adsabs/SciX_UAT_keywords huggingface dataset:
Deflection of Coronal Mass Ejections in Unipolar Ambient Magnetic Fields

The trajectories of coronal mass ejections (CMEs) are often seen to deviate substantially from a purely radial propagation direction. Such deviations occur predominantly in the corona and have been attributed to "channeling" or deflection of the eruptive flux by asymmetric ambient magnetic fields. Here, we investigate an additional mechanism that does not require any asymmetry of the preeruptive ambient field. Using magnetohydrodynamic numerical simulations, we show that the trajectories of CMEs through the solar corona can significantly deviate from the radial direction when propagation takes place in a unipolar radial field. We demonstrate that the deviation is most prominent below ~15 R ⊙ and can be attributed to an "effective I × B force" that arises from the intrusion of a magnetic flux rope with a net axial electric current into a unipolar background field. These results are important for predictions of CME trajectories in the context of space-weather forecasts, as well as for reaching a deeper understanding of the fundamental physics underlying CME interactions with the ambient fields in the extended solar corona.

Keywords: solar coronal mass ejections
Carbon Isotope Ratios in Planetary Nebulae: The Unexpected Enhancement of 13C

The 12C/13C ratio has been measured toward a sample of planetary nebulae (PNe) using millimeter observations of CO, HCN, HNC, CN, and other species, conducted with the 12 m antenna and the Submillimeter Telescope of the Arizona Radio Observatory. The observed nebulae spanned the entire lifetime of PNe, from ∼900 to 12,000 yr, and include well-known objects such as NGC 7293 (Helix), NGC 6720 (Ring), and NGC 2440, as well as relatively unexplored nebulae (M3-28, M2-48, and M3-55). In most cases, multiple molecules and transitions were used in the ratio determination, resulting in the most accurate values available to date, with 10%-40% uncertainties. The ratios found were unexpectedly low, lying in the range 12C/13C ∼1.0 ± 0.7-13.2 ± 4.9, with an average value of 3.7—drastically less than found in the envelopes of C-rich AGB stars, and, in some cases, lower than the minimum value achieved in equilibrium CNO burning. Such low values are expected for the two O-rich nebulae studied (M2-9 and M2-48), because of insufficient third dredge-up events. However, most of the PNe observed were clearly carbon-rich, as deduced from the large number of C-bearing molecules present in them. Because nucleosynthesis ceases in the PN stage, both the C/O and the 12C/13C ratios must reflect abundances at the end of the AGB. These consistently low 12C/13C ratios, combined with the bipolar/multipolar morphologies of all planetary nebulae observed, suggest an explosive process involving proton-capture occurred at the AGB-PN transition.

Keywords: planetary nebulae; isotope shifts; stellar nucleosynthesis; radio astronomy; molecular spectroscopy; interstellar molecules
Hot Subdwarf All Southern Sky Fast Transit Survey with the Evryscope

We have conducted a survey of candidate hot subdwarf (HSD) stars in the southern sky searching for fast transits, eclipses, and sinusoidal-like variability in the Evryscope light curves. The survey aims to detect transit signals from Neptune-size planets to gas giants, and eclipses from M-dwarfs and brown dwarfs. The other variability signals are primarily expected to be from compact binaries and reflection effect binaries. Due to the small size of HSDs (R ≈ 0.2 R⊙), transit and eclipse signals are expected to last only ≈20 minutes, but with large signal depths (up to completely eclipsing if the orientation is edge on). With its 2 minute cadence and continuous observation, the Evryscope is well placed to recover these fast transits and eclipses. The very large field of view (8150 deg2) is critical to obtain enough HSD targets, despite their rarity. We identified ≈11,000 potential HSDs from the 9.3 M Evryscope light curves for sources brighter than mg = 15. With our machine-learning spectral classifier, we flagged high confidence targets and estimate the total HSDs in the survey to be ≈1400. The light-curve search detected three planet transit candidates, shown to have stellar companions from follow-up analysis. We discovered several new compact binaries (including two with unseen degenerate companions), two eclipsing binaries with M-dwarf companions, as well as new reflection effect binaries and others with sinusoidal-like variability. Four of the discoveries are being published in separate follow-up papers, and we discuss the follow-up potential of the other discoveries.

