Table of contents for issue 1, volume 247, The Astrophysical Journal Supplement Series

Superhydrogenated polycyclic aromatic hydrocarbons (PAHs) may be present in H-rich and ultraviolet-poor benign regions. The addition of excess H atoms to PAHs converts the aromatic bonds into aliphatic bonds, the strongest of which falls near 3.4 μm. Therefore, superhydrogenated PAHs are often hypothesized to be a carrier of the 3.4 μm emission feature that typically accompanies the stronger 3.3 μm aromatic C–H stretching feature. To assess this hypothesis, we use density function theory to compute the infrared (IR) vibrational spectra of superhydrogenated PAHs and their ions of various sizes (ranging from benzene and naphthalene to perylene and coronene) and of various degrees of hydrogenation. For each molecule, we derive the intrinsic oscillator strengths of the 3.3 μm aromatic C–H stretch () and the 3.4 μm aliphatic C–H stretch (). By comparing the computationally derived mean ratio of with the mean ratio of the observed intensities , we find that the degree of superhydrogenation—the fraction of carbon atoms attached with extra hydrogen atoms—is only ∼2.2% for neutral PAHs, which predominantly emit the 3.3 and 3.4 μm features. We also determine for each molecule the intrinsic band strengths of the 6.2 μm aromatic C–C stretch () and the 6.85 μm aliphatic C–H deformation (). We derive the degree of superhydrogenation from the mean ratio of the observed intensities and for neutrals and for cations to be ≲3.1% for neutrals and ≲8.6% for cations. We conclude that astrophysical PAHs are primarily aromatic and are only marginally superhydrogenated.

We present a simple and effective multigrid-based Poisson solver of second-order accuracy in both gravitational potential and forces in terms of the one, two, and infinity norms. The method is especially suitable for numerical simulations using nested mesh refinement. The Poisson equation is solved from coarse to fine levels using a one-way interface scheme. We introduce antisymmetrically linear interpolation for evaluating the boundary conditions across the multigrid hierarchy. The spurious forces commonly observed at the interfaces between refinement levels are effectively suppressed. We validate the method using two- and three-dimensional density-force pairs that are sufficiently smooth for probing the order of accuracy.

Most large galaxies harbor supermassive black holes (SMBHs) in their centers, and galaxies merge. Consequently, binary SMBHs should be common in galactic nuclei. However, close binaries of SMBH (CB-SMBHs) with subparsec separation cannot be imaged directly using current facilities. Some indirect signatures, such as periodic signals in light curves and double peaks in the emission-line profile, have been used to find CB-SMBH candidates, but ambiguities still exist and no definitive conclusions can be made. We have recently proposed a new method focusing on kinematic signatures that can be derived from reverberation mapping of CB-SMBHs, one that offers a promising avenue to address this important problem. In this paper, we calculated models for a wide range of parameters, but broad-line regions of two BHs are close but still not merged. The purpose of this supplementary paper is to provide an atlas of two-dimensional transfer functions of CB-SMBHs with a wide range of orbital and geometrical parameters to aid more efficient identification of CB-SMBH candidates in reverberation mapping data.

We have studied the production of simple molecules on interstellar dust grains involving strong bonding via chemisorption on a graphite surface. Two classes of chemical simulations were run: models under isothermal conditions at temperatures from 150 to 400 K at 25 K intervals, and warm-up models starting at 10 K. For the isothermal models, physisorption does not occur appreciably, whereas for the warm-up models, it dominates at the lower temperatures before thermal desorption becomes rapid. We have made several simple approximations to determine what role, if any, chemisorption can play in the surface chemistry that occurs at temperatures above which icy mantles no longer cover the surface of dust grains. Our major finding is that the importance of chemisorption is greatly dependent on the efficiency of adsorption. Models having the lowest adsorption barrier show maximum abundances of chemisorbed species. Species such as CO, which are very efficiently formed in the gas phase at almost all temperatures (10–400 K), will not be strongly impacted by the existence of chemisorbed species. However, chemisorbed CO can achieve a reasonably high abundance (∼10⁻⁶). Species such as C₂H₂ and NH₃, which are less efficiently formed compared with CO in the gas phase, may show a change in their gas-phase abundance due to chemisorption. Several examples of this class of species can also show reasonably high abundances on grain surfaces due to chemisorption when the adsorption barrier is low.

We present high spatial resolution observations of ground-state OH masers achieved with the Australia Telescope Compact Array (ATCA). These observations targeted 253 pointing centers containing OH maser candidates at all four ground-state OH transitions identified in the Southern Parkes Large-Area Survey in Hydroxyl (SPLASH) across 96 deg² of the southern Galactic plane (332° < l < 334° and −2° < b < +2°, 344° < l < 355° and −2° < b < +2°, 358° < l < 4° and +2° < b < +6°, 5° < l < 10° and −2° < b < +2°). We detect maser emission toward 236 fields and suggest that 7 out of 17 nondetections are due to the slightly lower sensitivity of the ATCA observations, combined with some temporal variability. The superior resolution provided by the ATCA data has allowed us to identify 362 OH maser sites in the 236 target fields. Almost half (160 of 362) of these masers have been detected for the first time. Comparison between these 362 maser sites and information presented in the literature allowed us to categorize 238 sites as evolved star sites (66%), 63 as star formation (17%), 8 as supernova remnants, and 53 as unknown maser sites (15%). We present an analysis of the OH masers across the full SPLASH survey range (176 deg²) and find that the detection rate of 1.7 GHz radio continuum sources (18%) is lower than that previously found at 8.2 and 9.2 GHz (38%). We also find that the velocity separations of evolved star sites with symmetric 1612 MHz maser profiles are generally smaller than those with asymmetric profiles.

