J/ApJ/862/174 Spectroscopy obs. of RAVE J094921.8-161722 (Gull+, 2018)
The r-process alliance: discovery of the first metal-poor star with a combined
r- and s-process element signature.
Gull M., Frebel A., Cain M.G., Placco V.M., Ji A.P., Abate C., Ezzeddine R.,
Karakas A.I., Hansen T.T., Sakari C., Holmbeck E.M., Santucci R.M.,
Casey A.R., Beers T.C.
<Astrophys. J., 862, 174 (2018)>
=2018ApJ...862..174G 2018ApJ...862..174G
ADC_Keywords: Stars, metal-deficient; Stars, giant; Equivalent widths;
Abundances; Radial velocities; Optical
Keywords: early universe ; Galaxy: halo ; stars: abundances ;
stars: individual (RAVE J094921.8-161722) ; stars: Population II
Abstract:
We present a high-resolution (R∼35000), high signal-to-noise ratio
(S/N>200) Magellan/MIKE spectrum of the star RAVE J094921.8-161722, a
bright (V=11.3) metal-poor red giant star with [Fe/H]=-2.2, identified
as a carbon-enhanced metal-poor (CEMP) star from the RAVE survey. We
report its detailed chemical abundance signature of light fusion
elements and heavy neutron-capture elements. We find J0949-1617 to be
a CEMP star with s-process enhancement that must have formed from gas
enriched by a prior r-process event. Light neutron-capture elements
follow a low-metallicity s-process pattern, while the heavier
neutron-capture elements above Eu follow an r-process pattern. The Pb
abundance is high, in line with an s-process origin. Thorium is also
detected, as expected from an r-process origin, as Th is not produced
in the s-process. We employ nucleosynthesis model predictions that
take an initial r-process enhancement into account, and then determine
the mass transfer of carbon and s-process material from a putative
more massive companion onto the observed star. The resulting
abundances agree well with the observed pattern. We conclude that
J0949-1617 is the first bonafide CEMP-r+s star identified. This class
of objects has previously been suggested to explain stars with
neutron-capture element patterns that originate from neither the r-
nor the s-process alone. We speculate that J0949-1617 formed in an
environment similar to those of ultra-faint dwarf galaxies like
TucanaIII and ReticulumII, which were enriched in r-process elements
by one or multiple neutron star mergers at the earliest times.
Description:
RAVE J094921.8-161722 was first identified as a very metal-poor star
candidate from RAVE DR5 (Kunder+ 2017, III/279) and followed up with
medium-resolution spectroscopy obtained with the ESO/NTT and the SOAR
4.1m telescopes.
The NTT/EFOSC-2 data were gathered in 2015A, covering the wavelength
range 3300-5100Å with a resolving power R∼1900 and signal-to-noise
ratio S/N∼40 per pixel at 3900Å. The SOAR observations were carried
out in 2016A, using the Goodman Spectrograph, covering the wavelength
range 3550-5500Å with a resolving power of R∼1500 and S/N∼50 per
pixel at 3900Å.
RAVE J094921.8-161722 was then observed with the MIKE spectrograph on
the Magellan-Clay telescope at Las Campanas Observatory (LCO) on
2016 April 15 and 16, and again on 2017 June 5 (R∼28000 in the red and
R∼35000 in the blue). The resulting S/N per pixel in the 2017 spectrum
is 190 at ∼4000Å, 370 at ∼4700Å, 280 at ∼5200Å, and 470 at
∼6000Å.
We have complied heliocentric radial velocity measurements for
RAVE J094921.8-161722 covering ∼13yrs, although with a 7yr gap from
2009 to 2016; these are listed in Table 1.