Keywords: subdwarf stars; b subdwarf stars; o subdwarf stars; surveys; photometry; spectroscopy; stellar classification
Detecting Solar System Analogs through Joint Radial Velocity/Astrometric Surveys

Earth-mass exoplanets on year-long orbits and cool gas giants (CGG) on decade-long orbits lie at the edge of current detection limits. The Terra Hunting Experiment (THE) will take nightly radial velocity (RV) observations on HARPS3 of at least 40 bright nearby G and K dwarfs for 10 yr, with a target 1σ measurement error of ~0.3 m s-1, in search of exoplanets that are Earth-like in mass and temperature. However, RV observations can only provide minimum mass estimates, due to the mass-inclination degeneracy. Astrometric observations of these same stars, with sufficient precision, could break this degeneracy. Gaia will soon release ~100-200 astrometric observations of the THE stars with a 10 yr baseline and ~34.2 μas 1σ along-scan measurement error. The Nancy Grace Roman Space Telescope will be capable of precision astrometry using its wide field imager (target ~5-20 μas 1σ measurement error for bright stars) and could extend the astrometric observational baseline to ~25 yr. We simulate and model an observing program that combines data from these three telescopes. We find that (1) THE RVs and Gaia astrometry can detect Earth-like and CGG-like exoplanets around bright Sun-like stars at 10 pc and that (2) adding Roman astrometry improves the detection precision for CGG masses and periods by respective factors up to ~10 and ~4. Such a survey could provide insight into the prevalence of Solar System analogs, exoplanet architectures reminiscent of the mass and orbital separation hierarchy of our Solar System, for the nearest Sun-like stars.

Keywords: exoplanet detection methods; radial velocity; space astrometry; extrasolar rocky planets; extrasolar gaseous planets; solar system planets
Tracking and Seismological Analysis of Multiple Coronal Loops in an Active Region

We present a new method to track the position and evolution of coronal loops designed for observations such as active regions in which multiple loops appear in close proximity or overlap with each other along the observational line of sight. The method is based on modeling a time-distance map containing one or more loops and fitting the modeled map to observational data, as opposed to the commonly used technique of analyzing each frame independently. This allows us to control the variability of the model, informed by our physical interpretation, and use the trends present to help constrain the model parameters. We apply our method to an observation of a bundle of coronal loops previously investigated using a spatiotemporal autocorrelation method and compare our results. A benefit of our method is that it provides the time series for the position of the loops that may be used for further analysis using established seismological techniques. We demonstrate this by modeling the oscillation of several loops in response to flaring energy releases that occur during the observation, and we find evidence of loop evolution consistent with the Kelvin-Helmholtz instability.

Keywords: magnetohydrodynamics; solar coronal loops; solar corona; solar coronal seismology; solar coronal waves; solar extreme ultraviolet emission; astronomy data analysis
The Nature of HI-absorption-selected Galaxies at z ≈ 4

We report a Karl G. Jansky Very Large Array (JVLA) search for redshifted CO(1-0) or CO(2-1) emission, and a Hubble Space Telescope Wide Field Camera 3 (HST-WFC3) search for rest-frame near-ultraviolet (NUV) stellar emission, from seven HI-selected galaxies associated with high-metallicity ([M/H] ≥ -1.3) damped Lyα absorbers (DLAs) at z ≈ 4. The galaxies were earlier identified by Atacama Large Millimeter/submillimeter Array imaging of their [CII] 158 μm emission. We also used the JVLA to search for CO(2-1) emission from the field of a low-metallicity ([M/H] = -2.47) DLA at z ≈ 4.8. No statistically significant CO emission is detected from any of the galaxies, yielding upper limits of Mmol < (7.4-17.9) × 1010 × (αCO/4.36) M⊙ on their molecular gas mass. We detect rest-frame NUV emission from four of the seven [CII] 158 μm-emitting galaxies, the first detections of the stellar continuum from HI-selected galaxies at z ≳ 4. The HST-WFC3 images yield typical sizes of the stellar continua of ≈2-4 kpc and inferred dust-unobscured star formation rates (SFRs) of ≈5.0-17.5 M⊙ yr-1, consistent with, or slightly lower than, the total SFRs estimated from the far-infrared (FIR) luminosity. We further stacked the CO(2-1) emission signals of six [CII] 158 μm-emitting galaxies in the image plane. Our non-detection of CO(2-1) emission in the stacked image yields the limit Mmol < 4.1 × 1010 × (αCO/4.36) M⊙ on the average molecular gas mass of the six galaxies. Our molecular gas mass estimates and NUV SFR estimates in HI-selected galaxies at z ≈ 4 are consistent with those of main-sequence galaxies with similar [CII] 158 μm and FIR luminosities at similar redshifts. However, the NUV emission in the HI-selected galaxies appears more extended than that in main-sequence galaxies at similar redshifts.

