adsabs/SciX_UAT_keywords huggingface dataset:
Hunting for Planetary Nebulae toward the Galactic Center

We present near-infrared (IR) spectra of two planetary nebula (PN) candidates in close lines of sight toward the Galactic center (GC) using the Gemini Near-Infrared Spectrograph at Gemini North. High-resolution images from radio continuum and narrowband IR observations reveal ringlike or barrel-shaped morphologies of these objects, and their mid-IR spectra from the Spitzer Space Telescope exhibit rich emission lines from highly-excited species such as [S IV], [Ne III], [Ne V], and [O IV]. We also derive elemental abundances using the Cloudy synthetic models, and find an excess amount of the s-process element krypton in both targets, which supports their nature as PNe. We estimate foreground extinction toward each object using near-IR hydrogen recombination lines, and find significant visual extinctions (AV > 20). The distances inferred from the size versus surface brightness relation of other PNe are 9.0 ± 1.6 kpc and 7.6 ± 1.6 kpc for SSTGC 580183 and SSTGC 588220, respectively. These observed properties along with the abundance patterns and close proximity to Sgr A* (projected distances ≲20 pc) make it highly probable that these objects are the first confirmed PN objects in the nuclear stellar disk. The apparent scarcity of such objects resembles the extremely low rate of PN formation in old stellar systems, but is in line with the current rate of sustained star formation activity in the Central Molecular Zone.

Keywords: planetary nebulae; interstellar line emission; galactic center
Sensitivity of Polarization to Grain Shape. II. Aggregates

A previous study (Paper I) investigated the polarization properties of a variety of simple convex grain shapes, some of which were found to be consistent with the observed polarization properties of interstellar dust from far-ultraviolet to far-infrared. Here, we study the optical properties of 45 nonconvex shapes, all aggregates of N equal-sized spheres. We consider N = 2, N = 3, and N = 256 random aggregates obtained from three different aggregation schemes. We also consider "trimmed" N = 256 aggregates obtained by systematically trimming initially random aggregates to increase either flattening or elongation. The "macroporosities" of the studied aggregates range from (for the N = 2 bisphere) to (for the N = 256 "BA" aggregates). The only aggregates consistent with observations of starlight polarization and polarized thermal emission are shapes that have been trimmed to increase their asymmetry. If interstellar grains are high-porosity aggregates, there must be processes causing extreme elongation or flattening; if not, interstellar grains must be dominated by fairly compact structures, with at most moderate porosities. The ratio of polarization in the 10 μm silicate feature to starlight polarization in the optical is shown to be insensitive to porosity and shape. X-ray scattering may be the best tool to determine the porosity of interstellar grains. We propose that modest porosities of interstellar grains could be the result of "photolytic densification." High polarization fractions observed in some Class 0 cores require processes to reduce porosities and/or increase asymmetries of aggregates in dense regions.

Keywords: interstellar dust; radiative transfer
A Reinforcement Learning-Based Follow-up Framework

Classification and characterization of variable and transient phenomena are critical for astrophysics and cosmology. Given the volume of nightly data produced by ongoing and future surveys such as LSST, it is critical to develop automatic tools that assist in observation decision-making, maximizing scientific output without resource wastage. We propose a reinforcement learning-based recommendation system for real-time astronomical observation of sources. We assess whether it is worth making further observations and recommend the best instrument from a preexisting candidate set of instruments. Current possible choices include single-band, multiband, and spectroscopic observations, although it is generalizable to any other kind of instrumentation. We rely on a reward metric to make recommendations, which incorporates the gain in a classification sense and the cost incurred for the queried observations. This metric is flexible and easily adaptable to different application scenarios. We run 24 simulations in an offline setting with preexisting observations from Gaia DR2 and SDSS DR14. We propose four comparison strategies, including the baseline strategy, which recommends based on the most similar past cases to the current case. Our strategy surpasses all other strategies in regard to reward. We reach an accuracy of 0.932, comparable to using the accuracy reached using all possible resources (0.948) but with half the number of photometric observations and 1000 times fewer spectroscopic resources. The baseline strategy lacks the complexity to achieve competitive results with our proposed strategy. Our framework is meant to aid continuous online observation decision-making and can be extended to incorporate multiple environmental and observation conditions.

