Table of contents

We present the Virgo Environment Traced in CO (VERTICO) survey, a new effort to map ¹²CO (2–1), ¹³CO (2–1), and C¹⁸O (2–1) in 51 Virgo Cluster galaxies with the Atacama Compact Array, part of the Atacama Large Millimeter/submillimeter Array. The primary motivation of VERTICO is to understand the physical mechanisms that perturb molecular gas disks, and therefore star formation and galaxy evolution, in dense environments. This first paper contains an overview of VERTICO's design and sample selection, ¹²CO (2–1) observations, and data reduction procedures. We characterize global ¹²CO (2–1) fluxes and molecular gas masses for the 49 detected VERTICO galaxies, provide upper limits for the two nondetections, and produce resolved ¹²CO (2–1) data products (median resolution = 8'' ≈ 640 pc). Azimuthally averaged ¹²CO (2–1) radial intensity profiles are presented along with derived molecular gas radii. We demonstrate the scientific power of VERTICO by comparing the molecular gas size–mass scaling relation for our galaxies with a control sample of field galaxies, highlighting the strong effect that radius definition has on this correlation. We discuss the drivers of the form and scatter in the size–mass relation and highlight areas for future work. VERTICO is an ideal resource for studying the fate of molecular gas in cluster galaxies and the physics of environment-driven processes that perturb the star formation cycle. Upon public release, the survey will provide a homogeneous legacy data set for studying galaxy evolution in our closest cluster.

We derive stellar parameters and abundances ("stellar labels") of 40,034 late-B and A-type main-sequence stars extracted from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope Medium Resolution Survey (LAMOST–MRS). The primary selection of our early-type sample was obtained from LAMOST Data Release 7 based on spectral-line indices. We employed the Stellar Label Machine to derive their spectroscopic stellar parameters, drawing on Kurucz spectral synthesis models with 6000 < T_eff < 15,000 K and −1 < [M/H] < 1 dex. For a signal-to-noise ratio of ∼60, the cross validated scatter is ∼75 K, 0.06 dex, 0.05 dex, and ∼3.5 km s⁻¹ for T_eff, $\mathrm{log}g$, [M/H], and $v\sin i$, respectively. A comparison with objects with prior known stellar labels shows great consistency for all stellar parameters, except for $\mathrm{log}g$. Although this is an intrinsic caveat that comes from the MRS's narrow wavelength coverage, it only has a minor effect on estimates of the stellar rotation rates because of the decent spectral resolution and the profile-fitting method employed. The masses and ages of our early-type sample stars were inferred from nonrotating stellar evolution models. This paves the way for reviewing the properties of stellar rotation distributions as a function of stellar mass and age.

We comprehensively study the variability of Miras in the Large Magellanic Cloud by simultaneously analyzing light curves in 14 bands in the range of 0.5–24 μm. We model over 20 yr long, high-cadence I-band light curves collected by the Optical Gravitational Lensing Experiment (OGLE) and fit them to light curves collected in the remaining optical/near-infrared/mid-infrared bands to derive both the variability amplitude ratio and phase lag as a function of wavelength. We show that the variability amplitude ratio declines with increasing wavelength for both oxygen-rich (O-rich) and carbon-rich (C-rich) Miras, while the variability phase lag increases slightly with increasing wavelength. In a significant number of Miras, mostly the C-rich ones, the spectral energy distributions (SEDs) require the presence of a cool component (dust) in order to match the mid-IR data. Based on SED fits for a golden sample of 140 Miras, we calculated synthetic period–luminosity relations (PLRs) in 42 bands for the existing and future sky surveys that include OGLE, the VISTA Near-Infrared YJK_s Survey of the Magellanic Clouds System, Legacy Survey of Space and Time, Gaia, Spitzer, the Wide-field Infrared Survey Explorer, the James Webb Space Telescope, the Nancy Grace Roman Space Telescope (formerly WFIRST), and the Hubble Space Telescope. We show that the synthetic PLR slope decreases with increasing wavelength for both the O-rich and C-rich Miras in the range of 0.1–40 μm. Finally, we show the location and motions of Miras on the color–magnitude and color–color diagrams.

The main aim of the current work is to apply the Roe+Lax–Friedrichs (LF) hybrid entropy-stable scheme to the simulation of the three-dimensional ambient solar wind. The governing equations for the solar wind flow and magnetic field utilize the entropy-consistent nine-wave magnetic field divergence diminishing ideal magnetohydrodynamics (MHD) equations, which are symmetric and Galilean invariant with some nonconservative terms proportional to the divergence of magnetic field or the gradient of the Lagrange multiplier ψ. By using solenoidality-preserving and non-negativity-preserving reconstruction, the divergence error is further constrained, and the densities and pressures are reliably guaranteed. Moreover, the entropy is used as an auxiliary equation to completely avoid the appearance of negative pressure, which is independent of any numerical flux and can be retrofit into any MHD equations straightforwardly. All the properties referred to above make the newly developed scheme more handy and robust to cope with the high Mach number or low plasma β situations. After the experiments of the entropy consistency and the robustness of the proposed entropy-stable scheme through two simple tests, we carry out the simulation of the large-scale solar wind structures for Carrington Rotation 2183 (CR 2183) in a six-component grid system with the initial potential field obtained from the Helioseismic and Magnetic Imager magnetogram by retaining spherical harmonics of degree 50. The comparisons of the numerical results with the remote sensing observations and in situ data show that the new model has the capability to produce structured solar wind.

Numerical relativity is central to the investigation of astrophysical sources in the dynamical and strong-field gravity regime, such as binary black hole and neutron star coalescences. Current challenges set by gravitational-wave and multimessenger astronomy call for highly performant and scalable codes on modern massively parallel architectures. We present GR-Athena++, a general-relativistic, high-order, vertex-centered solver that extends the oct-tree, adaptive mesh refinement capabilities of the astrophysical (radiation) magnetohydrodynamics code Athena++. To simulate dynamical spacetimes, GR-Athena++ uses the Z4c evolution scheme of numerical relativity coupled to the moving puncture gauge. We demonstrate stable and accurate binary black hole merger evolutions via extensive convergence testing, cross-code validation, and verification against state-of-the-art effective-one-body waveforms. GR-Athena++ leverages the task-based parallelism paradigm of Athena++ to achieve excellent scalability. We measure strong-scaling efficiencies above 95% for up to ∼1.2 × 10⁴ CPUs and excellent weak scaling is shown up to ∼10⁵ CPUs in a production binary black hole setup with adaptive mesh refinement. GR-Athena++ thus allows for the robust simulation of compact binary coalescences and offers a viable path toward numerical relativity at exascale.

Glycolonitrile (HOCH₂CN) is an attractive interstellar prebiotic molecule. Glycolonitrile is considered not only as a possible precursor for glycine but also as a key intermediate for adenine formation. Recently, HOCH₂CN was detected toward IRAS 16293−2422 B with the Atacama Large Millimeter/submillimeter Array (ALMA). In this study we perform a comprehensive modeling study on HOCH₂CN chemistry under the physical conditions of IRAS 16293−2422 B's cold envelope and hot corino evolutions using the astrochemical code NAUTILUS and the updated gas-grain chemical network. Our studies not only give the main reactions and the favorable physical conditions for the formation of HOCH₂CN but also uncover that the observed glycolonitrile in the cold envelope originates from the gradual accumulation of the gas-phase molecules during the ambient cloud, freefall collapse, and warm-up phases of the cold envelope evolution, and in the hot corino it mainly comes from the accumulated ices during the hot corino evolution. Using the updated chemical network, we also conduct chemical simulations under the physical conditions of Sagittarius (Sgr) B2(N) evolution. The simulation results show that varying the cosmic-ray ionization rate is needed to best reproduce the observational upper limits of HOCH₂CN and the observed abundances of CNCHO and CH₂CNH toward Sgr B2(N). Moreover, we predict that HOCHCNH, OCH₂CN, HOCHCN, HOCCNH, OCCNH, and OCCN have high abundances and may be detectable toward IRAS 16293−2422 B and Sgr B2(N).

