adsabs/SciX_UAT_keywords huggingface dataset:
Research on the Fiducial Fibre Coding and Identification Algorithm of the LAMOST Fibre Positioning System

To obtain the world coordinates of a measured object in camera measurement, a certain number of image control points should be established around the detected object as fiducial points for data processing. The precision of a fiducial point directly determines the measurement accuracy of the measured object in the camera measurement. Fiducial points in camera measurement are widely used in various fields of measurement, such as aerial surveys, close-range surveys, and 3D reconstruction. In addition, a fiducial point generally adopts an encoding structure to reduce the search cost in the detection. Camera measurement is used in the LAMOST fiber positioning system, which also requires fiducial points to ensure the accuracy of fiber positioning. Different from a general fiducial point, the whole system needs to operate under dark conditions during LAMOST observation, and optical fiber positioning is carried out by the "backlighting method", which measures the optical fiber spot under a dark background. In addition, fiber positioning needs to reach an accuracy of 40 μm at a distance of 20 m, which is difficult to achieve with the fiducial points used in general vision measurements. To meet the requirements of LAMOST optical fiber positioning with high accuracy, this paper presents a fiducial fiber and its recognition algorithm for optical fiber positioning of optical fiber spectroscopic telescopes. The fiducial fiber can be applied to a wide-field optical fiber spectroscopic telescope measurement system in a high-precision long-distance measurement environment. The experimental results show that fiducial fiber can ensure the accuracy of closed-loop positioning for LAMOST fiber units.

Keywords: astronomical instrumentation; astronomical techniques
Lower AGN Abundance in Galaxy Clusters at z < 0.5

Most galaxies in clusters have supermassive black holes (SMBHs) at their center, and a fraction of those SMBHs show strong activity. These active galactic nuclei (AGNs) are an important probe of environmental dependence of galaxy evolution, intracluster medium, and cluster-scale feedback. We investigated AGN fraction in one of the largest samples of X-ray selected clusters from the ROSAT and their immediate surrounding field regions below z < 0.5. We found a lower average AGN fraction in clusters (2.37 ± 0.39)% than for the fields (5.12 ± 0.16)%. The lower AGN fractions in clusters were measured, after dividing the clusters into five redshift intervals between 0.0 and 0.5, in each redshift interval, and we found an increase in the fraction for both cluster and field galaxies with redshift below z < 0.5, which clearly indicates an environment and redshift dependence. We further divided the clusters into low-mass and high-mass objects using a mass cut at log10(M500/M⊙) = 13.5, finding comparable AGN fractions for both classifications, while a significantly higher AGN fraction in field. We also measured increasing AGN fractions with cluster-centric distance for all redshift bins, further confirming the environmental dependence of AGN activities. In addition, we did not find an obvious trend between AGN fraction and Sloan Digital Sky Survey Mr absolute magnitudes among different redshift bins. We conclude that the lower AGN fraction in clusters relative to fields indicate that factors, such as inefficient galaxy mergers and ram pressure stripping, cause a deficit of cold gas available in high-density regions to fuel the central SMBH. Clusters and fields in the present universe have lost more gas relative to their high-redshift counterparts resulting in a lower AGN fraction observed today.

Keywords: active galactic nuclei; galaxy clusters; galaxies; quasars; infrared astronomy
Spectroscopic Confirmation of an M6 Dwarf Companion to the Nearby Star BD-08 2582

We report resolved optical spectroscopy for the nearby low-mass stellar system BD-08 2582AB. We confirm prior unpublished reports of the existence of the secondary, and the spectral data indicate a secondary type of M6 Ve, consistent with spectrophotometric estimates from Gaia astrometry. The secondary exhibits Hα emission at a level equivalent to other M6 dwarfs, and has a metallicity index in line with its well-studied solar-metallicity K7/M0 primary.