Objects:
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RA (ICRS) DE Designation(s)
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09 49 21.83 -16 17 22.1 RAVE J094921.8-161722 = TYC 6044-714-1
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 22 12 Radial velocities of the CEMP-r+s star
RAVE J094921.8-161722
table2.dat 44 618 Line list of RAVE J094921.8-161722
table4.dat 29 170 Line list of the λ4019 region
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See also:
B/eso : ESO Science Archive Catalog (ESO, 1991-2019)
III/279 : RAVE 5th data release (Kunder+, 2017)
J/A+A/439/129 : HERES II. Spectroscopic analysis (Barklem+, 2005)
J/ApJ/724/341 : Nucleosynthesis of massive metal-free stars (Heger+, 2010)
J/MNRAS/403/1413 : Updated stellar yields from AGB models (Karakas, 2010)
J/AJ/141/175 : Abundances in M15 RGB/RHB stars (Sobeck+, 2011)
J/AJ/142/193 : RAVE stellar elemental abundances (DR1) (Boeche+, 2011)
J/ApJ/769/57 : Equivalent widths of metal-poor stars (Frebel+, 2013)
J/ApJ/762/26 : Most metal-poor stars. II. Galactic halo stars (Yong+, 2013)
J/ApJ/794/58 : Metal-poor stars in the Galaxy thick disk (Beers+, 2014)
J/A+A/569/A43 : HE 2252-4225 abundance analysis (Mashonkina+, 2014)
J/A+A/571/A47 : Extensive linelist of CH in stellar atmospheres
(Masseron+, 2014)
J/ApJ/797/21 : Carbon-enhanced metal-poor stars (Placco+, 2014)
J/AJ/147/136 : Stars of very low metal abundance. VI. (Roederer+, 2014)
J/A+A/581/A22 : 67 CEMP-s stars model analysis (Abate+, 2015)
J/ApJ/830/93 : Abundances of Ret II brightest red giant members (Ji+, 2016)
J/ApJ/821/37 : Abundances of metal-poor star HD 94028 (Roederer+, 2016)
J/ApJ/847/142 : Ultra-metal-poor stars LTE & NLTE abund. (Ezzeddine+, 2017)
J/ApJ/838/44 : Abundances of Tuc III brightest members (Hansen+, 2017)
J/A+A/607/A91 : CS 29497-004 abundances (Hill+, 2017)
J/A+A/608/A46 : Constraining cosmic scatter (Reggiani+, 2017)
J/AJ/155/256 : Spectro. validation of RAVE metal-poor stars (Placco+, 2018)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 11 A11 "Y/M/D" Date UT date of observation
13- 17 F5.1 km/s HRV [389.5/392.5] Heliocentric radial velocity (1)
19- 22 A4 --- Obs Observatory/Survey (1)
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Note (1): Typical uncertainties of the LCO/Magellan MIKE measurements are
1-2km/s, from comparison with well-studied stars observed during the
same night. Repeat RAVE measurements taken from DR5 (Kunder+ 2017,
III/279) have uncertainties of 0.6-0.7km/s. High-resolution follow-up
spectra obtained with the Astrophysical Research Consortium Echelle
Spectrograph on the 3.5m telescope at Apache Point Observatory (APO)
yield velocity uncertainties ∼2km/s. Observations taken with the South
African Large Telescope (SALT) using the high-resolution spectrograph
have ±1km/s uncertainties. All measurements agree remarkable well
each other, which strongly constrains potential radial velocity
variations of RAVE J094921.8-161722 to less than a few km/s.
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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- 6 A6 --- Ion Species identifier
8- 14 F7.2 0.1nm lambda [3360/7511.1] Wavelength in Angstrom
16- 20 F5.2 eV ExPot [-0.6/5]? Excitation potential
22- 28 F7.3 [-] log(gf) [-10.3/3]? log oscillator strength
30- 35 F6.2 10-13m EW [2.3/361.5]? Equivalent width in milli-Angstrom
37- 37 A1 --- f_EW [s] Indicates abundance was measured using
a synthetic spectrum
39- 44 F6.3 [-] loge [-1.7/7.4] log absolute abundance
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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- 6 A6 --- Ion Species identifier
8- 15 F8.3 0.1nm lambda [4018/4020.6] Wavelength in Angstroms
17- 22 F6.3 eV ExPot [0/14.5] Excitation potential
24- 29 F6.3 [-] log(gf) [-9.8/0.6] log oscillator strength
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 01-Aug-2019