J/ApJ/882/40 Lanthanide fraction distribution of metal-poor stars (Ji+, 2019)
The lanthanide fraction distribution in metal-poor stars: a test of neutron star
mergers as the dominant r-process site.
Ji A.P., Drout M.R., Hansen T.T.
<Astrophys. J., 882, 40 (2019)>
=2019ApJ...882...40J 2019ApJ...882...40J
ADC_Keywords: Abundances; Stars, metal-deficient; Stars, neutron
Keywords: Nuclear astrophysics; Neutron stars; R-process; Stellar abundances;
Transient sources
Abstract:
Multimessenger observations of the neutron star merger GW170817 and
its kilonova proved that neutron star mergers can synthesize large
quantities of r-process elements. If neutron star mergers in fact
dominate all r-process element production, then the distribution of
kilonova ejecta compositions should match the distribution of
r-process abundance patterns observed in stars. The lanthanide
fraction (XLa) is a measurable quantity in both kilonovae and
metal-poor stars, but it has not previously been explicitly calculated
for stars. Here we compute the lanthanide fraction distribution of
metal-poor stars ([Fe/H]<-2.5) to enable comparison to current and
future kilonovae. The full distribution peaks at log XLa~-1.8, but
r-process-enhanced stars ([Eu/Fe]>0.7) have distinctly higher
lanthanide fractions: logXLa≳-1.5. We review observations of
GW170817 and find general consensus that the total logXLa=-2.2±0.5,
somewhat lower than the typical metal-poor star and inconsistent with
the most highly r-enhanced stars. For neutron star mergers to remain
viable as the dominant r-process site, future kilonova observations
should be preferentially lanthanide-rich (including a population of
∼10% with logXLa>-1.5). These high-XLa kilonovae may be fainter
and more rapidly evolving than GW170817, posing a challenge for
discovery and follow-up observations. Both optical and (mid-)infrared
observations will be required to robustly constrain kilonova
lanthanide fractions. If such high-XLa kilonovae are not found in
the next few years, that likely implies that the stars with the
highest r-process enhancements have a different origin for their
r-process elements.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table4.dat 79 254 Star data table
refs.dat 69 38 References
--------------------------------------------------------------------------------
See also:
J/ApJ/530/783 : The r-process enriched giant HD 115444 (Westin+, 2000)
J/A+A/416/1117 : Abundances in the early Galaxy (Cayrel+, 2004)
J/ApJ/617/1091 : La and Eu abundances in 85 stars (Simmerer+, 2004)
J/A+A/439/129 : HERES II. Spectroscopic analysis (Barklem+, 2005)
J/ApJ/645/613 : Abundances of HD 221170 (Ivans+, 2006)
J/AJ/132/85 : Equivalent width of 33 metal-poor RHB (Preston+, 2006)
J/ApJ/681/1524 : Detailed abundances for 28 metal-poor stars (Lai+, 2008)
J/A+A/516/A46 : HE 2327-5642 abundance analysis (Mashonkina+, 2010)
J/ApJ/724/975 : Heavy elements abund. of metal-poor stars (Roederer+, 2010)
J/ApJ/711/573 : Abundances in a halo stellar stream (Roederer+, 2010)
J/ApJ/742/54 : CASH project II. Extremely metal-poor stars (Hollek+, 2011)
J/A+A/548/A34 : Abundances of carbon-enhanced metal-poor stars (Allen+, 2012)
J/ApJ/778/56 : Hamburg/ESO Survey extremely metal-poor stars (Cohen+, 2013)
J/ApJ/771/67 : Abundances for 97 metal-poor stars. II. (Ishigaki+, 2013)
J/ApJ/775/L27 : Chemical abundances in a metal-poor RGB star (Johnson+, 2013)