Keywords: low mass stars; close binary stars; solar neighborhood; m dwarf stars; stellar activity
Observed Power and Frequency Variations of Solar Rossby Waves with Solar Cycles

Several recent studies utilizing different helioseismic methods have confirmed the presence of large-scale vorticity waves known as solar Rossby waves within the Sun. Rossby waves are distinct from acoustic waves, typically with longer periods and lifetimes, and their general properties, even if only measured at the surface, may be used to infer properties of the deeper convection zone, such as the turbulent viscosity and entropy gradients that are otherwise difficult to observe. In this study, we utilize 12 yr of inverted subsurface velocity fields derived from the Solar Dynamics Observatory/Helioseismic and Magnetic Imager's time-distance and ring-diagram pipelines to investigate the properties of the solar equatorial Rossby waves. By covering the maximum and the decline phases of Solar Cycle 24, these data sets enable a systematic analysis of any potential cycle dependence of these waves. Our analysis provides evidence of a correlation between the average power of equatorial Rossby waves and the solar cycle, with stronger Rossby waves during the solar maximum and weaker waves during the minimum. Our result also shows that the frequency of the Rossby waves is lower during the magnetic active years, implying a larger retrograde drift relative to the solar rotation. Although the underlying mechanism that enhances the Rossby wave power and lowers its frequency during the cycle maximum is not immediately known, this observation has the potential to provide new insights into the interaction of large-scale flows with the solar cycle.

Keywords: solar cycle; helioseismology; solar oscillations; solar physics
Discovery of the First Known Asteroid Confined within the Orbit of Venus

We report on the discovery by the Zwicky Transient Facility of an asteroid orbiting entirely within the orbit of Venus, the first known example of this orbital class. The asteroid's perihelion is closer to the Sun than the aphelion of Mercury, and its diameter is estimated at about 1.8 km assuming an albedo of 0.2. The object was first observed on 2020 January 4 in four exposures obtained 7 minutes apart during an evening twilight survey. Its IAU-recognized designation is 594913 'Ayló'chaxnim.

Keywords: small solar system bodies; near-earth objects; asteroids
Solar Energetic Particles Produced by a Slow Coronal Mass Ejection at ∼0.25 au

We present an analysis of Parker Solar Probe (PSP) IS⊙IS observations of ∼30-300 keV n-1 ions on 2018 November 11 when PSP was about 0.25 au from the Sun. Five hours before the onset of a solar energetic particle (SEP) event, a coronal mass ejection (CME) was observed by STEREO-A/COR2, which crossed PSP about a day later. No shock was observed locally at PSP, but the CME may have driven a weak shock earlier. The SEP event was dispersive, with higher energy ions arriving before the lower energy ones. Timing suggests the particles originated at the CME when it was at ∼7.4R⊙. SEP intensities increased gradually from their onset over a few hours, reaching a peak, and then decreased gradually before the CME arrived at PSP. The event was weak, having a very soft energy spectrum (-4 to -5 spectral index). The earliest arriving particles were anisotropic, moving outward from the Sun, but later, the distribution was observed to be more isotropic. We present numerical solutions of the Parker transport equation for the transport of 30-300 keV n-1 ions assuming a source comoving with the CME. Our model agrees well with the observations. The SEP event is consistent with ion acceleration at a weak shock driven briefly by the CME close to the Sun, which later dissipated before arriving at PSP, followed by the transport of ions in the interplanetary magnetic field.

Keywords: solar energetic particles; interplanetary particle acceleration; interplanetary shocks
A Ghost in Boötes: The Least-Luminous Disrupted Dwarf Galaxy

We report the discovery of Specter, a disrupted ultrafaint dwarf galaxy revealed by the H3 Spectroscopic Survey. We detected this structure via a pair of comoving metal-poor stars at a distance of 12.5 kpc, and further characterized it with Gaia astrometry and follow-up spectroscopy. Specter is a 25° × 1° stream of stars that is entirely invisible until strict kinematic cuts are applied to remove the Galactic foreground. The spectroscopic members suggest a stellar age τ ≳ 12 Gyr and a mean metallicity $\langle [\mathrm{Fe}/{\rm{H}}]\rangle =-{1.84}_{-0.18}^{+0.16}$ , with a significant intrinsic metallicity dispersion ${\sigma }_{[\mathrm{Fe}/{\rm{H}}]}={0.37}_{-0.13}^{+0.21}$ . We therefore argue that Specter is the disrupted remnant of an ancient dwarf galaxy. With an integrated luminosity M V ≈ -2.6, Specter is by far the least-luminous dwarf galaxy stream known. We estimate that dozens of similar streams are lurking below the detection threshold of current search techniques, and conclude that spectroscopic surveys offer a novel means to identify extremely low surface brightness structures.

