An official website of the United States government
Abstract The interplay and correlation between the $$^{22}$$ 22 Ne $$(\alpha ,\gamma )^{26}$$ ( α , γ ) 26 Mg and the competing $$^{22}$$ 22 Ne $$(\alpha ,n)^{25}$$ ( α , n ) 25 Mg reaction plays an important role for the interpretation of the $$^{22}$$ 22 Ne $$(\alpha ,n)^{25}$$ ( α , n ) 25 Mg reaction as a neutron source in the s - and n -processes. This paper provides a summary and new data on the $$\alpha $$ α -cluster and single-particle structure of the compound nucleus $$^{26}$$ 26 Mg and the impact on the reaction rate of these two competing processes in stellar helium burning environments.
more »
« less
Stellar Neutrino Emission across the Mass–Metallicity Plane
Abstract We explore neutrino emission from nonrotating, single-star models across six initial metallicities and 70 initial masses from the zero-age main sequence to the final fate. Overall, across the mass spectrum, we find metal-poor stellar models tend to have denser, hotter, and more massive cores with lower envelope opacities, larger surface luminosities, and larger effective temperatures than their metal-rich counterparts. Across the mass–metallicity plane we identify the sequence (initial CNO →14N →22Ne →25Mg →26Al →26Mg →30P →30Si) as making primary contributions to the neutrino luminosity at different phases of evolution. For the low-mass models we find neutrino emission from the nitrogen flash and thermal pulse phases of evolution depend strongly on the initial metallicity. For the high-mass models, neutrino emission at He-core ignition and He-shell burning depends strongly on the initial metallicity. Antineutrino emission during C, Ne, and O burning shows a strong metallicity dependence with22Ne(α,n)25Mg providing much of the neutron excess available for inverse-βdecays. We integrate the stellar tracks over an initial mass function and time to investigate the neutrino emission from a simple stellar population. We find average neutrino emission from simple stellar populations to be 0.5–1.2 MeV electron neutrinos. Lower metallicity stellar populations produce slightly larger neutrino luminosities and averageβdecay energies. This study can provide targets for neutrino detectors from individual stars and stellar populations. We provide convenient fitting formulae and open access to the photon and neutrino tracks for more sophisticated population synthesis models.
more »
« less
- PAR ID:
- 10480813
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal Supplement Series
- Volume:
- 270
- Issue:
- 1
- ISSN:
- 0067-0049
- Format(s):
- Medium: X Size: Article No. 5
- Size(s):
- Article No. 5
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Many of the short-lived radioactive nuclei that were present in the early solar system can be produced in massive stars. In the first paper in this series, we focused on the production of26Al in massive binaries. In our second paper, we considered rotating single stars; two more short-lived radioactive nuclei,36Cl and41Ca; and the comparison to the early solar system data. In this work, we update our previous conclusions by further considering the impact of binary interactions. We used the MESA stellar evolution code with an extended nuclear network to compute massive (10–80M⊙), binary stars at various initial periods and solar metallicity (Z= 0.014), up to the onset of core collapse. The early solar system abundances of26Al and41Ca can be matched self-consistently by models with initial masses ≥25M⊙, while models with initial primary masses ≥35M⊙can also match36Cl. Almost none of the models provide positive net yields for19F, while for22Ne the net yields are positive from 30M⊙and higher. This leads to an increase by a factor of approximately 4 in the amount of22Ne produced by a stellar population of binary stars, relative to single stars. In addition, besides the impact on the stellar yields, our 10M⊙primary star undergoing Case A mass transfer ends its life as a white dwarf instead of as a core-collapse supernova. This demonstrates that binary interactions can also strongly impact the evolution of stars close to the supernova boundary.more » « less
-
Abstract One of the most important stellar neutron sources is the22Ne($$\alpha ,n$$ )25Mg reaction, which gets activated both during the helium intershell burning in asymptotic giant branch stars and in core helium and shell carbon burning in massive stars. The22Ne($$\alpha ,n$$ )25Mg reaction serves as the main neutron producer for the weaks-process and provides a short but strong neutron exposure during the helium flash phase of the mains-process, significantly affecting the abundances at thes-process branch points. The cross section needs to be known at very low energies, as close as possible to the neutron threshold at$$E_\alpha =$$ 562 keV (Q= −478 keV), but both direct and indirect measurements have turned out to be very challenging, leading to significant uncertainties. Here we discuss the current status of the reaction, including recent and upcoming measurements, and provide a discussion on the astrophysical implications as well as an outlook into the near future.more » « less
-
Abstract Isotope variations of nucleosynthetic origin among solar system solid samples are well documented, yet the origin of these variations is still uncertain. The observed variability of 54 Cr among materials formed in different regions of the protoplanetary disk has been attributed to variable amounts of presolar, chromium-rich oxide (chromite) grains, which exist within the meteoritic stardust inventory and most likely originated from some type of supernova explosion. To investigate if core-collapse supernovae (CCSNe) could be the site of origin of these grains, we analyze yields of CCSN models of stars with initial masses 15, 20, and 25 M ⊙ , and solar metallicity. We present an extensive abundance data set of the Cr, Mg, and Al isotopes as a function of enclosed mass. We find cases in which the explosive C ashes produce a composition in good agreement with the observed 54 Cr/ 52 Cr and 53 Cr/ 52 Cr ratios as well as the 50 Cr/ 52 Cr ratios. Taking into account that the signal at atomic mass 50 could also originate from 50 Ti, the ashes of explosive He burning also match the observed ratios. Addition of material from the He ashes (enriched in Al and Cr relative to Mg to simulate the make-up of chromite grains) to the solar system’s composition may reproduce the observed correlation between Mg and Cr anomalies, while material from the C ashes does not present significant Mg anomalies together with Cr isotopic variations. In all cases, nonradiogenic, stable Mg isotope variations dominate over the variations expected from 26 Al.more » « less
-
Abstract We investigate dust attenuation and its dependence on viewing angle for 308 star-forming galaxies at 1.3 ≤z≤ 2.6 from the MOSFIRE Deep Evolution Field survey. We divide galaxies with a detected Hαemission line and coverage of Hβinto eight groups by stellar mass, star formation rate (SFR), and inclination (i.e., axis ratio), and we then stack their spectra. From each stack, we measure the Balmer decrement and gas-phase metallicity, and then we compute the medianAVand UV continuum spectral slope (β). First, we find that none of the dust properties (Balmer decrement,AV, orβ) varies with the axis ratio. Second, both stellar and nebular attenuation increase with increasing galaxy mass, showing little residual dependence on SFR or metallicity. Third, nebular emission is more attenuated than stellar emission, and this difference grows even larger at higher galaxy masses and SFRs. Based on these results, we propose a three-component dust model in which attenuation predominantly occurs in star-forming regions and large, dusty star-forming clumps, with minimal attenuation in the diffuse ISM. In this model, nebular attenuation primarily originates in clumps, while stellar attenuation is dominated by star-forming regions. Clumps become larger and more common with increasing galaxy mass, creating the above mass trends. Finally, we argue that a fixed metal yield naturally leads to mass regulating dust attenuation. Infall of low-metallicity gas increases the SFR and lowers the metallicity, but leaves the dust column density mostly unchanged. We quantify this idea using the Kennicutt–Schmidt and fundamental metallicity relations, showing that galaxy mass is indeed the primary driver of dust attenuation.more » « less
