September 2025 · 9 Articles · Pages 1–147
September 2025
Open Access9 Articles · Pages 1–147
We perform a detailed frequency analysis of 48 Delta Scuti stars observed during the Kepler mission using four years of continuous short-cadence photometry. Iterative prewhitening reveals between 12 and 180 significant pulsation frequencies per star, spanning both pressure and gravity mode domains. We identify regular frequency spacings in 19 stars consistent with asymptotic theory predictions, enabling mode identification and constraints on the internal rotation profiles. Our results highlight the diagnostic power of space-based asteroseismology for probing the interior structure of intermediate-mass pulsators.
We present detailed chemical abundance determinations for 27 metal-poor ([Fe/H] < −2.0) halo stars based on high-resolution, high signal-to-noise VLT/UVES spectra. We measure abundances of 22 elements from carbon through europium using spectrum synthesis and equivalent width methods. The observed alpha-element enhancements and neutron-capture element patterns provide new constraints on the relative contributions of core-collapse supernovae and neutron star mergers to early Galactic chemical enrichment, with three stars showing r-process enhancement consistent with a single prolific nucleosynthesis event.
We present deep 21-cm emission-line observations of the circumgalactic medium surrounding 12 nearby spiral galaxies obtained with the MeerKAT radio telescope. Column density sensitivity of 5 × 10^17 cm^−2 per 5 km/s channel reveals extended neutral hydrogen envelopes reaching 2–3 times the optical radius in eight systems. We detect diffuse gaseous filaments connecting two galaxy pairs, providing direct evidence of cold gas accretion along cosmic web filaments. The total circumgalactic H I masses correlate with host galaxy star formation rate, supporting models of baryon cycling in galaxy evolution.
We construct two-dimensional radiative transfer models of five protoplanetary disks in the Ophiuchus star-forming region, constrained by multi-wavelength ALMA continuum observations at Bands 3, 6, and 7. By simultaneously fitting the spectral energy distributions and resolved millimeter visibilities, we derive dust temperature profiles that reveal midplane temperatures 20–40% cooler than previous estimates based on single-band analyses. These revised thermal structures shift the predicted snow lines of major volatile species inward by 5–15 au, with direct implications for models of planetesimal composition and giant planet core accretion.
We analyze flux ratio anomalies in a sample of 24 quadruply-imaged gravitationally lensed quasars observed with HST and Keck adaptive optics imaging. By comparing the observed flux ratios with smooth lens model predictions, we detect significant anomalies in 15 systems that require the presence of dark matter subhalos with masses in the range 10^6–10^9 solar masses. The inferred subhalo mass function is consistent with cold dark matter predictions and disfavors warm dark matter models with particle masses below 5 keV, providing independent constraints complementary to Lyman-alpha forest and satellite galaxy studies.
We reconstruct the star formation histories of 18 dwarf satellite galaxies in the Local Group using deep HST color-magnitude diagrams reaching below the oldest main-sequence turnoff. By fitting synthetic stellar populations to the observed distributions, we determine quenching timescales ranging from rapid (<500 Myr) for the closest satellites to extended (2–4 Gyr) for more distant systems. The correlation between quenching timescale and pericentric distance supports ram pressure stripping as the primary quenching mechanism, with tidal interactions playing a secondary role for the most massive satellites.
The Wide Field Camera 3 on the Hubble Space Telescope has been the workhorse instrument for exoplanet atmospheric spectroscopy over the past decade. This review synthesizes results from transmission and emission spectroscopy surveys of over 70 transiting exoplanets observed with WFC3, covering the detection of water vapor, cloud and haze properties, and constraints on atmospheric metallicity across the mass-temperature parameter space. We critically evaluate systematic uncertainties including stellar contamination and instrumental ramps, and assess how WFC3 results have laid the groundwork for the JWST era of exoplanet characterization.
We present VLT/MUSE integral field spectroscopy of the central region of the Galactic globular cluster NGC 3201, providing radial velocities for 3,200 individual stars within the half-light radius. Jeans modeling of the stellar velocity dispersion profile reveals a central mass excess of approximately 800 solar masses that cannot be accounted for by a concentration of stellar-mass remnants alone. While an intermediate-mass black hole provides the best fit to the kinematic data, we discuss alternative explanations including a cluster of unresolved stellar-mass black holes retained through dynamical interactions.
We report the discovery of a recurrent nova candidate in the bulge of M31, identified through systematic monitoring with the Zwicky Transient Facility. The source has exhibited three outbursts in 2023, 2024, and 2025, each reaching a peak absolute magnitude of M_R = −8.1 with a rapid decline time of t_2 = 4 days. Spectroscopic follow-up during the 2025 eruption reveals broad Balmer and He II emission lines characteristic of a high-mass white dwarf accreting near the Chandrasekhar limit, making this system a candidate Type Ia supernova progenitor worthy of continued monitoring.