Constructing a fast and efficient estimator for the B-mode power spectrum of the cosmic microwave background (CMB) is of critical importance for CMB science. For a general CMB survey, the Quadratic Maximum Likelihood (QML) estimator for CMB polarization has been proved to be the optimal estimator with minimal uncertainties, but it is computationally very expensive. In this article, we propose two new QML methods for B-mode power spectrum estimation. We use the Smith–Zaldarriaga approach to prepare the pure B-mode map and the E-mode recycling method to obtain a leakage free B-mode map. We then use the scalar QML estimator to analyze the scalar pure B map (QML-SZ) or B-mode map (QML-TC). The QML-SZ and QML-TC estimators have similar error bars as the standard QML estimators but their computational cost is nearly one order of magnitude smaller. The basic idea is that one can construct the pure B-mode CMB map by using the E–B separation method proposed by Smith & Zaldarriaga (SZ) or the one considering the template cleaning (TC) technique, then apply the QML estimator to these scalar fields. By simulating potential observations of space-based and ground-based detectors, we test the reliability of these estimators by comparing them with the corresponding results of the traditional QML estimator and the pure B-mode pseudo-C_ℓ estimator.

We present the results of surveying [C i] ³P₁–³P₀, ¹²CO J = 4 − 3, and 630 μm dust continuum emission for 36 nearby ultra/luminous infrared galaxies (U/LIRGs) using the Band 8 receiver mounted on the Atacama Compact Array of the Atacama Large Millimeter/submillimeter Array. We describe the survey, observations, data reduction, and results; the main results are as follows. (i) We confirmed that [C i] ³P₁–³P₀ has a linear relationship with both the ¹²CO J = 4 − 3 and 630 μm continuum. (ii) In NGC 6052 and NGC 7679, ¹²CO J = 4 − 3 was detected but [C i] ³P₁–³P₀ was not detected with a [C i] ³P₁–³P₀/¹²CO J = 4 − 3 ratio of ≲0.08. Two possible scenarios of weak [C i] ³P₁–³P₀ emission are C⁰-poor/CO-rich environments and an environment with an extremely large [C i] ³P₁–³P₀ missing flux. (iii) There is no clear evidence showing that galaxy mergers, AGNs, and dust temperatures control the ratios of [C i] ³P₁–³P₀/¹²CO J = 4 − 3 and ${L}_{[{\rm{C}}\,{\rm\small{I}}](1-0)}^{{\prime} }/{L}_{630\mu {\rm{m}}}$. (iv) We compare our nearby U/LIRGs with high-z galaxies, such as galaxies on the star formation main sequence (MS) at z ∼ 1 and submillimeter galaxies (SMGs) at z = 2–4. We found that the mean value for the [C i] ³P₁–³P₀/¹²CO J = 4 − 3 ratio of U/LIRGs is similar to that of SMGs but smaller than that of galaxies on the MS.

In this work, we continue large-scale ab initio computations for single ionized lanthanides. Extended atomic calculations for the set of ions from Pr ii (Z = 59) to Gd ii (Z = 64) have been performed in our previous work. In this study, ions from Tb ii (Z = 65) to Yb ii (Z = 70) are analyzed. By employing the same multiconfiguration Dirac–Hartree–Fock and relativistic configuration interaction methods that are implemented in the general-purpose relativistic atomic structure package GRASP2018, the energy levels and transition data of electric dipole (E1) transitions are computed. These computations are based on the strategies (with small variations) of Paper I. Accuracy of data is evaluated by comparing the computed energy levels with the data provided by the National Institute of Standards and Technology (NIST) database and with data from various methods. We obtain the average accuracy in the energy level compared with the NIST database: 6%, 5%, 4%, 5%, 3%, and 3% for Tb ii, Dy ii, Ho ii, Er ii, Tm ii, and Yb ii, respectively. We also provide extensive comparison of transition probabilities and wavelengths. Our results reach the average accuracy of transition wavelengths: 9%, 9%, 9%, 3%, 4%, and 11% for Tb ii, Dy ii, Ho ii, Er ii, Tm ii, and Yb ii, respectively.

We present a morphological and spectral study of a sample of 99 BL Lac objects using the LOFAR Two-Metre Sky Survey Second Data Release (LDR2). Extended emission has been identified at gigahertz frequencies around BL Lac objects, but with LDR2 it is now possible to systematically study their morphologies at 144 MHz, where more diffuse emission is expected. LDR2 reveals the presence of extended radio structures around 66/99 of the BL Lac nuclei, with angular extents ranging up to 115'', corresponding to spatial extents of 410 kpc. The extended emission is likely to be both unbeamed diffuse emission and beamed emission associated with relativistic bulk motion in jets. The spatial extents and luminosities of the extended emission are consistent with the unification scheme for active galactic nuclei, where BL Lac objects correspond to low-excitation radio galaxies with the jet axis aligned along the line of sight. While extended emission is detected around the majority of BL Lac objects, the median 144–1400 MHz spectral index and core dominance at 144 MHz indicate that the core component contributes ∼42% on average to the total low-frequency flux density. A stronger correlation was found between the 144 MHz core flux density and the γ-ray photon flux (r = 0.69) than between the 144 MHz extended flux density and the γ-ray photon flux (r = 0.42). This suggests that the radio-to-γ-ray connection weakens at low radio frequencies because the population of particles that give rise to the γ-ray flux are distinct from the electrons producing the diffuse synchrotron emission associated with spatially extended features.

Understanding the origins of small-scale flats of CCDs and their wavelength-dependent variations plays an important role in high-precision photometric, astrometric, and shape measurements of astronomical objects. Based on the unique flat data of 47 narrowband filters provided by JPAS-Pathfinder, we analyze the variations of small-scale flats as a function of wavelength. We find moderate variations (from about 1.0% at 390 nm to 0.3% at 890 nm) of small-scale flats among different filters, increasing toward shorter wavelengths. Small-scale flats of two filters close in central wavelengths are strongly correlated. We then use a simple physical model to reproduce the observed variations to a precision of about ±0.14% by considering the variations of charge collection efficiencies, effective areas, and thicknesses between CCD pixels. We find that the wavelength-dependent variations of the small-scale flats of the JPAS-Pathfinder camera originate from inhomogeneities of the quantum efficiency (particularly charge collection efficiency), as well as the effective area and thickness of CCD pixels. The former dominates the variations in short wavelengths, while the latter two dominate at longer wavelengths. The effects on proper flat-fielding, as well as on photometric/flux calibrations for photometric/slitless spectroscopic surveys, are discussed, particularly in blue filters/wavelengths. We also find that different model parameters are sensitive to flats of different wavelengths, depending on the relations between the electron absorption depth, photon absorption length, and CCD thickness. In order to model the wavelength-dependent variations of small-scale flats, a small number (around 10) of small-scale flats with well-selected wavelengths are sufficient to reconstruct small-scale flats in other wavelengths.

In this paper, we present a provably positive, divergence-free constrained transport (CT) scheme to simulate the steady-state solar wind ambient with the three-dimensional magnetohydrodynamics numerical model. The positivity can be lost in two ways: one way is in the reconstruction process, and the other is in the updating process when the variables are advanced to the next time step. We adopt a self-adjusting strategy to bring the density and pressure into the permitted range in the reconstruction process, and use modified wave speeds in the Harten–Lax–van Leer flux to ensure the positivity in the updating process. The CT method can keep the magnetic fields divergence-free if the magnetic fields are divergence-free initially. Thus, we combine the least-squares reconstruction of the magnetic fields with the divergence-free constraints to make the magnetic fields globally solenoidal initially. Furthermore, we adopt a radial basis function method to interpolate variables at boundaries that can keep the magnetic field locally divergence-free. To verify the capability of the model in producing structured solar wind, the modeled results are compared with Parker Solar Probe (PSP) in situ observations during its first two encounters, as well as Wind observations at 1 au. Additionally, a solar maximum solar wind background is simulated to show the property of the model's ability to preserve the positivity. The results show that the model can provide a relatively satisfactory comparison with PSP or Wind observations, and the divergence error is about 10⁻¹⁰ for all of the tests in this paper.

