Sazuna/UAT_keywords huggingface dataset:
Multigroup Radiation Magnetohydrodynamics Based on Discrete Ordinates including Compton Scattering. We present a formulation and numerical algorithm to extend the scheme for gray radiation magnetohydrodynamics (MHD) developed by Jiang to include the frequency dependence via the multigroup approach. The entire frequency space can be divided into an arbitrary number of groups in the lab frame, and we follow the time-dependent evolution of frequency-integrated specific intensities along discrete rays inside each group. Spatial transport of photons is done in the lab frame while all the coupling terms are solved in the fluid rest frame. Lorentz transformation is used to connect different frames. The radiation transport equation is solved fully implicitly in time while the MHD equations are evolved explicitly so that time step is not limited by the speed of light. A finite volume approach is used for transport in both spatial and frequency spaces to conserve the radiation energy density and momentum. The algorithm includes photon absorption, electron scattering, as well as Compton scattering, which is calculated by solving the Kompaneets equation. The algorithm is accurate for a wide range of optical depth conditions and can handle both radiation-pressure- and gas-pressure-dominated flows. It works for both Cartesian and curvilinear coordinate systems with adaptive mesh refinement. We provide a variety of test problems including a radiating sphere, shadow test, absorption of a moving gas, Bondi-type flows, as well as a collection of test problems for thermal and bulk Compton scattering. We also discuss examples where frequency dependence can make a big difference compared with the gray approach.

Keywords: Radiative transfer simulations, Computational methods, Astrophysical fluid dynamics, Radiative transfer
Temperature Spectra of Interstellar Dust Grains Heated by Cosmic Rays. III. Mixed-composition Grains. Icy grains in the interstellar medium and star formation regions consist of a variety of materials. Such composite grains interact differently with cosmic-ray (CR) particles compared to simple single-material grains. We aim to calculate the spectra of energies and temperatures of mixed-composition grains undergoing whole-grain heating by CRs. The grains were assumed to consist of a mixture of carbon and olivine, covered by ices consisting of carbon oxides and water. The energy and temperature spectra for grains with radii 0.05, 0.1, and 0.2 μm impacted by CRs were calculated for eight values of column density, relevant to molecular clouds and star-forming cores. The approach takes into account changes in ice thickness and composition with increasing column density. These detailed data for CR interaction with interstellar grains are intended for applications in astrochemical models. The main finding is that a more accurate approach on grain heat capacity and other factors prevent frequent heating of 0.1 μm or larger icy grains to high temperatures.

Keywords: Interstellar dust, Interstellar molecules, Astrochemistry, Dark interstellar clouds, Cosmic rays
Polarization-sensitive Compton Scattering by Accelerated Electrons. We describe upgrades to a numerical code that computes synchrotron and inverse-Compton emission from relativistic plasma including full polarization. The introduced upgrades concern a scattering kernel that is now capable of scattering the polarized and unpolarized photons on a nonthermal population of electrons. We describe the scheme to approach this problem and we test the numerical code against a known analytic solution. Finally, using the upgraded code, we predict the polarization of light that is scattered off subrelativistic thermal or relativistic thermal and nonthermal free electrons. The upgraded code enables more realistic simulations of emissions from plasma jets associated with accreting compact objects.

Keywords: General relativity, Polarimetry, Black holes, Radiative transfer
Performance of Sequential Phase Diversity with Dynamical Solar Scenes. Phase diversity techniques are usually based on the comparison of synchronously acquired pairs of focused-defocused images. This way, differences between both images are avoided except from random pixel variations due to noise on the detector and the phase diversity itself. In some astronomical instruments, though, the two images are not taken simultaneously. This work studies the impact of carrying out phase diversity with pairs of asynchronously acquired images while observing an evolving solar scene. We evaluate the performance of this technique as a function of the time gap between the images through the use of a magnetohydrodynamical simulation of the solar scene as observed by an instrument. We describe the incident wave front with two numbers of Zernike polynomials (20 or 32) to explore their effect on the wave front sensing accuracy and we employ two levels of noise to study their impact in the object restoration. We find that a time gap among our simulation images smaller than ~10 s has a negligible impact on the performance of the method. The rms error of the Zernike coefficients fitting worsens exponentially from there on, but the evolution is similar no matter the number of polynomials used in the fitting. Meanwhile, the quality of the object restoration benefits from lower noise levels, but it decreases linearly with the time gap independently of the amount of noise.