Keywords: computational methods; astronomy data analysis; astrostatistics tools; variable stars; neural networks
Far-ultraviolet to Near-infrared Observations of SN 2023ixf: A High-energy Explosion Engulfed in Complex Circumstellar Material

We present early-phase panchromatic photometric and spectroscopic coverage spanning the far-ultraviolet to near-infrared regime of the nearest hydrogen-rich core-collapse supernova (SN) in the last 25 yr, SN 2023ixf. We observe early "flash" features in the optical spectra due to confined dense circumstellar material (CSM). We observe high-ionization absorption lines (Fe II, Mg II) in the ultraviolet spectra from very early on. We also observe a multipeaked emission profile of Hα in the spectrum beginning at ~16 days, which indicates ongoing interaction of the SN ejecta with a preexisting shell-shaped CSM having an inner radius of ~75 au and an outer radius of ~140 au. The shell-shaped CSM is likely a result of enhanced mass loss ~35-65 yr before the explosion assuming a standard red supergiant wind. The UV spectra are dominated by multiple highly ionized narrow absorption and broad emission features from elements such as C, N, O, Si, Fe, and Ni. Based on early light-curve models of Type II SNe, we infer that the nearby dense CSM confined to 7 ± 3 × 1014 cm (~45 au) is a result of enhanced mass loss (10-3.0±0.5 M ⊙ yr-1) two decades before the explosion.

Keywords: core-collapse supernovae; type ii supernovae; observational astronomy; extreme ultraviolet astronomy; near infrared astronomy
PSR J0437-4715: The Argentine Institute of Radioastronomy 2019-2020 Observational Campaign

We present the first-year data set of high-cadence, long-duration observations of the bright millisecond pulsar J0437-4715 obtained in the Argentine Institute of Radioastronomy (IAR). Using two single-dish 30 m radio antennas, we gather more than 700 hr of good-quality data with timing precision better than 1 μs. We characterize the white and red timing noise in IAR's observations, we quantify the effects of scintillation, and we perform single-pulsar searches of continuous gravitational waves, setting constraints in the nHz-μHz frequency range. We demonstrate IAR's potential for performing pulsar monitoring in the 1.4 GHz radio band for long periods of time with a daily cadence. In particular, we conclude that the ongoing observational campaign of the millisecond pulsar J0437-4715 can contribute to increase the sensitivity of the existing pulsar-timing arrays.

Keywords: pulsar timing method; millisecond pulsars; radio pulsars
Evolution of the Postmerger Remnants from the Coalescence of Oxygen-Neon and Carbon-Oxygen White Dwarf Pairs

Although multidimensional simulations have investigated the processes of double white dwarf (WD) mergers, postmerger evolution only focused on the carbon-oxygen (CO) or helium (He) WD merger remnants. In this work, we investigate for the first time the evolution of the remnants stemming from the merger of oxygen-neon (ONe) WDs with CO WDs. Our simulation results indicate that the merger remnants can evolve to hydrogen- and helium-deficient giants with a maximum radius of about 300 R ⊙. Our models show evidence that merger remnants more massive than 1.95 M ⊙ can ignite Ne before significant mass loss ensues, and they thus would become electron-capture supernovae. However, remnants with initial masses less than 1.90 M ⊙ will experience further core contraction and longer evolutionary time before reaching the conditions for Ne burning. Therefore, their fates are more dependent on mass-loss rates due to stellar winds and thus more uncertain. Relatively high mass-loss rates would cause such remnants to end their lives as ONe WDs. Our evolutionary models can naturally explain the observational properties of the double WD merger remnant IRAS 00500+6713 (J005311). As previously suggested in the literature, we propose and justify that J005311 may be the remnant from the coalescence of an ONe WD and a CO WD. We deduce that the final outcome of J005311 would be a massive ONe WD rather than a supernova explosion. Our investigations may be able to provide possible constraints on the wind mass-loss properties of the giants that have CO-dominant envelopes.