Keywords: dwarf galaxies; low surface brightness galaxies; stellar streams
Deep Einstein@Home All-sky Search for Continuous Gravitational Waves in LIGO O3 Public Data

We present the results of an all-sky search for continuous gravitational waves in the public LIGO O3 data. The search covers signal frequencies 20.0 Hz ≤ f ≤ 800.0 Hz and a spin-down range down to -2.6 × 10-9 Hz s-1, motivated by detectability studies on synthetic populations of Galactic neutron stars. This search is the most sensitive all-sky search to date in this frequency/spin-down region. The initial search was performed using the first half of the public LIGO O3 data (O3a), utilizing graphical processing units provided in equal parts by the volunteers of the Einstein@Home computing project and by the ATLAS cluster. After a hierarchical follow-up in seven stages, 12 candidates remain. Six are discarded at the eighth stage, by using the remaining O3 LIGO data (O3b). The surviving six can be ascribed to continuous-wave fake signals present in the LIGO data for validation purposes. We recover these fake signals with very high accuracy with our last stage search, which coherently combines all O3 data. Based on our results, we set upper limits on the gravitational-wave amplitude h 0 and translate these into upper limits on the neutron star ellipticity and on the r-mode amplitude. The most stringent upper limits are at 203 Hz, with h 0 = 8.1 × 10-26 at the 90% confidence level. Our results exclude isolated neutron stars rotating faster than 5 ms with ellipticities greater than $5\times {10}^{-8}\left[\tfrac{d}{100\,\mathrm{pc}}\right]$ within a distance d from Earth and r-mode amplitudes $\alpha \geqslant {10}^{-5}\left[\tfrac{d}{100\,\mathrm{pc}}\right]$ for neutron stars spinning faster than 150 Hz.

Keywords: gravitational waves; gravitational wave astronomy; neutron stars
Post-merger Jets from Supermassive Black Hole Coalescences as Electromagnetic Counterparts of Gravitational Wave Emission

As a powerful source of gravitational waves (GW), a supermassive black hole (SMBH) merger may be accompanied by a relativistic jet that leads to detectable electromagnetic (EM) emission. We model the propagation of post-merger jets inside a pre-merger wind bubble formed by disk winds, and calculate multiwavelength EM spectra from the forward shock region. We show that the nonthermal EM signals from SMBH mergers are detectable up to the detection horizon of future GW facilities such as the Laser Interferometer Space Antenna (LISA). Calculations based on our model predict slowly fading transients with time delays from days to months after the coalescence, leading to implications for EM follow-up observations after the GW detection.

Keywords: non-thermal radiation sources; supermassive black holes; relativistic jets; gravitational wave sources
Are Active Galactic Nuclei in Post-starburst Galaxies Driving the Change or Along for the Ride?

We present an analysis of 10 ks snapshot Chandra observations of 12 shocked post-starburst galaxies, which provide a window into the unresolved question of active galactic nuclei (AGN) activity in post-starburst galaxies and its role in the transition of galaxies from active star formation to quiescence. While seven of the 12 galaxies have statistically significant detections (with two more marginal detections), the brightest only obtained 10 photons. Given the wide variety of hardness ratios in this sample, we chose to pursue a forward-modeling approach to constrain the intrinsic luminosity and obscuration of these galaxies, rather than stacking. We constrain the intrinsic luminosity of obscured power laws based on the total number of counts and spectral shape, itself mostly set by the obscuration, with hardness ratios consistent with the data. We also tested thermal models. While all the galaxies have power-law models consistent with their observations, a third of the galaxies are better fit as an obscured power law and another third are better fit as thermal emission. If these post-starburst galaxies, early in their transition, contain AGNs, then these are mostly confined to lower obscuration (N H ≤ 1023 cm-2) and lower luminosity (L 2-10 keV ≤ 1042 erg s-1). Two galaxies, however, are clearly best fit as significantly obscured AGNs. At least half of this sample shows evidence of at least low-luminosity AGN activity, though none could radiatively drive out the remaining molecular gas reservoirs. Therefore, these AGNs are more likely along for the ride, having been fed gas by the same processes driving the transition.