Keywords: Astronomical techniques, Astronomical instrumentation, Solar instruments
Optimal Defocus for Phase Diversity Wave Front Retrieval. Phase diversity techniques are widely employed in solar astronomy to evaluate and correct the aberrations stemming from atmospheric turbulences, the telescope, and its instruments. The method uses information provided by a pair of images. One of them is usually focused while the other one is defocused. The amount of defocus to be induced is somehow arbitrary, though. In this work we carry out a series of numerical experiments with artificial solar images to investigate the performance of phase diversity for different choices of the relative defocus among the two images. The experiments allow us to determine the amount of defocus that produces the best wave front restoration when changing: (1) the number of Zernike polynomials of the retrieved and/or incident wave fronts; (2) the signal-to-noise ratio of the images; (3) the amplitude of the incident aberrations; and (4) the observed scene. We find a correlation between the amount of defocus needed for optimal restorations and the number of Zernike polynomials employed in the optimization. Values larger than the typically accepted choice of 1λ (peak to peak) are obtained in most cases.

Keywords: Astronomical techniques, Astronomical instrumentation, Solar instruments
New Methanol Maser Transitions and Maser Variability Identified from an Accretion Burst Source G358.93-0.03. The high-mass young stellar object G358.93-0.03 underwent an accretion burst during the period from 2019 January to June. Given its extraordinary conditions, a number of new maser transitions may have been naturally excited during the burst stage. Searching for new maser lines and monitoring maser variability associated with the accretion burst event are important for understanding the complex conditions of the massive star formation toward G358.93-0.03. In this work, using the Shanghai 65 m Tianma Radio Telescope, we continuously monitored the multiple maser (including methanol and water) transitions toward G358.93-0.03 during the burst in the period from 2019 March 14 to May 20. There were 23 CH3OH maser transitions and one H2O maser transition detected from the monitoring. Nearly all the detected maser transitions toward this source have dramatic variations in their intensities within a short period of ~2 months. Eight new methanol transitions from G358.93-0.03 were identified to be masering in our observations based on their spectral profile, line width, intensity, and the rotation diagram. During the monitoring, the gas temperature of the clouds in the case of saturated masers can show a significant decline, indicating that the maser clouds were going through a cooling process, possibly associated with the propagation of a heat wave induced by the accretion burst. Some of the maser transitions were even detected with the second flares in 2019 April, which may be associated with the process of the heat-wave propagation induced by the same accretion burst acting on different maser positions.

Keywords: Accretion, Massive stars, Young stellar objects, Star formation, Interstellar masers
Supermassive Black Hole and Broad-line Region in NGC 5548: Results from Five-season Reverberation Mapping. NGC 5548 is one of the active galactic nuclei (AGNs) selected for our long-term spectroscopic monitoring with the Lijiang 2.4 m telescope, aiming at investigating the origin and evolution of broad-line regions (BLRs), accurately measuring the mass of supermassive black holes (SMBHs), and understanding the structure and evolution of the AGN. We have performed five-season observations for NGC 5548 with the median sampling interval ranging from 1.25 to 3 days. The light curves of the 5100 Å continuum and broad emission lines are measured after subtracting contamination of the host galaxy starlight. The time lags of the broad He II, He I, Hγ, and Hβ lines with respect to the 5100 Å continuum are obtained for each season and their mean time lags over the five seasons are 0.69, 4.66, 4.60, and 8.43 days, respectively. The Hγ and Hβ velocity-resolved lag profiles in the seasons of 2015, 2018, 2019, and 2021 are constructed, from which an "M-shaped" structure is found in 2015 but disappears after 2018. Our five-season reverberation mapping (RM) yields an average virial SMBH mass of M •/107 M ⊙ = 14.22, with a small standard deviation of 1.89. By combining the previous 18 RM campaigns and our five-season campaign for NGC 5548, we find that there exists a time lag of 3.5 yr between the changes in the BLR size and optical luminosity. In addition, we construct the BLR radius-luminosity relation and the virial relation for NGC 5548.

