adsabs/SciX_UAT_keywords huggingface dataset:
The Cosmos in Its Infancy: JADES Galaxy Candidates at z > 8 in GOODS-S and GOODS-N

We present a catalog of 717 candidate galaxies at z > 8 selected from 125 square arcmin of NIRCam imaging as part of the JWST Advanced Deep Extragalactic Survey (JADES). We combine the full JADES imaging data set with data from the JWST Extragalactic Medium Survey and First Reionization Epoch Spectroscopic COmplete Survey (FRESCO) along with extremely deep existing observations from Hubble Space Telescope (HST)/Advanced Camera for Surveys (ACS) for a final filter set that includes 15 JWST/NIRCam filters and five HST/ACS filters. The high-redshift galaxy candidates were selected from their estimated photometric redshifts calculated using a template-fitting approach, followed by visual inspection from seven independent reviewers. We explore these candidates in detail, highlighting interesting resolved or extended sources, sources with very red long-wavelength slopes, and our highest-redshift candidates, which extend to z phot ∼ 18. Over 93% of the sources are newly identified from our deep JADES imaging, including 31 new galaxy candidates at z phot > 12. We also investigate potential contamination by stellar objects, and do not find strong evidence from spectral energy distribution fitting that these faint high-redshift galaxy candidates are low-mass stars. Using 42 sources in our sample with measured spectroscopic redshifts from NIRSpec and FRESCO, we find excellent agreement to our photometric redshift estimates, with no catastrophic outliers and an average difference of <Δz = z phot ‑ z spec> = 0.26. These sources comprise one of the most robust samples for probing the early buildup of galaxies within the first few hundred million years of the Universe's history.

Keywords: extragalactic astronomy; redshift surveys; james webb space telescope; high-redshift galaxies; galaxies
Shiva and Shakti: Presumed Proto-Galactic Fragments in the Inner Milky Way

Using Gaia Data Release 3 astrometry and spectroscopy, we study two new substructures in the orbit–metallicity space of the inner Milky Way: Shakti and Shiva. They were identified as two confined, high-contrast overdensities in the (L z , E) distribution of bright (G < 16) and metal-poor (‑2.5 < [M/H] < ‑ 1.0) stars. Both have stellar masses of M ⋆ ≳ 107 M ⊙, and are distributed on prograde orbits inside the solar circle in the Galaxy. Both structures have an orbit-space distribution that points toward an accreted origin; however, their abundance patterns—from APOGEE—are such that are conventionally attributed to an in situ population. These seemingly contradictory diagnostics could be reconciled if we interpret the abundances [Mg/Fe], [Al/Fe], [Mg/Mn] versus [Fe/H] distribution of their member stars merely as a sign of rapid enrichment. This would then suggest one of two scenarios. Either these prograde substructures were created by some form of resonant orbit trapping of the field stars by the rotating bar; a plausible scenario proposed by Dillamore et al. Or, Shakti and Shiva were protogalactic fragments that formed stars rapidly and coalesced early, akin to the constituents of the poor old heart of the Milky Way, just less deep in the Galactic potential and still discernible in orbit space.

Keywords: milky way stellar halo; galactic abundances; galactic archaeology; galaxy kinematics; surveys
QTT Ultra-wideband Signal Acquisition and Baseband Data Recording System Design Based on the RFSoC Platform

The 110 m QiTai radio Telescope (QTT) will be equipped with multiple Ultra-WideBand (UWB) receivers in the primary and Gregory focus to achieve continuous frequency coverage from 270 MHz to 115 GHz, which poses great challenges to signal acquisition, transmission, and real-time processing. Aiming at 10 GHz and above full-bandwidth acquisition and multi-scientific processing for the QTT UWB signals, an experimental system with high-speed signal acquisition, 100 Gb network multi-path distribution, and fast recording is designed by using advanced direct RF-sampling technology and heterogeneous architecture. The system employs a ZCU111 board to digitize dual-polarization signals with a sampling rate of 4.096 GigaSamples-Per-Second and 12-bit quantization. The collected wideband signals are channelized into 2048 chunks, which are then assembled into 16 sets of digital narrow basebands with 128 MHz bandwidth and transmitted to the processing servers through two 100 Gb ports. A HASPIPE pipeline, UWB_HASHPIPE is designed to receive and store multiple subbands in parallel. Data distribution links can be flexibly configured based on IP addresses and port numbers. The system is verified by pulsar observation experiments on the Nanshan 26 m telescope. 512 MHz bandwidth is selected from the collected L-band receiver signals and recorded in VDIF file format with 8 parallel instances. The test results show that the data integrity is excellent, and the signal-to-noise ratio of the band-merged pulsar profile is stronger than single subband data. This paper provides a high-performance and flexible solution for the design of versatile UWB backends. Meanwhile, the developed platform can be integrated into QTT backends for baseband data collection and Very Long Baseline Interferometry observation.