A nonlinear force-free field (NLFFF) extrapolation is widely used to reconstruct the three-dimensional magnetic field in the solar corona from the observed photospheric magnetic field. However, the pressure gradient and gravitational forces are ignored in the NLFFF model, even though the photospheric and chromospheric magnetic fields are not in general force-free. Here we develop a magnetohydrodynamic (MHD) relaxation method that reconstructs the solar atmospheric (chromospheric and coronal) magnetic field as a non-force-free magnetic field (NFFF) in magnetohydrostatic equilibrium where the Lorentz, pressure gradient, and gravitational forces are balanced. The system of basic equations for the MHD relaxation method is derived, and mathematical properties of the system are investigated. A robust numerical solver for the system is constructed based on the modern high-order shock capturing scheme. Two-dimensional numerical experiments that include the pressure gradient and gravitational forces are also demonstrated.

A few dozen dwarf satellite galaxies of the Milky Way have been discovered, which are often viewed as the remaining building blocks of our Galaxy. The follow-up spectroscopy showed that dwarf galaxies have a sizeable spread in their metallicities. Several scenarios were suggested to explain the metallicity spread, which can be tested by the structural patterns of stellar subpopulations with distinct metallicities. However, such chemical plus structural examination, which we refer to as “chemostructural study,” is hindered by the lack of stars with spectroscopic metallicity. Here we propose the Ca–by photometry as an alternative way to secure metallicities for a 2–3 orders of magnitude larger stellar sample than the spectroscopic sample and thus enable us to perform a chemostructural study on dwarf galaxies. In particular, we use the hk index [≡(Ca − b) − (b − y)], whose validity as a photometric metallicity indicator (and crass insensitivity to age) for red-giant-branch stars was upheld via Galactic globular clusters, and observe three dwarf spheroidal galaxies—Draco, Sextans, and Canes Venatici I (CVnI)—with Subaru/Suprime-Cam. We find that in all the galaxies the metal-rich stellar populations are more centrally concentrated than the metal-poor counterparts, suggesting that the central regions of the galaxies underwent extended star formation. Such a negative radial metallicity gradient for Sextans and CVnI opposes the traditional spectroscopic results. We also find that their metallicity distribution functions (MDFs) can be characterized by a unimodal, skewed Gaussian shape with a metal-rich peak and a metal-poor tail. We discuss their features in the chemo-structure and MDF in terms of dwarf galaxy formation theories.

Many astrophysical observations and measurement techniques that rely on data from images include an image registration step. The results of such techniques thus heavily rely on the precision of the registration. We present an Iterative Phase Correlation (IPC) algorithm, which is an extension of the well-known phase correlation method of image registration and is ideally suited for problems, where the subpixel registration accuracy plays a crucial role. Furthermore, a sophisticated and reliable method of optimal IPC parameter estimation is described. The paper includes examples of such optimized parameters for Solar Dynamics Observatory (SDO)/Helioseismic and Magnetic Imager, SDO/Atmospheric Imaging Assembly, and Solar Terrestrial Relations Observatory A/B Sun Earth Connection Coronal and Heliospheric Investigation images. The new method (both with or without the parameter optimization step) significantly outperforms standard image registration methods, such as (non-iterative) phase correlation or (normalized) cross correlation in the sense of subpixel accuracy. A step-by-step pseudocode implementation is also included.

Monitoring chromospheric and photospheric indexes of magnetic activity can provide valuable information, especially the interaction between different parts of the atmosphere and their response to magnetic fields. We extract chromospheric indexes, S and , for 59,816 stars from LAMOST spectra in the LAMOST–Kepler program, and photospheric index, R_eff, for 5575 stars from Kepler light curves. The log R_eff shows positive correlation with log . We estimate the power-law indexes between R_eff and for F-, G-, and K-type stars, respectively. We also confirm the dependence of both chromospheric and photospheric activity on stellar rotation. Ca iiH and K emissions and photospheric variations generally decrease with increasing rotation periods for stars with rotation periods exceeding a few days. The power-law indexes in exponential decay regimes show different characteristics in the two activity–rotation relations. The updated largest sample including the activity proxies and reported rotation periods provides more information to understand the magnetic activity for cool stars.