Keywords: white dwarf stars; stellar mergers
Solar Wind Magnetic Field Correlation Length: Correlation Functions versus Cross-field Displacement Diffusivity Test

The estimate of the solar wind magnetic fields' parallel correlation length, λ, be it from the measured fields' correlation functions or their spectral power at "zero" frequency, have long pointed toward short values on the order of 0.01 au. Evaluation of the mean cross-field displacements (CFDs), however, fails to show the decorrelation and resulting diffusion at the expected scales, pointing instead toward λ values on the order of 0.1 au or more. In an effort to understand this "order-of-magnitude" discrepancy and reconcile the approaches using correlation functions and the CFD diffusivity test, both approaches are applied here, with renewed attention to the "details" as well as the broader sense of the calculations, to a large, 20 yr long set of magnetic field and flow data from the ACE spacecraft. It is found that solar wind intervals too short relative to λ are a likely reason for some underestimate through the correlation-function approach, causing a premature drop of the correlation functions. Once converged to their long-time limit, however, the correlation functions produce magnetic field correlation lengths very much consistent with the magnetic-field-line (MFL) correlation lengths of the diffusivity test, with nearly matching distributions of the correlation lengths corrected by the proper ratio of their theoretical estimates. The fields' correlation lengths mostly range from 0.03 to 0.08 au, and the MFL correlation lengths from 0.04 to 0.3 au, with peaks at 0.075 and 0.15 au, likely due to nonlinear and quasilinear regimes of MFL wandering. As for the power-at-zero-frequency approach, it is doomed by the solar rotation.

Keywords: magnetic fields; interplanetary turbulence; space plasmas; heliosphere
Asymmetric Structure of the Solar Wind and Heliosphere from IBEX Observations

Our heliosphere is formed by the interaction between the dynamic solar wind (SW) and partially ionized, local interstellar medium. "Pickup ions" (PUIs) are produced by charge exchange between SW ions and interstellar neutral atoms and propagate with the SW into the outer heliosphere. Neutralization of these PUIs in the heliosheath creates energetic neutral atoms (ENAs) that are observed near Earth by the Interstellar Boundary Explorer (IBEX). In this study, we analyze the evolution of ENAs observed by IBEX between ∼0.5 and 6 keV from 2009 to 2018, presenting the evolution of ENA spectral indices as a function of latitude in different regions of the sky. Our results show that IBEX ENA spectra reflect unique differences in the northern and southern polar coronal holes (PCHs) as a function of latitude and time. ENA spectra reflect a delayed closure of the southern PCH compared to the north by ∼1-2 yr in solar cycle 24, but then a rapid opening of the southern PCH beginning ∼1-2 yr later, in agreement with evolving SW speeds emanating from the PCHs. While ENA spectra from the front and flanks of the heliosphere exhibit similar behavior, ENA spectra from the back behave differently, suggesting that the heliotail and ENA source structures are significantly different. The mean ENA spectral index observed by IBEX evolves gradually and quasi-periodically over the ∼11 yr solar cycle, reflecting large-scale changes in the PCHs and SW speed. The standard deviation of the spectral index exhibits bumps at times when the SW dynamic pressure changes abruptly.

Keywords: solar activity; solar cycle; heliosheath; interstellar medium; pickup ions; solar wind; heliosphere
Data-driven Model of Temporal Evolution of Solar Mg II h and k Profiles over the Solar Cycle

The solar radiation in the cores of the Mg II h and k spectral lines plays a significant role in the illumination of prominences, coronal mass ejections (CMEs), spicules, flare loops, and surges. Moreover, the radiation in these lines strongly correlates with solar magnetic activity and the ultraviolet solar spectral irradiance affecting the photochemistry, especially of oxygen and nitrogen, in the middle atmosphere of the Earth. This work provides a data-driven model of temporal evolution of the solar full-disk Mg II h and k profiles over the solar cycle. The capability of the model to reproduce the Mg II h and k profiles for an arbitrary date is statistically assessed. Based on selected 76 IRIS near-UV full-Sun mosaics covering almost the full solar cycle 24, we find the parameters of double-Gaussian fits of the disk-averaged Mg II h and k profiles and a model of their temporal evolution parameterized by the Bremen composite Mg II index. The model yields intensities within the uncertainties of the observed data in more than 90% of the reconstructed profiles assuming a statistically representative set of Bremen Mg II index values in the range of 0.150-0.165. The relevant full-disk Mg II h and k calibrated profiles with uncertainties and spectral irradiances are provided as an online machine-readable table. The model yields Mg II h and k profiles representing the disk incident radiation for the radiative-transfer modeling of prominences, CMEs, spicules, flare loops, and surges observed at arbitrary time.