Keywords: radio spectroscopy; radio telescopes; astronomical techniques; astronomy data acquisition; astronomical instrumentation
Spectroscopic Properties of the Astrochemical Molecules [Al, O, Si] x (x = 0, +1)

Aluminum and silicon are present in large quantities in the interstellar medium, making the triatomic species consisting of both elements intriguing with regard to the foundations of astrochemistry. Spectroscopic parameters have been calculated via high-level ab initio methods to assist with laboratory and observational detection of [Al, O, Si] x (x = 0,+1). All [Al, O, Si] x (x = 0,+1) isomers exist in the linear geometry, with linear AlOSi (X 2Π) and linear AlOSi+ (X 1Δ) being the most stable neutral and cationic species, respectively. Formation of the neutral species most likely occurs via reaction of AlO/SiO on an Si/Al dust grain surface, respectively. The cation molecules may form via ion-neutral reaction or as a consequence of photoionization. The rotational frequencies of linear AlOSi (X 2Π) have been calculated using vibrationally corrected rotational constants and centrifugal distortion to lead experimental and observational radio detection. The rotational frequencies are discussed for three temperatures indicative of various astronomical environments: the central circumstellar envelope (CSE) (100 K), outer CSE (30 K), and the interstellar medium (3 K). At 100 K, the lines originating from J' > 30 are the best candidates for detection via ground-based telescope. Anharmonic vibrational analysis revealed various Fermi resonances that may complicate the vibrational spectrum of linear AlOSi (X 2Π). Finally, electronic spectroscopy may be the best means for laboratory detection of linear AlOSi (X 2Π), due to the presence of two overlapping electronic transitions with large oscillator strengths occurring at approximately 250 nm.

Keywords: astrochemistry; circumstellar dust; photodissociation regions; molecular spectroscopy
Blackbody Temperature of 200+ Stellar Flares Observed with the CoRoT Satellite

We estimated blackbody temperature for 209 flares observed at 69 F-K stars, significantly increasing the number of flare temperature determinations. We used the Blue and Red channels obtained by the 27 cm telescope of the CoRoT satellite at high cadence and long duration. The wavelength limits of the channels were estimated using spectra from the Pickles library for the spectral type and luminosity class of each star, provided by the Exodat Database. The temperatures were obtained from the flare energy Blue-to-Red ratio, using the flare equivalent duration and stellar flux in both channels. The expected value of the analyzed flares is equal to 6400 K with a standard deviation of 2800 K, where the mean stellar spectral type, weighted by the number of flares in each spectral subclass, is equal to G6. Contrary to our results, a stellar white-light flare is often assumed to emit as a blackbody with a temperature of 9000 or 10,000 K. Our estimates agree, however, with values obtained for solar flares. The GAIA G-band transmissivity is comparable to that of the CoRoT White channel, which allows us to calibrate the flares to the Gaia photometric system. The energy in the G band of the analyzed flares varies between 1032 and 1037 erg, and the flare area ranges from 30 μsh to 3 sh (solar hemisphere). The energy release per area in a flare is proportional to ${T}_{\mathrm{flare}}^{2.6}$ , at least up to 10,000 K.

Keywords: stellar flares; optical flares; astrostatistics; artificial satellites; stellar rotation; stellar properties
Tests of Conservation Laws in Post-Newtonian Gravity with Binary Pulsars