Keywords: post-starburst galaxies; active galactic nuclei; low-luminosity active galactic nuclei; galaxy evolution; x-ray astronomy
Reprocessing of a Green Bank 43 m Telescope Survey of Unidentified Bright Radio Sources for Pulsars and Radio Bursts

We have reprocessed a set of observations of 75 bright, unidentified, steep-spectrum polarized radio sources taken with the Green Bank 43 m telescope to find previously undetected sub-millisecond pulsars and radio bursts. The (null) results of the first search of these data were reported by Schmidt et al.. Our reprocessing searched for single pulses out to a dispersion measure (DM) of 1000 pc cm-3 which were classified using the Deep Learning based classifier FETCH. We also searched for periodicities at a wider range of DMs and accelerations. Our search was sensitive to highly accelerated, rapidly rotating pulsars (including sub-millisecond pulsars) in compact binary systems as well as to highly dispersed impulsive signals, such as fast radio bursts. No pulsars or astrophysical burst signals were found in the reprocessing.

Keywords: surveys; radio pulsars
ZFIRE: The Beginning of the End for Massive Galaxies at z 2 and Why Environment Matters

We use ZFIRE and ZFOURGE observations with the spectral energy distribution fitting tool PROSPECTOR to reconstruct the star formation histories (SFHs) of protocluster and field galaxies at z ~ 2 and compare our results to the TNG100 run of the IllustrisTNG cosmological simulation suite. In the observations, we find that massive protocluster galaxies ( $\mathrm{log}[{M}_{* }/{M}_{\odot }]$ > 10.5) form 45% ± 8% of their total stellar mass in the first 2 Gyr of the universe, compared to 31% ± 2% formed in the field galaxies. In both observations and simulations, massive protocluster galaxies have a flat/declining SFH with decreasing redshift compared to rising SFH in their field counterparts. Using IllustrisTNG, we find that massive galaxies ( $\mathrm{log}[{M}_{* }/{M}_{\odot }]\geqslant 10.5$ ) in both environments are on average ≈190 Myr older than low-mass galaxies ( $\mathrm{log}[{M}_{* }/{M}_{\odot }]=9\mbox{--}9.5$ ). However, the difference in mean stellar ages of cluster and field galaxies is minimal when considering the full range in stellar mass ( $\mathrm{log}[{M}_{* }/{M}_{\odot }]\geqslant 9$ ). We explore the role of mergers in driving the SFH in IllustrisTNG and find that massive cluster galaxies consistently experience mergers with low gas fraction compared to other galaxies after 1 Gyr from the big bang. We hypothesize that the low gas fraction in the progenitors of massive cluster galaxies is responsible for the reduced star formation.

Keywords: galaxy evolution; galaxy environments; star formation; hydrodynamical simulations; high-redshift galaxy clusters
The 30 Doradus Molecular Cloud at 0.4 pc Resolution with the Atacama Large Millimeter/submillimeter Array: Physical Properties and the Boundedness of CO-emitting Structures

We present results of a wide-field (approximately 60 × 90 pc) Atacama Large Millimeter/submillimeter Array mosaic of CO(2-1) and 13CO(2-1) emission from the molecular cloud associated with the 30 Doradus star-forming region in the Large Magellanic Cloud (LMC). Three main emission complexes, including two forming a bow-tie-shaped structure extending northeast and southwest from the central R136 cluster, are resolved into complex filamentary networks. Consistent with previous studies, we find that the central region of the cloud has higher line widths at a fixed size relative to the rest of the molecular cloud and to other LMC clouds, indicating an enhanced level of turbulent motions. However, there is no clear trend in gravitational boundedness (as measured by the virial parameter) with distance from R136. Structures observed in 13CO are spatially coincident with filaments and are close to a state of virial equilibrium. In contrast, 12CO structures vary greatly in virialization, with low CO surface brightness structures outside of the main filamentary network being predominantly unbound. The low surface brightness structures constitute ~10% of the measured CO luminosity; they may be shredded remnants of previously star-forming gas clumps, or alternatively the CO-emitting parts of more massive, CO-dark structures.

