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In this series of papers we have presented the results of a spectroscopic survey of luminous stars in the nearby spirals M31 and M33. Here, we present spectroscopy of 132 additional stars. Most have emission-line spectra, including luminous blue variables (LBVs) and candidate LBVs, Fe ii emission line stars, the B[e] supergiants, and the warm hypergiants. Many of these objects are spectroscopically similar and are often confused with each other. We examine their similarities and differences and propose the following guidelines that can be used to help distinguish these stars in future work. (1) The B[e] supergiants have emission lines of [O i] and [Fe ii] in their spectra. Most of the spectroscopically confirmed sgB[e] stars also have warm circumstellar dust in their spectral energy distributions (SEDs). (2) Confirmed LBVs do not have the [O i] emission lines in their spectra. Some LBVs have [Fe ii] emission lines, but not all. Their SEDs show free–free emission in the near-infrared but no evidence for warm dust. Their most important and defining characteristic is the S Dor-type variability. (3) The warm hypergiants spectroscopically resemble the LBVs in their dense wind state and the B[e] supergiants. However, they are very dusty. Some have [Fe ii] and [O i] emission in their spectra like the sgB[e] stars, but are distinguished by their A- and F-type absorption-line spectra. In contrast, the B[e] supergiant spectra have strong continua and few if any apparent absorption lines. Candidate LBVs should share the spectral characteristics of the confirmed LBVs with low outflow velocities and the lack of warm circumstellar dust. [ABSTRACT FROM AUTHOR]

Voyager 1 has been moving through the very local interstellar medium (VLISM) from the time that it crossed the heliopause on 2012/DOY 238 to 2020/DOY 292. Three notable objects in the magnetic field of the VLISM have been observed: two shocks and one pressure front. This paper reports the observation of a fourth object observed near 2020/DOY 147. There were no upstream electron plasma oscillations of the type often observed ahead of shocks, abrupt increases in energetic particles, or fluctuations in the 48 s increments of the magnetic field associated with this feature, suggesting that it was probably not a shock. This feature was associated with a relatively large increase in the magnetic field strength (B2/B1 = 1.35) and in the electron density determined by the Plasma Wave Science experiment (N2/N1 = 1.36) using a new method described in this paper. This feature appears to be a pressure front associated with a compressive wave in the VLISM. The two shocks and the two pressure fronts were associated with the four largest maxima observed in B(t) between 2012/DOY 238 and 2020/DOY 292. Each feature was associated with a jump–ramp structure. The jump–ramp structures were separated by long relatively undisturbed quiet intervals. [ABSTRACT FROM AUTHOR]

In the first paper of this series, we demonstrated that neural networks can robustly and efficiently estimate kinematic parameters for optical emission-line spectra taken by SITELLE at the Canada–France–Hawaii Telescope. This paper expands upon this notion by developing an artificial neural network to estimate the line ratios of strong emission lines present in the SN1, SN2, and SN3 filters of SITELLE. We construct a set of 50,000 synthetic spectra using line ratios taken from the Mexican Million Model database replicating H ii regions. Residual analysis of the network on the test set reveals the network's ability to apply tight constraints to the line ratios. We verified the network's efficacy by constructing an activation map, checking the [ N ii ] doublet fixed ratio, and applying a standard k-fold cross-correlation. Additionally, we apply the network to SITELLE observations of M33; the residuals between the algorithm's estimates and values calculated using standard fitting methods show general agreement. Moreover, the neural network reduces the computational costs by two orders of magnitude. Although standard fitting routines do consistently well depending on the signal-to-noise ratio of the spectral features, the neural network can also excels at predictions in the low signal-to-noise regime within the controlled environment of the training set as well as on observed data when the source spectral properties are well constrained by models. These results reinforce the power of machine learning in spectral analysis. [ABSTRACT FROM AUTHOR]

Identifying the accelerators of Galactic cosmic ray (CR) protons with energies up to a few PeV (1015 eV) remains a theoretical and observational challenge. Supernova remnants (SNRs) represent strong candidates because they provide sufficient energetics to reproduce the CR flux observed at Earth. However, it remains unclear whether they can accelerate particles to PeV energies, particularly after the very early stages of their evolution. This uncertainty has prompted searches for other source classes and necessitates comprehensive theoretical modeling of the maximum proton energy, E max , accelerated by an arbitrary shock. While analytic estimates of E max have been put forward in the literature, they do not fully account for the complex interplay between particle acceleration, magnetic field amplification, and shock evolution. This paper uses a multizone, semianalytic model of particle acceleration based on kinetic simulations to place constraints on E max for a wide range of astrophysical shocks. In particular, we develop relationships between E max , shock velocity, size, and ambient medium. We find that SNRs can only accelerate PeV particles under a select set of circumstances, namely, if the shock velocity exceeds ∼104 km s−1 and escaping particles drive magnetic field amplification. However, older and slower SNRs may still produce observational signatures of PeV particles due to populations accelerated when the shock was younger. Our results serve as a reference for modelers seeking to quickly produce a self-consistent estimate of the maximum energy accelerated by an arbitrary astrophysical shock. 11 Presented as a thesis to the Department of Astronomy and Astrophysics, The University of Chicago, in partial fulfillment of the requirements for a Ph.D. degree. [ABSTRACT FROM AUTHOR]

Owing to its unevenly distributed crustal fields, Mars acts as a unique obstacle to the solar wind. In the presence of the crustal fields, the transport of the planetary ions on the dayside ionosphere exhibits north–south asymmetry. Additionally, the heavy-ion loss in the magnetotail is affected by the crustal fields. In this paper, a three-dimensional multispecies magnetohydrodynamic model is employed to simulate Mars–solar wind interactions. Numerical results indicate that the meridional transport is dominant in most areas on the dayside ionosphere. In the presence of the crustal fields, the meridional transport on the southern hemisphere (southward transport) is reduced by more than 70% above the strong crustal sources, and the zonal velocity shows local changes inside strong and weak crustal field regions. These effects result in an increase or decrease in the number density of the heavy ions reaching the terminator, thereby influencing the thickness of the ionosphere. Decreased southward velocity leads to a reduction in the heavy-ion loss on the southern magnetotail. The radial outward flux is reduced by more than 30% for O2+ and CO2+ and by 10% for O+. This study shows that in addition to the zonal transport, the meridional transport is important for the day-to-night transport on the dayside of Mars. Collectively, the horizontal plasma transport, controlled by crustal fields, is associated with the altered ionosphere structure and reduced heavy-ion loss in the magnetotail. [ABSTRACT FROM AUTHOR]

We present precise photometric estimates of stellar parameters, including effective temperature, metallicity, luminosity classification, distance, and stellar age, for nearly 26 million stars using the methodology developed in the first paper of this series, based on the stellar colors from the Stellar Abundances and Galactic Evolution Survey (SAGES) Data Release 1 and Gaia Early Data Release 3. The optimal design of stellar-parameter sensitive uv filters by SAGES has enabled us to determine photometric-metallicity estimates down to −3.5, similar to our previous results with the SkyMapper Southern Survey (SMSS), yielding a large sample of over five million metal-poor ([Fe/H] ≤ −1.0) stars and nearly one million very metal-poor ([Fe/H] ≤ −2.0) stars. The typical precision is around 0.1 dex for both dwarf and giant stars with [Fe/H] > −1.0, and 0.15–0.25/0.3–0.4 dex for dwarf/giant stars with [Fe/H] < −1.0. Using the precise parallax measurements and stellar colors from Gaia, effective temperature, luminosity classification, distance, and stellar age are further derived for our sample stars. This huge data set in the Northern sky from SAGES, together with similar data in the Southern sky from SMSS, will greatly advance our understanding of the Milky Way, in particular its formation and evolution. [ABSTRACT FROM AUTHOR]