Keywords: galaxies; high-redshift galaxies
Beyond BPT: A New Multidimensional Diagnostic Diagram for Classifying Power Sources Tested Using the SAMI Galaxy Survey

Current methods of identifying the ionizing source of nebular emission in galaxies are well defined for the era of single-fiber spectroscopy, but still struggle to differentiate the complex and overlapping ionization sources in some galaxies. With the advent of integral field spectroscopy, the limits of these previous classification schemes are more apparent. We propose a new method for distinguishing the ionizing source in resolved galaxy spectra by use of a multidimensional diagnostic diagram that compares emission-line ratios with velocity dispersion on a spaxel-by-spaxel basis within a galaxy. This new method is tested using the Sydney-Australian-Astronomical-Observatory Multi-object Integral-Field Spectrograph Galaxy Survey (SAMI) Data Release 3 (DR3), which contains 3068 galaxies at z < 0.12. Our results are released as ionization maps available alongside the SAMI DR3 public data. Our method accounts for a more diverse range of ionization sources than the standard suite of emission-line diagnostics; we find 1433 galaxies with a significant contribution from non-star-forming ionization using our improved method as compared to 316 galaxies identified using only emission-line ratio diagnostics. Within these galaxies, we further identify 886 galaxies hosting unique signatures inconsistent with standard ionization by H II regions, active galactic nuclei, or shocks. These galaxies span a wide range of masses and morphological types and comprise a sizable portion of the galaxies used in our sample. With our revised method, we show that emission-line diagnostics alone do not adequately differentiate the multiple ways to ionize gas within a galaxy.

Keywords: warm ionized medium; classification systems; galaxy classification systems; active galactic nuclei; shocks; star formation
Implications of the Conformal Constraint on Sound Speed on the Radius of PSR J0952-0607 within Rastall Gravity

It has been shown that the nonminimal coupling between geometry and matter can provide models for massive compact stars that are consistent with the conformal bound on the sound speed, $0\leqslant {c}_{s}^{2}\leqslant {c}^{2}/3$ , where the core density approaches a few times the nuclear saturation density. We impose the conformal upper bound on the sound speed on Rastall's field equations of gravity, with Krori-Barua potentials in the presence of an anisotropic fluid as a matter source, to estimate the radius of the most massive pulsar ever observed, PSR J0952-0607. For its measured mass M = 2.35 ± 0.17 M ⊙, we obtain a radius R = 14.087 ± 1.0186 km as inferred by the model. We investigate a possible connection between Rastall gravity and the MIT bag model with an equation of state, ${p}_{r}(\rho )\approx {c}_{s}^{2}\left(\rho -{\rho }_{{\rm{s}}}\right)$ , in the radial direction, with ${c}_{s}=c/\sqrt{3}$ and a surface density ρ s slightly above the nuclear saturation density ρ nuc = 2.7 × 1014 g cm-3. The corresponding mass-radius diagram is in agreement with our estimated value of the radius and with astrophysical observations of other pulsars at 68% confidence level.

