On the Brightest Horizontal Branch Population II Star γ Piscium

The bright star γ Psc is among the nearest Population II giants located in the red clump region. Here we demonstrate that γ Psc is actually a core-helium burning horizontal branch star. As such, the τ ≃ 12 Gyr old γ Psc is found to be slightly over-massive at M HB = 0.97 ± 0.12 M ⊙, which suggests that it is possibly a rejuvenated source.

Contribution of Gaia Sausage to the Galactic Stellar Halo Revealed by K Giants and Blue Horizontal Branch Stars from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope, Sloan Digital Sky Survey, and Gaia

We explore the contribution of the Gaia Sausage to the stellar halo of the Milky Way by making use of a Gaussian mixture model (GMM) and applying it to halo star samples of Large Sky Area Multi-Object Fiber Spectroscopic Telescope K giants, Sloan Extension for Galactic Understanding and Exploration K giants, and Sloan Digital Sky Survey blue horizontal branch stars. The GMM divides the stellar halo into two parts, of which one represents a more metal-rich and highly radially biased component associated with an ancient, head-on collision referred to as the Gaia Sausage, and the other one is a more metal-poor and isotropic halo. A symmetric bimodal Gaussian is used to describe the distribution of spherical velocity of the Gaia Sausage, and we find that the mean absolute radial velocity of the two lobes decreases with the Galactocentric radius. We find that the Gaia Sausage contributes about 41%–74% of the inner (Galactocentric radius r gc < 30 kpc) stellar halo. The fraction of stars of the Gaia Sausage starts to decline beyond r gc ∼ 25–30 kpc, and the outer halo is found to be significantly less influenced by the Gaia Sausage than the inner halo. After the removal of halo substructures found by integrals of motion, the contribution of the Gaia Sausage falls slightly within r gc ∼ 25 kpc but is still as high as 30%–63%. Finally, we select several possible Sausage-related substructures consisting of stars on highly eccentric orbits. The GMM/Sausage component agrees well with the selected substructure stars in their chemodynamical properties, which increases our confidence in the reliability of the GMM fits.

AstroSat Study of the Globular Cluster NGC 2298: Probable Evolutionary Scenarios of Hot Horizontal Branch Stars

We present the far-UV (FUV) photometry of images acquired with UVIT on AstroSat to probe the horizontal branch (HB) population of the Galactic globular cluster NGC 2298. UV-optical color–magnitude diagrams (CMDs) are constructed for member stars in combination with Hubble Space Telescope UV Globular Cluster Survey data for the central region and Gaia and ground-based photometric data for the outer region. A blue HB (BHB) sequence with a spread and four hot HB stars are detected in all FUV-optical CMDs and are compared with theoretical updated BaSTI isochrones and synthetic HB models with a range in helium abundance, suggesting that the hot HB stars are helium enhanced when compared to the BHB. The estimated effective temperature, radius, and luminosity of HB stars, using the best spectral energy distribution fits, were compared with various HB models. BHB stars span a temperature range from 7500 to 12,250 K. Three hot HB stars have 35,000–40,000 K, whereas one star has around ∼100,000 K. We suggest the following evolutionary scenarios: two stars are likely to be the progeny of extreme HB (EHB) stars formed through an early hot-flasher scenario, one is likely to be an EHB star with probable helium enrichment, and the hottest HB star, which is about to enter the white dwarf cooling phase, could have evolved from the BHB phase. Nevertheless, these are interesting spectroscopic targets to understand the late stages of evolution.

The Far-away Blues: Exploring the Furthest Extents of the Boötes I Ultra-faint Dwarf Galaxy

Establishing the spatial extents and the nature of the outer stellar populations of dwarf galaxies is necessary for the determination of their total masses, current dynamical states, and past evolution. We here describe our investigation of the outer stellar content of the Boötes I ultra-faint dwarf galaxy, a satellite of the the Milky Way. We identify candidate member blue horizontal branch and blue straggler stars of Boötes I, both tracers of the underlying ancient stellar population, using a combination of multiband Pan-STARRS photometry and Gaia astrometry. We find a total of twenty-four candidate blue horizontal branch member stars with apparent magnitudes and proper motions consistent with membership of Boötes I, nine of which reside at projected distances beyond the nominal King profile tidal radius derived from earlier fits to photometry. We also identify four blue straggler stars of appropriate apparent magnitude to be at the distance of Boötes I, but all four are too faint to have high-quality astrometry from Gaia. The outer blue horizontal branch stars that we have identified confirm that the spatial distribution of the stellar population of Boötes I is quite extended. The morphology on the sky of these outer envelope candidate member stars is evocative of tidal interactions, a possibility that we explore further with simple dynamical models.