We develop a two-dimensional B-spline approach in the cylindrical coordinate system to simulate spectra of lithium in magnetic fields of white dwarf stars. The advantage of the current approach is that it can be applied to calculate both low- and high-lying states, while the theoretical methods for describing magnetized lithium in the literature are limited to the treatment of the ground state and low-lying excited states. The magnetized atomic states are calculated with symmetries , , , , and , and the lowest 10 atomic states of each symmetry are involved. The magnetic field strengths stride a scope of field strengths of white dwarf stars. Atomic data of absorption spectra corresponding to transitions from the ground state or low-lying excited states to high-lying excited states are reported for magnetized lithium. These atomic data include energy levels, wavelengths, and oscillator strengths. Comparison is made between our results, and theoretical and experimental data reported in the literature. The current two-dimensional B-spline approach can systematically produce atomic data to model discrete atomic spectra of both low- and high-lying states of lithium in magnetic white dwarf stars.

The determination of extrasolar planet masses with the radial velocity (RV) technique requires spectroscopic Doppler information from the planet’s host star, which varies with stellar brightness and temperature. We analyze the Doppler information in spectra from dwarfs of spectral types F–M utilizing empirical information from HARPS and CARMENES data and model spectra. We revisit the question of whether optical or near-infrared instruments are more efficient for RV observations in low-mass stars, and we come to the conclusion that an optical setup (BVR bands) is more efficient than a near-infrared one (YJHK) in dwarf stars hotter than 3200 K. We publish a catalog of 46,480 well-studied F–M dwarfs in the solar neighborhood, and we compare its distribution to more than 1 million stars from Gaia DR2. For all stars, we estimate the RV photon noise achievable in typical observations under the assumption of no activity jitter and slow rotation. We find that with an ESPRESSO-like instrument at an 8 m telescope, a photon noise limit of 10 cm s⁻¹ or lower can be reached in more than 280 stars in a 5 minute observation. At 4 m telescopes, a photon noise limit of 1 m s⁻¹ can be reached in a 10 minute exposure in approximately 10,000 predominantly Sun-like stars with a HARPS-like (optical) instrument. The same applies to ∼3000 stars for a red optical setup that covers the R and I bands and ∼700 stars for a near-infrared instrument. For the latter two, many of the targets are nearby M dwarfs. Finally, we identify targets in which Earth-mass planets within the liquid water habitable zone can cause RV amplitudes comparable to the RV photon noise. Assuming the same exposure times as above, we find that an ESPRESSO-like instrument can reach this limit for 1 M_⊕ planets in more than 1000 stars. The optical, red optical, and near-infrared configurations reach the limit for 2 M_⊕ planets in approximately 500, 700, and 200 stars, respectively. An online tool is provided to estimate the RV photon noise as a function of stellar temperature and brightness and wavelength coverage.

We present strong gravitational lensing models for 37 galaxy clusters from the Sloan Digital Sky Survey Giant Arcs Survey. We combine data from multi-band Hubble Space Telescope Wide Field Camera 3 (WFC3) imaging, with ground-based imaging and spectroscopy from Magellan, Gemini, Apache Point Observatory, and the Multiple Mirror Telescope, in order to detect and spectroscopically confirm new multiply imaged lensed background sources behind the clusters. We report spectroscopic or photometric redshifts of sources in these fields, including cluster galaxies and background sources. Based on all available lensing evidence, we construct and present strong-lensing mass models for these galaxy clusters. The clusters span a redshift range of 0.176 < z < 0.66 with a median redshift of z = 0.45, and sample a wide range of dynamical masses, 1.5 < M₂₀₀ < 35 × 10¹⁴, as estimated from their velocity dispersions. As these clusters were selected as lenses primarily owing to a fortuitous alignment with background galaxies that results in giant arcs, they exhibit a wide range in Einstein radii, 13 < θ_E < 231 for a source at z = 2, with a median θ_E = 108. The reduced HST images and lens model outputs are made available to the scientific community as high-level data products with this publication.

We present here the c–o colors for identified Flora, Vesta, Nysa–Polana, Themis, and Koronis family members within the historic data set (2015–2018) of the Asteroid Terrestrial-impact Last Alert System (ATLAS). The Themis and Koronis families are known to be relatively pure C- and S-type Bus-DeMeo taxonomic families, respectively, and the extracted color data from the ATLAS broadband c- and o-filters of these two families are used to demonstrate that the ATLAS c–o color is a sufficient parameter to distinguish between the C- and S-type taxonomies. The Vesta and Nysa–Polana families are known to display a mixture of taxonomies possibly due to Vesta’s differentiated parent body origin and Nysa–Polana actually consisting of two nested families with differing taxonomies. Our data show that the Flora family also displays a large degree of taxonomic mixing and the data reveal a substantial H-magnitude dependence on color. We propose and exclude several interpretations for the observed taxonomic mix. Additionally, we extract rotation periods of all of the targets reported here and find good agreement with targets that have previously reported periods.