General relativity is a fully conservative theory, but there exist other possible metric theories of gravity. We consider nonconservative ones with a parameterized post-Newtonian parameter, ζ2. A nonzero ζ2 induces a self-acceleration for the center of mass of an eccentric binary pulsar system, which contributes to the second time derivative of the pulsar spin frequency, $\ddot{\nu }$ . In our work, using Will's method, we provide an improved analysis with four well-timed, carefully chosen binary pulsars. In addition, we extend Will's method and derive the effect of ${\zeta }_{2}$ on the third time derivative of the spin frequency, $\dddot{\nu }$ . For PSR B1913+16, the constraint from $\dddot{\nu }$ is even tighter than that from $\ddot{\nu }$ . We combine multiple pulsars with Bayesian inference, and obtain the upper limit, $\left|{\zeta }_{2}\right|\lt 1.3\times {10}^{-5}$ at the 95% confidence level, assuming a flat prior in ${\mathrm{log}}_{10}\left|{\zeta }_{2}\right|$ . It improves the existing bound by a factor of 3. Moreover, we propose an analytical timing formalism for ${\zeta }_{2}$ . Our simulated times of arrival with simplified assumptions show the capability of binary pulsars in limiting ζ2, and useful clues are extracted for real-data analysis in future. In particular, we discover that for PSRs B1913+16 and J0737-3039A, $\dddot{\nu }$ can yield more constraining limits than $\ddot{\nu }$ .

Keywords: gravitation; binary pulsars; pulsar timing method; millisecond pulsars; non-standard theories of gravity; gravitational interaction; relativistic binary stars
Evidence for Enrichment of Niobium-92 in the Outer Protosolar Disk

The short-lived radionuclide, niobium-92 (92Nb), has been used to estimate the site of nucleosynthesis for p-nuclei and the timing of planetary differentiation, assuming that it was uniformly distributed in the early solar system. Here, we present the internal niobium-zirconium (Nb-Zr) isochron dating of Northwest Africa (NWA) 6704, an achondrite thought to form in the outer protosolar disk due to nucleosynthetic isotope similarities with carbonaceous chondrites. The isochron defines an initial 92Nb/93Nb ratio of (2.72 ± 0.25) × 10-5 at the NWA 6704 formation, 4562.76 ± 0.30 million years ago. This corresponds to a 92Nb/93Nb ratio of (2.96 ± 0.27) × 10-5 at the time of solar system formation, which is ~80% higher than the values obtained from meteorites formed in the inner disk. The results suggest that a significant proportion of the solar 92Nb was produced by a nearby core-collapse supernova (CCSN) and that the outer disk was more enriched in CCSN ejecta, which could account for the heterogeneity of short-lived 26Al and nucleosynthetic stable-isotope anomalies across the disk. We propose that NWA 6704 serves as the best anchor for mapping relative Nb-Zr ages of objects in the outer solar system onto the absolute timescale.

Keywords: nucleosynthesis; solar system formation; supernovae; meteorites
No Self-shadowing Instability in 2D Radiation Hydrodynamical Models of Irradiated Protoplanetary Disks

Theoretical models of protoplanetary disks including stellar irradiation often show a spontaneous amplification of scale height perturbations, produced by the enhanced absorption of starlight in enlarged regions. In turn, such regions cast shadows on adjacent zones that consequently cool down and shrink, eventually leading to an alternating pattern of overheated and shadowed regions. Previous investigations have proposed this to be a real self-sustained process, the so-called self-shadowing or thermal wave instability, which could naturally form frequently observed disk structures such as rings and gaps, and even potentially enhance the formation of planetesimals. All of these, however, have assumed in one way or another vertical hydrostatic equilibrium and instantaneous radiative diffusion throughout the disk. In this work we present the first study of the stability of accretion disks to self-shadowing that relaxes these assumptions, relying instead on radiation hydrodynamical simulations. We first construct hydrostatic disk configurations by means of an iterative procedure and show that the formation of a pattern of enlarged and shadowed regions is a direct consequence of assuming instantaneous radiative diffusion. We then let these solutions evolve in time, which leads to a fast damping of the initial shadowing features in layers close to the disk surface. These thermally relaxed layers grow toward the midplane until all temperature extrema in the radial direction are erased in the entire disk. Our results suggest that radiative cooling and gas advection at the disk surface prevent a self-shadowing instability from forming, by damping temperature perturbations before these reach lower, optically thick regions.

