J/ApJ/821/37 Abundances of metal-poor star HD 94028 (Roederer+, 2016)
The diverse origins of neutron-capture elements in the metal-poor star HD 94028:
possible detection of products of i-process nucleosynthesis.
Roederer I.U., Karakas A.I., Pignatari M., Herwig F.
<Astrophys. J., 821, 37-37 (2016)>
=2016ApJ...821...37R 2016ApJ...821...37R (SIMBAD/NED BibCode)
ADC_Keywords: Abundances ; Equivalent widths ; Stars, metal-deficient ;
Spectra, ultraviolet
Keywords: nuclear reactions, nucleosynthesis, abundances; stars: abundances;
stars: AGB and post-AGB stars; stars: individual: HD 94028
Abstract:
We present a detailed analysis of the composition and nucleosynthetic
origins of the heavy elements in the metal-poor ([Fe/H]=-1.62±0.09)
star HD 94028. Previous studies revealed that this star is mildly
enhanced in elements produced by the slow neutron-capture process (s
process; e.g., [Pb/Fe]=+0.79±0.32) and rapid neutron-capture process
(r process; e.g., [Eu/Fe]=+0.22±0.12), including unusually large
molybdenum ([Mo/Fe]= +0.97±0.16) and ruthenium ([Ru/Fe]=+0.69±0.17)
enhancements. However, this star is not enhanced in carbon
([C/Fe]=-0.06±0.19). We analyze an archival near-ultraviolet
spectrum of HD 94028, collected using the Space Telescope Imaging
Spectrograph on board the Hubble Space Telescope, and other archival
optical spectra collected from ground-based telescopes. We report
abundances or upper limits derived from 64 species of 56 elements. We
compare these observations with s-process yields from low-metallicity
AGB evolution and nucleosynthesis models. No combination of s- and
r-process patterns can adequately reproduce the observed abundances,
including the super-solar [As/Ge] ratio (+0.99±0.23) and the
enhanced [Mo/Fe] and [Ru/Fe] ratios. We can fit these features when
including an additional contribution from the intermediate
neutron-capture process (i process), which perhaps operated through
the ingestion of H in He-burning convective regions in massive stars,
super-AGB stars, or low-mass AGB stars. Currently, only the i process
appears capable of consistently producing the super-solar [As/Ge]
ratios and ratios among neighboring heavy elements found in HD 94028.
Other metal-poor stars also show enhanced [As/Ge] ratios, hinting that
operation of the i process may have been common in the early Galaxy.
Description:
We use two NUV spectroscopic data sets of HD 94028 available in the
Mikulski Archive for Space Telescopes. These observations were made
using STIS on board the HST. One spectrum (data sets O5CN01-03,
GO-8197, PI. Duncan) has very high spectral resolution (R∼110000).
This spectrum covers ∼1885-2147Å with signal-to-noise ratios
(S/N)35/1 per pixel near 2140Å. The other spectrum (data sets
O56D06-07, GO-7402, PI. Peterson) has high spectral resolution
(R∼30000). This spectrum covers 2280-3117Å with S/N ranging from
∼20 near 2300Å to ∼40 near 3100Å.
Roederer et al. (2014, J/AJ/147/136) derived abundances from an
optical spectrum of HD 94028 taken using the Robert G. Tull Coude
Spectrograph on the Harlan J. Smith Telescope at McDonald Observatory,
Texas. We rederive abundances from this spectrum.
We also use an optical spectrum taken with the Ultraviolet and Visual
Echelle Spectrograph (UVES) on the Very Large Telescope (VLT) Kueyen
at Cerro Paranal, Chile. We obtained this spectrum from the ESO
Science Archive. This spectrum covers 3050-3860Å at R∼37000 with
S/N ranging from ∼40 near 3200Å to ∼130 near 3800Å.
Objects:
------------------------------------------------------
RA (ICRS) DE Designation(s)
------------------------------------------------------
10 51 28.12 +20 16 39.0 HD 94028 = TYC 1435-86-1
------------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 46 25 Abundances derived from lines examined in this study
table2.dat 35 93 NUV iron lines examined
table3.dat 49 64 Derived abundances in HD 94028
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See also:
J/ApJ/817/53 : Fe-group elemental abundances in HD84937 (Sneden+, 2016)
J/ApJ/812/109 : HST + Keck spectroscopy of bright CEMP-s stars (Placco+, 2015)
J/ApJS/216/1 : New FeI level energies from stellar spectra (Peterson+, 2015)
J/AJ/147/136 : Stars of very low metal abundance. VI. (Roederer+, 2014)
J/ApJS/211/20 : NiI transition probability measurements (Wood+, 2014)
J/ApJS/208/27 : Sun and HD 84937 TiII log(gf) and abundances (Wood+, 2013)
J/A+A/546/A90 : NLTE analysis of Sr lines (Bergemann+, 2012)
J/ApJ/750/76 : r-process peaks elements in HD 160617 (Roederer+, 2012)
J/AJ/141/175 : Abundances in M15 RGB/RHB stars (Sobeck+, 2011)
J/A+A/530/A138 : Geneva-Copenhagen survey re-analysis (Casagrande+, 2011)