Mapping of multiple lines such as the fine-structure emission from [C ii ] (157.7 μ m), [O iii ] (52 and 88.4 μ m), and rotational emission lines from CO are of particular interest for upcoming line intensity mapping (LIM) experiments at millimeter wavelengths, due to their brightness features. Several upcoming experiments aim to cover a broad range of scientific goals, from detecting signatures of the epoch of reionization to the physics of star formation and its role in galaxy evolution. In this paper, we develop a semianalytic approach to modeling line strengths as functions of the star formation rate (SFR) or infrared luminosity based on observations of local and high- z galaxies. This package, LIMpy (Line Intensity Mapping in Python), estimates the intensity and power spectra of [C ii ], [O iii ], and CO rotational transition lines up to the J levels (1–0) to (13–12) based both on analytic formalism and on simulations. We develop a relation among halo mass, SFR, and multiline intensities that permits us to construct a generic formula for the evolution of several line strengths up to z ∼ 10. We implement a variety of star formation models and multiline luminosity relations to estimate the astrophysical uncertainties on the intensity power spectrum of these lines. As a demonstration, we predict the signal-to-noise ratio of [C ii ] detection for an EoR-Spec-like instrument on the Fred Young Submillimeter Telescope. Furthermore, the ability to use any halo catalog allows the LIMpy code to be easily integrated into existing simulation pipelines, providing a flexible tool to study intensity mapping in the context of complex galaxy formation physics. [ABSTRACT FROM AUTHOR]

In this paper, we present YunMa, an exoplanet cloud simulation and retrieval package, which enables the study of cloud microphysics and radiative properties in exoplanetary atmospheres. YunMa simulates the vertical distribution and sizes of cloud particles and their corresponding scattering signature in transit spectra. We validated YunMa against results from the literature. When coupled to the TauREx 3 platform, an open Bayesian framework for spectral retrievals, YunMa enables the retrieval of the cloud properties and parameters from transit spectra of exoplanets. The sedimentation efficiency (f sed), which controls the cloud microphysics, is set as a free parameter in retrievals. We assess the retrieval performances of YunMa through 28 instances of a K2-18 b-like atmosphere with different fractions of H2/He and N2, and assuming water clouds. Our results show a substantial improvement in retrieval performances when using YunMa instead of a simple opaque cloud model and highlight the need to include cloud radiative transfer and microphysics to interpret the next-generation data for exoplanet atmospheres. This work also inspires instrumental development for future flagships by demonstrating retrieval performances with different data quality. [ABSTRACT FROM AUTHOR]

The observations from the Dark Energy Spectroscopic Instrument (DESI) will significantly increase the numbers of known extremely metal-poor stars by a factor of ∼10, improving the sample statistics to study the early chemical evolution of the Milky Way and the nature of the first stars. In this paper we report follow-up observations with high signal-to-noise ratio of nine metal-poor stars identified during the DESI commissioning with the Optical System for Imaging and Low-Resolution Integrated Spectroscopy (OSIRIS) instrument on the 10.4 m Gran Telescopio Canarias. The analysis of the data using a well-vetted methodology confirms the quality of the DESI spectra and the performance of the pipelines developed for the data reduction and analysis of DESI data. [ABSTRACT FROM AUTHOR]

The eruption of magnetic flux ropes (MFRs), often taking filaments together, leads to coronal mass ejections (CMEs). Theoretical studies propose that both the resistive magnetic reconnection and the ideal instability of an MFR system can release magnetic-free energy and accelerate CMEs (i.e., MFRs or filaments) during eruptions. Observations find that the full kinematic evolution of CMEs usually undergoes three phases: the initiation phase, impulsive acceleration phase, and propagation phase. The impulsive acceleration phase often starts and ceases simultaneously with the flare onset time and peak time, respectively. This synchronization can be explained by the positive feedback relationship between the acceleration of CMEs and flare magnetic reconnection, and suggests that the reconnection has the dominant contribution to the acceleration of CMEs. It is rare to see strong evidence that supports the dominant contribution of ideal instability to the acceleration. In this paper, we report an intriguing filament eruption that occurred on 2011 May 11. Its complete acceleration is well recorded by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. The kinematic analysis shows that the impulsive acceleration phase starts and ceases obviously earlier than the flare onset time and peak time, respectively, which means a complete asynchronization between the impulsive acceleration phase and flare rise phase, and strongly supports that the ideal instability plays a dominant role in this impulsive acceleration. Furthermore, the accompanied flare is a B-class one, also implying that the contribution of reconnection is negligible in the energy release process. [ABSTRACT FROM AUTHOR]

The population of metastable levels is key to high-precision density diagnostics of astrophysical plasmas. In photoionized plasmas, density is used to infer the distance from the ionizing source, which is otherwise difficult to obtain. Perfecting models that compute these populations is thus crucial. The present paper presents a semianalytic hydrogenic approximation for assessing the relative importance of different processes in populating atomic levels. This approximation shows that in the presence of a radiation source, photoexcitations and collisional excitations are both important over a wide range of plasma temperatures and ionizing spectra, while radiative recombination is orders of magnitude weaker. The interesting case of Fe+21 with a collisional radiative model with photoexcitation demonstrates this effect. The population of the first excited metastable level in Fe+21 is sensitive to the electron number density in the critical range of n e = 1012–1015 cm−3; it was observed to be significantly populated in the X-ray spectrum of the 2005 outburst of the X-ray binary GRO J1655-40. The present model shows that photoexcitation is the predominant process indirectly populating the metastable level. For the photoionized plasma in the GRO J1655-40 outflow, the model indicates a measured value of n e = (2.6 ± 0.5) × 1013 cm−3, implying a distance from the source of r = (4.4 ± 0.4) × 1010 cm. Finally, we show how the computed critical density and distance of Fe+21 yield the correct ionization parameter of the ion, independent of ionization balance calculations. [ABSTRACT FROM AUTHOR]

Active galactic nuclei (AGNs) are widely believed to be one of the promising acceleration sites of ultrahigh-energy cosmic rays (CRs). Essentially, AGNs are powered by the gravitational energy of matter falling into supermassive black holes. However, the conversion efficiency of gravitational to kinetic energy of CRs in AGNs, which is defined as the baryon loading factor η p , is not well known yet. After being accelerated, high-energy CRs could escape the host galaxy and enter the intracluster medium (ICM). These CRs can be confined within the galaxy cluster and produce γ -rays and neutrinos through proton–proton collisions with the ICM. In this paper, we study the diffusion of CRs in galaxy clusters and calculate the diffuse neutrino flux from the galaxy cluster population. Using the latest upper limits on the cumulative unresolved TeV–PeV neutrino flux from galaxy clusters posed by the IceCube Neutrino Observatory, we derive the upper limit of the average baryon loading factor as η p,grav ≲ 2 × 10−3 − 0.1 for the population of galaxy clusters. This constraint is more stringent than the one obtained from γ -ray observation on the Coma cluster. [ABSTRACT FROM AUTHOR]