Keywords: protoplanetary disks; hydrodynamical simulations; planet formation; radiative transfer simulations
Untangling the Sources of Abundance Dispersion in Low-metallicity Stars

We measure abundances of 12 elements (Na, Mg, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni) in a sample of 86 metal-poor (-2 ≲ [Fe/H] ≲ -1) subgiant stars in the solar neighborhood. Abundances are derived from high-resolution spectra taken with the Potsdam Echelle Polarimetric and Spectroscopic Instrument on the Large Binocular Telescope, modeled using iSpec and MOOG. By carefully quantifying the impact of photon-noise (<0.05 dex for all elements), we robustly measure the intrinsic scatter of abundance ratios. At fixed [Fe/H], the rms intrinsic scatter in [X/Fe] ranges from 0.04 (Cr) to 0.16 dex (Na), with a median of 0.08 dex. Scatter in [X/Mg] is similar, and accounting for [α/Fe] only reduces the overall scatter moderately. We consider several possible origins of the intrinsic scatter with particular attention to fluctuations in the relative enrichment by core-collapse supernovae (CCSN) and Type Ia supernovae and stochastic sampling of the CCSN progenitor mass distribution. The stochastic sampling scenario provides a good quantitative explanation of our data if the effective number of CCSN contributing to the enrichment of a typical sample star is N ~ 50. At the median metallicity of our sample, this interpretation implies that the CCSN ejecta are mixed over a gas mass ~6 × 104 M ⊙ before forming stars. The scatter of elemental abundance ratios is a powerful diagnostic test for simulations of star formation, feedback, and gas mixing in the early phases of the Galaxy.

Keywords: abundance ratios; high resolution spectroscopy; chemical enrichment; supernovae
On the Size of the Flare Associated with the Solar Proton Event in 774 AD

The 774 AD solar proton event (SPE) detected in cosmogenic nuclides had an inferred >1 GV (>430 MeV) fluence estimated to have been ∼30-70 times larger than that of the 1956 February 23 ground level event (GLE). The 1956 GLE was itself ∼2.5 times larger at >430 MeV than the episode of strong GLE activity from 1989 August-October. We use an inferred soft X-ray (SXR) class of X20 ± 10 for the 1956 February 23 eruptive flare as a bridge to the source flare for the 774 SPE. A correlation of the >200 MeV proton fluences of hard-spectra post-1975 GLEs with the SXR peak fluxes of their associated flares yields an SXR flare class of X285 ± 140 (bolometric energy of ∼(1.9 ± 0.7) × 1033 erg) for the 774 flare. This estimate is within theoretical determinations of the largest flare the Sun could produce based on the largest spot group yet observed. Assuming a single eruptive flare source for the 774 SPE, the above estimate indicates that the Sun can produce a threshold-level 1033 erg superflare. If the 774 event originated in two closely timed, equal-fluence SPEs, the inferred flare size drops to X180 ± 90 (∼(1.4 ± 0.5) × 1033 erg). We speculate on favorable solar conditions that can lead to enhanced shock acceleration of high-energy protons in eruptive flares.

Keywords: the sun; solar energetic particles; solar coronal mass ejection shocks; solar flares
Radiative Association between Neutral Radicals in the Interstellar Medium: CH3 + CH3O

Uncertainties in the production mechanisms of interstellar complex organic molecules call for a precise investigation of gas-phase synthetic routes for these molecules, especially at low temperatures. Here, we report a study of the gas-phase formation of dimethyl ether from the neutral radicals methyl and methoxy via the process of radiative association. This process may be important to synthesize dimethyl ether and species such as methyl formate, for which dimethyl ether is a precursor. The reaction is found to be rapid by the standards of radiative association, especially at 10 K, where its rate coefficient is calculated by two different methods to be 3 × 10-11 or 2 × 10-10 cm3 s-1; the lower rate is calculated with a more precise theory and is likely more accurate. Insertion of this reaction into the Nautilus network is found not to explain fully the abundance of dimethyl ether in cold and prestellar cores, especially in those cores with the highest dimethyl ether abundances.

Keywords: astrochemistry; reaction rates; interstellar molecules
Testing Strong Gravitational Lensing Effects of Supermassive Compact Objects with Regular Spacetimes

