Evaluating Helium Varations By Modeling Red Giant Branch Bump of Large Magellanic Cluster NGC 1978

Many evidence show that the Multiple Population (MP) features ex- ist not only in the old Galactic globular clusters but also in the intermediate-age clusters in the Megallanic Clouds (MCs), which are characterized by star-to-star abundance scatter of several elements, including Helium (He). The photometric properties of the red giant branch bump (RGBB) are proved to be related to the variation in helium abundances of the member stars of the star clusters. We use the “Modules for Experiments in Stellar Astrophysics” (MESA) stellar evolution code to calculate the evolution sequences of stars along the red giant branch with changing helium content. Following the RGB sequences, we then generate a lu- minosity function of the RGB stars within the grid of input helium abundances, which are compared with the observational data of an intermediate-age MC cluster NGC 1978. The result of the current study reveals that the star to star helium abundance variation is 0.03.

Properties of the Hyades, the eclipsing binary HD 27130, and the oscillating red giant ϵ Tauri

Context. The derivation of accurate and precise masses and radii is possible for eclipsing binary stars, allowing for insights into their evolution. When residing in star clusters, they provide measurements of even greater precision, along with additional information on their properties. Asteroseismic investigations of solar-like oscillations offers similar possibilities for single stars. Aims. We wish to improve the previously established properties of the Hyades eclipsing binary HD 27130 and re-assess the asteroseismic properties of the giant star ϵ Tau. The physical properties of these members of the Hyades can be used to constrain the helium content and age of the cluster. Methods. New multi-colour light curves were combined with multi-epoch radial velocities to yield masses and radii of HD 27130. Measurements of Teff were derived from spectroscopy and photometry, and verified using the Gaia parallax. We estimated the cluster age from re-evaluated asteroseismic properties of ϵ Tau while using HD 27130 to constrain the helium content. Results. The masses, radii, and Teff of HD 27130 were found to be M = 1.0245 ± 0.0024 M⊙, R = 0.9226 ± 0.015 R⊙, Teff = 5650 ± 50 K for the primary, and M = 0.7426 ± 0.0016 M⊙, R = 0.7388 ± 0.026 R⊙, Teff = 4300 ± 100 K for the secondary component. Our re-evaluation of ϵ Tau suggests that the previous literature estimates are trustworthy and that the HIPPARCOS parallax is more reliable than the Gaia DR2 parallax. Conclusions. The helium content of HD 27130 and, thus, of the Hyades is found to be Y = 0.27 but with a significant model dependency. Correlations with the adopted metallicity result in a robust helium enrichment law, with ΔY/ΔZ close to 1.2 We estimate the age of the Hyades to be 0.9 ± 0.1 (stat) ±0.1 (sys) Gyr, which is in slight tension with recent age estimates based on the cluster white dwarfs. The precision of the age estimate can be much improved via asteroseismic investigations of the other Hyades giants and by future improvements to the Gaia parallax for bright stars.

Detecting the signatures of helium in type Iax supernovae

Recent studies have argued that the progenitor system of type Iax supernovae must consist of a carbon-oxygen white dwarf accreting from a helium star companion. Based on existing explosion models invoking the pure deflagration of carbon-oxygen white dwarfs, we investigate the likelihood of producing spectral features due to helium in type Iax supernovae. From this scenario, we select those explosion models producing ejecta and 56Ni masses that are broadly consistent with those estimated for type Iax supernovae (0.014–0.478 M⊙ and ∼0.003–0.183 M⊙, respectively). To this end, we present a series of models of varying luminosities (−18.4 ≲ MV ≲ −14.5 mag) with helium abundances accounting for up to ∼36% of the ejecta mass, and covering a range of epochs beginning a few days before B-band maximum to approximately two weeks after maximum. We find that the best opportunity for detecting He I features is at near-infrared wavelengths, and in the post-maximum spectra of the fainter members of this class. We show that the optical spectrum of SN 2007J is potentially consistent with a large helium content (a few 10−2 M⊙), but argue that current models of accretion and material stripping from a companion struggle to produce compatible scenarios. We also investigate the presence of helium in all objects with near-infrared spectra. We show that SNe 2005hk, 2012Z, and 2015H contain either no helium or their helium abundances are constrained to much lower values (≲10−3 M⊙). For the faint type Iax supernova, SN 2010ae, we tentatively identify a small helium abundance from its near-infrared spectrum. Our results demonstrate the differences in helium content among type Iax supernovae, perhaps pointing to different progenitor channels. Either SN 2007J is an outlier in terms of its progenitor system, or it is not a true member of the type Iax supernova class.

Nanoindentation and TEM to Study the Cavity Fate after Post-Irradiation Annealing of He Implanted EUROFER97 and EU-ODS EUROFER

The effect of post-helium irradiation annealing on bubbles and nanoindentation hardness of two reduced activation ferritic martensitic steels for nuclear fusion applications (EUROFER97 and EU-ODS EUROFER) has been studied. Helium-irradiated EUROFER97 and EU-ODS EUROFER were annealed at 450 °C for 100 h in an argon atmosphere. The samples were tested by nanoindentation and studied by transmission electron microscopy extracting some focused ion beam lamellae containing the whole implanted zone (≈50 µm). A substantial increment in nanoindentation hardness was measured in the area with higher helium content, which was larger in the case of EUROFER97 than in EU-ODS EUROFER. In terms of microstructure defects, while EU-ODS EUROFER showed larger helium bubbles, EUROFER97 experienced the formation of a great population density of them, which means that the mechanism that condition the evolution of cavities for these two materials are different and completely dependent on the microstructure.