We present simulated galaxy spectral energy distributions (SEDs) from the far-ultraviolet (FUV) through the far-infrared (FIR), created using hydrodynamic simulations and radiative transfer calculations, suitable for the validation of SED modeling techniques. SED modeling is an essential tool for inferring star formation histories from nearby galaxy observations, but it is fraught with difficulty due to our incomplete understanding of stellar populations, chemical enrichment processes, and the nonlinear, geometry-dependent effects of dust on our observations. Our simulated SEDs will allow us to assess the accuracy of these inferences against galaxies with known ground truth. To create the SEDs, we use simulated galaxies from the Numerical Investigation of Hundred Astrophysical Objects suite and the radiative transfer code Stellar Kinematics Including Radiative Transfer. We explore different subgrid post-processing recipes, using color distributions and their dependence on axis ratios of galaxies in the nearby Universe to tune and validate them. We find that subgrid post-processing recipes that mitigate limitations in the temporal and spatial resolution of the simulations are required for producing FUV to FIR photometry that statistically reproduce the colors of galaxies in the nearby Universe. With this paper, we release resolved photometry and spatially integrated spectra for our sample galaxies, each from a range of different viewing angles. Our simulations predict that there is a large variation in attenuation laws among galaxies, and that from any particular viewing angle that energy balance between dust attenuation and re-emission can be violated by up to a factor of 3. These features are likely to affect SED modeling accuracy. [ABSTRACT FROM AUTHOR]

In this paper, using the latest Pantheon+ sample of Type Ia supernovae, baryon acoustic oscillation measurements, and observational Hubble data, we carry out a joint constraint on the Hubble constant H 0, the spatial curvature ΩK, and the sound horizon at the end of the drag epoch r d. To be model-independent, four cosmography models—i.e., the Taylor series in terms of redshift y 1 = z /(1 + z), y 2 = arctan (z) , y 3 = ln (1 + z) , and the Padé approximants—are used without the assumption of a flat Universe. The results show that H 0 is anticorrelated with ΩK and r d, indicating that smaller ΩK or r d would be helpful in alleviating the Hubble tension. The values of H 0 and r d are consistent with the estimate derived from the Planck cosmic microwave background data based on the flat ΛCDM model, but H 0 is in 2.3 ∼ 3.0 σ tension with that obtained by Riess et al. in all these cosmographic approaches. Meanwhile, a flat Universe is preferred by the present observations under all approximations except the third order of y 1 and y 2 of the Taylor series. Furthermore, according to the values of the Bayesian evidence, we found that the flat ΛCDM remains to be the most favored model by the joint data sets, and the Padé approximant of order (2,2), the third order of y 3 and y 1 are the top three cosmographic expansions that fit the data sets best, while the Taylor series in terms of y 2 are essentially ruled out. [ABSTRACT FROM AUTHOR]

Recently, some fast radio bursts (FRBs) have been reported to exhibit complex and diverse variations in Faraday rotation measurements (RM) and polarization, suggesting that dynamically evolving magnetization environments may surround them. In this paper, we investigate the Faraday conversion (FC) effect in a binary system involving an FRB source and analyze the polarization evolution of FRBs. For a strongly magnetized high-mass companion binary, when an FRB with ∼100% linear polarization passes through the radial magnetic field of the companion star, the circular polarization (CP) component will be induced and oscillate symmetrically around the point with the degree of CP equal to zero, the rate and amplitude of the oscillation decrease as the frequency increases. The very strong plasma column density in the HMCBs can cause CP to oscillate with frequency at a very drastic rate, which may lead to depolarization. Near the superior conjunction of the binary orbit, the DM varies significantly due to the dense plasma near the companion, and the significant FC also occurs in this region. As the pulsar moves away from the superior conjunction, the CP gradually tends toward zero and then returns to its value before incidence. We also investigate the effect of the rotation of the companion star. We find that a sufficiently significant RM reversal can be produced at large magnetic inclinations and the RM variation is very diverse. Finally, we apply this model to explain some polarization observations of PSR B1744-24A and FRB 20201124A. [ABSTRACT FROM AUTHOR]

Three generations of the Miniature X-ray Solar Spectrometer (MinXSS) have flown on small satellites with the goal "to explore the energy distribution of soft X-ray (SXR) emissions from the quiescent Sun, active regions, and during solar flares, and to model the impact on Earth's ionosphere and thermosphere." The primary science instrument is the Amptek X123 X-ray spectrometer that has improved with each generation of the MinXSS experiment. This third-generation MinXSS-3 has a higher energy resolution and larger effective area than its predecessors and is also known as the Dual-zone Aperture X-ray Solar Spectrometer (DAXSS). It was launched on the INSPIRESat-1 satellite on 2022 February 14, and INSPIRESat-1 has successfully completed its 6 month prime mission. The INSPIRESat-1 is in a dawn–dusk, Sun-synchronous orbit and therefore has had 24 hr coverage of the Sun during most of its mission so far. The rise of Solar Cycle 25 has been observed by DAXSS. This paper introduces the INSPIRESat-1 DAXSS solar SXR observations, and we focus the science results here on a solar occultation experiment and multiple flares on 2022 April 24. One key flare result is that the reduction of elemental abundances appears greatest during the flare impulsive phase, thus highlighting the important role of chromospheric evaporation during flares to inject warmer plasma into the coronal loops. Furthermore, these results are suggestive that the amount of chromospheric evaporation is related to flare temperature and intensity. [ABSTRACT FROM AUTHOR]

Line-intensity mapping (IM) experiments seek to perform statistical measurements of large-scale structure with spectral lines such as 21 cm, CO, and Ly α. A challenge in these observations is to ensure that astrophysical foregrounds, such as galactic synchrotron emission in 21 cm measurements, are properly removed. One method that has the potential to reduce foreground contamination is to cross correlate with a galaxy survey that overlaps with the IM volume. However, telescopes sensitive to high-redshift galaxies typically have small field of views compared to IM surveys. Thus, a galaxy survey for cross correlation would necessarily consist of pencil beams that sparsely fill the IM volume. In this paper, we develop the formalism to forecast the sensitivity of cross correlations between IM experiments and pencil-beam galaxy surveys. We find that a random distribution of pencil beams leads to very similar overall sensitivity as a lattice spaced across the IM survey and derive a simple formula for random configurations that agrees with the Fisher matrix formalism. We explore examples of combining high-redshift James Webb Space Telescope (JWST) observations with both an SPHEREx-like Ly α IM survey and a 21 cm experiment based on the Hydrogen Epoch of Reionization Array (HERA). We find that the JWST-SPHEREx case is promising, leading to a total signal-to-noise ratio of ∼5 after 100 total hours of JWST (at z = 7). We find that HERA is not well-suited for this approach owing to its drift-scan strategy, but that a similar experiment that can integrate down on one field could be. [ABSTRACT FROM AUTHOR]

The Cosmology Large Angular Scale Surveyor (CLASS) is a telescope array that observes the cosmic microwave background over 75% of the sky from the Atacama Desert, Chile, at frequency bands centered near 40, 90, 150, and 220 GHz. This paper describes the CLASS data pipeline and maps for 40 GHz observations conducted from 2016 August to 2022 May. We demonstrate how well the CLASS survey strategy, with rapid (∼10 Hz) front-end modulation, recovers the large-scale Galactic polarization signal from the ground: the mapping transfer function recovers ∼67% (85%) of EE and BB (VV) power at ℓ = 20 and ∼35% (47%) at ℓ = 10. We present linear and circular polarization maps over 75% of the sky. Simulations based on the data imply the maps have a white noise level of 110 μ K arcmin and correlated noise component rising at low- ℓ as ℓ −2.4. The transfer-function-corrected low- ℓ component is comparable to the white noise at the angular knee frequencies of ℓ ≈ 18 (linear polarization) and ℓ ≈ 12 (circular polarization). Finally, we present simulations of the level at which expected sources of systematic error bias the measurements, finding subpercent bias for the Λ cold dark matter EE power spectra. Bias from E -to- B leakage due to the data reduction pipeline and polarization angle uncertainty approaches the expected level for an r = 0.01 BB power spectrum. Improvements to the instrument calibration and the data pipeline will decrease this bias. [ABSTRACT FROM AUTHOR]