A laboratory study of state-to-state rate coefficients (STS rates) for H₂:H₂ inelastic collisions in the v = 0 state is reported. The study, which spans the 295–20 K thermal range, is based on the use of a kinetic master equation. It describes the time-space evolution of populations of H₂ rotational levels as induced by inelastic collisions. It is applied here to a supersonic jet of natural H₂. This medium bears a large amount of relevant data that allows for the establishment of best values and confidence margins for the dominant STS rates of H₂:H₂ inelastic collisions on an experimental basis. The primary experimental data derived from the supersonic jet are the local number density, the populations of the H₂ rotational levels, and their gradients along the jet by means of high-sensitivity Raman spectroscopy with superb space resolution. First, two sets of theoretical STS rates from the literature have been tested against the experiment. The set that shows a better agreement with the experiment has then been scaled to derive an improved set of experiment-scaled STS rates (ES rates). They allow the reproduction of more than 50 experimental population gradient data within a standard deviation <1.4% along the 295–20 K thermal range. The estimated uncertainty for the ES rates ranges from ≈3% near 300 K to ≈6% near 20 K. ES rates and uncertainties for H₂:H₂ ground-state inelastic collisions between 300 and 20 K are presented in machine-readable format. Other (incomplete) sets of theoretical rates from the literature are discussed.

The properties of the molecular gas can shed light on the physical conditions of quasar host galaxies and the effect of feedback from accreting supermassive black holes. We present a new CO(2–1) survey of 23 Palomar–Green quasars conducted with the Atacama Large Millimeter/submillimeter Array. CO emission was successfully detected in 91% (21/23) of the objects, from which we derive CO luminosities, molecular gas masses, and velocity line widths. Together with CO(1–0) measurements in the literature for 32 quasars (detection rate 53%), there are 15 quasars with both CO(1–0) and CO(2–1) measurements and, in total, 40 sources with CO measurements. We find that the line ratio of is subthermal and broadly consistent with nearby galaxies and other quasars previously studied. No clear correlation is found between R₂₁ and the intensity of the interstellar radiation field or the luminosity of the active nucleus. As with the general galaxy population, quasar host galaxies exhibit a strong, tight, and linear L_IR– relation, with a normalization consistent with that of starburst systems. We investigate the molecular-to-total-gas mass fraction with the aid of total gas masses inferred from dust masses previously derived from infrared observations. Although the scatter is considerable, the current data do not suggest that the CO-to-H₂ conversion factor of quasar host galaxies significantly differs from that of normal star-forming galaxies.

Extreme high-frequency-peaked BL Lac objects (EHBLs) are blazars that exhibit extremely energetic synchrotron emission. They also feature nonthermal gamma-ray emission whose peak lies in the very high-energy (VHE, E > 100 GeV) range, and in some sources exceeds 1 TeV: this is the case for hard-TeV EHBLs such as 1ES 0229+200. With the aim of increasing the EHBL population, 10 targets were observed with the MAGIC telescopes from 2010 to 2017, for a total of 265 hr of good-quality data. The data were complemented by coordinated Swift observations. The X-ray data analysis confirms that all but two sources are EHBLs. The sources show only a modest variability and a harder-when-brighter behavior, typical for this class of objects. At VHE gamma-rays, three new sources were detected and a hint of a signal was found for another new source. In each case, the intrinsic spectrum is compatible with the hypothesis of a hard-TeV nature of these EHBLs. The broadband spectral energy distributions (SEDs) of all sources are built and modeled in the framework of a single-zone, purely leptonic model. The VHE gamma-ray-detected sources were also interpreted with a spine–layer model and a proton synchrotron model. The three models provide a good description of the SEDs. However, the resulting parameters differ substantially in the three scenarios, in particular the magnetization parameter. This work presents the first mini catalog of VHE gamma-ray and multiwavelength observations of EHBLs.

We have applied the semi-empirical spectral analysis, developed by the Sloan Digital Sky Survey (SDSS)-IV/Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE2) Massive Star Team, to a large sample of new O- and B-type stars identified along the Sagittarius spiral arm, in the direction of the southern star clusters NGC3603 and NGC3576. We obtained H-band spectra for 265 point sources, using the APOGEE2-S spectrograph at the du Pont Telescope at the Las Campanas Observatory. We analyzed the associated spectral features deriving spectral types, as well as the massive star distribution along the line of sight. From a total of 265 science targets, 95 are classified as mid- to late-O-type stars (for which only 10 O-type stars are previously known in the literature), 38 are found to be early- to mid-B-type stars, and 32 are classified as either yellow or blue supergiants, completing a total of 165 massive stars.

We present version X of the hammurabi package, the HEALPix-based numeric simulator for Galactic polarized emission. Improving on its earlier design, we have fully renewed the framework with modern C++ standards and features. Multithreading support has been built in to meet the growing computational workload in future research. For the first time, we present precision profiles of the hammurabi line-of-sight integral kernel with multilayer HEALPix shells. In addition to fundamental improvements, this report focuses on simulating polarized synchrotron emission with Gaussian random magnetic fields. Two fast methods are proposed for realizing divergence-free random magnetic fields either on the Galactic scale where field alignment and strength modulation are imposed, or on a local scale where more physically motivated models like a parameterized magnetohydrodynamic (MHD) turbulence can be applied. As an example application, we discuss the phenomenological implications of Gaussian random magnetic fields for high Galactic latitude synchrotron foregrounds. In this, we numerically find B/E polarization-mode ratios lower than unity based on Gaussian realizations of either MHD turbulent spectra or in spatially aligned magnetic fields.