There have been a few previous studies claiming that the effects of geomagnetic storms strongly depend on the orientation of the magnetic cloud portion of coronal mass ejections (CMEs). Aparna & Martens, using halo-CME data from 2007 to 2017, showed that the magnetic field orientation of filaments at the location where CMEs originate on the Sun can be used to credibly predict the geoeffectiveness of the CMEs being studied. The purpose of this study is to extend their survey by analyzing the halo-CME data for 1996–2006. The correlation of filament axial direction on the solar surface and the corresponding Bz signatures at L1 are used to form a more extensive analysis for the results previously presented by Aparna & Martens. This study utilizes Solar and Heliospheric Observatory Extreme-ultraviolet Imaging Telescope 195 Å, Michelson Doppler Imager magnetogram images, and Kanzelhöhe Solar Observatory and Big Bear Solar Observatory Hα images for each particular time period, along with ACE data for interplanetary magnetic field signatures. Utilizing all these, we have found that the trend in Aparna & Martens' study of a high likelihood of correlation between the axial field direction on the solar surface and Bz orientation persists for the data between 1996 and 2006, for which we find a match percentage of 65%.

In this paper, we design an effective and robust model to solve the 3D single-fluid solar wind plasma magnetohydrodynamics (MHD) problem of low plasma β. This MHD model is formulated on a six-component composite grid system free of polar singularities. The computational domain ranges from the solar surface to the super-Alfvénic region. As common to all MHD codes, this code must handle the physical positivity-preserving property, time-step enlargement, and magnetic field divergence-free maintenance. To maintain physical positivity, we employ a positivity-preserving Harten–Lax–van Leer Riemann solver and take a self-adjusting and positivity-preserving method for variable reconstruction. To loosen the time-step limitation, we resort to the implicit lower–upper symmetric Gauss–Seidel method and keep the sparse Jacobian matrix diagonally dominant to improve the convergence rate. To deal with the constant theme of a magnetic field that is divergence-free, we adopt a globally solenoidality-preserving approach. After establishing the solar wind model, we use its explicit and implicit versions to numerically investigate the steady-state solar wind in Carrington rotations (CRs) 2172 and 2210. Both simulations achieve almost the same results for the two CRs and are basically consistent with solar coronal observations and mapped in situ interplanetary measurements. Furthermore, we use the implicit method to conduct an ad hoc simulation by multiplying the initial magnetic field of CR 2172 with a factor of 6. The simulation shows that the model can robustly and efficiently deal with the problem of a plasma β as low as about 5 × 10⁻⁷. Therefore, the established implicit solar wind MHD model is very promising for simulating complex and strong magnetic environments.

The IRAS Revised Bright Galaxy Sample (RBGS) comprises galaxies and unresolved mergers stronger than S = 5.24 Jy at λ = 60 μm with Galactic latitudes ∣b∣ > 5°. Nearly all are dusty star-forming galaxies whose radio continuum and far-infrared luminosities are proportional to their current rates of star formation. We used the MeerKAT array of 64 dishes to make 5 × 3 minutes snapshot observations at ν = 1.28 GHz covering all 298 southern (J2000 δ < 0°) RBGS sources identified with external galaxies. The resulting images have θ ≈ 75 FWHM resolution and rms fluctuations σ ≈ 20 μJy beam⁻¹ ≈ 0.26 K low enough to reveal even faint disk emission. The rms position uncertainties are σ_α ≈ σ_δ ≈ 1'' relative to accurate near-infrared positions, and the image dynamic ranges are DR ≳ 10⁴: 1. Cropped MeerKAT images of all 298 southern RBGS sources are available in FITS format from 10.48479/dnt7-6q05.

We present far-infrared (FIR) spectroscopy of supernova remnants (SNRs) based on the archival data of the Infrared Space Observatory taken with the Long Wavelength Spectrometer (LWS). Our sample includes previously unpublished profiles of line and continuum spectra for 20 SNRs in the Galaxy and Magellanic Clouds. In several SNRs including G21.5–0.9, G29.7–0.3, the Crab Nebula, and G320.4–1.2, we find evidence for broad [O i], [O iii], [N ii], and [C ii] lines with velocity dispersions up to a few 10³ km s⁻¹, indicating that they are associated with high-velocity SN ejecta. Our detection of Doppler-broadened atomic emission lines and a bright FIR continuum hints at the presence of newly formed dust in SN ejecta. For G320.4–1.2, we present the first estimate of an ejecta-dust mass of 0.1–0.2 M_⊙, which spatially coincides with the broad-line emission, by applying a blackbody model fit with components of the SNR and background emission. Our sample includes raster maps of 63 μm, 145 μm [O i], and 158 μm [C ii] lines toward SNRs Kes 79, CTB 109, and IC 443. Based on these line intensities, we suggest interacting shock types in these SNRs. Finally, we compare our LWS spectra of our sample SNRs with the spectra of several H ii regions, and discuss their FIR line intensity ratios and continuum properties. Follow-up observations with modern instruments (e.g., JWST and SOFIA) with higher spatial and spectral resolution are encouraged for an extensive study of the SN ejecta and the SN dust.

The origin of γ-ray flares observed from blazars is one of the major mysteries in jet physics. We have attempted to address this problem following a novel spectral energy distribution (SED) fitting technique that explored the flaring patterns identified in the broadband SEDs of two γ-ray bright blazars, 3C 279 (z = 0.54) and 3C 454.3 (z = 0.86), using near-simultaneous radio-to-γ-ray observations. For both sources, the γ-ray flux strongly correlates with the separation of the SED peaks and the Compton dominance. We propose that spectral hardening of the radiating electron population and/or enhancement of the Doppler factor can naturally explain these observations. In both cases, magnetic reconnection may play a pivotal role in powering the luminous γ-ray flares.

A solar active region is a source of disturbance for the Sun–terrestrial space environment and usually causes extreme space weather, such as geomagnetic storms. The main indicator of an active region is sunspots. Certain types of sunspots are related to extreme space weather caused by eruptive events such as coronal mass ejections or solar flares. Thus, the automatic classification of sunspot groups is helpful to predict solar activity quickly and accurately. This paper completed the automatic classification of a sunspot group data set based on the Mount Wilson classification scheme, which contains continuum and magnetogram images provided by the Solar Dynamics Observatory's Helioseismic and Magnetic Imager SHARP data from 2010 May 1 to 2017 December 12. After applying some data preprocessing steps such as image cropping and data standardization, the features of magnetic type in the data are more obvious, and the amount of data is increased. The processed data are spliced into two frames of single-channel data for the neural network to perform 3D convolution operations. This paper constructs a variety of convolutional neural networks with different structures and numbers of layers, selects 10 models as representatives, and chooses XGBoost, which is commonly used in ensemble-learning algorithms, to fuse the results of independent classification models. We found that XGBoost is an effective way to fuse models, which is proved by the relatively balanced high scores in the three magnetic types. The accuracy of the ensemble model is above 92%. The F1 scores of the magnetic types of Alpha, Beta, and Beta-x reached 0.95, 0.91, and 0.82 respectively.