Accretion plays a central role in the physics that governs the evolution and dispersal of protoplanetary disks. The primary goal of this paper is to analyze the stability over time of the mass accretion rate onto TW Hya, the nearest accreting solar-mass young star. We measure veiling across the optical spectrum in 1169 archival high-resolution spectra of TW Hya, obtained from 1998–2022. The veiling is then converted to accretion rate using 26 flux-calibrated spectra that cover the Balmer jump. The accretion rate measured from the excess continuum has an average of 2.51 × 10−9 M ⊙ yr−1 and a Gaussian distribution with an FWHM of 0.22 dex. This accretion rate may be underestimated by a factor of up to 1.5 because of uncertainty in the bolometric correction and another factor of 1.7 because of excluding the fraction of accretion energy that escapes in lines, especially Ly α. The accretion luminosities are well correlated with He line luminosities but poorly correlated with H α and H β luminosity. The accretion rate is always flickering over hours but on longer timescales has been stable over 25 years. This level of variability is consistent with previous measurements for most, but not all, accreting young stars. [ABSTRACT FROM AUTHOR]

Core-collapse supernova explosions play a wide role in astrophysics by producing compact remnants (neutron stars or black holes) and the synthesis and injection of many heavy elements into their host galaxy. Because they are produced in some of the most extreme conditions in the universe, they can also probe physics in extreme conditions (matter at nuclear densities and extreme temperatures and magnetic fields). To quantify the impact of supernovae on both fundamental physics and our understanding of the universe, we must leverage a broad set of observables of this engine. In this paper, we study a subset of these probes using a suite of one-dimensional, parameterized mixing models: ejecta remnants from supernovae, ultraviolet, optical and infrared light curves, and transient gamma-ray emission. We review the other diagnostics and show how the different probes tie together to provide a more clear picture of the supernova engine. Join us in improving and evolving this document through active community engagement. Instructions are provided at this link: https://github.com/clfryer/MM-SNe. [ABSTRACT FROM AUTHOR]

Turbulence plays a key role in forming the complex geometry of the large-scale current sheet (CS) and fast energy release in a solar eruption. In this paper, we present full 3D high-resolution simulations for the process of a moderate coronal mass ejection (CME) and the thermodynamical evolution of the highly confined CS. Copious elongated blobs are generated owing to tearing and plasmoid instabilities, giving rise to a higher reconnection rate, and undergo the splitting, merging, and kinking processes in a more complex way in 3D. A detailed thermodynamical analysis shows that the CS is mainly heated by adiabatic and numerical viscous terms, and thermal conduction is the dominant factor that balances the energy inside the CS. Accordingly, the temperature of the CS reaches to a maximum of about 20 MK, and the range of temperatures is relatively narrow. From the face-on view in the synthetic Atmospheric Imaging Assembly 131 Å, the downflowing structures with similar morphology to supra-arcade downflows are mainly located between the post-flare loops and loop top, while moving blobs can extend spikes higher above the loop top. The downward-moving plasmoids can keep the twisted magnetic field configuration until the annihilation at the flare loop top, indicating that plasmoid reconnection dominates in the lower CS. Meanwhile, the upward-moving ones turn into turbulent structures before arriving at the bottom of the CME, implying that turbulent reconnection dominates in the upper CS. The spatial distributions of the turbulent energy and anisotropy are addressed, which show a significant variation in the spectra with height. [ABSTRACT FROM AUTHOR]

Although the magnetic field structures of solar filaments have been studied for several decades, the detailed evolution of the structure around a filament prior to its eruption is rarely observed. On 2021 October 28 in AR 12887, a major solar flare (X1.0 class) occurred at 15:35 UT. Based on the Solar Dynamics Observatory high-spatial-resolution observations, we find this flare is associated with the eruption of two filaments, namely F1 and F2. The two filaments are initially independent. The western leg (WLEG) of F1 approaches the northern leg of F2, due to the continuous movement and rotation of the magnetic field in which the WLEG roots in. We find first that there are some threads wrapping the WLEG. Brightening and bidirectionally plasmoid flows that originate from a brightening are detected in these threads, then the threads disappear, and the two filaments connect. NLFFF extrapolation reveals that there is a toroidal magnetic structure enveloping the WLEG and corresponding spatially to the threads. It is expected that a filament is enveloped by toroidal magnetic fields. According to the observations and extrapolation, we suggest that these threads represent the toroidal magnetic fields wrapping the WLEG. This paper provides new details about the dynamics of the toroidal magnetic fields. Magnetic reconnection takes place in the toroidal fields and thus destroys the fields, then F1 and F2 connect, and subsequently, the two filaments erupt and the flare occurs. [ABSTRACT FROM AUTHOR]

Long-lived massive magnetars are expected to be remnants of some binary neutron star (BNS) mergers. In this paper, we argue that the magnetic powered flaring activities of these merged magnetars would occur dominantly in their early millisecond-period-spin phase, which is in the timescale of days. Such flares endure significant absorption by the ejecta from the BNS collision, and their detectable energy range is from 0.1 to 10 MeV, in a time lag of approximately days after the merger events indicated by the gravitational wave chirps. We estimate the rate of such flares in different energy ranges, and find that there could have been 0.1–10 cases detected by Fermi/GBM. A careful search for ∼10 ms spin-period modulation in weak short gamma-ray bursts (GRBs) may identify them from the archival data. The next-generation megaelectronvolt detectors could detect them at a mildly higher rate. The recent report on the Quasi-Period-Oscillation found in two BASTE GRBs should not be considered as cases of such flares, for they were detected in a lower energy range and with a much shorter period spin modulation. [ABSTRACT FROM AUTHOR]

The Gemini High-resolution Optical SpecTrograph (GHOST) is the newest high-resolution spectrograph to be developed for a large-aperture telescope, recently deployed and commissioned at the Gemini-South telescope. In this paper, we present the first science results from the GHOST spectrograph taking during its commissioning runs. We have observed the bright metal-poor benchmark star HD 122563, along with two stars in the ultrafaint dwarf galaxy Reticulum II (Ret ii), one of which was previously identified as a candidate member, but did not have a previous detailed chemical abundance analysis. We find that this candidate (GDR3 0928) to be a bona fide member of Ret ii, and from a spectral synthesis analysis it is also revealed to be a CEMP- r star, with significant enhancements in several light elements (C, N, O, Na, Mg, and Si), in addition to featuring an r -process enhancement like many other Ret ii stars. The light-element enhancements in this star resemble the abundance patterns seen in the CEMP-no stars of other ultrafaint dwarf galaxies, and are thought to have been produced by an independent source from the r -process. These unusual abundance patterns are thought to be produced by faint supernovae, which may be produced by some of the earliest generations of stars. [ABSTRACT FROM AUTHOR]

