Sazuna/UAT_keywords huggingface dataset:
A Spectroscopic Search for Dormant Black Holes in Low-metallicity Binaries. The discovery of the massive black hole (BH) system Gaia BH3 in pre-release Gaia DR4 data suggests that wide BH binaries with luminous companions may be significantly overrepresented at low metallicities. Motivated by this finding, we have initiated a spectroscopic survey of low-metallicity stars exhibiting elevated RUWE values in Gaia DR3, using the FEROS and Automated Planet Finder spectrographs. We identify promising BH binary candidates as objects with instantaneously measured radial velocities (RVs) that are very different from their mean RVs reported in Gaia DR3. Thus far, we have observed over 500 targets, including a nearly complete sample of stars with [Fe/H] &lt; ‑1.5, RUWE &gt; 2, and G &lt; 15. Our search has yielded one promising target exhibiting slow acceleration and an RV more than 98 km s‑1 different from its DR3 mean RV, as well as dozens of other candidates with smaller RV discrepancies. We quantify the sensitivity of our search using simulations, demonstrating that it recovers at least half of the BH companions within our selection criteria. We make all the spectra and RVs from our survey publicly available and encourage further follow-up.

Keywords: Binary stars, Stellar mass black holes
Carbon Burning Cannot Explain Puffy Hypervelocity White Dwarfs. Several hypervelocity white dwarfs (HVWDs) with space velocities of ≳1000 km s‑1 have recently been discovered. One possible origin of these stars is the dynamically driven double-degenerate double-detonation (D6) scenario, in which an accreting sub-Chandrasekhar mass carbon-oxygen (CO) WD detonates as a SN Ia. In this scenario, the less massive WD may survive its companion's detonation and be ejected as a HVWD. Most of the observed HVWDs are hotter and puffier than normal WDs, perhaps due to their recent proximity to a SN. In this work, we test whether these properties can be explained by long-lived stable carbon (C) burning in the interiors of CO WD donors triggered by a SN shock. We model the long-term evolution of CO WDs following rapid energy injection using 1D models. We find that stable C burning can be ignited in CO WDs with masses of 0.95–1.10 M⊙ if SN energy penetrates sufficiently deeply. The resulting born-again stars settle on the C-burning main sequence while they convert their interiors from C and O to Ne and Mg, where they have temperatures and radii similar to some of the observed HVWDs. However, the timescale over which C-burning WDs remain inflated is ≲105 yr, which is at least an order of magnitude shorter than the kinematic ages of observed hot HVWDs. We conclude that observed HVWDs are unlikely to be inflated by C burning. The stellar evolution of observed HVWDs remains an open problem.

Keywords: Stellar evolutionary models, White dwarf stars, Type Ia supernovae, Binary stars
The La Silla Schmidt Southern Survey. We present the La Silla Schmidt Southern Survey (LS4), a new wide-field, time-domain survey to be conducted with the 1 m ESO Schmidt telescope. The 268 megapixel LS4 camera mosaics 32 2k × 4k fully depleted CCDs, providing a ∼20 deg2 field of view with 1″ pixel‑1 resolution. The LS4 camera will have excellent performance at longer wavelengths: in a standard 45 s exposure the expected 5σ limiting magnitudes in g, i, z are ∼21.5, ∼20.9, and ∼20.3 mag (AB), respectively. The telescope design requires a novel filter holder that fixes different bandpasses over each quadrant of the detector. Two quadrants will have i band, while the other two will be g and z band with color information obtained by dithering targets across the different quadrants. The majority (90%) of the observing time will be used to conduct a public survey that monitors the extragalactic sky at both moderate (3 days) and high (1 day) cadence, as well as focused observations within the Galactic plane and bulge. Alerts from the public survey will be broadcast to the community via established alert brokers. LS4 will run concurrently with the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST). The combination of LS4+LSST will enable detailed holistic monitoring of many nearby transients: high-cadence LS4 observations will resolve the initial rise and peak of the light curve while less-frequent but deeper observations by LSST will characterize the years before and after explosion. Here, we summarize the primary science objectives of LS4 including microlensing events in the Galaxy, extragalactic transients powered by massive black holes or stellar explosions, the search for electromagnetic counterparts to multi-messenger events, and supernova cosmology.