Keywords: massive stars; millisecond pulsars; neutron star cores; non-standard theories of gravity; stellar structures
Relationship between Successive Flares in the Same Active Region and SHARP Parameters

A solar active region (AR) may produce multiple notable flares during its passage across the solar disk. We investigate successive flares from flare-eruptive ARs, and explore their relationship with solar magnetic parameters. We examine six ARs in this study, each with at least one major flare above X1.0. The Space-weather HMI Active Region Patch (SHARP) is employed in this study to parameterize the ARs. We aim to identify the most flare-related SHARP parameters and lay foundation for future practical flare forecasts. We first evaluate the correlation coefficients between the SHARP parameters and the successive flare production. Then we adopt a Natural Gradient Boost (NGBoost) method to analyze the relationship between the SHARP parameters and the successive flare bursts. Based on the correlation analysis and the importance distribution returned from NGBoost, we select the eight most flare-related SHARP parameters. Finally, we discuss the physical meanings of the eight selected parameters and their relationship with flare production.

Keywords: solar flares; solar active regions; solar magnetic fields
The TESS-Keck Survey. XVI. Mass Measurements for 12 Planets in Eight Systems

With JWST's successful deployment and unexpectedly high fuel reserves, measuring the masses of sub-Neptunes transiting bright, nearby stars will soon become the bottleneck for characterizing the atmospheres of small exoplanets via transmission spectroscopy. Using a carefully curated target list and observations from more than 2 yr of APF-Levy and Keck-HIRES Doppler monitoring, the TESS-Keck Survey is working toward alleviating this pressure. Here we present mass measurements for 11 transiting planets in eight systems that are particularly suited to atmospheric follow-up with JWST. We also report the discovery and confirmation of a temperate super-Jovian-mass planet on a moderately eccentric orbit. The sample of eight host stars, which includes one subgiant, spans early-K to late-F spectral types (T eff = 5200-6200 K). We homogeneously derive planet parameters using a joint photometry and radial velocity modeling framework, discuss the planets' possible bulk compositions, and comment on their prospects for atmospheric characterization.

Keywords: exoplanets; radial velocity
A Systematic Study on the Rise Time-Peak Luminosity Relation for Bright Optical Transients Powered by Wind Shock Breakout

A number of astrophysical transients originating from stellar explosions are powered by the collision of the ejected material with the circumstellar medium, which efficiently produces thermal radiation via shock dissipation. We investigate how such interaction-powered transients are distributed in the peak bolometric luminosity versus the rise time phase space. Taking advantage of less time-consuming one-dimensional simulations with spherical symmetry, we calculated more than 500 models with different circumstellar mass and radius, ejecta mass and energy, and chemical compositions. The peak bolometric luminosity, the total radiated energy, and the rise time of the interaction-powered emission are measured for each simulated light curve. We consider how these characteristic quantities are determined as a function of the model parameters and discuss possible implications for the observed populations of (potential) interaction-powered transients, such as Type IIn supernovae and fast blue optical transients.

Keywords: supernovae; circumstellar matter; hydrodynamics; shocks; stellar mass loss
Modeling Current and Future High-cadence Surveys of Repeating Fast Radio Burst Populations

In recent years, the Canadian Hydrogen Intensity Mapping Experiment (CHIME) interferometer has revealed a large number of fast radio bursts (FRBs), including a sizable population that demonstrates repeating behavior. This transit facility, employing a real-time FRB search pipeline, continually scans the sky with declinations between -10° and 90° for events with fluences ⪆0.4 Jy ms. We simulate a population of repeating FRBs by performing Monte Carlo simulations of underlying source populations processed through a mock CHIME/FRB observing pipeline. Assuming intrinsic repeater rates follow a Poisson distribution, we test assumptions about the burst populations of the repeater sample, and construct models of the FRB sample assuming various cosmological distributions. We infer the completeness of CHIME/FRB observations as a function of observing cadence and redshifts out to 0.5. We find that, if all simulated bursts have a fixed Poisson probability of repetition over their integrated time of observation, repeating burst detections across comoving volume should continue to grow near linearly on the order of decades. We predict that around 170 of the current CHIME/FRB one-off sources will ultimately repeat. We also make projections for FRB repeaters by future facilities and demonstrate that the number of repeaters they find could saturate on a ~3 yr timescale.