Recent work has pointed out the potential existence of a tight relation between the cosmological parameter Ωm, at fixed Ωb, and the properties of individual galaxies in state-of-the-art cosmological hydrodynamic simulations. In this paper, we investigate whether such a relation also holds for galaxies from simulations run with a different code that makes use of a distinct subgrid physics: Astrid. We also find that in this case, neural networks are able to infer the value of Ωm with a ∼10% precision from the properties of individual galaxies, while accounting for astrophysics uncertainties, as modeled in Cosmology and Astrophysics with MachinE Learning (CAMELS). This tight relationship is present at all considered redshifts, z ≤ 3, and the stellar mass, the stellar metallicity, and the maximum circular velocity are among the most important galaxy properties behind the relation. In order to use this method with real galaxies, one needs to quantify its robustness: the accuracy of the model when tested on galaxies generated by codes different from the one used for training. We quantify the robustness of the models by testing them on galaxies from four different codes: IllustrisTNG, SIMBA, Astrid, and Magneticum. We show that the models perform well on a large fraction of the galaxies, but fail dramatically on a small fraction of them. Removing these outliers significantly improves the accuracy of the models across simulation codes. [ABSTRACT FROM AUTHOR]

This paper addresses the first direct investigation of the energy budget in the solar corona. Exploiting joint observations of the same coronal plasma by Parker Solar Probe and the Metis coronagraph aboard Solar Orbiter and the conserved equations for mass, magnetic flux, and wave action, we estimate the values of all terms comprising the total energy flux of the proton component of the slow solar wind from 6.3 to 13.3 R ⊙. For distances from the Sun to less than 7 R ⊙, we find that the primary source of solar wind energy is magnetic fluctuations including Alfvén waves. As the plasma flows away from the low corona, magnetic energy is gradually converted into kinetic energy, which dominates the total energy flux at heights above 7 R ⊙. It is found too that the electric potential energy flux plays an important role in accelerating the solar wind only at altitudes below 6 R ⊙, while enthalpy and heat fluxes only become important at even lower heights. The results finally show that energy equipartition does not exist in the solar corona. [ABSTRACT FROM AUTHOR]

The secular evolution of disk galaxies is largely driven by resonances between the orbits of "particles" (stars or dark matter) and the rotation of non-axisymmetric features (spiral arms or a bar). Such resonances may also explain kinematic and photometric features observed in the Milky Way and external galaxies. In simplified cases, these resonant interactions are well understood: for instance, the dynamics of a test particle trapped near a resonance of a steadily rotating bar is easily analyzed using the angle-action tools pioneered by Binney, Monari, and others. However, such treatments do not address the stochasticity and messiness inherent to real galaxies—effects that have, with few exceptions, been previously explored only with complex N -body simulations. In this paper, we propose a simple kinetic equation describing the distribution function of particles near an orbital resonance with a rigidly rotating bar, allowing for diffusion of the particles' slow actions. We solve this equation for various values of the dimensionless diffusion strength Δ, and then apply our theory to the calculation of bar–halo dynamical friction. For Δ = 0, we recover the classic result of Tremaine and Weinberg that friction ultimately vanishes, owing to the phase mixing of resonant orbits. However, for Δ > 0, we find that diffusion suppresses phase mixing, leading to a finite torque. Our results suggest that stochasticity—be it physical or numerical—tends to increase bar–halo friction, and that bars in cosmological simulations might experience significant artificial slowdown, even if the numerical two-body relaxation time is much longer than a Hubble time. [ABSTRACT FROM AUTHOR]

Relativistically broadened and redshifted 6.4–6.9 keV iron K lines are observed from many accretion powered objects, including X-ray binaries and active galactic nuclei. The existence of gas close to the central engine implies large radiation intensities and correspondingly large gas densities if the gas is to remain partially ionized. Simple estimates indicate that high gas densities are needed to allow for the survival of iron against ionization. These are high enough that rates for many atomic processes are affected by mechanisms related to interactions with nearby ions and electrons. Radiation intensities are high enough that stimulated processes can be important. Most models currently in use for interpreting relativistic lines use atomic rate coefficients designed for use at low densities and neglect stimulated processes. In our work so far we have presented atomic structure calculations with the goal of providing physically appropriate models at densities consistent with line-emitting gas near compact objects. In this paper we apply these rates to photoionization calculations, and produce ionization balance curves and X-ray emissivities and opacities that are appropriate for high densities and high radiation intensities. The final step in our program will be presented in a subsequent paper in which model atmosphere calculations will incorporate these rates into synthetic spectra. [ABSTRACT FROM AUTHOR]

Details of the explosion mechanism of core-collapse supernovae (CCSNe) are not yet fully understood. There is now an increasing number of successful examples of reproducing explosions in the first-principles simulations, which have shown a slow increase of explosion energy. However, it was recently pointed out that the growth rates of the explosion energy of these simulations are insufficient to produce enough 56Ni mass to account for observations. We refer to this issue as the "nickel mass problem" (Ni problem, hereafter) in this paper. The neutrino-driven wind is suggested as one of the most promising candidates for the solution to the Ni problem in previous literature, but a multidimensional simulation for this is computationally too expensive to allow long-term investigations. In this paper, we first built a consistent model of the neutrino-driven wind with an accretion flow onto a protoneutron star, by connecting a steady-state solution of the neutrino-driven wind and a phenomenological mass accretion model. Comparing the results of our model with the results of first-principles simulations, we find that the total ejectable amount of the neutrino-driven wind is roughly determined within ∼1 s from the onset of the explosion and the supplementable amount at a late phase (te ≳ 1 s) remains Mej ≲ 0.01 M⊙ at most. Our conclusion is that it is difficult to solve the Ni problem by continuous injection of 56Ni by the neutrino-driven wind. We suggest that the total amount of synthesized 56Ni can be estimated robustly if simulations are followed up to ∼2 s. [ABSTRACT FROM AUTHOR]

Liu and collaborators recently proposed an elliptical accretion disk model for tidal disruption events (TDEs). They showed that the accretion disks of optical/UV TDEs are large and highly eccentric and suggested that the broad optical emission lines with complex and diverse profiles originate in a cool eccentric accretion disk of random inclination and orientation. In this paper, we calculate the radiation efficiency of the elliptical accretion disk and investigate the implications for observations of TDEs. We compile observational data for the peak bolometric luminosity and total radiation energy after peak brightness of 18 TDE sources and compare these data to the predictions from the elliptical accretion disk model. Our results show that the observations are consistent with the theoretical predictions and that the majority of the orbital energy of the stellar debris is advected into the black hole (BH) without being converted into radiation. Furthermore, we derive the masses of the disrupted stars and the masses of the BHs of the TDEs. The BH masses obtained in this paper are also consistent with those calculated with the MBH–σ* relation. Our results provide an effective method for measuring the masses of BHs in large numbers of TDEs to be discovered in ongoing and next-generation sky surveys, regardless of whether the BHs are located at the centers of galactic nuclei or wander in disks and halos. [ABSTRACT FROM AUTHOR]

The large spin–orbit misalignments in the DI Herculis stellar binary system have resolved the decades-long puzzle of the anomalously slow apsidal precession rate, but raise new questions regarding the origin of the obliquities. This paper investigates obliquity evolution in stellar binaries hosting modestly inclined circumbinary disks. As the disk and binary axes undergo mutual precession, each oblate star experiences a torque from its companion star, so that the spin and orbital axes undergo mutual precession. As the disk loses mass through a combination of winds and accretion, the system may be captured into a high-obliquity Cassini state (a spin–orbit resonance). The final obliquity depends on the details of the disk dispersal. We construct a simple disk model to emulate disk dispersal due to viscous accretion and photoevaporation, and identify the necessary disk properties for producing the observed obliquities in DI Herculis. The disk must be massive (at least 10% of the binary mass). If accretion onto the binary is suppressed, the observed high stellar obliquities are reproduced with a binary–disk inclination of ∼5°–10°, but if substantial accretion occurs, the inclination must be larger, ∼20°–30°. If moderate accretion occurs, initially the disk must lose its mass slowly, but eventually lose its remaining mass abruptly, analogous to the observed two-timescale behavior for disks around T-Tauri stars. The spin feedback on the binary orbit causes the binary–disk inclination to decay as the obliquity evolves, a feature that is absent from the standard Cassini state treatment. [ABSTRACT FROM AUTHOR]