Keywords: Sky surveys, Gravitational wave sources, Hubble constant, Gravitational microlensing, Supernovae, Astrophysical black holes
Direct Detection of Known Exoplanets in Reflected Light: Predicting Sky Position with Literature Orbit Solutions. The next generation of ground- and space-based observatories will enable direct imaging and characterization of cold, mature planets through thermal emission and, for the first time, reflected light detection. Known RV and astrometrically detected planets provide a known population for detection and characterization observations. However, many of the most promising targets lack orbital parameters of sufficient precision to confidently predict their location on relative to the star for a direct imaging campaign. We have developed projecc, an open source Python package designed to generate sky-plane planet location posteriors from literature orbit solutions. This tool aims to facilitate community preparation for direct imaging observations of known planets. In this work we describe projecc and use it to examine two case study systems relevant to reflected light imaging with ELTs: GJ 876 b, which we find has a well-constrained prediction, and Proxima Centauri b, whose location remains highly uncertain. We provide a web app for exploring reflected light planet targets and their orbit solutions, including predictions from literature for 17 additional planets, located at https://reflected-light-planets.streamlit.app/. We also discuss future upgrades to projecc.

Keywords: Extrasolar rocky planets, Orbital motion, Exoplanet detection methods, Orbital elements, Exoplanets, Orbits, Coronagraphic imaging, Direct imaging, Keplerian orbit
SKYSURF. VIII. Modeling SKYSURF Completeness Data for Comparison to the Hubble Space Telescope Exposure Time Calculator. Accurately assessing image source completeness is critical for interpreting measurements on telescope data. Using the Wide Field Camera 3 and Advanced Camera for Surveys data from the Hubble Space Telescope archival project "SKYSURF," we model galaxy completeness as a function of the exposure time and background of an image. This is accomplished by adding simulated objects with varying magnitudes and sizes into these images, and determining the detection rate for each set of parameters. The fifty percent completeness results are then compared to the Exposure Time Calculator (ETC), in order to assess the differences between the STSCI ETC and our analysis of the archival data. Ultimately, we find that, for extended galaxies, the ETC predicts a 1─2 mag fainter completeness limit than our data. We believe the difference is due to the ETC's flat surface brightness profiles being less accurate at predicting for extended sources compared to our more realistic profiles.

Keywords: Hubble Space Telescope, Sky surveys, Cosmic background radiation, HST photometry
PIST-Net: A Multimodal Deep Learning Framework for Red Giant Stellar Parameter Estimation. Red giant stars are pivotal for probing the formation and evolution of the Galaxy. Conventional methods for determining their parameters typically rely on high-precision, resource-demanding observations over long durations. In this work, we present a novel deep learning approach, the Photometric Image Spectral Transformer Net, which utilizes low-resolution spectra from LAMOST Data Release (DR) 10 and photometric data from SDSS DR17 for multimodal stellar parameter estimation. The proposed approach employs two specialized architectures: SP-Net for spectral data and ResNet for photometric images, which are subsequently fused using a transformer encoder for cross-modal integration. Our results demonstrate that this approach achieves promising performance in estimating five key physical parameters, including effective temperature (Teff), surface gravity ( logg ), metallicity ([M/H]), mass and radius. Notably, the model achieves particularly strong results for Teff and [M/H], with mean absolute errors of 0.025 and 0.021, respectively. This significantly outperforms models relying on a single modality. This study highlights the advantages of multimodal learning techniques in improving the accuracy of stellar parameter estimation, while reducing reliance on time-consuming observational methods. All code and data used in this study are available at GitHub (https://github.com/yuexiuya1/PIST-Net).