Keywords: interstellar medium; magellanic clouds; millimeter astronomy; giant molecular clouds; star forming regions
Progenitors of Low-redshift Gamma-Ray Bursts

The bimodal distribution of the observed duration of gamma-ray bursts (GRBs) has led to the identification of two distinct progenitors; compact star mergers, comprising either two neutron stars (NSs) or an NS and a black hole, for short GRBs (SGRBs), and the so-called collapsars for long GRBs (LGRBs). It is therefore expected that formation rate (FR) of LGRBs should be similar to the cosmic star formation rate (SFR), while that of SGRBs to be delayed relative to the SFR. The localization of some LGRBs in and around the star-forming regions of host galaxies and some SGRBs away from such regions support this expectation. Another distinct feature of SGRBs is their association with gravitational-wave (GW) sources and kilonovae. However, several independent investigations of the FRs of long and short bursts, using the Efron–Petrosian non-parametric method, have shown the presence of a mild luminosity evolution, and an LGRB FR that is significantly larger than SFR at low redshift, and similar to the FR of SGRBs. In addition, the recent discovery of association of two low-redshift LGRB 211211A and LGRB 230307A with a kilonova cast doubt about their collapsar origin. In this Letter we review these results and show that our results predict that about 60% ± 5% of LGRBs with redshift less than 2 could have compact star merger as progenitors increasing the expected rate of the GW sources and kilonovae significantly. The remaining 40% ± 5% have collapsars as progenitors, with some having associated supernovae.

Keywords: gamma-ray bursts; gravitational waves; star formation
Using a Quench Level Approximation to Estimate the Effect of Metallicity on the Abundances of N-bearing Species in H2-dominated Atmospheres

Variations in atmospheric elemental nitrogen can considerably affect the abundance of major nitrogen-bearing species such as NH3 and HCN. Also, due to vertical mixing and photochemistry, their abundance deviates from thermochemical equilibrium. The goal of this study is to understand the effect of atmospheric metallicity on the composition of NH3, N2, and HCN over a large parameter space in the presence of vertical mixing, which when combined with the work on CHO-bearing species in Soni & Acharyya can provide a comprehensive understanding of the effect of atmospheric metallicity. We used quenching approximations and a full chemical kinetics model for the calculations, and a comparison between these two methods was made. To generate thermal profiles, the petitRADTRANS code was used. Chemical timescales of NH3 and N2 are found to be complex functions of metallicity, while HCN is inversely proportional. Using quenched abundances of NH3 and CO, the quenched abundance of HCN can be constrained since it remains in equilibrium with NH3, CO, and H2O. Quenched NH3 increases with increasing K zz until a particular point, after which it becomes independent of vertical mixing. There is a sweet spot in the K zz parameter space to maximize the quenched HCN for a given T int and T equi; the parameter space moves toward a lower equilibrium temperature, and the abundance of HCN increases with metallicity. Finally, we used a data set of quenched abundances to provide a list of potential candidates in which the observation of HCN is possible.

Keywords: exoplanet atmospheres; metallicity; atmospheric composition
Compact Intermediate-mass Black Hole X-Ray Binaries: Potential LISA Sources?

The scientific aim of the space gravitational-wave (GW) detector Laser Interferometer Space Antenna (LISA) that was scheduled to launch in the early 2030s is to detect the low-frequency GW signals in the Galaxy. Its main candidate GW sources are compact binaries of white dwarfs and neutron stars. In this work, we examine whether compact intermediate-mass black hole (IMBH) X-ray binaries could be potential LISA sources. Our simulations indicate that an IMBH binary with a 1000 M⊙ IMBH and a 3 M⊙ donor star in an initial orbital period near the so-called bifurcation period of 0.77 day could evolve into an ultra-compact X-ray binary, which will emit GW signals with a maximum frequency of 2.5 mHz. According to the evolutionary tracks of characteristic strain, IMBH X-ray binaries with the initial donor-star masses of 1-3 M⊙ and the initial orbital periods slightly less than the bifurcation periods will be detectable by the LISA in a distance of 15 kpc. Assuming each of 60 Galactic globular clusters hosts a 1000 M⊙ IMBH, the maximum number of compact IMBH X-ray binaries that LISA will detect in the Galaxy should be less than ten. Therefore, the detectability of compact IMBH X-ray binaries by the LISA is not optimistic.

Keywords: black holes; gravitational waves; x-ray binary stars; stellar evolution; galaxy clusters