In this paper, we study stellar light curves from the Transiting Exoplanet Survey Satellite (TESS) for the presence of stellar flares. The main aim is to detect stellar flares using 2 minute cadence data and to perform a statistical analysis. To find and analyze stellar flares, we prepared the automatic software WARPFINDER. We implemented three methods described in this paper: trend, difference, and profile fitting. Automated searches for flares was accompanied by visual inspection. Using our software we analyzed the 2 minute cadence light curves of 330,000 stars located in the first 39 sectors of TESS observations. As a result, we detected over 25,000 stars showing flare activity with the total number of more than 140,000 flares. This means that about 7.7% of all the analyzed objects are flaring stars. The estimated flare energies range between 1031 and 1036 erg. We prepared a preliminary preview of the statistical distribution of parameters such as the flare duration, amplitude, and energy, and compared it with previous results. The relationship between stellar activity and spectral type, temperature, and mass was also statistically analyzed. Based on the scaling laws, we estimated the average values of the magnetic field strength and length of the flare loops. In our work, we used both single (about 60%), and double (about 40%) flare profiles to fit the observational data. The components of the double profile are supposed to be related to the direct heating of the photosphere by nonthermal electrons and back-warming processes. [ABSTRACT FROM AUTHOR]

In this paper, we discuss atomic processes modifying the soft X-ray spectra from optical depth effects like photoelectric absorption and electron scattering suppressing the soft X-ray lines. We also show the enhancement in soft X-ray line intensities in a photoionized environment via continuum pumping. We quantify the suppression/enhancement by introducing a “line modification factor (f mod).” If 0 ≤ f mod ≤ 1, the line is suppressed, which could be the case in both collisionally ionized and photoionized systems. If f mod ≥ 1, the line is enhanced, which occurs in photoionized systems. Hybrid astrophysical sources are also very common, where the environment is partly photoionized and partly collisionally ionized. Such a system is V1223 Sgr, an Intermediate Polar binary. We show the application of our theory by fitting the first-order Chandra Medium Energy Grating (MEG) spectrum of V1223 Sgr with a combination of Cloudy -simulated additive cooling-flow and photoionized models. In particular, we account for the excess flux for O vii, O viii, Ne ix, Ne x, and Mg xi lines in the spectrum found in a recent study, which could not be explained with an absorbed cooling-flow model. [ABSTRACT FROM AUTHOR]

Spatially extended halos of H i Ly α emission are now ubiquitously found around high-redshift star-forming galaxies. But our understanding of the nature and powering mechanisms of these halos is still hampered by the complex radiative transfer effects of the Ly α line and limited angular resolution. In this paper, we present resolved Multi Unit Spectroscopic Explorer (MUSE) observations of SGAS J122651.3+215220, a strongly lensed pair of L * galaxies at z = 2.92 embedded in a Ly α halo of L Ly α = (6.2 ± 1.3) Ă— 1042 erg sâˆ'1. Globally, the system shows a line profile that is markedly asymmetric and redshifted, but its width and peak shift vary significantly across the halo. By fitting the spatially binned Ly α spectra with a collection of radiative transfer galactic wind models, we infer a mean outflow expansion velocity of ≈211 km sâˆ'1, with higher values preferentially found on both sides of the system’s major axis. The velocity of the outflow is validated with the blueshift of low-ionization metal absorption lines in the spectra of the central galaxies. We also identify a faint (M 1500 ≈ âˆ'16.7) companion detected in both Ly α and the continuum, whose properties are in agreement with a predicted population of satellite galaxies that contribute to the extended Ly α emission. Finally, we briefly discuss the impact of the interaction between the central galaxies on the properties of the halo and the possibility of in situ fluorescent Ly α production. [ABSTRACT FROM AUTHOR]

Recent observations by the Large High Altitude Air Shower Observatory (LHAASO) have paved the way for the observational detection of PeVatrons in the Milky Way, thus revolutionizing the field of Îł -ray astrophysics. In this paper, we study one such detected source, LHAASO J1908+0621, and explore the origin of multi-TeV Îł -ray emission from this source. A middle-aged radio supernova remnant SNR G40.5â€"0.5 and a GeV pulsar PSR J1907+0602 are cospatial with LHAASO J1908+0621. Dense molecular clouds are also found to be associated with SNR G40.5â€"0.5. We explain the multi-TeV Îł -ray emission observed from the direction of LHAASO J1908+0621, by the hadronic interaction between accelerated protons that escaped from the SNR shock front and cold protons present inside the dense molecular clouds, and the leptonic emission from the pulsar wind nebula (PWN) associated with the pulsar J1907+0602. Moreover, we explain lower energy Îł -ray emission by considering the radiative cooling of the electrons that escaped from SNR G40.5â€"0.5. Finally, the combined lepto-hadronic scenario was used to explain the multiwavelength spectral energy distribution of LHAASO J1908+0621. Although not yet significant, an IceCube hotspot of neutrino emission is spatially associated with LHAASO J1908+0621, indicating a possible hadronic contribution. In this paper, we show that if a hadronic component is present in LHAASO J1908+0621, then the second-generation IceCube observatory will detect neutrinos from this source. [ABSTRACT FROM AUTHOR]

The interstellar medium (ISM) is turbulent over vast scales and in various phases. In this paper, we study turbulence with different tracers in four nearby star-forming regions: Orion, Ophiuchus, Perseus, and Taurus. We combine the APOGEE-2 and Gaia surveys to obtain the full six-dimensional measurements of positions and velocities of young stars in these regions. The velocity structure functions (VSFs) of the stars show a universal scaling of turbulence. We also obtain H α gas kinematics in these four regions from the Wisconsin H-Alpha Mapper. The VSFs of the H α are more diverse compared to those of stars. In regions with recent supernova activities, they show characteristics of local energy injections and higher amplitudes compared to the VSFs of stars and of CO from the literature. Such difference in amplitude of the VSFs can be explained by the different energy and momentum transport from supernovae into different phases of the ISM, thus resulting in higher levels of turbulence in the warm ionized phase traced by H α. In regions without recent supernova activities, the VSFs of young stars, H α, and CO are generally consistent, indicating well-coupled turbulence between different phases. Within individual regions, the brighter parts of the H α gas tend to have a higher level of turbulence than the low-emission parts. Our findings support a complex picture of the Milky Way ISM, where turbulence can be driven at different scales and inject energy unevenly into different phases. [ABSTRACT FROM AUTHOR]

This paper investigates a new methodology to search for periods in light curves of high-energy gamma-ray sources such as active galactic nuclei (AGNs). High-energy light curves have significant stochastic components, making period detection somewhat challenging. In our model, periodic terms, drifts of the light curves, and random walk with a correlation between flux points due to colored noise are taken into account independently. The parameters of the model are obtained directly from a Markov Chain Monte Carlo minimization. The time periods found are compared to the output of the publicly available Agatha program. The search method is applied to high-energy periodic AGN candidates from the Fermi-LAT catalog. The significance of periodic models over pure noise models is discussed. Finally, the variability of the period and amplitude of oscillating terms is studied on the most significant candidates. [ABSTRACT FROM AUTHOR]

