The Lanthanide Fraction Distribution in Metal-poor Stars: A Test of Neutron Star Mergers as the Dominant r-process Site

Ji, Alexander P.; Drout, M. R.; Hansen, Terese T.

doi:10.3847/1538-4357/ab3291

Cited by 62 publications

(56 citation statements)

References 202 publications

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“…J220423 has [ ] = -Ba Eu 0.80, compatible with an r-process origin of the neutron-capture element excess (Sneden et al 2008). The two nonenhanced stars J220409 and J220352 both exhibit extremely low Sr (and Ba) abundances similar to neutron-capture element abundances detected in other UFDs (Ji et al 2019a), supporting the dwarf galaxy classification of GruII (see Figure 3).…”

Section: Neutron-capture Elementssupporting

confidence: 61%

Chemical Analysis of the Ultrafaint Dwarf Galaxy Grus II. Signature of High-mass Stellar Nucleosynthesis*

Hansen¹,

Marshall²,

Simon³

et al. 2020

ApJ

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We present a detailed abundance analysis of the three brightest member stars at the top of the giant branch of the ultrafaint dwarf (UFD) galaxy GrusII. All stars exhibit a higher than expected [Mg/Ca] ratio compared to metalpoor stars in other UFD galaxies and in the Milky Way (MW) halo. Nucleosynthesis in high-mass ( 20 M e) corecollapse supernovae has been shown to create this signature. The abundances of this small sample (three) stars suggests the chemical enrichment of GrusII could have occurred through substantial high-mass stellar evolution, and is consistent with the framework of a top-heavy initial mass function. However, with only three stars it cannot be ruled out that the abundance pattern is the result of a stochastic chemical enrichment at early times in the galaxy. The most metal-rich of the three stars also possesses a small enhancement in rapid neutron-capture (r-process) elements. The abundance pattern of the r-process elements in this star matches the scaled r-process pattern of the solar system and r-process enhanced stars in other dwarf galaxies and in the MW halo, hinting at a common origin for these elements across a range of environments. All current proposed astrophysical sites of r-process element production are associated with high-mass stars, thus the possible top-heavy initial mass function of GrusII would increase the likelihood of any of these events occurring. The time delay between the α and r-process element enrichment of the galaxy favors a neutron star merger as the origin of the r-process elements in GrusII. Unified Astronomy Thesaurus concepts: Chemical abundances (224); Dwarf galaxies (416); Chemically peculiar stars (226); Stellar abundances (1577)

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Section: Neutron-capture Elementssupporting

confidence: 61%

Chemical Analysis of the Ultrafaint Dwarf Galaxy Grus II. Signature of High-mass Stellar Nucleosynthesis*

Hansen¹,

Marshall²,

Simon³

et al. 2020

ApJ

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“…Under the assumption that all the neutron-capture elements in J1830-4555 were produced by a single merger of neutron stars, we can estimate the lanthanide fraction that would be measured if we were to observe this merger's kilonova directly. Following the methods in Ji et al (2019), we estimate the lanthanide fraction to be = -X log 1.47…”

Section: The Light-element Abundance Patternmentioning

confidence: 99%

The R-process Alliance: The Peculiar Chemical Abundance Pattern of RAVE J183013.5−455510*

Placco

Santucci

Yuan

et al. 2020

ApJ

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We report on the spectroscopic analysis of RAVE J183013.5−455510, an extremely metal-poor star, highly enhanced in CNO, and with discernible contributions from the rapid neutron-capture process. There is no evidence of binarity for this object. At [ ] Fe H =−3.57, this star has one of the lowest metallicities currently observed, with 18 measured abundances of neutron-capture elements. The presence of Ba, La, and Ce abundances above the solar system r-process predictions suggests that there must have been a non-standard source of r-process elements operating at such low metallicities. One plausible explanation is that this enhancement originates from material ejected at unusually high velocities in a neutron star merger event. We also explore the possibility that the neutroncapture elements were produced during the evolution and explosion of a rotating massive star. In addition, based on comparisons with yields from zero-metallicity faint supernova, we speculate that RAVE J1830−4555 was formed from a gas cloud pre-enriched by both progenitor types. From analysis based on Gaia DR2 measurements, we show that this star has orbital properties similar to the Galactic metal-weak thick-disk stellar population.

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“…For the top two panels, we draw the model curve assuming that (i) the homogeneous Y, Zr abundances are [Y/H] = −2.7, [Zr/H] = −2.3, (ii) the homogeneous Eu abundance is [Eu/H] = −2.1, and (iii) the NSM ejecta has [Y/Eu] = −1.0, [Zr/Eu] = −0.9. The last conditions are motivated by the abundance ratio of r-II stars (Montes et al 2007;Ji et al 2019;Tsujimoto et al 2020). Note that this ratio is lanthanide-rich by ∼ 0.5 dex compared to the solar r-process abundance.…”

Section: Discussionmentioning

confidence: 99%

Internal r-process abundance spread of M15 and a single stellar population model

Tarumi,

Yoshida,

Inoue

2021

Preprint

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The member stars in globular cluster M15 show a substantial spread in the abundances of r-process elements. We argue that a rare and prolific r-process event enriched the natal cloud of M15 in an inhomogeneous manner. To critically examine the possibility, we perform cosmological galaxy formation simulations and study the physical conditions for the inhomogeneous enrichment. We explore a large parameter space of the merger event time and the site. Our simulations reproduce the large r-process abundance spread if a neutron-star merger occurs at ∼ 100 pc away from the formation site of the cluster and in a limited time range of a few tens million years before the formation. Interestingly, a bimodal feature is found in the Eu abundance distribution in some cases, similarly to that inferred from recent observations. M15 member stars do not show clear correlation between the abundances of Eu and light elements such as Na that is expected in models with two stellar populations. We thus argue that a majority of the stars in M15 are formed in a single burst. The ratio of heavy to light r-process element abundance [Eu/Y] ∼ 1.0 is consistent with that of the so-called r-II stars, suggesting that a lanthanide-rich r-process event dominantly enriched M15.

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The Lanthanide Fraction Distribution in Metal-poor Stars: A Test of Neutron Star Mergers as the Dominant r-process Site

Cited by 62 publications

References 202 publications

Chemical Analysis of the Ultrafaint Dwarf Galaxy Grus II. Signature of High-mass Stellar Nucleosynthesis*

Chemical Analysis of the Ultrafaint Dwarf Galaxy Grus II. Signature of High-mass Stellar Nucleosynthesis*

The R-process Alliance: The Peculiar Chemical Abundance Pattern of RAVE J183013.5−455510*

Internal r-process abundance spread of M15 and a single stellar population model

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