Keywords: radio transient sources
Three-dimensional, Time-dependent MHD Simulation of Disk-Magnetosphere-Stellar Wind Interaction in a T Tauri, Protoplanetary System

We present a three-dimensional, time-dependent MHD simulation of the short-term interaction between a protoplanetary disk and the stellar corona in a T Tauri system. The simulation includes the stellar magnetic field, self-consistent coronal heating and stellar wind acceleration, and a disk rotating at sub-Keplerian velocity to induce accretion. We find that, initially, as the system relaxes from the assumed initial conditions, the inner part of the disk winds around and moves inward and close to the star as expected. However, the self-consistent coronal heating and stellar wind acceleration build up the original state after some time, significantly pushing the disk out beyond 10R ⋆. After this initial relaxation period, we do not find clear evidence of a strong, steady accretion flow funneled along coronal field lines, but only weak, sporadic accretion. We produce synthetic coronal X-ray line emission light curves, which show flare-like increases that are not correlated with accretion events nor with heating events. These variations in the line emission flux are the result of compression and expansion due to disk-corona pressure variations. Vertical disk evaporation evolves above and below the disk. However, the disk-stellar wind boundary stays quite stable, and any disk material that reaches the stellar wind region is advected out by the stellar wind.

Keywords: protoplanetary disks
Constraining Warm Dark Matter and Population III Stars with the Global 21 cm Signal

Upcoming ground- and space-based experiments may have sufficient accuracy to place significant constraints upon high-redshift star formation, Reionization, and dark matter (DM) using the global 21 cm signal of the intergalactic medium. In the early universe, when the relative abundance of low-mass DM halos was important, measuring the global signal would place constraints on the damping of structure formation caused by DM having a higher relic velocity (warm dark matter, or WDM) than in cold dark matter. Such damping, however, can be mimicked by altering the star formation efficiency (SFE) and can be difficult to detect because of the presence of Population III stars with unknown properties. We study these various cases and their degeneracies with the WDM mass parameter m X using a Fisher matrix analysis. We study the m X = 7 keV case and a star formation model that parameterizes the SFE as a strong function of halo mass and include several variations of this model along with three different input noise levels for the likelihood; we also use a minimum halo virial temperature for collapse near the molecular cooling threshold. We find that when the likelihood includes only Population II stars, m X is constrained to an uncertainty of ~0.4 keV for all models and noise levels at the 68% confidence level. When the likelihood includes weak Population III stars, m X ~ 0.3 keV, and if Population III star formation is relatively efficient, m X ~ 0.1 keV uncertainty, with tight Population III star formation parameter constraints. Our results show that the global 21 cm signal is a promising test-bed for WDM models, even in the presence of strong degeneracies with astrophysical parameters.

Keywords: cosmology; large-scale structure of the universe; observational cosmology; dark matter; star formation; population iii stars; warm dark matter
Multiband Nonthermal Radiative Study of PeVatron Candidate Pulsar Wind Nebula HESS J1849-000

Pulsar wind nebula HESS J1849-000 is one of the sources that may emit PeV γ-ray photons based on the recent measurement by the Tibet Air Shower Array and the Large High Altitude Air Shower Observatory. We use a time-dependent model to investigate the nonthermal radiative properties of HESS J1849-000. Observed multiband data are produced well by relativistic leptons through synchrotron radiation and inverse Compton processes, and the particle transport and cooling processes are analyzed. Our results show that the particle adiabatic loss dominates over the synchrotron loss and inverse Compton losses, and the particle advection dominates over diffusion for the low-energy band. On the other hand, the particle synchrotron loss dominates over the adiabatic loss and inverse Compton losses, and the diffusion dominates over advection for the high-energy band. Furthermore, particle transport would be playing a significant role in the low-energy band, whereas the particle cooling processes may play a more important role in the high-energy band. The current diffusion coefficient 3.4 × 1026 cm2 s‑1 at an electron energy of 1 TeV is derived, which implies a slow diffusion mechanism may occur within the nebula. More importantly, our model suggests that the particle's maximum energy is 3.6 PeV, which makes HESS J1849-000 a PeVatron candidate.

Keywords: pulsars; pulsar wind nebulae