Our aim is to measure the interstellar ¹⁴N/¹⁵N ratio across the Galaxy, to establish a standard data set on interstellar ammonia isotope ratios, and to provide new constraints on the Galactic chemical evolution. The (J, K) = (1, 1), (2, 2), and (3, 3) lines of ¹⁴NH₃ and ¹⁵NH₃ were observed with the Shanghai Tianma 65 m radio telescope (TMRT) and the Effelsberg 100 m telescope toward a large sample of 210 sources. One hundred fourty-one of these sources were detected by the TMRT in ¹⁴NH₃. Eight of them were also detected in ¹⁵NH₃. For 10 of the 36 sources with strong NH₃ emission, the Effelsberg 100 m telescope successfully detected their ¹⁵NH₃(1, 1) lines, including 3 sources (G081.7522, W51D, and Orion-KL) with detections by the TMRT telescope. Thus, a total of 15 sources are detected in both the ¹⁴NH₃ and ¹⁵NH₃ lines. Line and physical parameters for these 15 sources are derived, including optical depths, rotation and kinetic temperatures, and total column densities. ¹⁴N/¹⁵N isotope ratios were determined from the ¹⁴NH₃/¹⁵NH₃ abundance ratios. The isotope ratios obtained from both telescopes agree for a given source within the uncertainties, and no dependence on heliocentric distance and kinetic temperature is seen. ¹⁴N/¹⁵N ratios tend to increase with galactocentric distance, confirming a radial nitrogen isotope gradient. This is consistent with results from recent Galactic chemical model calculations, including the impact of superasymptotic giant branch stars and novae.

Research has analytically shown that the energy-conserving implicit nonsymplectic scheme of Bacchini, Ripperda, Chen, and Sironi provides a first-order accuracy to numerical solutions of a six-dimensional conservative Hamiltonian system. Because of this, a new second-order energy-conserving implicit scheme is proposed. Numerical simulations of a galactic model hosting a BL Lacertae object and magnetized rotating black hole background support these analytical results. The new method with appropriate time steps is used to explore the effects of varying the parameters on the presence of chaos in the two physical models. Chaos easily occurs in the galactic model as the mass of the nucleus, the internal perturbation parameter, and the anisotropy of the potential of the elliptical galaxy increase. The dynamics of charged particles around the magnetized Kerr spacetime is easily chaotic for larger energies of the particles, smaller initial angular momenta of the particles, and stronger magnetic fields. The chaotic properties are not necessarily weakened when the black-hole spin increases. The new method can be used for any six-dimensional Hamiltonian problems, including globally hyperbolic spacetimes with readily available (3 + 1) split coordinates.

In an optical monitoring program to characterize the variability properties of blazars, we observed 10 sources from the Roma-BZCAT catalog for 26 nights in V and R bands during 2014 October to 2015 June with two telescopes located in India. The sample includes mainly newly discovered BL Lacertae objects (BL Lacs) for which the redshift of some sources is not yet known. We present the results of flux and color variations of the sample on intraday and short timescales obtained by using the power-enhanced F-test and the nested-ANOVA tests, along with their spectral behavior. We find significant intraday variability in the single flat-spectrum radio quasar in our sample, having an amplitude of variation ∼12%. Although a few of the BL Lacs showed probable variation in some nights, none of them passed the variability tests at 99.9% significance level. We find that 78% of the sample showed significant negative color–magnitude correlations, i.e., a redder-when-brighter spectral evolution. Those that do not show strong or clear chromatism predominantly exhibit a redder-when-brighter trend. Unlike on hourly timescales, the high-synchrotron-peaked blazars in the sample (BZGJ0656+4237, BZGJ0152+0147, and BZBJ1728+5013) show strong flux variation on timescales of days to months, where again we detect a decreasing trend of the spectral slope with brightness. We observe a global steepening of the optical spectrum with increasing flux on the intranight timescale for the entire blazar sample. The nonvariability in the BL Lacs in our sample might be caused by the distinct contribution from the disk as well as from other components in the studied energy range.

We present Breakthrough Listen's Exotica Catalog as the centerpiece of our efforts to expand the diversity of targets surveyed in the Search for Extraterrestrial Intelligence (SETI). As motivation, we introduce the concept of survey breadth, the diversity of objects observed during a program. Several reasons for pursuing a broad program are given, including increasing the chance of a positive result in SETI, commensal astrophysics, and characterizing systematics. The Exotica Catalog is a 963 entry collection of 816 distinct targets intended to include "one of everything" in astronomy. It contains four samples: the Prototype sample, with an archetype of every known major type of nontransient celestial object; the Superlative sample of objects, with the most extreme properties; the Anomaly sample of enigmatic targets that are in some way unexplained; and the Control sample, with sources not expected to produce positive results. As far as we are aware, this is the first object list in recent times with the purpose of spanning the breadth of astrophysics. We share it with the community in hopes that it can guide treasury surveys and as a general reference work. Accompanying the catalog is an extensive discussion of the classification of objects and a new classification system for anomalies. Extensive notes on the objects in the catalog are available online. We discuss how we intend to proceed with observations in the catalog, contrast it with our extant Exotica efforts, and suggest how similar tactics may be applied to other programs.

We present PHANGS–ALMA, the first survey to map CO J = 2 → 1 line emission at ∼1'' ∼100 pc spatial resolution from a representative sample of 90 nearby (d ≲ 20 Mpc) galaxies that lie on or near the z = 0 "main sequence" of star-forming galaxies. CO line emission traces the bulk distribution of molecular gas, which is the cold, star-forming phase of the interstellar medium. At the resolution achieved by PHANGS–ALMA, each beam reaches the size of a typical individual giant molecular cloud, so that these data can be used to measure the demographics, life cycle, and physical state of molecular clouds across the population of galaxies where the majority of stars form at z = 0. This paper describes the scientific motivation and background for the survey, sample selection, global properties of the targets, Atacama Large Millimeter/submillimeter Array (ALMA) observations, and characteristics of the delivered data and derived data products. As the ALMA sample serves as the parent sample for parallel surveys with MUSE on the Very Large Telescope, the Hubble Space Telescope, AstroSat, the Very Large Array, and other facilities, we include a detailed discussion of the sample selection. We detail the estimation of galaxy mass, size, star formation rate, CO luminosity, and other properties, compare estimates using different systems and provide best-estimate integrated measurements for each target. We also report the design and execution of the ALMA observations, which combine a Cycle 5 Large Program, a series of smaller programs, and archival observations. Finally, we present the first 1'' resolution atlas of CO emission from nearby galaxies and describe the properties and contents of the first PHANGS–ALMA public data release.

The momentum diffusion of charged energetic particles is an important mechanism of the transport process in astrophysics, the physics of fusion devices, and laboratory plasmas. In addition to the momentum diffusion term for a uniform field, we obtain an additional momentum diffusion term due to the focusing effect of the large-scale magnetic field. After evaluating the coefficient of the additional momentum diffusion term, we find that it is determined by the sign of the focusing characteristic length and the cross helicity of the turbulent magnetic field. Furthermore, by deriving the mean momentum change rate contributed from the additional momentum diffusion term, we identify that the focused field provides an additional momentum loss or gain process.

We report multiepoch radial velocities, rotational velocities, and atmospheric parameters for 37 T-type brown dwarfs observed with Keck/NIRSPEC. Using a Markov Chain Monte Carlo forward-modeling method, we achieve median precisions of 0.5 and 0.9 km s⁻¹ for radial and rotational velocities, respectively. All of the T dwarfs in our sample are thin-disk brown dwarfs. We confirm previously reported moving group associations for four T dwarfs. However, the lack of spectral indicators of youth in two of these sources suggests that these are chance alignments. We confirm two previously unresolved binary candidates, the T0+T4.5 2MASS J11061197+2754225 and the L7+T3.5 2MASS J21265916+7617440, with orbital periods of 4 and 12 yr, respectively. We find a kinematic age of 3.5 ± 0.3 Gyr for local T dwarfs, consistent with nearby late M dwarfs (4.1 ± 0.3 Gyr). Removal of thick-disk L dwarfs in the local ultracool dwarf sample gives a similar age for L dwarfs (4.2 ± 0.3 Gyr), largely resolving the local L dwarf age anomaly. The kinematic ages of local late M, L, and T dwarfs can be accurately reproduced with population simulations incorporating standard assumptions of the mass function, star formation rate, and brown dwarf evolutionary models. A kinematic dispersion break is found at the L4–L6 subtypes, likely reflecting the terminus of the stellar main sequence. We provide a compilation of precise radial velocities for 172 late M, L, and T dwarfs within ∼20 pc of the Sun.