We present laboratory measurements of the phase functions and degree of linear polarization (DLP) curves of a selection of millimeter-sized cosmic dust analog particles. The set includes particles with similar sizes but diverse internal structure (compact and porous) and absorbing properties. The measured phase functions are found to be in all cases very different from those of micron-sized particles. They show a monotonic decrease with increasing phase angle from the back- to the side-scattering region, reaching a minimum at large phase angles before a steep increase of the forward peak. This is in stark contrast to the phase functions of micron-sized particles, which are rather flat at low and intermediate phase angles. The maximum of the DLP for millimeter-sized compact particles is shifted toward larger phase angles (∼130°) compared to that of micron-sized particles (∼90°). Porosity plays an important role in the measured DLP curves: the maximum significantly decreases for increasing porosity as a result of multiple scattering within the particle. Large porous particles with highly absorbing inclusions can reproduce both the OSIRIS/Rosetta phase functions and ground-based DLP observations of comet 67P/Churyumov–Gerasimenko.

We study the statistical properties of 320 bulges of disk galaxies in the Carnegie-Irvine Galaxy Survey, using robust structural parameters of galaxies derived from image fitting. We apply the Kormendy relation to classify classical and pseudo bulges and characterize the bulge dichotomy with respect to the structural properties of the bulges and the physical properties of the host galaxies. We confirm previous findings that pseudo bulges on average have smaller Sérsic indices, lower bulge-to-total ratios, and fainter surface brightnesses than classical bulges. Our sizable sample statistically shows that pseudo bulges are more intrinsically flattened than classical bulges. Pseudo bulges are most frequent (incidence ≳80%) in late-type spirals (later than Sc). Our measurements support the picture in which pseudo bulges arose from star formation induced by inflowing gas, while classical bulges were born out of violent processes such as mergers and coalescence of clumps. We reveal differences with the literature that warrant attention: (1) the bimodal distribution of Sérsic indices presented by previous studies is not reproduced in our study; (2) classical and pseudo bulges have similar relative bulge sizes; and (3) the pseudo bulge fraction is considerably smaller in early-type disks than reported in previous studies based on one-dimensional surface brightness profile fitting. We attribute these differences to our improved image quality, more robust bulge-to-disk decomposition technique, and to the different classification criteria that we applied. Moreover, we find that barred galaxies do not host more pseudo bulges or more prominent pseudo bulges than unbarred galaxies. Various implications of these findings are discussed.

Coronal mass ejections (CMEs) are the primary sources of intense disturbances at Earth, where their geoeffectiveness is largely determined by their dynamic pressure and internal magnetic field, which can be significantly altered during interactions with other CMEs in interplanetary space. We analyze three successive CMEs that erupted from the Sun during 2017 September 4–6, investigating the role of CME–CME interactions as a source of the associated intense geomagnetic storm ( nT on September 7). To quantify the impact of interactions on the (geo)effectiveness of individual CMEs, we perform global heliospheric simulations with the European Heliospheric Forecasting Information Asset (EUHFORIA) model, using observation-based initial parameters with the additional purpose of validating the predictive capabilities of the model for complex CME events. The simulations show that around 0.45 au, the shock driven by the September 6 CME started compressing a preceding magnetic ejecta formed by the merging of two CMEs launched on September 4, significantly amplifying its B_z until a maximum factor of 2.8 around 0.9 au. The following gradual conversion of magnetic energy into kinetic and thermal components reduced the B_z amplification until its almost complete disappearance around 1.8 au. We conclude that a key factor at the origin of the intense storm triggered by the 2017 September 4–6 CMEs was their arrival at Earth during the phase of maximum B_z amplification. Our analysis highlights how the amplification of the magnetic field of individual CMEs in spacetime due to interaction processes can be characterized by a growth, a maximum, and a decay phase, suggesting that the time interval between the CME eruptions and their relative speeds are critical factors in determining the resulting impact of complex CMEs at various heliocentric distances (helioeffectiveness).

Connected to the experiment performed at the Stockholm electron beam ion trap, a systematic relativistic configuration-interaction calculation is carried out to compare with the experimental spectra. In particular, separate rate coefficients are calculated for dominant recombination and excitation processes in the range of the impact electron energy determined by the experiment. By means of the relevant experimental parameters, the presently calculated dielectronic recombination rate coefficients for and S¹⁴⁺ ions and electron-impact excitation ones for S¹⁵⁺, S¹⁴⁺, and S¹³⁺ ions are employed further to synthesize overall theoretical spectra for comparison with the experimentally measured spectra. Overall, very good agreements with the experimental results are found except for one missing excitation peak around the impact electron energy 2.52 keV, which cannot be explained by the present calculations and thus remains open.