J/ApJ/787/10 : Solar s-process contrib. with GCE model (Bisterzo+, 2014)
J/ApJ/797/44 : Evolution and nucleosynthesis of AGB stars (Fishlock+, 2014)
J/A+A/569/A43 : HE 2252-4225 abundance analysis (Mashonkina+, 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/ApJ/807/171 : SkyMapper Survey metal-poor star spectrosc. (Jacobson+, 2015)
J/ApJ/798/110 : Equivalent widths of LAMOST metal-poor stars (Li+, 2015)
J/MNRAS/460/884 : EMBLA survey. Galactic bulge metal-poor stars (Howes+, 2016)
J/ApJ/830/93 : Abund. of the Ret II brightest red giant members (Ji+, 2016)
J/AJ/151/82 : The 4 brightest red giants in Ret 2 (Roederer+, 2016)
J/ApJ/838/44 : Abundances of the brightest member of Tuc III (Hansen+, 2017)
J/A+A/607/A91 : CS 29497-004 abundances (Hill+, 2017)
J/ApJ/844/18 : RAVE J203843.2-002333 high-resolution spec. (Placco+, 2017)
J/ApJ/851/L21 : UV-NIR obs. compilation of GW170817 (Villar+, 2017)
J/ApJ/869/50 : Barium abundances of red giant branch stars (Duggan+, 2018)
J/ApJ/858/92 : RPA Southern Pilot Search of 107 Stars (Hansen+, 2018)
J/AJ/156/179 : Highly r-process-enhanced field stars (Roederer+, 2018)
J/ApJ/865/129 : Abundance analysis of HD 222925 (Roederer+, 2018)
J/ApJ/868/110 : R-Process Alliance: 1st release in Gal. halo (Sakari+, 2018)
Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 24 A24 --- Star Star (1)
26- 31 A6 --- Ref Reference (see refs.dat file)
33- 34 I2 --- Nel [3/33] Number of elements
36- 40 F5.2 --- [Fe/H] [-4.1/-2.3] Abundance, [Fe/H]
42- 46 F5.2 --- [Sr/Fe] [-1.6/1.8]? Abundance, [Sr/Fe]
48- 52 F5.2 --- [Ba/Fe] [-1.7/2.3] Abundance, [Ba/Fe]
54- 58 F5.2 --- [Eu/Fe] [-0.6/2.8] Abundance, [Eu/Fe]
60- 64 F5.2 --- logXLa-A07 [-3.1/-1]? log, XLa fraction,
Arnould et al. (2007PhR...450...97A 2007PhR...450...97A) (2)
66- 70 F5.2 --- logXLa-S08 [-3.5/-1.1]? log, XLa fraction,
Sneden et al. (2008ARA&A..46..241S 2008ARA&A..46..241S) (2)
72- 79 A8 --- Sample Sample (3)
--------------------------------------------------------------------------------
Note (1): CS22783-055 is a misprint for CS22873-055; corrected at CDS.
Note (2): The lanthanide fraction (XLa) is the mass ratio between the
high-opacity lanthanides (atomic numbers Z=57-71) and the total mass.
See Section 2 for the determination of the lanthanide fraction distribution
from metal-poor stars.
Note (3): Sample as follows:
H18 = Hansen et al. (2018, J/ApJ/858/92);
JINAbase = Abohalima & Frebel (2018ApJS..238...36A 2018ApJS..238...36A);
R18 = Roederer et al. (2018, J/AJ/156/179);
S18 = Sakari et al. (2018, J/ApJ/868/110).
------------------------------------------------------------------------
Sample Total Metal-poor Metal-poor Metal-poor
star r-dominated r-dominated r-dominated
number Has Sr, Ba, Eu ≥5 neutron-capture
elements
------------------------------------------------------------------------
JINAbase 426 146 143 120
R18 83 56 45 30
S18 125 32 32 30
H18 107 39 31 -
------------------------------------------------------------------------
Metal-poor: [Fe/H]<-2.5; r-dominated: [Ba/Eu]<-0.4.
For the S18 sample, we instead use [Fe/H]<-2.3 to account for non-LTE
metallicities.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: refs.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 A6 --- Ref Reference code
8- 26 A19 --- BibCode Bibcode of the reference
28- 48 A21 --- Auth First author's name
50- 69 A20 --- Cat VizieR catalog reference
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 09-Feb-2021