Keywords: Fundamental parameters of stars, Red giant stars, Neural networks
The Rayleigh Criterion: Resolution Limits of Astronomical Periodograms. The Rayleigh criterion determines the resolution limit of a periodogram, which is the minimum frequency separation required to barely resolve two sinusoids. Failing to consider the Rayleigh criterion may result in incorrect interpretations of long-period signals or spurious claims that two closely spaced periodogram peaks represent two distinct physical processes. Resolution considerations can help astronomers decide which periodogram peaks truly represent oscillatory signals, a question that is of great importance for exoplanet detection. We demonstrate how applying the Rayleigh criterion can help observers avoid false positive detections caused by uneven observing cadence or insufficient observing time baseline. We present three synthetic data sets that showcase the importance of the Rayleigh criterion in interpreting the generalized Lomb–Scargle and Bayesian periodograms. Our synthetic data sets illustrate (1) a single oscillation with a split Lomb–Scargle periodogram peak resulting from uneven observing cadence can be mistaken for two oscillations if the Rayleigh criterion is neglected, (2) oversampling a periodogram's frequency grid does not improve resolution, and (3) observing time baseline requirements for resolving two closely spaced oscillations. We use the Rayleigh criterion to revisit detections of planets, stellar activity, and differential rotation from four published data sets. We show that the frequency separation between planet 55 Cnc d and the activity cycle is too small to distinguish the two phenomena based on published radial velocities (RVs) alone. Likewise, the contested 4970 days planet orbiting HD 99492 cannot be statistically separated from zero frequency. We determine that a cubic polynomial better explains the long-term RV variability of Barnard's star than a sinusoid model. Finally, our re-analysis of Kepler observations of two active stars shows that the signals previously attributed to differential rotation can be modeled by a Gaussian process with a single quasiperiodicity. This work demonstrates the importance of considering Rayleigh resolution when constructing a time-domain model.

Keywords: Light curves, Lomb-Scargle periodogram, Period search , Exoplanet detection methods, Time series analysis
Artificial Satellite Trails Detection Using U-Net Deep Neural Network and Line Segment Detector Algorithm. With the rapid increase in the number of artificial satellites, astronomical imaging is experiencing growing interference. When these satellites reflect sunlight, they produce streak-like artifacts in photometry images. Such satellite trails can introduce false sources and cause significant photometric errors. As a result, accurately identifying the positions of satellite trails in observational data has become essential. In this work, we propose a satellite trail detection model that combines the U-Net deep neural network for image segmentation with the Line Segment Detector algorithm. The model is trained on 375 simulated images of satellite trails, generated using data from the Mini-SiTian Array. Experimental results show that for trails with a signal-to-noise ratio greater than 3, the detection rate exceeds 99%. Additionally, when applied to real observational data from the Mini-SiTian Array, the model achieves a recall of 79.57% and a precision of 74.56%.

Keywords: Artificial satellites, Astronomical techniques, Astronomy data analysis
Advances in the QTT Digital Backend: Design, Implementation and Verification. The Xinjiang Qitai Radio Telescope (QTT) in China is equipped with a variety of receivers covering 270 MHz–116 GHz (initially 50 GHz), presenting unique signal acquisition challenges due to varying bandwidths, beams, and locations, along with extreme data rates. To address these challenges, we developed the Wanxiang digital backend employing Radio Frequency System-on-Chip (RFSoC) technology for RF-direct signal digitization and an elastic high-performance computing (HPC) cluster for multifunctional post-processing. The system supports multiple observation modes, including pulsars, transients, spectral lines, continuum, and very long baseline interferometry/baseband. High-performance shielded enclosures minimize electromagnetic radiation from digital devices in receiver cabins. A 100 Gb s‑1 network enables massive data transfer to the HPC cluster for real-time processing, integrating radio frequency interference mitigation, raw voltage capture, and coordinated observation capabilities. The scalable architecture enables expansion via additional RFSoC and computing nodes. We present verification results including custom RFSoC development, electromagnetic compatibility design and test, software implementation, and successful pulsar observations, demonstrating the system's readiness for scientific operations. This integrated solution significantly enhances signal fidelity while optimizing resource utilization for QTT's advanced research capabilities.