Keywords: Supermassive black holes, Reverberation mapping, Active galactic nuclei, Time domain astronomy
Properties of a Supercritical Quasi-perpendicular Interplanetary Shock Propagating in the Terrestrial Foreshock Region. We investigate the properties of an interplanetary (IP) shock (M  f  = 2.1, θ = 80°) that was detected by Wind on 1999 September 12 and was magnetically connected to the terrestrial bow shock. Key results are obtained concerning how the IP shock modifies the terrestrial foreshock electron and ion dynamics: (1) Intensive Langmuir waves were detected downstream of the IP shock due to the enhanced penetrating terrestrial foreshock electron beams. (2) Whistler heat flux instabilities associated with the oblique precursor whistler pitch-angle scatter the suprathermal electrons, together with the normal betatron acceleration that occurs across the IP shock. (3) The IP shock interacts with the antisunward propagating Alfvén waves/fluctuations, and the shocked plasma shows both Alfvénic and mirror-mode features where Alfvén waves were separated into two parts propagating in opposite directions. (4) Intense specularly reflected gyrating ions were detected around the IP shock, which indicates that the energy dissipation effects at the IP shock depend on both reflected ions and the waves intrinsic to the shock. These results provide new insights into the interaction between an IP shock and the terrestrial foreshock.

Keywords: Interplanetary shocks, Solar wind, Planetary bow shocks, Alfven waves, Shocks
Stellar Chromospheric Activity Database of Solar-like Stars Based on the LAMOST Low-Resolution Spectroscopic Survey. A stellar chromospheric activity database of solar-like stars is constructed based on the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) Low-Resolution Spectroscopic Survey. The database contains spectral bandpass fluxes and indexes of Ca II H and K lines derived from 1,330,654 high-quality LRS spectra of solar-like stars. We measure the mean fluxes at line cores of the Ca II H and K lines using a 1 Å rectangular bandpass and a 1.09 Å FWHM triangular bandpass, as well as the mean fluxes of two 20 Å wide pseudocontinuum bands on the two sides of the lines. Three activity indexes, S rec based on the 1 Å rectangular bandpass and S tri and S  L  based on the 1.09 Å FWHM triangular bandpass, are evaluated from the measured fluxes to quantitatively indicate the chromospheric activity level. The uncertainties of all the obtained parameters are estimated. We also produce spectrum diagrams of Ca II H and K lines for all the spectra in the database. The entity of the database is composed of a catalog of spectral sample and activity parameters and a library of spectrum diagrams. Statistics reveal that the solar-like stars with a high level of chromospheric activity (S rec &gt; 0.6) tend to appear in the parameter range of T eff (effective temperature) &lt; 5500 K, 4.3 &lt; log g (surface gravity) &lt; 4.6, and -0.2 &lt; [Fe/H] (metallicity) &lt; 0.3. This database, with more than 1 million high-quality LAMOST LRS spectra of Ca II H and K lines and basal chromospheric activity parameters, can be further used for investigating activity characteristics of solar-like stars and the solar-stellar connection.

Keywords: Solar analogs, Sky surveys, Astronomy databases, Stellar chromospheres, Stellar activity, Spectroscopy
A Q-band Line Survey toward Orion KL Using the Tianma Radio Telescope. We have conducted a line survey toward Orion KL using the Q-band receiver of the Tianma 65 m radio telescope (TMRT), covering 34.8-50 GHz with a velocity resolution between 0.79 and 0.55 km s-1, respectively. The observations reach a sensitivity of the level of 1-8 mK, proving that the TMRT is sensitive for conducting deep-line surveys. In total, 597 Gaussian features are extracted. Among them, 177 radio recombination lines (RRLs) are identified, including 126, 40, and 11 RRLs of hydrogen, helium, and carbon, with a maximum Δn of 16, 7, and 3, respectively. The carbon RRLs are confirmed to originate from photodissociation regions with a V LSR ~ 9 km s-1. In addition, 371 molecular transitions of 53 molecular species are identified. Twenty-one molecular species of this survey were not firmly detected in the Q band by Rizzo et al., including species such as H2CS, HCOOH, C2H5OH, ${{\rm{H}}}_{2}^{13}$ CO, H2CCO, CH3CHO, CH2OCH2, HCN υ 2 = 1, and CH3OCHO υ  t  = 1. In particular, the vibrationally excited states of ethyl cyanide (C2H5CN υ13/υ21) are for the first time firmly detected in the Q band. NH3 (15,15) and (16,16) are identified, and they are so far the highest transitions of the NH3 inversion lines detected toward Orion KL. All of the identified lines can be reproduced by a radiative transfer model.