We compare and contrast gravitational lensing, in the strong field limit, by the photon sphere in spherically symmetric regular electrically charged (REC) black holes (0 < b ≤ b E ) and with those by corresponding REC no-horizon spacetimes (b > b E ). Here, b is an additional parameter due to the charge and the value b = b E ≈ 0.226 corresponds to an extremal black hole with degenerate horizons. Interestingly, the spacetime admits a photon sphere for 0 < b ≤ b P ≈ 0.247 and an anti-photon sphere only for b E < b ≤ b P . With no-horizon spacetime, images by lensing from the inside of the photon sphere (u < u ps) can also appear. Interestingly, for the case of u < u ps the deflection angle α D increases with u. We analyze the lensing observables by modeling compact objects Sgr A*, M87*, NGC 4649, and NGC 1332 as black holes and no-horizon spacetimes. The angular position θ ∞ and photon sphere radius x ps decrease with increasing parameter b. Our findings suggest that the angular separations (s) and magnification (r) of relativistic images inside the photon sphere may be higher than those outside. Moreover, the time delay for Sgr A* and M87* can reach ~8.8809 and ~12,701.8 minutes, respectively, at b = 0.2, deviating from Schwarzschild black holes by ~2.615 and ~4677 minutes. These deviations are insignificant for Sgr A* because it is too small, but they are sufficient for astronomical observation of M87* and some other black holes. With EHT bounds on the θ sh of Sgr A* and M87* within the 1σ region, placing bounds on the parameter b, our analysis concludes that REC black holes agree with the EHT results in finite space, whereas the corresponding REC no-horizon spacetimes are completely ruled out.

Keywords: strong gravitational lensing; astrophysical black holes; event horizons; photon sphere; gravitational deflection; compact objects
Analysis of Five Double-lined Spectroscopic Eclipsing Binaries Observed with TESS and LAMOST

Based on analysis of high-precision photometry from the Transiting Exoplanet Survey Satellite combining with spectroscopy from the medium-resolution spectra of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope, we investigated five double-lined spectroscopic eclipsing binaries (TIC 0165626871, TIC 0159105847, TIC 0122446076, TIC 0349294422, and TIC 0155968973). With the help of Wilson-Devinney program, we accurately derived their absolute stellar parameters. TIC 0165626871, TIC 0159105847, and TIC 0122446076 were identified as detached binaries, while TIC 0349294422 and TIC 0155968973 were recognized as A-subtype and W-subtype W UMa-type systems, respectively. Especially, absolute parameters of four binaries except for TIC 0122446076 were obtained for the first time. TIC 0165626871 also shows light variations of out-of-eclipse phases, which are probably contributed by starspots. The light pulsations of TIC 0122446076 could originate from the primary star that is located in the classical Cepheid instability strip. Evolutionary states of all stars were also discussed.

Keywords: eclipsing binary stars
Elliptical Accretion Disk as a Model for Tidal Disruption Events

Elliptical accretion disk models for tidal disruption events (TDEs) have been recently proposed and independently developed by two groups. Although these two models are characterized by a similar geometry, their physical properties differ considerably. In this paper, we further investigate the properties of the elliptical accretion disk of the nearly uniform distribution of eccentricity within the disk plane. Our results show that the elliptical accretion disks have distinctive hydrodynamic structures and spectral energy distributions, associated with TDEs. The soft X-ray photons generated at pericenter and nearby are trapped in the disk and advected around the ellipse because of large electron scattering opacity. They are absorbed and reprocessed into emission lines and low-frequency continuum via recombination and bremsstrahlung emission. Because of the rapid increase of bound-free and free-free opacities with radius, the low-frequency continuum photons become trapped in the disk at large radius and are advected through apocenter and back to the photon-trapping radius. Elliptical accretion disks predict sub-Eddington luminosities and emit mainly at the photon-trapping radius of thousands of Schwarzschild radii with a blackbody spectrum of nearly single temperature of typically about 3 × 104 K. Because of the self-regulation, the photon-trapping radius expands and contracts following the rise and fall of accretion rate. The radiation temperature is nearly independent of BH mass and accretion rate and varies weakly with the stellar mass and the viscosity parameter. Our results are well consistent with the observations of optical/UV TDEs.

Keywords: accretion; black hole physics; active galaxies; supermassive black holes; tidal disruption; galaxy accretion disks
The Behavior of HgMn Stars in the Far UV-Paper 23: HD 144844

The analysis of four high resolution spectra of the Mn P Ga star HD 144844 recorded by the SWP camera on board the International Ultraviolet Explorer does not reveal variations of the far ultraviolet flux of this star from 1994 July 1st to July 12th. The IUE spectra sample four different rotational phases of the rotational period derived recently from the Kepler lightcurve which shows that the far ultraviolet flux of HD 144844 is not modulated by rotation. However a previous low resolution SWP spectrum taken in August 1989 has significantly more FUV flux shortwards of 1700 Å than the spectra collected in 1994 July. On the the first spectrum of the 1994 July observations, the Al II resonance line at 1670.79 Å is split into two components probably reflecting the orbital motions of HD 144844 and its companion.

Keywords: chemically peculiar stars; helium-weak stars