We present new observational benchmarks of rapid neutron-capture process (
- NSF-PAR ID:
- 10337155
- Date Published:
- Journal Name:
- The Astrophysical Journal Supplement Series
- Volume:
- 260
- Issue:
- 2
- ISSN:
- 0067-0049
- Page Range / eLocation ID:
- 27
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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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. -
null (Ed.)Context. NGC 6522 is a moderately metal-poor bulge globular cluster ([Fe/H]∼−1.0), and it is a well-studied representative among a number of moderately metal-poor blue horizontal branch clusters located in the bulge. The NGC 6522 abundance pattern can give hints on the earliest chemical enrichment in the central Galaxy. Aims. The aim of this study is to derive abundances of the light elements C and N; alpha elements O, Mg, Si, Ca, and Ti; odd-Z elements Na and Al; neutron-capture elements Y, Zr, Ba, La, and Nd; and the r-process element Eu. We verify if there are first- and second-generation stars: we find clear evidence of Na-Al, Na-N, and Mg-Al correlations, while we cannot identify the Na-O anti-correlation from our data. Methods. High-resolution spectra of six red giants in the bulge globular cluster NGC 6522 were obtained at the 8m VLT UT2-Kueyen telescope with both the UVES and GIRAFFE spectrographs in FLAMES+UVES configuration. In light of Gaia data, it turned out that two of them are non-members, but these were also analysed. Spectroscopic parameters were derived through the excitation and ionisation equilibrium of Fe i and Fe ii lines from UVES spectra. The abundances were obtained with spectrum synthesis. Comparisons of abundances derived from UVES and GIRAFFE spectra were carried out. Results. The present analysis combined with previous UVES results gives a mean radial velocity of vhel = −15.62±7.7 km s−1 and a r metallicity of [Fe/H] = −1.05±0.20 for NGC 6522. Mean abundances of alpha elements for the present four member stars are enhanced with [O/Fe]=+0.38, [Mg/Fe]=≈+0.28, [Si/Fe]≈+0.19, and [Ca/Fe]≈+0.13, together with the iron-peak element [Ti/Fe]≈+0.13, and the r-process element [Eu/Fe]=+0.40. The neutron-capture elements Y, Zr, Ba, and La show enhancements in the +0.08 < [Y/Fe] < +0.90, 0.11 < [Zr/Fe] < +0.50, 0.00 < [Ba/Fe] < +0.63, 0.00 < [La/Fe] < +0.45, and -0.10 < [Nd/Fe] < +0.70 ranges. We also discuss the spread in heavy-element abundances.more » « less
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Context. NGC 6522 is a moderately metal-poor bulge globular cluster ([Fe/H] ~ −1.0), and it is a well-studied representative among a number of moderately metal-poor blue horizontal branch clusters located in the bulge. The NGC 6522 abundance pattern can give hints on the earliest chemical enrichment in the central Galaxy. Aims. The aim of this study is to derive abundances of the light elements C and N; alpha elements O, Mg, Si, Ca, and Ti; odd-Z elements Na and Al; neutron-capture elements Y, Zr, Ba, La, and Nd; and the r -process element Eu. We verify if there are first- and second-generation stars: we find clear evidence of Na–Al, Na–N, and Mg–Al correlations, while we cannot identify the Na–O anti-correlation from our data. Methods. High-resolution spectra of six red giants in the bulge globular cluster NGC 6522 were obtained at the 8m VLT UT2-Kueyen telescope with both the UVES and GIRAFFE spectrographs in FLAMES+UVES configuration. In light of Gaia data, it turned out that two of them are non-members, but these were also analysed. Spectroscopic parameters were derived through the excitation and ionisation equilibrium of Fe I and Fe II lines from UVES spectra. The abundances were obtained with spectrum synthesis. Comparisons of abundances derived from UVES and GIRAFFE spectra were carried out. Results. The present analysis combined with previous UVES results gives a mean radial velocity of v r hel = −15.62±7.7 km s −1 and a metallicity of [Fe/H] = −1.05 ± 0.20 for NGC 6522. Mean abundances of alpha elements for the present four member stars are enhanced with [O/Fe] = +0.38, [Mg/Fe] = ≈+0.28, [Si/Fe] ≈ +0.19, and [Ca/Fe] ≈ +0.13, together with the iron-peak element [Ti/Fe] ≈ +0.13, and the r -process element [Eu/Fe] = +0.40. The neutron-capture elements Y, Zr, Ba, and La show enhancements in the +0.08 < [Y/Fe] < +0.90, 0.11 < [Zr/Fe] < +0.50, 0.00 < [Ba/Fe] < +0.63, 0.00 < [La/Fe] < +0.45, and −0.10 < [Nd/Fe] < +0.70 ranges. We also discuss the spread in heavy-element abundances.more » « less