The period versus mass diagrams (i.e., rotational sequences) of open clusters provide crucial constraints for angular momentum evolution studies. However, their memberships are often heavily contaminated by field stars, which could potentially bias the interpretations. In this paper, we use data from Gaia DR2 to reassess the memberships of seven open clusters with ground- and space-based rotational data, and present an updated view of stellar rotation as a function of mass and age. We use the Gaia astrometry to identify the cluster members in phase space, and the photometry to derive revised ages and place the stars on a consistent mass scale. Applying our membership analysis to the rotational sequences reveals that: (1) the contamination in clusters observed from the ground can reach up to ∼35%; (2) the overall fraction of rotational outliers decreases substantially when the field contaminants are removed, but some outliers persist; (3) there is a sharp upper edge in the rotation periods at young ages; (4) at young ages, stars in the 1.0–0.6M_⊙ range inhabit a global maximum of rotation periods, potentially providing an optimal window for habitable planets. Additionally, we see clear evidence for a strongly mass-dependent spin-down process. In the regime where rapid rotators are leaving the saturated domain, the rotational distributions broaden (in contradiction with popular models), which we interpret as evidence that the torque must be lower for rapid rotators than for intermediate ones. The cleaned rotational sequences from ground-based observations can be as constraining as those obtained from space.

We present high-sensitivity CH 9 cm ON/OFF observations toward 18 extragalactic continuum sources that have been detected with OH 18 cm absorption in the Millennium survey with the Arecibo telescope. CH emission was detected toward 6 of the 18 sources. The excitation temperature of CH has been derived directly through analyzing all detected ON and OFF velocity components. The excitation temperature of CH 3335 MHz transition ranges from −54.5 to −0.4 K and roughly follows a log-normal distribution peaking within [−5, 0] K, which implies overestimation by 20% to more than 10 times during calculating CH column density by assuming the conventional value of −60 or −10 K. Furthermore, the column density of CH would be underestimated by a factor of 1.32 ± 0.03 when adopting local thermal equilibrium assumption instead of using the CH three hyperfine transitions. We found a correlation between the column density of CH and OH following log N(CH) = (1.80 ± 0.49) log N(OH) −11.59 ± 6.87. The linear correlation between the column density of CH and H₂ is consistent with that derived from visible wavelengths studies, confirming that CH is one of the best tracers of H₂ components in diffuse molecular gas.

With continuous measurements from space-borne cosmic-ray detectors such as AMS-02 and PAMELA, precise spectra of galactic cosmic rays over the 11 yr solar cycle have become available. For this study, we utilize proton and helium spectra below 10 GV from these missions from 2006 to 2017 to construct a cosmic-ray transport model for a quantitative study of the processes of solar modulation. This numerical model is based on Parker's transport equation, which includes four major transport processes. The Markov Chain Monte Carlo method is utilized to search the relevant parameter space related to the drift and the diffusion coefficients by reproducing and fitting the mentioned observed spectra. The resulting best-fit normalized χ² is mainly less than 1. It is found that (1) when reproducing these observations the parameters required for the drift and diffusion coefficients exhibit a clear time dependence, with the magnitude of the diffusion coefficients anticorrelated with solar activity; (2) the rigidity dependence of the resulting mean free paths varies with time, and their rigidity dependence at lower rigidity can even have a larger slope than at higher rigidity; (3) using a single set of modulation parameters for each pair of observed proton and helium spectra, most spectra are reproduced within observational uncertainty; and (4) the simulated proton-to-helium flux ratio agrees with the observed values in terms of its long-term time dependence, although some discrepancy exists, and the difference is mostly coming from the underestimation of proton flux.

We present radio observations (1–40 GHz) for 36 classical novae, representing data from over five decades compiled from the literature, telescope archives, and our own programs. Our targets display a striking diversity in their optical parameters (e.g., spanning optical fading timescales, t₂ = 1–263 days), and we find a similar diversity in the radio light curves. Using a brightness temperature analysis, we find that radio emission from novae is a mixture of thermal and synchrotron emission, with nonthermal emission observed at earlier times. We identify high brightness temperature emission (T_B > 5 × 10⁴ K) as an indication of synchrotron emission in at least nine (25%) of the novae. We find a class of synchrotron-dominated novae with mildly evolved companions, exemplified by V5589 Sgr and V392 Per, that appear to be a bridge between classical novae with dwarf companions and symbiotic binaries with giant companions. Four of the novae in our sample have two distinct radio maxima (the first dominated by synchrotron and the later by thermal emission), and in four cases the early synchrotron peak is temporally coincident with a dramatic dip in the optical light curve, hinting at a common site for particle acceleration and dust formation. We publish the light curves in a machine-readable table and encourage the use of these data by the broader community in multiwavelength studies and modeling efforts.

Solar flare formation mechanisms and their corresponding predictions have commonly been difficult topics in solar physics for decades. The traditional forecasting method manually constructs a statistical relationship between the measured values of solar active regions and solar flares that cannot fully utilize the information related to solar flares contained in observational data. In this article, we first used neural-network methods driven by the measured magnetogram and magnetic characteristic parameters of the sunspot group to learn the prediction model and predict solar flares. The prediction fusion model is based on a deep neural network, convolutional neural network, and bidirectional long short-term memory neural network and can predict whether a sunspot group will have a flare event above class M or class C in the next 24 or 48 hr. The real skill statistics (TSS) and F1 scores were used to evaluate the performances of our fusion model. The test results clearly show that this fusion model can make full use of the information related to solar flares and combine the advantages of each independent model to capture the evolution characteristics of solar flares, which is a much better performance than traditional statistical prediction models or any single machine-learning method. We also proposed two frameworks, namely F1_FFM and TSS_FFM, which optimize the F1 score and TSS score, respectively. The cross validation results show that they have their respective advantages in the F1 score and TSS score.

We attempt to visually classify the morphologies of 18,190 molecular clouds, which are identified in the ¹²CO(1–0) spectral line data over ∼450 deg² of the second Galactic quadrant from the Milky Way Imaging Scroll Painting project. Using the velocity-integrated intensity maps of the ¹²CO(1–0) emission, molecular clouds are first divided into unresolved and resolved ones. The resolved clouds are further classified as nonfilaments or filaments. Among the 18,190 molecular clouds, ∼25% are unresolved, ∼64% are nonfilaments, and ∼11% are filaments. In the terms of the integrated flux of ¹²CO(1–0) spectra of all 18,190 molecular clouds, ∼90% are from filaments, ∼9% are from nonfilaments, and the remaining ∼1% are from unresolved sources. Although nonfilaments are dominant in the number of the discrete molecular clouds, filaments are the main contributor of ¹²CO emission flux. We also present the number distributions of the physical parameters of the molecular clouds in our catalog, including their angular sizes, velocity spans, peak intensities of ¹²CO(1–0) emission, and ¹²CO(1–0) total fluxes. We find that there is a systematic difference between the angular sizes of the nonfilaments and filaments, with the filaments tending to have larger angular scales. The H₂ column densities of them are not significantly different. We also discuss the observational effects, such as those induced by the finite spatial resolution, beam dilution, and line-of-sight projection, on the morphological classification of molecular clouds in our sample.

