Abundances of Elements Lighter than Scandium in the Atmosphere of the Standard Giant Star α Sex (HD 87887, A0 III)

The abundances of elements lighter than scandium in the atmosphere of the A0 III giant, α Sex, are derived using archival ultraviolet and optical spectra. Most of the strongest lines present in the far-ultraviolet spectrum of α Sex can be attributed to chemical elements lighter than calcium. The synthesis of selected lines in the optical and ultraviolet yields new abundances, in particular for elements which have few lines in the optical range. Helium, oxygen, silicon and sulfur are found to have solar abundances, most other elements are underabundant. Aluminium may be marginally overabundant. The lines of chlorine are probably present in the FUV but they are too blended to derive the abundance of chlorine.

L199, A NEW VARIABLE STAR IN M13

During a routine study of the variable stars of Messier 13 (NGC 6205 = Cl 1639+365) we have discovered the variability of L199 (TYC 2588-1386-2), a red giant star member of the cluster: using the photometric data –in V band– obtained in the 2019 and 2020 campaigns we have verified its variability. Data from the Zwicky Transient Facility (ZTF) and Deras et al. (2019) were utilized to determine its type of variability and period estimation: our data suggest that it is a semiregular red giant, similar to the other variables of this type of the cluster, whose cycles of photometric variation are not identical; we derived a period of ~27 days (although without a regular periodicity) and an amplitude smaller: 0.08 ± 0.03 magnitudes in V band although they may be somewhat larger or smaller. With this discovery the cluster now has 63 variable stars.

Discovery of new globular clusters in the Sagittarius dwarf galaxy

Context. Globular clusters (GCs) are witnesses of the past accretion events onto the Milky Way. In particular, the GCs of the Sagittarius (Sgr) dwarf galaxy are important probes of an on-going merger. Aims. Our main goal is to search for new GC members of this dwarf galaxy using the VISTA Variables in the Via Lactea Extended Survey (VVVX) near-infrared database combined with the Gaia Early Data Release 3 (EDR3) optical database. Methods. We investigated all VVVX-enabled discoveries of GC candidates in a region covering about 180 sq. deg. toward the bulge and the Sgr dwarf galaxy. We used multiband point-spread function photometry to obtain deep color-magnitude diagrams (CMDs) and luminosity functions (LFs) for all GC candidates, complemented by accurate Gaia-EDR3 proper motions (PMs) to select Sgr members and variability information to select RR Lyrae which are potential GC members. Results. After applying a strict PM cut to discard foreground bulge and disk stars, the CMDs and LFs for some of the GC candidates exhibit well defined red giant branches and red clump giant star peaks. We selected the best Sgr GCs, estimating their distances, reddenings, and associated RR Lyrae. Conclusions. We discover 12 new Sgr GC members, more than doubling the number of GCs known in this dwarf galaxy. In addition, there are 11 other GC candidates identified that are uncertain, awaiting better data for confirmation.

DFT study of “unlayered graphene solid” formation, in liquid carbon droplets at low pressures

This atomistic modeling study is companion to new experimental work on carbon vapor slow-cooled in (a) the laboratory and (b) the atmosphere of ancient carbon-synthesizing stars. It specifically follows up on TEM clues about the nucleation of unlayered graphene sheets in a solidifying carbon liquid, to show that 5 atom loops may help explain evidence for faceted pentacones in a slow-cooled melt. This is also first in a series of modeling studies that may open the door to laboratory studies of (i) condensation in cool-giant star atmospheres and (ii) liquid carbon at low pressures. Graphic abstract

Grass/Legume Compatibility in the Derived Savanna Regions of Western State of Nigeria

THE grass/legume compatibility between six grasses and three legumes were studied at Fashola State Farm in the derived savanna region of Western State of Nigeria. The highest herbage yields per hectare per annum were obtained from the mixed swards. The yields of legumes were smaller in the mixtures with the tall than in the short grasses. It was concluded that in this area, Stylosanthes gracillis was compatible with the elephant and Guinea grasses. Pueraria Phaseoloids was compatible with the Northern Gambia and the mulasses grasses, while the Centrosema pubescence combined well with the giant star grasses.

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.

The Gaia-ESO Survey: an extremely Li-rich giant in globular cluster NGC 1261

Lithium-rich stars in globular clusters are rare. Only 14 have been found so far, in different evolutionary phases from dwarfs to giants. Different mechanisms have been proposed to explain this enhancement, but it is still an open problem. Using spectra collected within the Gaia-ESO Survey, obtained with the GIRAFFE spectrograph at the ESO Very Large Telescope, we present the discovery of the first Li-rich star in the cluster NGC 1261, the second star known in the red giant branch bump phase. The star shows an extreme Li overabundance of A(Li)LTE = 3.92 ± 0.14, corresponding to A(Li)NLTE = 3.40 dex. We propose that the Li enhancement is caused by fresh Li production through an extra mixing process (sometimes referred to as cool bottom burning). Alternatively, it could be a pre-existing Li overabundance caused by mass-transfer from a red giant star; this mechanism does not enhance the barium abundance and thus we observe low barium. To unambiguously explain the Li enhancement in globular cluster stars, however, a reliable determination of the abundance of key species like Be, 6Li, 12C/13C, and several s-process elements is required, as well as detailed modelling of chromospheric activity indicators.