We present new observational benchmarks of rapid neutron-capture process (
This content will become publicly available on December 8, 2024
The heaviest chemical elements are naturally produced by the rapid neutron-capture process (
- Award ID(s):
- 1927130
- PAR ID:
- 10543565
- Publisher / Repository:
- Science
- Date Published:
- Journal Name:
- Science
- Volume:
- 382
- Issue:
- 6675
- ISSN:
- 0036-8075
- Page Range / eLocation ID:
- 1177 to 1180
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
Abstract r -process) nucleosynthesis for elements at and between the first (A ∼ 80) and second (A ∼ 130) peaks. Our analysis is based on archival ultraviolet and optical spectroscopy of eight metal-poor stars with Se (Z = 34) or Te (Z = 52) detections, whoser -process enhancement varies by more than a factor of 30 (−0.22 ≤ [Eu/Fe] ≤ +1.32). We calculate ratios among the abundances of Se, Sr through Mo (38 ≤Z ≤ 42), and Te. These benchmarks may offer a new empirical alternative to the predicted solar systemr -process residual pattern. The Te abundances in these stars correlate more closely with the lighterr -process elements than the heavier ones, contradicting and superseding previous findings. The small star-to-star dispersion among the abundances of Se, Sr, Y, Zr, Nb, Mo, and Te (≤0.13 dex, or 26%) matches that observed among the abundances of the lanthanides and thirdr -process-peak elements. The concept ofr -process universality that is recognized among the lanthanide and third-peak elements inr -process-enhanced stars may also apply to Se, Sr, Y, Zr, Nb, Mo, and Te, provided the overall abundances of the lighterr -process elements are scaled independently of the heavier ones. The abundance behavior of the elements Ru through Sn (44 ≤Z ≤ 50) requires further study. Our results suggest that at least one relatively common source in the early Universe produced a consistent abundance pattern among some elements spanning the first and secondr -process peaks. -
Context. In recent years, theR -Process Alliance (RPA) has conducted a successful search for stars that are enhanced in elements produced by the rapid neutron-capture (r -)process. In particular, the RPA has uncovered a number of stars that are strongly enriched in lightr -process elements, such as Sr, Y, and Zr. These so-called limited-r stars were investigated to explore the astrophysical production site(s) of these elements.Aims. We investigate the possible formation sites for light neutron-capture elements by deriving detailed abundances for neutron-capture elements from high-resolution spectra with a high signal-to-noise ratio of three limited-r stars.Methods. We conducted a kinematic analysis and a 1D local thermodynamic equilibrium spectroscopic abundance analysis of three stars. Furthermore, we calculated the lanthanide mass fraction (X La) of our stars and of limited-r stars from the literature.Results. We found that the abundance pattern of neutron-capture elements of limited-r stars behaves differently depending on their [Ba/Eu] ratios, and we suggest that this should be taken into account in future investigations of their abundances. Furthermore, we found that theX Laof limited-r stars is lower than that of the kilonova AT2017gfo. The latter seems to be in the transition zone between limited-rX Laand that ofr -I andr -II stars. Finally, we found that unliker -I andr -II stars, the current sample of limited-r stars is largely born in the Galaxy and is not accreted. -
Abstract We present stellar parameters and chemical abundances of 47 elements detected in the bright (
V = 11.63) very metal-poor ([Fe/H] = −2.20 ± 0.12) star 2MASS J22132050−5137385. We observed this star using the Magellan Inamori Kyocera Echelle spectrograph as part of ongoing work by theR -Process Alliance. The spectrum of 2MASS J22132050−5137385 exhibits unusually strong lines of elements heavier than the iron group, and our analysis reveals that these elements were produced by rapid neutron-capture (r -process) nucleosynthesis. We derive a europium enhancement, [Eu/Fe] = +2.45 ± 0.08, that is higher than any otherr -process-enhanced star known at present. This star is only the eighthr -process-enhanced star where both thorium and uranium are detected, and we calculate the age of ther -process material, 13.6 ± 2.6 Gyr, from the radioactive decay of these isotopes. This star contains relatively large enhancements of elements that may be produced as transuranic fission fragments, and we propose a new method using this characteristic to assess ther -process yields and gas dilution in samples ofr -process-enhanced stars. Assuming a canonical baryonic minihalo mass of 106M ⊙and a 1% metal retention rate, this star formed in a cloud of only ∼600M ⊙. We conclude that 2MASS J22132050−5137385 exhibits a high level ofr -process enhancement because it formed in an environment where ther -process material was less diluted than average. -
Abstract Whereas light-element abundance variations are a hallmark of globular clusters, there is little evidence for variations in neutron-capture elements. A significant exception is M15, which shows a star-to-star dispersion in neutron-capture abundances of at least one order of magnitude. The literature contains evidence both for and against a neutron-capture dispersion in M92. We conducted an analysis of archival Keck/HIRES spectra of 35 stars in M92, 29 of which are giants, which we use exclusively for our conclusions. M92 conforms to the abundance variations typical of massive clusters. Like other globular clusters, its neutron-capture abundances were generated by the
r -process. We confirm a star-to-star dispersion inr -process abundances. Unlike M15, the dispersion is limited to “first-generation” (low-Na, high-Mg) stars, and the dispersion is smaller for Sr, Y, and Zr than for Ba and the lanthanides. This is the first detection of a relation between light-element and neutron-capture abundances in a globular cluster. We propose that a source of the mainr -process polluted the cluster shortly before or concurrently with the first generation of star formation. The heavierr -process abundances were inhomogeneously distributed while the first-generation stars were forming. The second-generation stars formed after several crossing times (∼0.8 Myr); hence, the second generation shows nor -process dispersion. This scenario imposes a minimum temporal separation of 0.8 Myr between the first and second generations. -
Abstract As LIGO-Virgo-KAGRA enters its fourth observing run, a new opportunity to search for electromagnetic counterparts of compact object mergers will also begin. The light curves and spectra from the first “kilonova” associated with a binary neutron star merger (NSM) suggests that these sites are hosts of the rapid neutron capture (“
r ”) process. However, it is unknown just how robust elemental production can be in mergers. Identifying signposts of the production of particular nuclei is critical for fully understanding merger-driven heavy-element synthesis. In this study, we investigate the properties of very neutron-rich nuclei for which superheavy elements (Z ≥ 104) can be produced in NSMs and whether they can similarly imprint a unique signature on kilonova light-curve evolution. A superheavy-element signature in kilonovae represents a route to establishing a lower limit on heavy-element production in NSMs as well as possibly being the first evidence of superheavy-element synthesis in nature. Favorable NSM conditions yield a mass fraction of superheavy elementsX Z ≥104≈ 3 × 10−2at 7.5 hr post-merger. With this mass fraction of superheavy elements, we find that the component of kilonova light curves possibly containing superheavy elements may appear similar to those arising from lanthanide-poor ejecta. Therefore, photometric characterizations of superheavy-element rich kilonova may possibly misidentify them as lanthanide-poor events.