In 2017, an Atacama Large Millimeter/submillimeter Array (ALMA) high-frequency long baseline campaign was organized to test image capabilities with baselines up to 16 km at submillimeter (submm) wavelengths. We investigated image qualities using ALMA receiver Bands 7, 8, 9, and 10 (285–875 GHz) by adopting band-to-band (B2B) phase referencing in which a phase calibrator is tracked at a lower frequency. For B2B phase referencing, it is expected that a closer phase calibrator to a target can be used, comparing to standard in-band phase referencing. In the first step, it is ensured that an instrumental phase offset difference between low- and high-frequency Bands can be removed using a differential gain calibration in which a phase calibrator is certainly detected while frequency switching. In the next step, comparative experiments are arranged to investigate the image quality between B2B and in-band phase referencing with phase calibrators at various separation angles. In the final step, we conducted long baseline imaging tests for a quasar at 289 GHz in Band 7 and 405 GHz in Band 8 and complex structure sources of HL Tau and VY CMa at ∼670 GHz in Band 9. The B2B phase referencing was successfully applied, allowing us to achieve an angular resolution of 14 × 11 and 10 × 8 mas for HL Tau and VY CMa, respectively. There is a high probability of finding a low-frequency calibrator within 54 in B2B phase referencing, bright enough to use an 8 s scan length combined with a 7.5 GHz bandwidth.

Observations of the Sun as a star have been key to guiding models of stellar atmospheres and additionally provide useful insights on the effects of granulation and stellar activity on radial velocity measurements. Most high-resolution solar atlases contain telluric lines that span the optical and limit the spectral regions useful for analysis. We present here a telluric-corrected solar atlas covering 0.5–1.0 μm derived from solar spectra taken with a Fourier transform spectrograph at the Institut für Astrophysik, Göttingen. This atlas is the highest-resolution spectrum with a wavelength calibration precise to ±10 m s⁻¹ across this 500 nm spectral window. We find that the atlas matches to within 3% of the telluric-corrected Kitt Peak atlas in regions containing telluric absorption weaker than 50% in transmission. The telluric component of the spectral data is fit with a semiempirical model composed of Lorentz profiles initialized to the High-resolution Transmission Molecular Absorption Database (HITRAN) parameters for each absorption feature. Comparisons between the best-fit telluric parameters describing the Lorentz profile for each absorption feature and the original HITRAN values in general show excellent agreement considering the effects atmospheric pressure and temperature have on our final parameters. However, we identify a small subset of absorption features with larger offsets relative to the cataloged line parameters. We make our final solar atlas available online. We additionally make available the telluric spectra extracted from the data that, given the high resolution of the spectrum, would be useful for studying the time evolution of telluric line shapes and their impact on Doppler measurements.

We describe the observations and resultant galaxy cluster catalog from the 2770 deg² SPTpol Extended Cluster Survey (SPT-ECS). Clusters are identified via the Sunyaev–Zel’dovich (SZ) effect and confirmed with a combination of archival and targeted follow-up data, making particular use of data from the Dark Energy Survey (DES). With incomplete follow-up we have confirmed as clusters 244 of 266 candidates at a detection significance ξ ≥ 5 and an additional 204 systems at 4 < ξ < 5. The confirmed sample has a median mass of and a median redshift of z = 0.49, and we have identified 44 strong gravitational lenses in the sample thus far. Radio data are used to characterize contamination to the SZ signal; the median contamination for confirmed clusters is predicted to be ∼1% of the SZ signal at the ξ > 4 threshold, and <4% of clusters have a predicted contamination >10% of their measured SZ flux. We associate SZ-selected clusters, from both SPT-ECS and the SPT-SZ survey, with clusters from the DES redMaPPer sample, and we find an offset distribution between the SZ center and central galaxy in general agreement with previous work, though with a larger fraction of clusters with significant offsets. Adopting a fixed Planck-like cosmology, we measure the optical richness–SZ mass () relation and find it to be 28% shallower than that from a weak-lensing analysis of the DES data—a difference significant at the 4σ level—with the relations intersecting at λ = 60. The SPT-ECS cluster sample will be particularly useful for studying the evolution of massive clusters and, in combination with DES lensing observations and the SPT-SZ cluster sample, will be an important component of future cosmological analyses.

Compared with previous space-borne surveys, the Transiting Exoplanet Survey Satellite (TESS) provides a unique and new approach to observe solar system objects. While its primary mission avoids the vicinity of the ecliptic plane by approximately six degrees, the scale height of the solar system debris disk is large enough to place various small body populations in the field of view. In this paper we present the first data release of photometric analysis of TESS observations of small solar system bodies, focusing on the bright end of the observed main-belt asteroid and Jovian Trojan populations. This data release, named TSSYS-DR1, contains 9912 light curves obtained and extracted in a homogeneous manner, and triples the number of bodies with unambiguous fundamental rotation characteristics, namely where accurate periods and amplitudes are both reported. Our catalog clearly shows that the number of bodies with long rotation periods are definitely underestimated by all previous ground-based surveys, by at least an order of magnitude.