Keywords: Star forming regions, Molecular spectroscopy, H II regions, Molecular clouds
A Population of Dipper Stars from the Transiting Exoplanet Survey Satellite Mission. Dipper stars are a classification of young stellar objects that exhibit dimming variability in their light curves, dropping in brightness by 10%–50%, likely induced by occultations due to circumstellar disk material. This variability can be periodic, quasiperiodic, or aperiodic. Dipper stars have been discovered in young stellar associations via ground-based and space-based photometric surveys. We present the detection and characterization of the largest collection of dipper stars to date: 293 dipper stars, including 234 new dipper candidates. We have produced a catalog of these targets, which also includes young stellar variables that exhibit predominately burst-like variability and symmetric variability (equal parts bursting and dipping). The total number of catalog sources is 414. These variable sources were found in a visual survey of TESS light curves, where dip-like variability was observed. We found a typical age among our dipper sources of &lt;5 Myr, with the age distribution peaking at ≈2 Myr, and a tail of the distribution extending to ages older than 20 Myr. Regardless of the age, our dipper candidates tend to exhibit infrared excess, which is indicative of the presence of disks. TESS is now observing the ecliptic plane, which is rich in young stellar associations, so we anticipate many more discoveries in the TESS data set. A larger sample of dipper stars would enhance the census statistics of light-curve morphologies and dipper ages.

Keywords: W Virginis variable stars, Classical T Tauri stars, Photometry, Pre-main sequence
Jupiter and Saturn as Spectral Analogs for Extrasolar Gas Giants and Brown Dwarfs. With the advent of direct-imaging spectroscopy, the number of spectra from brown dwarfs and extrasolar gas giants is growing rapidly. Many brown dwarfs and extrasolar gas giants exhibit spectroscopic and photometric variability, which is likely the result of weather patterns. However, for the foreseeable future, point-source observations will be the only viable method to extract brown dwarf and exoplanet spectra. Models have been able to reproduce the observed variability, but ground-truth observations are required to verify their results. To that end, we provide visual and near-infrared spectra of Jupiter and Saturn obtained from the Cassini VIMS instrument. We disk-integrate the VIMS spectral cubes to simulate the spectra of Jupiter and Saturn as if they were directly imaged exoplanets or brown dwarfs. We present six empirical disk-integrated spectra for both Jupiter and Saturn with phase coverage of 1.°7-133.°5 and 39.°6-110.°2, respectively. To understand the constituents of these disk-integrated spectra, we also provide end-member (single-feature) spectra for permutations of illumination and cloud density, as well as for Saturn's rings. In tandem, these disk-integrated and end-member spectra provide the ground truth needed to analyze point-source spectra from extrasolar gas giants and brown dwarfs. Lastly, we discuss the impact that icy rings, such as Saturn's, have on disk-integrated spectra and consider the feasibility of inferring the presence of rings from direct-imaging spectra.