Keywords: Radio spectroscopy, Astronomy data acquisition, Astronomical techniques, Radio telescopes, Astronomical instrumentation
Characterization of the Cherenkov Photon Background for Low-noise Silicon Detectors in Space. Future space observatories that seek to perform imaging and spectroscopy of faint astronomical sources will require ultra-low-noise detectors that are sensitive over a broad wavelength range. Silicon charge-coupled devices (CCDs), such as EMCCDs, skipper CCDs, multi-amplifier sensing CCDs, and single-electron sensitive read out CCDs have demonstrated the ability to detect and measure single photons from X-ray energies to near the silicon band gap (∼1.1 μm), making them candidate technologies for this application. In this context, we study a relatively unexplored source of low-energy background coming from Cherenkov radiation produced by energetic cosmic rays traversing a silicon detector. We present a model for Cherenkov photon production and absorption that is calibrated to laboratory data, and we use this model to characterize the residual background rate for ultra-low-noise silicon detectors in space. We study how the Cherenkov background rate depends on detector thickness, variations in solar activity, and the contribution of heavy cosmic ray species (Z &gt; 2). We find that for thick silicon detectors, such as those required to achieve high quantum efficiency at long wavelengths, the rate of cosmic-ray-induced Cherenkov photon production is comparable to other detector and astrophysical backgrounds. We apply our Cherenkov background model to simulated spectroscopic observations of extra-solar planets, and we find that thick detectors continue to outperform their thinner counterparts at longer wavelengths despite a larger Cherenkov background rate. Furthermore, we find that minimal masking of cosmic-ray tracks continues to maximize the signal-to-noise ratio of very faint sources despite the existence of extended halos of Cherenkov photons.

Keywords: CCD observation, Exoplanets, Space observatories, Astronomical detectors, Space telescopes
Ground-based Mid-IR Direct Imaging: The Origin of the Thermal Background on the Keck II Telescope and Correcting Instrumental Systematics. Mid-IR wavelengths are of particular interest to exoplanet science due to the fact they can extend the searchable parameter space to planets that are older and/or colder. However, a significant source of uncertainty at mid-IR wavelengths on ground-based telescopes is the thermal background. This background comes from blackbody radiation in the atmosphere and telescope and is therefore dependent on instrument design and atmospheric conditions. When performing imaging observations, this background manifests as a slowly varying, inhomogeneous signal throughout the image, underlying our data. Photometry at mid-IR can greatly constrain atmospheric models but existing data are usually scarce or have significant error bars due to the difficulty of subtracting the background. Using M-band direct imaging observing sequences on NIRC2, we evaluate the thermal background of the Keck II telescope and attempt to subtract the background in a more comprehensive way. For our primary science target, the forming protoplanet AB Aur b, we present a contrast upper limit of 2 × 10‑4 in M-band and address the limiting factors in our observation due to the thermal background. We determine that the origin of the systematic components of the thermal background comes from the K-mirror and find that the thermal background is also strongly influenced by emission from the secondary spiders on Keck II.

Keywords: Proplyds, Direct imaging, Sky noise, Astronomical instrumentation
JWST NIRSpec's Cosmic Ray Experience at L2. We characterize cosmic ray interactions in blanked-off JWST Near Infrared Spectrograph (NIRSpec) "dark" exposures. In its Sun/Earth-Moon L2 halo orbit, JWST encounters energetic ions that penetrate NIRSpec's radiation shielding. The shielded cosmic ray hit rate decreased from approximately 4.3 to 2.3 ions cm−2 s−1 during the first three years of operation. A typical hit affects about 7.1 pixels necessitating mitigation during calibration and deposits around 6 keV in the λco = 5.4 μm HgCdTe detector material (equivalent to ∼5200 charges). The corresponding linear energy transfer is about 0.86 keV μm−1. As we are currently near solar maximum, galactic cosmic ray flux is expected to increase as solar activity declines, leading to an anticipated rise in the NIRSpec rate from 2.3 to 4.3 ions cm−2 s−1 by early 2027 and potentially reaching ∼6 ions cm−2 s−1 in the early 2030s. We investigate rare, large "snowball" hits and, less frequently, events with secondary showers that pose significant calibration challenges. We explore their possible origins as heavy ions, secondary particles from shielding, or inelastic scattering in the HgCdTe detector material. We discuss the implications of these findings for future missions including the Nancy Grace Roman Space Telescope.

