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.

Near-UV Reddening Observed in the Reflectance Spectrum of High-inclination Centaur 2012 DR30

Centaurs with high orbital inclinations and perihelia (i > 60°; q ≳ 5 au) are a small group of poorly understood minor planets that are predicted to enter the giant planet region of the solar system from the inner Oort Cloud. As such, they are one of the few samples of relatively unaltered Oort Cloud material that can currently be directly observed. Here we present two new reflectance spectra of one of the largest of these objects, 2012 DR30, in order to constrain its color and surface composition. Contrary to reports that 2012 DR30 has variable optical color, we find that consistent measurements of its spectral gradient from most new and published data sets at 0.55–0.8 μm agree with a spectral gradient of S ′ ≃ 10 % ± 1 % / 0.1 μ m within their uncertainties. The spectral variability of 2012 DR30 at near-UV/blue and near-IR wavelengths, however, is still relatively unconstrained; self-consistent rotationally resolved follow-up observations are needed to characterize any spectral variation in those regions. We tentatively confirm previous detections of water ice on the surface of 2012 DR30, and we also consistently observe a steady steepening of the gradient of its spectrum from λ ∼ 0.6 μm toward near-UV wavelengths. Plausible surface materials responsible for the observed reddening may include ferric oxides contained within phyllosilicates and aromatic refractory organics.

Evolution of the Ultraviolet Upturn at 0.3 < z < 1: Exploring Helium-rich Stellar Populations

We measure the near-UV (rest-frame ∼2400 Å) to optical color for early-type galaxies in 12 clusters at 0.3 < z < 1.0. We show that this is a suitable proxy for the more common far-ultraviolet bandpass used to measure the ultraviolet upturn and find that the upturn is detected to z = 0.6 in these data, in agreement with previous work. We find evidence that the strength of the upturn starts to wane beyond this redshift and largely disappears at z = 1. Our data are most consistent with models where early-type galaxies contain minority stellar populations with non-cosmological helium abundances, up to around 46%, formed at z ≥ 3, resembling globular clusters with multiple stellar populations in our Galaxy. This suggests that elliptical galaxies and globular clusters share similar chemical evolution and star formation histories. The vast majority of the stellar mass in these galaxies also must have been in place at z > 3.

A Review on Colorimetric Sensing of Tumor Markers Based on Enzyme-Mimicking Nanomaterials

: Nanomedicine is an arising field that exploits nanotechnology concepts for pioneered therapy and diagnostics. Colorimetric sensors for tumor markers have displayed interesting benefits compared to conventional systems in clinical laboratory diagnosis. Colorimetric immunoassay based approaches show up-and-coming results since the goal cancer marker is determined with high sensitivity but without the utilize of advanced/expensive techniques through an effortless optical color change. Also, colorimetric biosensor has the potential to detect proteins in biological fluids swiftly with high sensitivity, and they are anticipated to play a progressively serious role in tumor diagnosis. We are reviewed (covering the period 2015–2020) various studies performed based on colorimetric sensing strategy using nanostructured materials (highly efficient enzyme mimics, artificial enzymes or nanozymes) in the detection of various tumor antigens in biological fluids are reviewed. Specifically, we highlight the recent progress and efforts in the construction of colorimetric immunosensors. Colorimetric immunosensors can be roughly divided into two main categories: transition metal nanozyme-based sensing and noble metal nanozyme-based sensings.