J/ApJ/778/149 Abundances for 3 stars in Sgr dSph (McWilliam+, 2013)
Chemistry of the Sagittarius dwarf galaxy: a top-light initial mass function,
outflows, and the r-process.
McWilliam A., Wallerstein G., Mottini M.
<Astrophys. J., 778, 149 (2013)>
=2013ApJ...778..149M 2013ApJ...778..149M
ADC_Keywords: Abundances ; Equivalent widths
Keywords: galaxies: abundances; galaxies: dwarf; stars: abundances;
stars: late-type
Abstract:
From chemical abundance analysis of stars in the Sagittarius dwarf
spheroidal galaxy (Sgr), we conclude that the α-element
deficiencies cannot be due to the Type Ia supernova (SN Ia) time-delay
scenario of Tinsley. Instead, the evidence points to low [α/Fe]
ratios resulting from an initial mass function (IMF) deficient in the
highest mass stars. The critical evidence is the 0.4 dex deficiency of
[O/Fe], [Mg/Fe], and other hydrostatic elements, contrasting with the
normal trend of r-process [Eu/Fe]r with [Fe/H]. Supporting evidence
comes from the hydrostatic element (O, Mg, Na, Al, Cu) [X/Fe] ratios,
which are inconsistent with iron added to the Milky Way (MW) disk
trends. Also, the ratio of hydrostatic to explosive (Si, Ca, Ti)
element abundances suggests a relatively top-light IMF. Abundance
similarities with the LMC, Fornax, and IC 1613 suggest that their
α-element deficiencies also resulted from IMFs lacking the most
massive SNe II. The top-light IMF, as well as the normal trend of
r-process [Eu/Fe]r with [Fe/H] in Sgr, indicates that massive SNe II
(≳30M☉) are not major sources of r-process elements. High
[La/Y] ratios, consistent with leaky-box chemical evolution, are
confirmed but ∼0.3 dex larger than theoretical asymptotic giant branch
(AGB) predictions. This suggests that a substantial increase in the
theoretical 13C pocket in low-mass AGB stars is required. Sgr has
the lowest [Rb/Zr] ratios known, consistent with pollution by low-mass
(≲2M☉) AGB stars near [Fe/H]=-0.6, likely resulting from
leaky-box chemical evolution. The [Cu/O] trends in Sgr and the MW
suggest that Cu yields increase with both metallicity and stellar
mass, as expected from Cu production by the weak s-process in massive
stars. Finally, we present an updated hyperfine splitting line list,
an abundance analysis of Arcturus, and further develop our error
analysis formalism.
Description:
We acquired high-resolution spectra of three stars on the fainter
giant branch of M54 in 2007 July. The stars were chosen to be
relatively bright (V∼16.2) and isolated, with colors indicating that
these were late K-type giants, not M giants. The spectra were obtained
using the Magellan Echelle spectrograph, MIKE, with a 0.5 arcsec slit,
corresponding to R∼48000.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
stars.dat 70 3 Observations and adopted model atmosphere
parameters (tables 1 and 6)
table2.dat 62 149 Line List
table4.dat 26 349 Hyperfine splitting list
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See also:
J/MNRAS/418/284 : s-process in low-metallicity stars. II. (Bisterzo+, 2011)
J/MNRAS/404/1529 : s-process in low-metallicity stars (Bisterzo+, 2010)
J/ApJ/708/1290 : A 2MASS view of the Sgr dSph. VI. (Chou+, 2010)
J/A+A/520/A95 : Abundances of red giants in M54 & Sgr dSph (Carretta+, 2010)
J/A+A/505/117 : Abundances of RGB stars in 15 GCs (Carretta+, 2009)
J/A+A/465/815 : Abundances of Sgr dSph stars (Sbordone+, 2007)
J/A+A/433/185 : Detailed abundance analysis of F & G dwarfs (Bensby+, 2005)
J/A+A/420/183 : Spectroscopy in solar neighborhood (Allende Prieto+ 2004)
J/A+A/414/503 : Abundances in the Sgr dSph (Bonifacio+, 2004)
J/AJ/118/1245 : Elemental abundances in five stars in M54 (Brown+, 1999)
Byte-by-byte Description of file: stars.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- LSSF [242/266] Star identifier (1)
5- 6 I2 h RAh Hour of right ascension (J2000)
8- 9 I2 min RAm Minute of right ascension (J2000)
11- 14 F4.1 s RAs Second of right ascension (J2000)
16 A1 --- DE- Sign of declination (J2000)
17- 18 I2 deg DEd Degree of declination (J2000)
20- 21 I2 arcmin DEm Arcminute of declination (J2000)
23- 24 I2 arcsec DEs Arcsecond of declination (J2000)
26- 31 F6.3 mag Vmag [16.2/16.3] V-band magnitude (1)
33- 36 I4 s Exp [5700/8100] Exposure time
38- 39 I2 --- S/N [39/50] Signal-to-noise ratio
41- 45 F5.1 km/s HRV [131.8/145.4] Heliocentric radial velocity
47- 50 I4 K Teff Effective temperature
52- 55 F4.2 [cm/s2] logg Surface gravity
57- 60 F4.1 [-] [A/H] Abundance [A/H]
62- 64 F3.1 km/s Vt Microturbulent velocity (ξ)
66- 70 F5.2 [-] [FeI/H] Abundance [FeI/H]
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Note (1): Star identifications and V magnitudes are from the shallow
M54 frame data of Layden & Sarajedini (2000, J/AJ/119/1760;
<Cl* NGC 6715 LSSF NNN> in Simbad).
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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- 5 A5 --- Ion Ion identification (1)
7- 13 F7.2 0.1nm lambda [5119.1/8772.9] Wavelength in Angstroms (1)
15- 18 F4.2 eV ExPot [0/6.2] Lower level excitation potential χ
21- 23 I3 10-13m EW-242 ? Equivalent width in Star 242 (mÅ)
24 A1 --- u_EW-242 [:] Uncertainty flag in EW-242
26- 30 F5.2 [-] DA-242 ? differential abundance for star 242 (2)
33- 35 I3 10-13m EW-247 ? Equivalent width in Star 247 (mÅ)
36 A1 --- u_EW-247 [:] Uncertainty flag in EW-247
38- 42 F5.2 [-] DA-247 ? differential abundance for star 247 (2)
43 A1 --- u_DA-247 [:] Uncertainty flag in Del-247
45- 47 I3 10-13m EW-266 ? Equivalent width in Star 266 (mÅ)
48 A1 --- u_EW-266 [:] Uncertainty flag in EW-266
50- 54 F5.2 [-] DA-266 ? differential abundance for star 266 (2)
55 A1 --- u_DA-266 [:] Uncertainty flag in Del-266
57- 62 A6 --- Note Abundance note(s) (3)
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Note (1): Multiple entries appear when a line occurs in adjacent orders.
Note (2): Relative to Arcturus (E(X)*-E(X)Arcturus).
Note (3): Abundance measurement method(s) employed for spectrum synthesis
profile calculations:
ss = spectral synthesis;
ew = equivalent width;
hfs = hyperfine splitting;
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- A [51/153] Atomic weight (isotope)
4- 8 A5 --- Ion Ion identification
10- 18 F9.4 0.1nm lambda [5119/8390] Wavelength in Angstroms
20- 26 F7.4 [-] logFi [-5.4/-0.1] Log of the isotopic fraction times
the hyperfine gf value
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 27-Apr-2015