109/218 : Catalogue of globular cluster profiles (Trager+ 1995)
J/AJ/120/1841 : Abundance & Kinematic of Halo & Disk Stars (Fulbright 2000)
J/A+A/381/500 : Eu abundances in F and G disk stars (Koch+, 2002)
J/MNRAS/340/304 : [X/Fe] of Galactic disc F and G dwarfs (Reddy+, 2003)
J/A+A/416/1117 : Abundances in the early Galaxy (Cayrel+, 2004)
J/AJ/127/1545 : Abundance ratios of 4 stars in Pal 12 (Cohen+, 2004)
J/ApJ/617/1091 : La and Eu abundances in 85 stars (Simmerer+, 2004)
J/AJ/128/1177 : Galactic stellar abundances (Venn+, 2004)
J/A+A/439/129 : HERES II. Spectroscopic analysis (Barklem+, 2005)
J/ApJ/626/446 : Effective temperature scale of FGK stars (Ramirez+, 2005)
J/MNRAS/367/1329 : Elemental abundances for 176 stars (Reddy+, 2006)
J/ApJ/655/492 : Equivalent widths of 26 metal-poor stars (Aoki+, 2007)
J/A+A/465/815 : Abundances of Sgr dSph stars (Sbordone+, 2007)
J/A+A/490/625 : Abundances of NGC 6121 red giants (Marino+, 2008)
J/AJ/136/375 : Chemical composition of LMC red giants (Mucciarelli+, 2008)
J/A+A/480/379 : Abundances of 59 red giants in LMC (Pompeia+, 2008)
J/A+A/501/519 : Extremely metal-poor stars abundances (Bonifacio+, 2009)
J/ApJS/182/51 : Transitions of rare earth elements (Lawler+, 2009)
J/ApJ/695/L134 : Chemical anomalies in old LMC clusters (Mucciarelli+, 2009)
J/A+A/520/A95 : Abundances of red giants in M54 & Sgr dSph (Carretta+, 2010)
J/A+A/513/A62 : Sgr dSph VIMOS photom. & RVs (Giuffrida+, 2010)
J/A+A/523/A17 : Individual stars in Fornax dSph center (Letarte+, 2010)
J/A+A/546/A90 : NLTE analysis of Sr lines (Bergemann+, 2012)
J/AJ/144/88 : Spectroscopy of 6 LMC & 3 SMC RR Lyrae (Haschke+, 2012)
J/AJ/144/4 : Dwarf galaxies in the Local Group (McConnachie+, 2012)
J/ApJ/751/102 : Equivalent widths of 9 RGB in Carina dSph (Venn+, 2012)
J/ApJ/778/149 : Abundances for 3 stars in Sgr dSph (McWilliam+, 2013)
J/ApJ/787/10 : Solar s-processes with GCE model (Bisterzo+, 2014)
J/A+A/562/A146 : Chemical abundances of 8 metal-poor stars (Ishigaki+, 2014)
J/AJ/148/67 : Abundances of 156 bulge red giants (Johnson+, 2014)
J/ApJ/797/21 : Carbon-enhanced metal-poor stars (Placco+, 2014)
J/ApJS/214/26 : Line lists for CN isotopes transitions (Sneden+, 2014)
J/ApJ/805/189 : Highly likely members of the Sgr stream (Hyde+, 2015)
J/A+A/581/A70 : NLTE EWs and corrections BaII lines (Korotin+, 2015)
J/ApJS/220/13 : Co I transition probabilities (Lawler+, 2015)
J/ApJ/817/53 : Fe-group abundance analysis in HD84937 (Sneden+, 2016)
J/A+A/605/A46 : Sgr dSph nucleus stars abundances (Mucciarelli+, 2017)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1-24 A24 --- Name Star name
26-27 I2 h RAh [18/19] Hour of right ascension (J2000)
29-30 I2 min RAm Minute of right ascension (J2000)
32-37 F6.3 s RAs Second of right ascension (J2000)
39 A1 --- DE- [-] Sign of declination (J2000)
40-41 I2 deg DEd [29/32] Degree of declination (J2000)
43-44 I2 arcmin DEm Arcminute of declination (J2000)
46-51 F6.3 arcsec DEs Arcsecond of declination (J2000)
53-57 I5 s Exp [2410/12685] Total observing time
59-63 F5.1 arcmin Sep [7.8/176.6] Distance to centre of M54 (1)
65-69 F5.1 km/s HRV [127.4/167.2] Heliocentric radial velocity
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Note (1): The distance to the center of M54 is listed, showing that all the
stars are clearly outside the tidal radius of M54 (7.4'; Trager+
1995, J/AJ/109/218) but centrally located in Sgr. Hence, the stars are
not part of M54 but the main body of Sgr (see Figure 1).
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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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1-24 A24 --- Name Star identifier
26-29 I4 K Teff [4250/4975] Effective temperature
31-34 F4.2 [cm/s2] logg [0.03/2] Log of surface gravity
36-40 F5.2 [Sun] [Fe/H] [-3/-1] Abundance [Fe/H]
42-45 F4.2 km/s xi [1.3/2.5] Microturbulence velocity ξ
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 8 F8.3 0.1nm Wave [4018.6/4019.4] Wavelength in Angstroms
10- 18 F9.5 --- Ion [23/606.1] Numeric atom/ion identifier (1)
20- 24 F5.3 eV ExPot [0/5.4] Excitation potential
26- 31 F6.3 [-] log(gf) [-9.2/-0.5] log of the oscillator strength
33- 37 F5.3 eV Edis [3.4/6.3]? Dissociation energy
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Note (1): X.Y where X is the atomic number and Y is the ionization level,
e.g. 26.0 is Fe I, 26.1 is Fe II, etc.
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Nomenclature notes:
Sgr JHHMMSS.ss+DDMMSS.ss stars are in Simbad,
Sgr NNNNNNN stars are <[HEM2018] Sgr NNNNNNN> in Simbad.
History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 03-Jan-2019