We present the results from the timing and spectral study of Mrk 421 based mainly on the Swift data in the X-ray energy range obtained during the time interval 2015 December–2018 April. The most extreme X-ray flaring activity on long-term, daily, and intraday timescales was observed during the 2 month period that started in 2017 December, when the 0.3–10 keV flux exceeded a level of 5 × 10⁻⁹ erg cm⁻² s⁻¹, recorded only twice previously. While the TeV-band and X-ray variabilities were mostly correlated, the source often varied in a complex manner in the MeV–GeV and radio–UV energy ranges, indicating that the multifrequency emission of Mrk 421 could not always be generated in a single zone. The longer-term flares at X-rays and γ-rays showed a lognormal character, possibly indicating a variability imprint of the accretion disk onto the jet. A vast majority of the 0.3–10 keV spectra were consistent with the log-parabolic model, showing relatively low spectral curvature and correlations between the different spectral parameters, predicted in the case of the first- and second-order Fermi processes. The position of the synchrotron spectral energy distribution peak showed an extreme variability on diverse timescales between the energies E_p < 0.1 and >15 keV, with 15% of the spectra peaking at the hard X-ray, and was related to the peak height as with α ∼ 0.6, which is expected for the transition from Kraichnan-type turbulence into the “hard sphere” one. The 0.3–300 GeV spectra showed features of the hadronic contribution, jet–star interaction, and upscatter in the Klein–Nishina regime in different time intervals.

Previous measurements of stellar properties for K2 stars in the Ecliptic Plane Input Catalog largely relied on photometry and proper motion measurements, with some added information from available spectra and parallaxes. Combining Gaia DR2 distances with spectroscopic measurements of effective temperatures, surface gravities, and metallicities from the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) DR5, we computed updated stellar radii and masses for 26,838 K2 stars. For 195,250 targets without a LAMOST spectrum, we derived stellar parameters using random forest regression on photometric colors trained on the LAMOST sample. In total, we measured spectral types, effective temperatures, surface gravities, metallicities, radii, and masses for 222,088 A, F, G, K, and M-type K2 stars. With these new stellar radii, we performed a simple reanalysis of 299 confirmed and 517 candidate K2 planet radii from Campaigns 1–13, elucidating a distinct planet radius valley around 1.9 R_⊕, a feature thus far only conclusively identified with Kepler planets, and tentatively identified with K2 planets. These updated stellar parameters are a crucial step in the process toward computing K2 planet occurrence rates.

Sixty-five Planck Galactic cold clumps (PGCCs) from the first quadrant (IQuad) and 39 from the anticenter direction region (ACent) were observed in ¹²CO, ¹³CO, and C¹⁸O J = 1–0 lines using the 13.7 m telescope of the Purple Mountain Observatory. All the targets were detected in all three lines, except for 12 IQuad and 8 ACent PGCCs without C¹⁸O detection. Seventy-six and 49 velocity components were obtained in IQuad and ACent respectively; 146 cores were extracted from 76 IQuad clumps and 100 cores from 49 ACent clumps. The average T_ex of IQuad cores and ACent cores is 12.4 K and 12.1 K, respectively. The average line widths of ¹³CO of IQuad cores and ACent cores are 1.55 km s⁻¹ and 1.77 km s⁻¹, respectively. Among the detected cores, 24 in IQuad and 13 in ACent have asymmetric line profiles. The small blue excesses, ∼0.03 in IQuad and 0.01 in ACent, indicate that star formation is not active in these PGCC cores. Power-law fittings of the core mass function to the high-mass end give indices of −0.57 in IQuad and −1.02 in ACent, which are flatter than the slope of the initial mass function given by Salpeter. The large turnover masses of 28 for IQuad cores and 77 for ACent cores suggest low star formation efficiencies in PGCCs. The correlation between virial mass and gas mass indicates that most PGCC cores in both regions are not likely pressure-confined.

We present a new extended and detailed set of models for classical Cepheid pulsators at solar chemical composition (Z = 0.02, Y = 0.28) based on a well-tested nonlinear hydrodynamical approach. In order to model the possible dependence on crucial assumptions such as the mass–luminosity relation of central helium burning intermediate-mass stars or the efficiency of superadiabatic convection, the model set was computed by varying not only the pulsation mode and the stellar mass but also the mass–luminosity relation and the mixing length parameter that is used to close the system of nonlinear hydrodynamical and convective equations. The dependence of the predicted boundaries of the instability strip as well as of both light and radial velocity curves on the assumed mass–luminosity and the efficiency of superadiabatic convection is discussed. Nonlinear period–mass–luminosity–temperature, period–radius, and period–mass–radius relations are also computed. The theoretical atlas of bolometric light curves for both the fundamental and first overtone mode has been converted in the Gaia filters G, G_BP, and G_BR and the corresponding mean magnitudes have been derived. Finally, the first theoretical period–luminosity–color and period–Wesenheit relations in the Gaia filters are provided and the resulting theoretical parallaxes are compared with Gaia Data Release 2 results for both fundamental and first overtone Galactic Cepheids.