Observing nearby galaxies with submillimeter telescopes on the ground has two major challenges. First, the brightness is significantly reduced at long submillimeter wavelengths compared to the brightness at the peak of the dust emission. Second, it is necessary to use a high-pass spatial filter to remove atmospheric noise on large angular scales, which has the unwelcome side effect of also removing the galaxy's large-scale structure. We have developed a technique for producing high-resolution submillimeter images of galaxies of large angular size by using the telescope on the ground to determine the small-scale structure (the large Fourier components) and a space telescope (Herschel or Planck) to determine the large-scale structure (the small Fourier components). Using this technique, we are carrying out the HARP and SCUBA-2 High Resolution Terahertz Andromeda Galaxy Survey (HASHTAG), an international Large Program on the James Clerk Maxwell Telescope, with one aim being to produce the first high-fidelity high-resolution submillimeter images of Andromeda. In this paper, we describe the survey, the method we have developed for combining the space-based and ground-based data, and we present the first HASHTAG images of Andromeda at 450 and 850 μm. We also have created a method to predict the CO(J = 3–2) line flux across M31, which contaminates the 850 μm band. We find that while normally the contamination is below our sensitivity limit, it can be significant (up to 28%) in a few of the brightest regions of the 10 kpc ring. We therefore also provide images with the predicted line emission removed.

Data from the Transiting Exoplanet Survey Satellite (TESS) have produced of the order of one million light curves at cadences of 120 s and especially 1800 s for every ∼27 day observing sector during its two-year nominal mission. These data constitute a treasure trove for the study of stellar variability and exoplanets. However, to fully utilize the data in such studies a proper removal of systematic-noise sources must be performed before any analysis. The TESS Data for Asteroseismology group is tasked with providing analysis-ready data for the TESS Asteroseismic Science Consortium, which covers the full spectrum of stellar variability types, including stellar oscillations and pulsations, spanning a wide range of variability timescales and amplitudes. We present here the two current implementations for co-trending of raw photometric light curves from TESS, which cover different regimes of variability to serve the entire seismic community. We find performance in terms of commonly used noise statistics meets expectations and is applicable to a wide range of intrinsic variability types. Further, we find that the correction of light curves from a full sector of data can be completed well within a few days, meaning that when running in steady state our routines are able to process one sector before data from the next arrives. Our pipeline is open-source and all processed data will be made available on the websites of the TESS Asteroseismic Science Operations Center and the Mikulski Archive for Space Telescopes.

Massive stars play key roles in many astrophysical processes. Deriving the atmospheric parameters of massive stars is important to understanding their physical properties, and thus the atmospheric parameters are key inputs to trace the evolution of massive stars. Here we report our work on adopting the data-driven technique called stellar label machine (SLAM) with the nonlocal thermal equilibrium TLUSTY synthetic spectra as the training data set to estimate the stellar parameters of Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) optical spectra for early-type stars. We apply two consistency tests to verify this machine-learning method and compare stellar labels given by SLAM with the labels in the literature for several objects having high-resolution spectra. We provide the stellar labels of effective temperature (T_eff), surface gravity ($\mathrm{log}g$), metallicity ([M/H]), and projected rotational velocity ($v\sin i$) for 3931 and 578 early-type stars from the LAMOST low-resolution survey (LRS) and medium-resolution survey (MRS), respectively. To estimate the average statistical uncertainties of our results, we calculated the standard deviation between the predicted stellar label and the prelabeled published values from the high-resolution spectra. The uncertainties of the four parameters are σ(T_eff) = 2185 K, $\sigma (\mathrm{log}g)=0.29$ dex, and $\sigma (v\sin i)=11\,\mathrm{km}\,{{\rm{s}}}^{-1}$ for MRS, and σ(T_eff) = 1642 K, $\sigma (\mathrm{log}g)=0.25$ dex, and $\sigma (v\sin i)=42\,\mathrm{km}\,{{\rm{s}}}^{-1}$ for LRS spectra, respectively. We note that the parameters of T_eff, $\mathrm{log}g$, and [M/H] can be better constrained using LRS spectra than using MRS spectra, most likely due to their broad wavelength coverage, while $v\sin i$ is constrained better by MRS spectra than by LRS spectra, probably due to the relatively accurate line profiles of MRS spectra.

Neutrinos have a unique quantum feature as flavor conversions. Recent studies suggested that collective neutrino oscillations play important roles in high-energy astrophysical phenomena. The quantum kinetic equation (QKE) is capable of describing the neutrino flavor conversion, transport, and matter collision self-consistently. However, we have experienced many technical difficulties in their numerical implementation. In this paper, we present a new QKE solver based on a Monte Carlo (MC) approach. This is an upgraded version of our classical MC neutrino transport solver; in essence, a flavor degree of freedom including mixing state is added into each MC particle. This extension requires updating numerical treatments of collision terms, in particular for scattering processes. We deal with the technical problem by generating a new MC particle at each scattering event. To reduce statistical noise inherent in MC methods, we develop the effective mean free path method. This suppresses a sudden change of flavor state due to collisions without increasing the number of MC particles. We present a suite of code tests to validate these new modules with comparison to the results reported in previous studies. Our QKE-MC solver is developed with fundamentally different philosophy and design from other deterministic and mesh methods, suggesting that it will be complementary to others and potentially provide new insights into physical processes of neutrino dynamics.

The multiconfiguration Dirac–Hartree–Fock (MCDHF) and relativistic configuration interaction methods are used to provide excitation energies, lifetimes, and radiative transition data for the 604 (699, 702, 704, 704, 704, and 699) lowest levels of the 3s²3p², 3s3p³, 3s²3p3d, 3p⁴, 3s3p²3d, 3s²3d², 3p³3d, 3s3p3d², 3s3d³, 3p3d³, 3p²3d², 3s²3p4s, 3s²3p4p, 3s²3p4d, 3s²3p4f, 3s3p²4s, 3s3p²4p, 3s3p²4d, 3s3p²4f, 3s²3d4s, 3s²3d4p, 3p³4s, 3p³4p, 3s3p3d4s, 3s²3p5s, and 3s²3p5p configurations in Cr xi, (Mn xii, Fe xiii, Co xiv, Ni xv, Cu xvi, and Zn xvii). Previous line identifications of Fe xiii and Ni xv in the EUV and X-ray wavelength ranges are reviewed by comprehensively comparing the MCDHF theoretical results with available experimental data. Many recent identifications of Fe xiii and Ni xv lines are confirmed, and several new identifications for these two ions are proposed. A consistent atomic data set with spectroscopic accuracy is provided for the lowest hundreds of levels for Si-like ions of iron-group elements of astrophysical interest, for which experimental values are scarce. The uncertainty estimation method suggested by Kramida, applied to the comparison of the length and velocity line strength values, is used for ranking the transition data. The correlation of the latter with the gauge dependency patterns of the line strengths is investigated.

We present the 3 mm wavelength spectra of 28 local galaxy merger remnants obtained with the Large Millimeter Telescope. Sixteen molecular lines from 14 different molecular species and isotopologues were identified, and 21 out of 28 sources were detected in one or more molecular lines. On average, the line ratios of the dense gas tracers, such as HCN (1–0) and HCO⁺(1–0), to ¹³CO (1–0) are 3–4 times higher in ultra/luminous infrared galaxies (U/LIRGs) than in non-LIRGs in our sample. These high line ratios could be explained by the deficiency of ¹³CO and high dense gas fractions suggested by high HCN (1–0)/¹²CO (1–0) ratios. We calculate the IR-to-HCN (1–0) luminosity ratio as a proxy of the dense gas star formation efficiency. There is no correlation between the IR/HCN ratio and the IR luminosity, while the IR/HCN ratio varies from source to source ((1.1–6.5) × 10³L_☉/(K km s⁻¹ pc²)). Compared with the control sample, we find that the average IR/HCN ratio of the merger remnants is higher by a factor of 2–3 than those of the early/mid-stage mergers and nonmerging LIRGs, and it is comparable to that of the late-stage mergers. The IR-to-¹²CO (1–0) ratios show a similar trend to the IR/HCN ratios. These results suggest that star formation efficiency is enhanced by the merging process and maintained at high levels even after the final coalescence. The dynamical interactions and mergers could change the star formation mode and continue to impact the star formation properties of the gas in the postmerger phase.