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Context. Phosphorus (P) is considered to be one of the key elements for life, making it an important element to look for in the abundance analysis of spectra of stellar systems. Yet, only a select number of spectroscopic studies exist to estimate the phosphorus abundances and investigate its trend across a range of metallicities. This is due to the lack of good phosphorus lines in the optical wavelength region and the requirement of careful manual analysis of the blended phosphorus lines in near-infrared H-band spectra obtained with individual observations and surveys such as the Apache Point Observatory Galactic Evolution Experiment (APOGEE). Aims. Based on a consistent and systematic analysis of high-resolution, near-infrared Immersion GRating INfrared Spectrograph (IGRINS) spectra of 38 K giant stars in the Solar neighborhood, we present and investigate the phosphorus abundance trend in the metallicity range of −1.2 dex < [Fe/H] < 0.4 dex. Furthermore, we compare this trend with the available chemical evolution models to shed some light on the origin and evolution of phosphorus. Methods. We have observed full H - and K -band spectra at a spectral resolving power of R = 45 000 with IGRINS mounted on the Gemini South telescope, the Discovery Channel Telescope, and the Harlan J Smith Telescope at McDonald Observatory. Abundances were determined from spectral lines by modeling the synthetic spectrum that best matches the observed spectrum by χ 2 minimization. For this task, we used the Spectroscopy Made Easy (SME) tool in combination with one-dimensional (1D) Model Atmospheres in a Radiative and Convective Scheme (MARCS) stellar atmosphere models. The investigated sample of stars have reliable stellar parameters estimated using optical FIber-fed Echelle Spectrograph (FIES) spectra obtained in a previous study of a set of stars called Giants in the Local Disk (GILD). In order to determine the phosphorus abundances from the 16482.92 Å phosphorus line, we needed to take special care blending the CO( v = 7−4) line. With the stellar parameters known, we thus determined the C, N, and O abundances from atomic carbon and a range of nonblended molecular lines (CO, CN, and OH) which are plentiful in the H-band region of K giant stars, assuring an appropriate modeling of the blending CO( v = 7−4) line. Results. We present the [P/Fe] versus [Fe/H] trend for K giant stars in the metallicity range of −1.2 dex < [Fe/H] < 0.4 dex and enhanced phosphorus abundances for two metal-poor s-rich stars. We find that our trend matches well with the compiled literature sample of prominently dwarf stars and the limited number of giant stars. Our trend is found to be higher by ~0.05−0.1 dex compared to the theoretical chemical evolution trend resulting from the core collapse supernova (type II) of massive stars with the phosphorus yields arbitrarily increased by a factor of 2.75. Thus the enhancement factor might need to be ~0.05−0.1 dex higher to match our trend. We also find an empirically determined primary behavior for phosphorus. Furthermore, the phosphorus abundance is found to be elevated by ~0.6−0.9 dex in the two s-enriched stars compared to the theoretical chemical evolution trend.more » « less
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Abstract We apply a novel statistical analysis to measurements of 16 elemental abundances in 34,410 Milky Way disk stars from the final data release (DR17) of APOGEE-2. Building on recent work, we fit median abundance ratio trends [X/Mg] versus [Mg/H] with a 2-process model, which decomposes abundance patterns into a “prompt” component tracing core-collapse supernovae and a “delayed” component tracing Type Ia supernovae. For each sample star, we fit the amplitudes of these two components, then compute the residuals Δ[X/H] from this two-parameter fit. The rms residuals range from ∼0.01–0.03 dex for the most precisely measured APOGEE abundances to ∼0.1 dex for Na, V, and Ce. The
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