The J-region asymptotic giant branch (JAGB) method is a new standard candle that is based on the stable intrinsic J -band magnitude of color-selected carbon stars, and has a precision comparable to other primary distance indicators such as Cepheids and the TRGB. We further test the accuracy of the JAGB method in the Local Group galaxy M33. M33's moderate inclination, low metallicity, and nearby proximity make it an ideal laboratory for tests of systematics in local distance indicators. Using high-precision optical BVI and near-infrared JHK photometry, we explore the application of three independent distance indicators: the JAGB method, the Cepheid Leavitt law, and the TRGB. We find: ÎĽ 0(TRGB I ) = 24.72 ± 0.02 (stat) ± 0.07 (sys) mag, ÎĽ 0(TRGBNIR) = 24.72 ± 0.04 (stat) ± 0.10 (sys) mag, ÎĽ 0(JAGB) = 24.67 ± 0.03 (stat) ± 0.04 (sys) mag, and ÎĽ 0(Cepheid) = 24.71 ± 0.04 (stat) ± 0.01 (sys) mag. For the first time, we also directly compare a JAGB distance using ground-based and space-based photometry. We measure ÎĽ 0(JAGBF110W) = 24.71 ± 0.06 (stat) ± 0.05 (sys) mag using the (F814Wâˆ'F110W) color combination to effectively isolate the JAGB stars. In this paper, we measure a distance to M33 accurate to 2% and provide further evidence that the JAGB method is a powerful extragalactic distance indicator that can effectively probe a local measurement of the Hubble constant using spaced-based observations. We expect to measure the Hubble constant via the JAGB method in the near future, using observations from the James Webb Space Telescope. [ABSTRACT FROM AUTHOR]

The typical spectrum of the prompt emission of gamma-ray bursts (GRBs) indicates that the electron cooling is suppressed in spite of the strong magnetic field in the standard synchrotron model. Recent particle-in-cell simulations show that the particle acceleration by magnetic reconnection in a magnetically dominated plasma can lead to small pitch angles especially in a low-energy region. Such a small pitch angle prevents electrons from cooling via synchrotron radiation. In this paper, taking into account the effects of the synchrotron cooling and the adiabatic cooling, we numerically calculate the synchrotron spectra with anisotropic electron distributions. If we require a Poynting flux larger than 1050 erg sâˆ'1 as the model is motivated by magnetic reconnection, the bulk Lorentz factor of ∼1000 and the electron minimum Lorentz factor of Îł min ∼ 104 are required to reproduce the typical GRB spectrum. [ABSTRACT FROM AUTHOR]

Diffusive shock acceleration is a prominent mechanism for producing energetic particles in space and in astrophysical systems. Such energetic particles have long been predicted to affect the hydrodynamic structure of the shock, in turn leading to CR spectra flatter than the test-particle prediction. However, in this work along with a companion paper, we use self-consistent hybrid (kinetic ion–fluid electron) simulations to show for the first time how CR-modified shocks actually produce steeper spectra. The steepening is driven by the enhanced advection of CRs embedded in magnetic turbulence downstream of the shock, in what we call the "postcursor." These results are consistent with multiwavelength observations of supernovae and supernova remnants and have significant phenomenological implications for space/astrophysical shocks in general. [ABSTRACT FROM AUTHOR]

To investigate the chemical abundance of broad-line region clouds in quasars at high redshifts, we performed near-infrared spectroscopy of six luminous quasars at z ∼ 2.7 with the WINERED spectrograph mounted on the New Technology Telescope at the La Silla Observatory, Chile. The measured Fe ii /Mg ii flux ratios nearly matched with the published data for 0.7 ≲ z ≲ 1.6, suggesting that there is no evolution over a long period of cosmic time, which is consistent with previous studies. To derive the chemical abundances from the measured equivalent widths (EWs), their dependence on nonabundance factors must be corrected. In our previous paper, we proposed a method to derive the [Mg/Fe] abundance ratio and the [Fe/H] abundance by correcting the dependence of EW(Mg ii) and EW(Fe ii) on the Eddington ratio. To the best of our knowledge, that was the first report to discuss the star formation history through a direct comparison with chemical evolution models. In the present study, we further investigated the dependence of EWs on luminosity, which is known as the Baldwin effect (BEff). Additional correction for the BEff significantly affects the derived chemical abundances for the six luminous quasars at z ∼ 2.7, and the resultant abundances agree well with the prediction of chemical evolution models. Given that most distant quasars found thus far are biased toward luminous ones, the correction of the measured EWs for the BEff is crucial for extending the chemical evolution study to higher redshifts. [ABSTRACT FROM AUTHOR]

The goal of the SunPy project is to facilitate and promote the use and development of community-led, free, and open source data analysis software for solar physics based on the scientific Python environment. The project achieves this goal by developing and maintaining the sunpy core package and supporting an ecosystem of affiliated packages. This paper describes the first official stable release (version 1.0) of the core package, as well as the project organization and infrastructure. This paper concludes with a discussion of the future of the SunPy project. [ABSTRACT FROM AUTHOR]

The dominant reservoirs of elemental nitrogen in protoplanetary disks have not yet been observationally identified. Likely candidates are HCN, NH3, and N2. The relative abundances of these carriers determine the composition of planetesimals as a function of disk radius due to strong differences in their volatility. A significant sequestration of nitrogen in carriers less volatile than N2 is likely required to deliver even small amounts of nitrogen to the Earth and potentially habitable exoplanets. While HCN has been detected in small amounts in inner disks (<10 au), so far only relatively insensitive upper limits on inner disk NH3 have been obtained. We present new Gemini-TEXES high-resolution spectroscopy of the 10.75 μm band of warm NH3, and use two-dimensional radiative transfer modeling to improve previous upper limits by an order of magnitude to at 1 au. These NH3 abundances are significantly lower than those typical for ices in circumstellar envelopes (). We also consistently retrieve the inner disk HCN gas abundances using archival Spitzer spectra, and derive upper limits on the HCN ice abundance in protostellar envelopes using archival ground-based 4.7 μm spectroscopy ([HCNice]/[H2Oice] < 1.5%–9%). We identify the NH3/HCN ratio as an indicator of chemical evolution in the disk, and we use this ratio to suggest that inner disk nitrogen is efficiently converted from NH3 to N2, significantly increasing the volatility of nitrogen in planet-forming regions. [ABSTRACT FROM AUTHOR]

We characterize the variability in nearly continuous optical observations of the bright radio-loud quasar 3C 273 and nine additional active galactic nuclei detected with the Fermi Gamma-ray Space Telescope Large Area Telescope (Fermi-LAT). Optical observations were obtained during the K2 mission with the Kepler spacecraft for periods of 49 to 83 days conducted with ≃1 minute (short) or ≃30 minutes (long) cadences in 2015–2017. 3C 273 was quiescent during the course of the observations, varying by only a factor of 1.02. Three objects, PKS 0047+023, PKS 1216-10, and PKS B2320-035, were active, varying by factors of 1.8–3.4. Six other objects were comparatively quiet, varying by factors of less than 1.4. Power spectral densities (PSDs) were calculated for each object. Overall, the slopes of most PSDs, as well as those we reported in an earlier paper, were in the range −2.0 to −2.7 and are consistent with those produced by turbulence in the relativistic jet, and not by "hot spots" in the disk emission. Mechanisms operating in the jet other than turbulence, such as "mini-jets" or "jet-in-jets", may also produce the observed range of PSD slopes. Both accretion disk and jet models are plausible origins for the 3C 273 optical variability during the K2 observations. [ABSTRACT FROM AUTHOR]