We present rotation curve fits to 175 late-type galaxies from the Spitzer Photometry and Accurate Rotation Curves database using seven dark matter (DM) halo profiles: pseudo-isothermal, Burkert, Navarro–Frenk–White (NFW), Einasto, Di Cintio et al. (2014, hereafter DC14), cored-NFW, and a new semi-empirical profile named Lucky13. We marginalize over the stellar mass-to-light ratio, galaxy distance, disk inclination, halo concentration, and halo mass (and an additional shape parameter for Einasto) using a Markov Chain Monte Carlo method. We find that cored halo models, such as the DC14 and Burkert profiles, generally provide better fits to rotation curves than the cuspy NFW profile. The stellar mass-halo mass relation from abundance matching is recovered by all halo profiles once imposed as a Bayesian prior, whereas the halo mass–concentration relation is not reproduced in detail by any halo model. We provide an extensive set of figures as well as best-fit parameters in machine-readable tables to facilitate model comparison and the exploration of DM halo properties.

We present a catalog of 316 trans-Neptunian bodies (TNOs) detected from the first four seasons (“Y4” data) of the Dark Energy Survey (DES). The survey covers a contiguous 5000 deg² of the southern sky in the grizY optical/NIR filter set, with a typical TNO in this part of the sky being targeted by 25–30 Y4 exposures. This paper focuses on the methods used to detect these objects from the ≈60,000 Y4 exposures, a process made challenging by the absence of the few-hour repeat observations employed by TNO-optimized surveys. Newly developed techniques include: transient/moving object detection by comparison of single-epoch catalogs to catalogs of “stacked” images; quantified astrometric error from atmospheric turbulence; new software for detecting TNO linkages in a temporally sparse transient catalog, and for estimating the rate of spurious linkages; use of faint stars to determine the detection efficiency versus magnitude in all exposures. Final validation of the reality of linked orbits uses a new “sub-threshold confirmation” test, wherein we demand the object be detectable in a stack of the exposures in which the orbit indicates an object should be present, but was not individually detected. This catalog contains all validated TNOs which were detected on ≥6 unique nights in the Y4 data, and is complete to r ≲ 23.3 mag with virtually no dependence on orbital properties for bound TNOs at distance 30 au < d < 2500 au. The catalog includes 245 discoveries by DES, 139 not previously published. The final DES TNO catalog is expected to yield >0.3 mag more depth, and arcs of >4 yr for nearly all detections.

We present the fourth Fermi Large Area Telescope catalog (4FGL) of γ-ray sources. Based on the first eight years of science data from the Fermi Gamma-ray Space Telescope mission in the energy range from 50 MeV to 1 TeV, it is the deepest yet in this energy range. Relative to the 3FGL catalog, the 4FGL catalog has twice as much exposure as well as a number of analysis improvements, including an updated model for the Galactic diffuse γ-ray emission, and two sets of light curves (one-year and two-month intervals). The 4FGL catalog includes 5064 sources above 4σ significance, for which we provide localization and spectral properties. Seventy-five sources are modeled explicitly as spatially extended, and overall, 358 sources are considered as identified based on angular extent, periodicity, or correlated variability observed at other wavelengths. For 1336 sources, we have not found plausible counterparts at other wavelengths. More than 3130 of the identified or associated sources are active galaxies of the blazar class, and 239 are pulsars.

Hilda asteroids orbit at the outer edge, or just outside of the Main Belt, occupying the 2:3 mean motion resonance with Jupiter. It is known that the group shows a mixed taxonomy that suggests the mixed origin of Hilda members, having migrated to the current orbit both from the outer Main Belt and from the Trojans swarms. But there are still few observations for comparative studies to help us understand the Hilda group in deeper detail. We identified 125 individual light curves of Hilda asteroids observed by the K2 mission. We found that despite of the mixed taxonomies, the Hilda group highly resembles the Trojans in the distribution of rotation periods and amplitudes, and even the LR group (mostly C- and X-type) Hildas follow this rule. Contrary to the Main Belt, the Hilda group lacks the very fast rotators. The ratio of extremely slow rotators (P > 100 hr) is a surprising 18%, which is unique in the solar system. The occurrence rate of asteroids with multiple periods (4%) and asteroids with three maxima in the light curves (5%) can be signs of a high rate of binarity, which we can estimate as 25% within the Hilda group.

We search for RR Lyrae stars (RRLs) in 27 nearby (<100 kpc) ultra-faint dwarf satellite galaxies using the Gaia DR2 catalog of RRLs. Based on proper motions, magnitudes, and location on the sky, we associate 47 Gaia RRLs with 14 different satellites. Distances based on RRLs are provided for those galaxies. We have identified RRLs for the first time in the Tucana II dwarf galaxy, and find additional members in Ursa Major II, Coma Berenices, Hydrus I, Bootes I, and Bootes III. In addition we have identified candidate extra-tidal RRLs in six galaxies, which suggests they may be undergoing tidal disruption. We found 10 galaxies have no RRLs either in Gaia or in the literature. However, given the known completeness of Gaia DR2 we cannot conclude these galaxies indeed lack variable stars of this type.