Wolf–Rayet ([WR]) and weak-emission-line (wels) central stars of planetary nebulae (PNs) have hydrogen-deficient atmospheres, whose origins are not well understood. In the present study, we have conducted plasma diagnostics and abundance analyses of 18 Galactic PNs surrounding [WR] and wels nuclei, using collisionally excited lines (CELs) and optical recombination lines (ORLs) measured with the Wide Field Spectrograph on the Australian National University 2.3 m telescope at the Siding Spring Observatory complemented with optical archival data. Our plasma diagnostics imply that the electron densities and temperatures derived from CELs are correlated with the intrinsic nebular Hβ surface brightness and excitation class, respectively. Self-consistent plasma diagnostics of heavy-element ORLs of N²⁺ and O²⁺ suggest that a small fraction of cool (≲7000 K), dense (∼10⁴–10⁵ cm⁻³) materials may be present in some objects, though with large uncertainties. Our abundance analyses indicate that the abundance discrepancy factors (ADFs ≡ ORLs/CELs) of O²⁺ are correlated with the dichotomies between forbidden-line and He i temperatures. Our results likely point to the presence of a tiny fraction of cool, oxygen-rich dense clumps within diffuse warm ionized nebulae. Moreover, our elemental abundances derived from CELs are mostly consistent with asymptotic giant branch models in the range of initial masses from 1.5 to 5 M_⊙. Further studies are necessary to understand better the origins of abundance discrepancies in PNs around [WR] and wels stars.

We present a catalog of 536 fast radio bursts (FRBs) detected by the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst (CHIME/FRB) Project between 400 and 800 MHz from 2018 July 25 to 2019 July 1, including 62 bursts from 18 previously reported repeating sources. The catalog represents the first large sample, including bursts from repeaters and nonrepeaters, observed in a single survey with uniform selection effects. This facilitates comparative and absolute studies of the FRB population. We show that repeaters and apparent nonrepeaters have sky locations and dispersion measures (DMs) that are consistent with being drawn from the same distribution. However, bursts from repeating sources differ from apparent nonrepeaters in intrinsic temporal width and spectral bandwidth. Through injection of simulated events into our detection pipeline, we perform an absolute calibration of selection effects to account for systematic biases. We find evidence for a population of FRBs—composing a large fraction of the overall population—with a scattering time at 600 MHz in excess of 10 ms, of which only a small fraction are observed by CHIME/FRB. We infer a power-law index for the cumulative fluence distribution of $\alpha =-1.40\pm 0.11({\rm{stat.}}{)}_{-0.09}^{+0.06}({\rm{sys.}})$, consistent with the −3/2 expectation for a nonevolving population in Euclidean space. We find that α is steeper for high-DM events and shallower for low-DM events, which is what would be expected when DM is correlated with distance. We infer a sky rate of $[820\pm 60({\rm{stat.}}{)}_{-200}^{+220}({\rm{sys.}})]/{\rm{sky}}/{\rm{day}}$ above a fluence of 5 Jy ms at 600 MHz, with a scattering time at 600 MHz under 10 ms and DM above 100 pc cm⁻³.

We present 226 large ultra-diffuse galaxy (UDG) candidates (r_e > 53, μ_0,g > 24 mag arcsec⁻²) in the SDSS Stripe 82 region recovered using our improved procedure developed in anticipation of processing the entire Legacy Surveys footprint. The advancements include less constrained structural parameter fitting, expanded wavelet filtering criteria, consideration of Galactic dust, estimates of parameter uncertainties and completeness based on simulated sources, and refinements of our automated candidate classification. We have a sensitivity ∼1 mag fainter in μ_0,g than the largest published catalog of this region. Using our completeness-corrected sample, we find that (1) there is no significant decline in the number of UDG candidates as a function of μ_0,g to the limit of our survey (∼26.5 mag arcsec⁻²); (2) bluer candidates have smaller Sérsic n; (3) most blue (g–r < 0.45 mag) candidates have μ_0,g ≲ 25 mag arcsec⁻² and will fade to populate the UDG red sequence we observe to ∼26.5 mag arcsec⁻²; (4) any red UDGs that exist significantly below our μ_0,g sensitivity limit are not descendent from blue UDGs in our sample; and (5) candidates with lower μ_0,g tend to smaller n. We anticipate that the final SMUDGes sample will contain ∼30 × as many candidates.

We perform a systematic X-ray spectroscopic analysis of 57 local luminous and ultraluminous infrared galaxy systems (containing 84 individual galaxies) observed with the Nuclear Spectroscopic Telescope Array and/or Swift/BAT. Combining soft X-ray data obtained with Chandra, XMM-Newton, Suzaku, and/or Swift/XRT, we identify 40 hard (>10 keV) X-ray–detected active galactic nuclei (AGNs) and constrain their torus parameters with the X-ray clumpy torus model XCLUMPY. Among the AGNs at z < 0.03, for which sample biases are minimized, the fraction of Compton-thick (N_H ≥ 10²⁴ cm⁻²) AGNs reaches ${64}_{-15}^{+14}$% (6/9 sources) in late mergers, while it is ${24}_{-10}^{+12}$% (3/14 sources) in early mergers, consistent with the tendency reported by Ricci et al. We find that the bolometric AGN luminosities derived from the infrared data increase but the X-ray to bolometric luminosity ratios decrease with merger stage. The X-ray-weak AGNs in late mergers ubiquitously show massive outflows at subparsec to kiloparsec scales. Among them, the most luminous AGNs (L_bol,AGN ∼ 10⁴⁶ erg s⁻¹) have relatively small column densities of ≲10²³ cm⁻² and almost super-Eddington ratios (λ_Edd ∼ 1.0). Their torus covering factors (C_T⁽²²⁾ ∼ 0.6) are larger than those of Swift/BAT-selected AGNs with similarly high Eddington ratios. These results suggest a scenario where, in the final stage of mergers, multiphase strong outflows are produced due to chaotic quasi-spherical inflows, and the AGN becomes extremely X-ray weak and deeply buried due to obscuration by inflowing and/or outflowing material.

KAPPA is a database and software for the calculation of the optically thin spectra for the non-Maxwellian κ-distributions that were recently diagnosed in the plasma of solar coronal loops, flares, as well as in the transition region. KAPPA is based on the widely used CHIANTI database and reproduces many of its capabilities for κ-distributions. Here we perform a major update of the KAPPA database, including a near-complete recalculation of the ionization, recombination, excitation, and deexcitation rates for all ions in the database, as well as an implementation of the two-ion model for calculations of relative-level populations (and intensities) if these are modified by ionization and recombination from or to excited levels. As an example of KAPPA usage, we explore novel diagnostics of κ, and show that O iii lines near 500 and 700 Å provide a strong sensitivity to κ, with some line intensity ratios changing by a factor of up to 2–4 compared to Maxwellian. This is much larger than previously employed diagnostics of κ.

While it is well recognized that both the Galactic interstellar extinction curves and the gas-phase abundances of dust-forming elements exhibit considerable variations from one sight line to another, as yet most of the dust extinction modeling efforts have been directed to the Galactic average extinction curve, which is obtained by averaging over many clouds of different gas and dust properties. Therefore, any details concerning the relationship between the dust properties and the interstellar environments are lost. Here we utilize the wealth of extinction and elemental abundance data obtained by space telescopes and explore the dust properties of a large number of individual sight lines. We model the observed extinction curve of each sight line and derive the abundances of the major dust-forming elements (i.e., C, O, Si, Mg, and Fe) required to be tied up in dust (i.e., dust depletion). We then confront the derived dust depletions with the observed gas-phase abundances of these elements and investigate the environmental effects on the dust properties and elemental depletions. It is found that for the majority of the sight lines the interstellar oxygen atoms are fully accommodated by gas and dust and therefore there does not appear to be a "missing oxygen" problem. For those sight lines with an extinction-to-hydrogen column density A_V/N_H ≳ 4.8 × 10⁻²² mag cm² H⁻¹ there are shortages of C, Si, Mg, and Fe elements for making dust to account for the observed extinction, even if the interstellar C/H, Si/H, Mg/H, and Fe/H abundances are assumed to be protosolar abundances augmented by Galactic chemical evolution.