Convective Overshooting in Extreme Horizontal-branch Stars Using MESA with the k-omega Model*

To explore overshoot mixing beyond the convective core in core helium-burning stars, we use the k−ω model, which is incorporated into the Modules of Experiments in Stellar Astrophysics to investigate overshoot mixing in the evolution of subdwarf B (sdB) stars. Our results show that the development of the convective core can be divided into three stages. The mass of the convective core increases monotonically when the radiative temperature gradient, ∇rad, monotonically decreases outwardly, and overshoot mixing presents an exponential decay similar to Herwig. The splitting of the convective core occurs repeatedly when the minimum value of ∇rad near the convective boundary is smaller than the adiabatic temperature gradient, ∇ad. The mass at the outer boundary of the convective shell M sc can exceed 0.2 M ⊙ after the central helium abundance drops to about Y c ≈ 0.45. It is close to the convective core masses derived by asteroseismology for younger models (0.22 to ∼0.28 M ⊙). In the final stage, “core breathing pulses” occurred two or three times. Helium was injected into the convective core by overshoot mixing and increased the lifetime of sdB stars. The mass of the mixed region M mixed can rise to 0.303 M ⊙ by the end. The oxygen content in the central core of our g-mode sdB models is about 80% by mass. The high amounts of oxygen deduced from asteroseismology may be evidence supporting the existence of core breathing pulses.

Euphorbia sahyadrica (Euphorbiaceae), a new species of succulent shrub from the wet zone of the northern Western Ghats, Maharashtra, India

Euphorbia sahyadrica (Euphorbiaceae), a new succulent species belonging to Euphorbia subg. Euphorbia sect. Euphorbia is described and illustrated from the Raigad district of Maharashtra, India. It is related to E. nivulia but differs in its shrub-like habit, bark with closely-packed horizontal branch scars, elliptical-shaped leaf with short petiole and easily visible lateral veins, protruding tubercles with two pairs of spines per spine shield, bisexual cyathia in the central sessile position on the cyme, and capsules that have laterally tapering cocci without bulging suture lines between the cocci.

Global fits of axion-like particles to XENON1T and astrophysical data

The excess of electron recoil events seen by the XENON1T experiment has been interpreted as a potential signal of axion-like particles (ALPs), either produced in the Sun, or constituting part of the dark matter halo of the Milky Way. It has also been explained as a consequence of trace amounts of tritium in the experiment. We consider the evidence for the solar and dark-matter ALP hypotheses from the combination of XENON1T data and multiple astrophysical probes, including horizontal branch stars, red giants, and white dwarfs. We briefly address the influence of ALP decays and supernova cooling. While the different datasets are in clear tension for the case of solar ALPs, all measurements can be simultaneously accommodated for the case of a sub-dominant fraction of dark-matter ALPs. Nevertheless, this solution requires the tuning of several a priori unknown parameters, such that for our choices of priors a Bayesian analysis shows no strong preference for the ALP interpretation of the XENON1T excess over the background hypothesis.

Options for the treatment of the femoral hernia with atrophy of the public bone in the formed femoral canal

Femoral hernias make up 2–4 % of the total number of patients with hernias [1], the results of their treatment do not tend to improve [2–6].The aim of the study was to establish the incidence of atrophy of the pubic periosteum in patients with femoral hernia and to analyze the possible methods of surgery in their treatment.Material and methods. The analysis of the treatment of 249 patients with femoral hernias for the period from 1996 to 2021 was carried out. There were 61 men (24.5%), women – 188 (75.5%). in 14 (5.6%), atrophy of the pubic periosteum was revealed during operations. Since 2009, patients with femoral hernia and atrophy of the pubic periosteum began to use the "Method for the treatment of inguinal and femoral hernias" (patent for invention No. 2445002, authors V.I. Belokonev, A.V. Vavilov, A.V. Zharov, Yu. V. Ponomareva, A.G. Nogoga) [11], which was performed by inguinal access.Conclusions. In 5.6% of patients with femoral hernia and a long history, under the influence of the hernial sac, atrophy of the pubic periosteum occurs.A method of treating femoral and inguinal hernias by closing the hernial orifice with an elastic mesh with a protrusion at the medial edge of the mesh corresponding to the distance from the medial edge of the pupar ligament at the level of the femoral vein to the lower edge of the superior horizontal branch of the pubic bone (patent for invention No. 2445002) is an effective method of treating patients with hernias with destruction of the pubic bone periosteum in the femoral canal.