Keywords: solar chromosphere; solar ultraviolet emission; solar cycle
The Effect of Stream Interaction Regions on ICME Structures Observed in Longitudinal Conjunction

We study two interplanetary coronal mass ejections (ICMEs) observed at Mercury and at 1 au by spacecraft in longitudinal conjunction, investigating the question: what causes the drastic alterations observed in some ICMEs during propagation, while other ICMEs remain relatively unchanged? Of the two ICMEs, the first one propagated relatively self-similarly, while the second one underwent significant changes in its properties. We focus on the presence or absence of large-scale corotating structures in the ICME propagation space between Mercury and 1 au, which have been shown to influence the orientation of ICME magnetic structures and the properties of ICME sheaths. We determine the flux rope orientation at the two locations using force-free flux rope fits as well as the classification by Nieves-Chinchilla et al. We also use measurements of plasma properties at 1 au, the size evolution of the sheaths and magnetic ejecta with heliocentric distance, and identification of structures in the propagation space based on in situ data, remote-sensing observations, and simulations of the steady-state solar wind to complement our analysis. Results indicate that the changes observed in one ICME were likely caused by a stream interaction region, while the ICME exhibiting little change did not interact with any transients between Mercury and 1 au. This work provides an example of how interactions with corotating structures in the solar wind can induce fundamental changes in ICMEs. Our findings can help lay the foundation for improved predictions of ICME properties at 1 au.

Keywords: solar coronal mass ejections; corotating streams; heliosphere
Outflows Driven from a Magnetic Pseudodisk

Outflows play a pivotal role in star formation as one of its most visible markers and a means of transporting mass, momentum, and angular momentum from the infalling gas into the surrounding molecular cloud. Their wide reach (at least thousands of astrnomical units) is a contrast to typical disk sizes (∼10–100 au). We employ high-resolution three-dimensional nested-grid nonideal magnetohydrodynamic (MHD) simulations to study outflow properties in the Class 0 phase. We find that no disk wind is driven from the extended centrifugal disk that has weak magnetic coupling. The low-velocity winds emerge instead from the infalling magnetic pseudodisk. Much of the disk actually experiences an infall of matter rather than outflowing gas. Some of the pseudodisk wind (PD-wind) moves inward to regions above the disk and either falls onto the disk or proceeds upward. The upward flow gives the impression of a disk wind above a certain height even if the gas is originally emerging from the pseudodisk. The PD-wind has the strongest flow coming from a disk interaction zone that lies just outside the disk and is an interface between the inwardly advected magnetic field of the pseudodisk and the outwardly diffusing magnetic field of the disk. The low-velocity wind exhibits the features of a flow driven by the magnetic pressure gradient force in some regions and those of a magnetocentrifugal wind in other regions. We interpret the structure and dynamics of the outflow zone in terms of the basic physics of gravity, angular momentum, magnetic fields, and nonideal MHD.

Keywords: gravitational collapse; magnetic fields; magnetohydrodynamics; star formation; stellar winds; circumstellar disks
Validation and Improvement of the Pan-STARRS Photometric Calibration with the Stellar Color Regression Method

As one of the best ground-based photometric data set, Pan-STARRS1 (PS1) has been widely used as the reference to calibrate other surveys. In this work, we present an independent validation and recalibration of the PS1 photometry using spectroscopic data from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) DR7, and photometric data from the corrected Gaia Early Data Release 3 (EDR3) with the Stellar Color Regression (SCR) method. Using per band typically a total of 1.5 million LAMOST-PS1-Gaia stars as standards, we show that the PS1 photometric calibration precisions in the grizy filters are around 4 ~ 5 mmag when averaged over 20' regions. However, significant large- and small-scale spatial variation of magnitude offset, up to over 1%, probably caused by the calibration errors in the PS1, are found for all the grizy filters. The calibration errors in different filters are uncorrelated, and are slightly larger for the g and y filters. We also detect moderate magnitude-dependent errors (0.005, 0.005, 0.005, 0.004, 0.003 mag per magnitude in the 14-17 mag range for the grizy filters, respectively) in the PS1 photometry by comparing with the Gaia EDR3 and other catalogs. The errors are likely caused by the systematic uncertainties in the PSF magnitudes. We provide two-dimensional maps to correct for such magnitude offsets in the LAMOST footprint at different spatial resolutions from 20' to 160'. The results demonstrate the power of the SCR method in improving the calibration precision of wide-field surveys when combined with the LAMOST spectroscopy and Gaia photometry.