Keywords: Space telescopes, Astronomical instrumentation
Theory of Exozodi Sources and Dust Evolution. Exozodiacal dust disks (exozodis) are populations of warm (∼300 K) or hot (∼1000 K) dust, located in or interior to a star's habitable zone, detected around ∼25% of main-sequence stars as excess emission over the stellar photosphere at mid- or near-infrared wavelengths. Often too plentiful to be explained by an in situ planetesimal belt, exozodi dust is usually thought to be transported inwards from further out in the system. There is no consensus on which (if any) of various proposed dynamical models is correct, yet it is vital to understand exozodis given the risk they pose to direct imaging and characterisation of Earth-like planets. This article reviews current theoretical understanding of the origin and evolution of exozodi dust. It also identifies key questions pertinent to the potential for exozodis to impact exoplanet imaging and summarises current understanding of the answer to them informed by exozodi theory. These address how exozodi dust is delivered, its size and spatial distribution, and the effect of its composition on exozodi observability, as well as the connection between hot and warm exozodis. Also addressed are how common different exozodi levels are and how that level can be predicted from system properties, as well as the features that planets impart in dust distributions and how exozodis affect a planet's physical properties and habitability. We conclude that exozodis present both a problem and an opportunity, e.g., by introducing noise that makes planets harder to detect, but also identifying systems in which ingredients conducive to life, like water and volatiles, are delivered to the habitable zone.

Keywords: Exoplanet dynamics, Debris disks, Exozodiacal dust, Planetesimals
An Introduction to Dust Evolution and Vertical Transport in Protoplanetary Disks. This tutorial is an introduction to observational studies of dust transport and evolution in protoplanetary disks. Spatially resolved observations of disks at multiple wavelengths can allow us to infer the distribution of various dust grains and gas species. Combining these observations offers a more complete understanding of dust structure and properties across different disk locations. For example, by better characterizing the disk's vertical structure, observations help to constrain the level of vertical settling and identify regions of high dust density, which are favorable for grain growth and planet formation. This tutorial describes various methodologies for inferring dust properties and vertical height of different tracers, as an introduction for beginners.

Keywords: Radiative transfer equation, Dust continuum emission, Protoplanetary disks, Exoplanet formation
The Spectrum and Polarization Variation Study at Short-term Timescales for Four Luminous Blazars. Blazars exhibit complex variability of fluxes, spectra, and polarizations, whose underlying mechanisms remain an open question. We analyze short-term spectral and polarization variability in four luminous flat-spectrum radio quasars (3C 454.3, B2 1633+382, PKS 1510─08, CTA 102) using optical photometric, polarimetric, and spectroscopic data from the Steward Observatory (2008─2018). We find that optical flux correlates positively with polarization degree in 12 of 13 flare segments. Three sources demonstrate redder-when-brighter trend, contrasting with CTA 102's distinctive bluer-when-brighter behavior during its 2016─2017 outburst. The BWB trend could be explained by the peak-frequency modulation within the shock-in-jet model. Polarization angle trajectories show diverse rotation patterns, including clockwise, anticlockwise, and oscillations, that currently lack a universal theoretical explanation. Nevertheless, a unified two-component model successfully explains both spectral trends and correlations between the polarization and fluxes through varying jet-to-disk flux ratios, providing critical constraints on blazar physics.

Keywords: Blazars, Flat-spectrum radio quasars, Relativistic jets, Galaxy accretion disks