J/ApJ/743/140 : Abundances (Be,α) in metal-poor stars (Boesgaard+, 2011)
J/ApJS/187/149 : StarCAT: STIS UV echelle spectra of stars (Ayres, 2010)
J/ApJ/724/975 : Metal-poor star heavy element abundances (Roederer+, 2010)
J/A+A/503/541 : Neutral Li in stars non-LTE calculations (Lind+, 2009)
J/A+A/440/321 : Chemical abundances in 43 metal-poor stars (Jonsell+, 2005)
J/ApJ/617/1091 : La and Eu abundances in 85 stars (Simmerer+, 2004)
J/AJ/124/1144 : Orbits of 171 single-lined spectroscopic bin. (Latham, 2002)
J/ApJ/562/528 : Teff and log(g) of low-metallicity stars (Snider+, 2001)
J/A+A/354/169 : Metal-poor field stars abundances (Gratton+, 2000)
J/AJ/107/2240 : Proper motion stars survey. XII. (Carney+, 1994)
http://www.nist.gov/pml/data/asd.cfm : NIST atomic spectra database
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 A4 --- Sp Species
6- 12 F7.2 0.1nm lambda [1890.4/3499] Wavelength in Angstroms
14- 17 F4.2 eV ExPot [0/3.3] Excitation potential in eV
19- 24 F6.3 [-] log(gf) [-1.4/0.4] Log of degeneracy times oscillator
strength
26- 30 F5.3 [-] e_log(gf) [0.002/0.08]? Uncertainty in log(gf)
32- 33 I2 --- Ref [1/15] Line Reference (1)
35- 35 A1 --- l_logeps Limit flag on logeps
37- 41 F5.2 [-] logeps [-0.7/2.6] Log ε abundance
43- 46 F4.2 [-] e_logeps [0.05/0.3]? Uncertainty in logeps
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Note (1): Line reference as follows:
1 = Roederer & Lawler 2012, J/ApJ/750/76;
2 = Holmgren (1975PhyS...11...15H 1975PhyS...11...15H), using HFS from
Roederer & Lawler 2012, J/ApJ/750/76;
3 = Sikstrom et al. (2001JPhB...34..477S 2001JPhB...34..477S);
4 = Wickliffe et al. (1994JQSRT..51..545W 1994JQSRT..51..545W);
5 = Xu et al. (2006A&A...452..357X 2006A&A...452..357X);
6 = Hansen et al. (2012A&A...545A..31H 2012A&A...545A..31H)
for both log gf value and HFS;
7 = Morton (2000ApJS..130..403M 2000ApJS..130..403M);
8 = Roederer et al. (2012ApJ...747L...8R 2012ApJ...747L...8R);
9 = log gf value from the Database on Rare Earths At Mons University
(DREAM), using HFS/IS from Roederer & Lawler 2012, J/ApJ/750/76;
10 = Kedzierski et al. (2010AcSpe..65..248K 2010AcSpe..65..248K), using HFS from
Roederer & Lawler 2012, J/ApJ/750/76;
11 = Roederer et al. (2010ApJ...714L.123R 2010ApJ...714L.123R), using HFS from
Roederer et al. (2012ApJS..203...27R 2012ApJS..203...27R);
12 = Nilsson et al. (2008EPJD...49...13N 2008EPJD...49...13N);
13 = Ivarsson et al. (2004A&A...425..353I 2004A&A...425..353I);
14 = Den Hartog et al. (2005ApJ...619..639D 2005ApJ...619..639D);
15 = Biemont et al. (2000MNRAS.312..116B 2000MNRAS.312..116B), using HFS from
Roederer et al. (2012ApJS..203...27R 2012ApJS..203...27R).
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Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 A4 --- Sp Species
6- 12 F7.2 0.1nm lambda [2078.1/3091.6] Wavelength in Angstroms
14- 17 F4.2 eV ExPot [0/6] Excitation potential in eV
19- 23 F5.2 --- log(gf) [-3/0.8] Log of degeneracy times oscillator
strength
25- 29 F5.1 0.1pm EW [23/186] Equivalent width in milli Angstroms
31- 35 F5.3 [-] logeps [5.1/6.7] Log ε abundance
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- Sp Species
7- 8 I2 --- N [1/96] Number of lines used in derived
abundance
10- 10 A1 --- f_logeps Limit flag on logeps
12- 16 F5.2 [-] logeps [-1/7.6] Log ε abundance
18- 18 A1 --- l_[X/Fe] Limit flag on [X/Fe]
20- 24 F5.2 --- [X/Fe] [-1.8/1.9]? Abundance (1)
26- 29 F4.2 --- s_[X/Fe] [0.03/0.4]? Uncertainty in [X/Fe],
statistical (σ-stat) (2)
31- 34 F4.2 --- e_[X/Fe] [0.09/0.4]? Uncertainty in [X/Fe], total (3)
36- 39 F4.2 --- sigI [0/0.4]? Uncertainty in [X/Fe], Error 1 (4)
41- 44 F4.2 --- sigII [0/0.4]? Uncertainty in [X/Fe], Error 2 (4)
46- 49 F4.2 --- logepsSun [0.1/8.7]? Solar Reference Abundance
--------------------------------------------------------------------------------
Note (1): [X/Fe] abundance ratios are computed using the Solar reference
abundances given in Asplund et al. (2009ARA&A..47..481A 2009ARA&A..47..481A).
Note (2): The statistical uncertainty, σ-stat, is computed from equation
A17 of McWilliam et al. (1995AJ....109.2757M 1995AJ....109.2757M), which includes
uncertainties in the equivalent widths or synthesis matching and
log(gf) values.
Note (3): The total uncertainty, σ-tot, is computed from equation A16 of
McWilliam et al. (1995AJ....109.2757M 1995AJ....109.2757M), which includes the
statistical uncertainty and uncertainties in the model atmosphere
parameters.
Note (4): σ-I and σ-II uncertainties are computed from
approximations of equations A19 and A20 of McWilliam et al.
(1995AJ....109.2757M 1995AJ....109.2757M), which give uncertainties in the abundance
ratios.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 03-Jun-2016