Keywords: stellar photometry; astronomy data analysis; calibration
Emission Line Profile Variations in the Early Coronal Phase of the Nova V2944 Ophiuchi

V2944 Ophiuchi was a Fe II type novae that reached moderate excitation and displayed large variations among the profiles of its emission lines. The profiles become increasingly double-peaked as the ionization level of the parent ion increases. At the extremes, H I and O I have flat-topped profiles while the coronal features [Si VII] and [Ca VIII] peak in the line wings and have centers that fall to near the continuum level. He II, N V, and [Si VI] display intermediate behavior but in the same sense that the line center depth is smallest for He II and largest for [Si VI. A possible explanation for these profile variations is that the emission line region is ring-like in structure and becomes increasingly flattened as line excitation increases.

Keywords: novae
Calcium Bright Knots and the Formation of Chromospheric Anemone Jets on the Sun

Space-based observations show that the solar atmosphere from the solar chromosphere to the solar corona is filled with small-scale jets and is linked with small-scale explosions. These jets may be produced by mechanisms similar to those of large-scale flares and such jets may be related to the heating of the corona and chromosphere as well as the acceleration of solar wind. The chromospheric anemone jets on the Sun remain puzzling because their footpoints (or bright knots) have not been well resolved and the formation process of such enigmatic small-scale jets remains unclear. We propose a new model for chromospheric jets using the 3D magnetohydrodynamic simulations, which show that the continuous, upward rising of small-scale twisted magnetic flux ropes in a magnetized solar chromosphere drives small-scale magnetic reconnection and the launching of several small-scale jets during the evolution of the chromospheric anemone jets. Our new, self-consistent, 3D computer modeling of small-scale, but ever-changing flux rope emergence in the magnetized solar atmosphere is fully consistent with observations and provides a universal mechanism for nanoflare and jet formation.

Keywords: solar chromosphere; solar magnetic reconnection
No UV-bright Eruptions from SN 2023ixf in GALEX Imaging 15-20 yr Before Explosion

We analyze pre-explosion ultraviolet imaging of the nearby Type II supernova SN 2023ixf in search of precursor variability. No outbursts are seen in observations obtained 15-20 yr prior to explosion to a limit of L NUV ≈ 1000 L ⊙ and L FUV ≈ 2000 L ⊙. The time period of these non-detections roughly corresponds to changes in the circumstellar density inferred from early spectra and photometry.

Keywords: circumstellar dust; supernovae
Synthetic Absorption Lines from Simulations of Multiphase Gas in Galactic Winds

Supernova-driven galactic winds are multiphase streams of gas that are often observed flowing at a range of velocities out of star-forming regions in galaxies. In this study, we use high-resolution 3D simulations of multiphase galactic winds modeled with the hydrodynamics code Cholla to investigate the connection between numerical studies and observations. Using a simulated interaction between a hot T ~ 107 K supernova-driven wind and a cool T ~ 104 K cloud of interstellar material, we create mock observables, including the optical depth (τ) and covering fraction (Cf), of six commonly observed ions (Si II, C II, Si IV, C IV, N V, and O VI) as a function of gas velocity. We compare our mock observables to surveys of galactic winds in the literature, finding good agreement with velocities and profiles of the low ions. We then compute "empirical" values for the optical depth and covering fraction following observational techniques, and compare them to the values calculated directly from the simulation data. We find that the empirically computed values tend to underestimate the "true" value of τ for ions with high optical depth and overestimate the "true" value of τ for ions with low optical depth relative to the simulated data. The empirically estimated covering fractions match our direct calculations very well for the low-ionization ions; for the high-ionization ions, the empirical covering fractions underestimate the directly computed values by up to ~40%.

Keywords: galactic winds; supernovae; hydrodynamical simulations