To investigate the role of active galactic nucleus (AGN) X-ray irradiation on the interstellar medium (ISM), we systematically analyzed Chandra and Atacama Large Millimeter/submillimeter Array CO (J = 2–1) data for 26 hard X-ray (>10 keV) selected AGNs at redshifts below 0.05. While Chandra unveils the distribution of X-ray-irradiated gas via Fe-Kα emission, the CO (J = 2–1) observations reveal that of cold molecular gas. At high resolutions ≲1'', we derive Fe-Kα and CO (J = 2–1) maps for the nuclear 2'' region and for the external annular region of 2''–4'', where 2'' is ∼100–600 pc for most of our AGNs. First, focusing on the external regions, we find the Fe-Kα emission for six AGNs above 2σ. Their large equivalent widths (≳1 keV) suggest a fluorescent process as their origin. Moreover, by comparing the 6–7 keV/3–6 keV ratio, as a proxy of Fe-Kα, and CO (J = 2–1) images for three AGNs with the highest significant Fe-Kα detections, we find a possible spatial separation. These suggest the presence of X-ray-irradiated ISM and the change in the ISM properties. Next, examining the nuclear regions, we find that (1) the 20–50 keV luminosity increases with the CO (J = 2–1) luminosity; (2) the ratio of CO (J = 2–1)/HCN (J = 1–0) luminosities increases with 20–50 keV luminosity, suggesting a decrease in the dense gas fraction with X-ray luminosity; and (3) the Fe-Kα-to-X-ray continuum luminosity ratio decreases with the molecular gas mass. This may be explained by a negative AGN feedback scenario: the mass accretion rate increases with gas mass, and simultaneously, the AGN evaporates a portion of the gas, which possibly affects star formation.

In this work, we present a catalog of cataclysmic variables (CVs) identified from the sixth data release (DR6) of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). To single out the CV spectra, we introduce a novel machine-learning algorithm called UMAP to screen out a total of 169,509 Hα emission spectra, and obtain a classification accuracy of the algorithm of over 99.6% from the cross-validation set. We then apply the template-matching program PyHammer v2.0 to the LAMOST spectra to obtain the optimal spectral type with metallicity, which help us identify the chromospherically active stars and potential binary stars from the 169,509 spectra. After visually inspecting all of the spectra, we identify 323 CV candidates from the LAMOST database, among them 52 objects are new. We further classify the new CV candidates in subtypes based on their spectral features, including five DN subtypes during outbursts, five NL subtypes, and four magnetic CVs (three AM Her type and one IP type). We also find two CVs that have been previously identified by photometry and confirm their previous classification with the LAMOST spectra.

We present a performance test of the point-spread function (PSF) deconvolution algorithm applied to astronomical integral field unit (IFU) spectroscopy data for restoration of galaxy kinematics. We deconvolve the IFU data by applying the Lucy–Richardson algorithm to the 2D image slice at each wavelength. We demonstrate that the algorithm can effectively recover the true stellar kinematics of the galaxy, by using mock IFU data with a diverse combination of surface brightness profile, signal-to-noise ratio, line-of-sight geometry, and line-of-sight velocity distribution (LOSVD). In addition, we show that the proxy of the spin parameter ${\lambda }_{{R}_{e}}$ can be accurately measured from the deconvolved IFU data. We apply the deconvolution algorithm to the actual SDSS-IV MaNGA IFU survey data. The 2D LOSVD, geometry, and ${\lambda }_{{R}_{e}}$ measured from the deconvolved MaNGA IFU data exhibit noticeable differences compared to the ones measured from the original IFU data. The method can be applied to any other regular-grid IFU data to extract the PSF-deconvolved spatial information.

The identification of an emission line is unambiguous when multiple spectral features are clearly visible in the same spectrum. However, in many cases, only one line is detected, making it difficult to correctly determine the redshift. We developed a freely available unsupervised machine-learning algorithm based on unbiased topology (UMLAUT) that can be used in a very wide variety of contexts, including the identification of single emission lines. To this purpose, the algorithm combines different sources of information, such as the apparent magnitude, size and color of the emitting source, and the equivalent width and wavelength of the detected line. In each specific case, the algorithm automatically identifies the most relevant ones (i.e., those able to minimize the dispersion associated with the output parameter). The outputs can be easily integrated into different algorithms, allowing us to combine supervised and unsupervised techniques and increasing the overall accuracy. We tested our software on WISP (WFC3 IR Spectroscopic Parallel) survey data. WISP represents one of the closest existing analogs to the near-IR spectroscopic surveys that are going to be performed by the future Euclid and Roman missions. These missions will investigate the large-scale structure of the universe by surveying a large portion of the extragalactic sky in near-IR slitless spectroscopy, detecting a relevant fraction of single emission lines. In our tests, UMLAUT correctly identifies real lines in 83.2% of the cases. The accuracy is slightly higher (84.4%) when combining our unsupervised approach with a supervised approach we previously developed.

We present the deepest Spitzer/InfraRed Array Camera (IRAC) 3.6, 4.5, 5.8, and 8.0 μm wide-area mosaics yet over the Great Observatories Origins Deep Survey (GOODS)-N and GOODS-S fields as part of the GOODS Reionization Era wide-Area Treasury from Spitzer (GREATS) project. We reduced and mosaicked in a self-consistent way observations taken by the 11 different Spitzer/IRAC programs over the two GOODS fields from 12 yr of Spitzer cryogenic and warm-mission data. The cumulative depth in the 3.6 μm and 4.5 μm bands amounts to ∼4260 hr, ∼1220 hr of which are new very deep observations from the GREATS program itself. In the deepest area, the full-depth mosaics reach ≳200 hr over an area of ∼100 arcmin², corresponding to a sensitivity of ∼29 AB magnitude at 3.6 μm (1σ for point sources). Archival cryogenic 5.8 μm and 8.0 μm band data (a cumulative 976 hr) are also included in the release. The mosaics are projected onto the tangential plane of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey/GOODS at a 03 pixel⁻¹ scale. This paper describes the methodology enabling, and the characteristics of, the public release of the mosaic science images, the corresponding coverage maps in the four IRAC bands, and the empirical point-spread functions (PSFs). These PSFs enable mitigation of the source blending effects by taking into account the complex position-dependent variation in the IRAC images. The GREATS data products are in the Infrared Science Archive. We also release the deblended 3.6–8.0 μm photometry 9192 Lyman-break galaxies at z ∼ 3.5–10. GREATS will be the deepest mid-infrared imaging until the James Webb Space Telescope and, as such, constitutes a major resource for characterizing early galaxy assembly.

We present the results of a multiplicity survey for a magnitude-limited sample of 31 classical Be stars conducted with the Navy Precision Optical Interferometer and the Mark III Stellar Interferometer. The interferometric observations were used to detect companions in 10 previously known binary systems. For two of these sources (66 Oph and β Cep) new orbital solutions were obtained, while for a third source (υ Sgr) our observations provide the first direct, visual detection of the hot companion to the primary star. Combining our interferometric observations with an extensive literature search, we conclude that an additional four sources (o Cas, 15 Mon, β Lyr, and β Cep) also contain wider binary components that are physical companions to the narrow binaries, thus forming hierarchical multiple systems. Among the sources not previously confirmed as spectroscopic or visual binaries, BK Cam was resolved on a number of nights within a close physical proximity of another star with relative motion possibly suggesting a physical binary. Combining our interferometric observations with an extensive literature search, we provide a detailed listing of companions known around each star in the sample, and discuss the multiplicity frequency in the sample. We also discuss the prospects for future multiplicity studies of classical Be stars by long-baseline optical interferometry.