Keywords: Saturn, Brown dwarfs, Jupiter, Direct imaging, Extrasolar gaseous planets
Optical Variability of Eight FRII-type Quasars with 13 yr Photometric Light Curves. We characterize the optical variability properties of eight lobe-dominated radio quasars (QSOs): B2 0709+37, FBQS J095206.3+235245, PG 1004+130, [HB89] 1156+631, [HB89] 1425+267, [HB89] 1503+691, [HB89] 1721+343, and 4C +74.26, systematically monitored for a duration of 13 yr since 2009. The quasars are radio-loud objects with extended radio lobes that indicate their orientation close to the sky plane. Five of the eight QSOs are classified as giant radio quasars. All quasars showed variability during our monitoring, with magnitude variations between 0.3 and 1 mag for the least variable and the most variable QSOs, respectively. We performed both structure function (SF) analysis and power spectral density (PSD) analysis for the variability characterization and search for characteristic timescales and periodicities. As a result of our analysis, we obtained relatively steep SF slopes (α ranging from 0.49 to 0.75) that are consistent with the derived PSD slopes (~2-3). All the PSDs show a good fit to single power-law forms, indicating a red-noise character of variability between timescales of ~13 yr and weeks. We did not measure reliable characteristic timescales of variability from the SF analysis, which indicates that the duration of the gathered data is too short to reveal them. The absence of bends in the PSDs (change of slope from ≥1 to ~0) on longer timescales indicates that optical variations are most likely caused by thermal instabilities in the accretion disk.

Keywords: Radio loud quasars, Galaxy photometry, Active galaxies, Quasars
High-resolution Hubble Space Telescope Imaging Survey of Local Star-forming Galaxies. I. Spatially Resolved Obscured Star Formation with Hα and Paschen-β Recombination Lines. We present a sample of 24 local star-forming galaxies observed with broadband and narrowband photometry from the Hubble Space Telescope (HST) that are part of the Great Observatories All-sky Luminous Infrared Galaxies Survey of local luminous and ultraluminous infrared galaxies. With narrowband filters around the emission lines Hα (and [N II]) and Paβ, we obtain robust estimates of the dust attenuation affecting the gas in each galaxy, probing higher attenuation than can be traced by the optical Balmer decrement Hα/Hβ alone by a factor of &gt;1 mag. We also infer the dust attenuation toward the stars via a spatially resolved spectral energy distribution fitting procedure that uses all available HST imaging filters. We use various indicators to obtain the star formation rate (SFR) per spatial bin and find that Paβ traces star-forming regions where the Hα and the optical stellar continuum are heavily obscured. The dust-corrected Paβ SFR recovers the 24 μm inferred SFR with a ratio of -0.14 ± 0.32 dex and the SFR inferred from the 8 to 1000 μm infrared luminosity at -0.04 ± 0.23 dex. Both in a spatially resolved and integrated sense, rest-frame near-infrared recombination lines can paint a more comprehensive picture of star formation across cosmic time, particularly with upcoming JWST observations of Paschen-series line emission in galaxies as early as the epoch of reionization.

Keywords: Interstellar dust extinction, Star formation, Interstellar medium, Extragalactic astronomy, Luminous infrared galaxies
To E or Not to E : Numerical Nuances of Global Coronal Models. In recent years, global coronal models have experienced an ongoing increase in popularity as tools for forecasting solar weather. Within the domain of up to 21.5 R ☉, magnetohydrodynamics (MHD) is used to resolve the coronal structure using magnetograms as inputs at the solar surface. Ideally, these computations would be repeated with every update of the solar magnetogram so that they could be used in the ESA Modeling and Data Analysis Working Group magnetic connectivity tool (http://connect-tool.irap.omp.eu/). Thus, it is crucial that these results are both accurate and efficient. While much work has been published showing the results of these models in comparison with observations, not much of it discusses the intricate numerical adjustments required to achieve these results. These range from the details of boundary condition formulations to adjustments as large as enforcing parallelism between the magnetic field and velocity. By omitting the electric field in ideal MHD, the description of the physics can be insufficient and may lead to excessive diffusion and incorrect profiles. We formulate inner boundary conditions that, along with other techniques, reduce artificial electric field generation. Moreover, we investigate how different outer boundary condition formulations and grid design affect the results and convergence, with special focus on the density and radial component of the B -field. The significant improvement in accuracy of real magnetic map-driven simulations is illustrated for an example of the 2008 eclipse.

Keywords: Active solar corona, Space weather, Heliosphere, Magnetohydrodynamical simulations