Type IIb supernovae (SNe IIb) present a unique opportunity for investigating the evolutionary channels and mechanisms governing the evolution of stripped-envelope SN progenitors due to a variety of observational constraints. Comparison of these constraints with the full distribution of theoretical properties not only helps determine the prevalence of observed properties in nature, but can also reveal currently unobserved populations. In this follow-up paper, we use the large grid of models presented in Sravan et al. to derive distributions of single and binary SNe IIb progenitor properties and compare them to constraints from three independent observational probes: multiband SN light curves, direct progenitor detections, and X-ray/radio observations. Consistent with previous work, we find that while current observations exclude single stars as SN IIb progenitors, SN IIb progenitors in binaries can account for them. We also find that the distributions indicate the existence of an unobserved dominant population of binary SNe IIb at low metallicity that arise due to mass transfer initiated on the Hertzsprung Gap. In particular, our models indicate the existence of a group of highly stripped (envelope mass ∼0.1–0.2M☉) progenitors that are compact (<50R☉) and blue (Teff ≲ 105 K) with ∼104.5–105.5L☉ and low-density circumstellar mediums. As discussed in Sravan et al., this group is necessary to account for SN IIb fractions and likely exist regardless of metallicity. The detection of the unobserved populations indicated by our models would support weak stellar winds and inefficient mass transfer in SN IIb progenitors. [ABSTRACT FROM AUTHOR]

Large planetary spin–orbit misalignments (obliquities) may strongly influence atmospheric circulation and tidal heating in a planet. A promising avenue to generate obliquities is via spin–orbit resonances, where the spin and orbital precession frequencies of a planet cross each other as the system evolves in time. One such mechanism involves a dissipating (mass-losing) protoplanetary disk that drives orbital precession of an interior planet. We study this scenario analytically in this paper, and obtain the mapping between the general initial spin orientation and the final obliquity. We show that (i) under adiabatic evolution (i.e., the disk dissipates at a sufficiently slow rate), the final planetary obliquity as a function of the initial spin orientation bifurcates into distinct tracks governed by interactions with the resonance; and (ii) under nonadiabatic evolution, a broad range of obliquities can be excited. We obtain analytical expressions for the final obliquities for various regimes of parameter space. The dynamical system studied in this paper is an example of "Colombo's top," and our analysis and results can be adapted to other applications. [ABSTRACT FROM AUTHOR]

We carry out a comprehensive analysis of supernova SN 2001em covering a period of 19 yr since discovery. SN 2001em is the oldest supernova known to have undergone a metamorphosis from a stripped envelope to an interacting supernova. An early spectrum indicates it exploded as a Type Ib supernova. Later, the ejecta caught up with a dense circumstellar H-shell, ejected a few thousand years before the explosion, triggering interaction between the supernova ejecta and the dense shell, producing radio, X-ray, and Hα emission. We use archival data with the Very Large Array in radio bands and with Chandra, XMM-Newton, and Swift-XRT in X-ray bands, along with published Hα measurements. We combine these data with our low radio frequency observations with the Giant Metrewave Radio Telescope at two epochs covering three frequencies. While the observations missed the phase when the shock entered the dense shell, the X-rays indicate that the shock came out of the dense shell at around 1750 days. The data suggest a forward shock origin of the X-ray emission. Radio data show a spectral inversion at late epochs (days) at around 3 GHz, which mimics the properties of the central absorbed component seen in SN 1986J. A possible explanation for this component is that the progenitor of SN 2001em was a massive binary system that had undergone a period of common-envelope evolution. The hydrogen envelope from the SN 2001em progenitor may have been lost as a result of binary interaction. [ABSTRACT FROM AUTHOR]

Recent studies of early-type galaxies have suggested that the initial mass function (IMF) slope is bottom-heavy; that is, they contain a larger fraction of low-mass stars than the Milky Way. However, measurements of the IMF remain challenging in unresolved galaxies because features in their observed spectra are sensitive to a number of factors, including the stellar age, metallicity, and elemental abundances, in addition to the IMF. In this paper, we use new high signal-to-noise IMACS (Magellan) spectra to study the elliptical shell galaxy NGC 3923 at optical (3700–6600 Å) and near-infrared (7900–8500 Å) wavelengths, as a function of radius. We have undertaken a number of independent approaches to better understand the uncertainties in our results. (1) We compare two different stellar population model libraries; (2) we undertake spectral index fitting as well as full spectral fitting; (3) we have performed simulations for which we a priori know the input IMF and that closely match our data; (4) we also investigate the effects of including a two-component rather than a single stellar population. We show that our results are sensitive to the assumptions we make and to the methods we use. In addition, we evaluate the accuracy and precision of our results based on simulated mock data. We find some indication (although assumption dependent) for a bottom-heavy IMF in the mass range 0.5–1.0 M⊙, while the IMF in the mass range 0.08–0.5 M⊙ appears to be Milky Way–like and constant. Including near-infrared data in our analysis gives consistent results and improves the precision. [ABSTRACT FROM AUTHOR]

The Soft X-ray Spectrometer on board Hitomi, with the unprecedented resolving power of R ∼ 1250, allowed the detection of members of the Fe xxv Kα complex emission spectra from the center of the Perseus Cluster. In this paper, we introduce a novel method of measuring the column density using the optically thin (Case A) to optically thick (Case B) transition for one- and two-electron systems. We compare the Fe xxv K α line ratios computed with CLOUDY with that from the Hitomi observations in the outer region of the Perseus core using collision strengths from different atomic data sets, and obtain good agreement. We also show the effect of turbulence on Fe xxv Kα line ratios and interplay between column density and metallicity. Additionally, we discuss the atomic number dependence of transition probabilities for allowed and unallowed transitions, which causes highly charged He-like systems, such as Fe xxv , to behave fundamentally differently from He i. [ABSTRACT FROM AUTHOR]

With the advent of space-based precision photometry missions, the quantity and quality of starspot light curves has greatly increased. This paper presents a large number of starspot models and their resulting light curves to (1) better determine light-curve metrics and methods that convey useful physical information and (2) understand how the underlying degeneracies of the translation from physical starspot distributions to the resulting light curves obscure that information. We explore models of relatively active stars at several inclinations while varying the number of (dark) spots, random spot distributions in position and time, timescales of growth and decay, and differential rotation. We examine the behavior of absolute and differential variations of individual intensity dips and overall light curves and demonstrate how complex spot distributions and behaviors result in light curves that typically exhibit only one or two dips per rotation. Unfortunately, simplistic "one- or two-spot" or "active longitude" descriptions or modeling of light curves can often be highly misleading. We also show that short "activity cycles" can easily be simply due to random processes. It turns out to be quite difficult to disentangle the competing effects of spot lifetime and differential rotation, but under most circumstances, spot lifetime is the more influential of the two. Many of the techniques tried to date only work when spots live for many rotations. These include autocorrelation degradation for spot lifetimes and periodograms for both global and differential rotation. Differential rotation may be nearly impossible to accurately infer from light curves alone unless spots live for many rotations. The Sun and solar-type stars its age or older are unfortunately the most difficult type of case. Further work is needed to have increased confidence in light-curve inferences. [ABSTRACT FROM AUTHOR]