adsabs/SciX_UAT_keywords huggingface dataset:
Nebular Models of Sub-Chandrasekhar Mass Type Ia Supernovae: Clues to the Origin of Ca-rich Transients

We use non-local thermal equilibrium radiative transport modeling to examine observational signatures of sub-Chandrasekhar mass double detonation explosions in the nebular phase. Results range from spectra that look like typical and subluminous Type Ia supernovae (SNe) for higher mass progenitors to spectra that look like Ca-rich transients for lower mass progenitors. This ignition mechanism produces an inherent relationship between emission features and the progenitor mass as the ratio of the nebular [Ca II]/[Fe III] emission lines increases with decreasing white dwarf mass. Examining the [Ca II]/[Fe III] nebular line ratio in a sample of observed SNe we find further evidence for the two distinct classes of SNe Ia identified in Polin et al. by their relationship between Si II velocity and B-band magnitude, both at time of peak brightness. This suggests that SNe Ia arise from more than one progenitor channel, and provides an empirical method for classifying events based on their physical origin. Furthermore, we provide insight to the mysterious origin of Ca-rich transients. Low-mass double detonation models with only a small mass fraction of Ca (1%) produce nebular spectra that cool primarily through forbidden [Ca II] emission.

Keywords: type ia supernovae; white dwarf stars; hydrodynamical simulations; hydrodynamics; radiative transfer simulations; astronomical simulations; supernovae
Time-resolved Low-resolution Spectra of BLAP-009 and BLAP-014

We present time resolved low resolution spectra of BLAP-009 and BLAP-014 collected with SPRAT on the Liverpool Telescope. The spectra were median-stacked in four ranges of phase. It was intended to note the variation in the shape of the helium absorption lines as a function of phase, but they do not appear to vary with time in low resolution spectra. The lack of clear offsets in the absorption lines suggest that there can only be small radial velocity due to either unseen companion or rapid expansion/contraction of the envelope.

Keywords: blue large-amplitude pulsators; pulsating variable stars; spectroscopy
Estimating Microlensing Parameters from Observables and Stellar Isochrones with pyLIMASS

We present pyLIMASS, a novel algorithm for estimating the physical properties of the lensing system in microlensing events. The main idea of pyLIMASS is to combine all available information regarding the microlensing event, defined as observables, and to estimate the parameter distributions of the system, such as the lens mass and distance. The algorithm is based on isochrones for the stars model and combines the observables using a Gaussian mixture approach. After describing the mathematical formalism and its implementation, we discuss the algorithm's performance on simulated and published events. Generally, the pyLIMASS estimations are in good agreement (i.e., within 1σ) with the results of the selected published events, making it an effective tool to estimate the lens properties and their distribution. The applicability of the method was tested by using a catalog of realistically simulated events that could be observed by the future Galactic Bulge Time Domain Survey of the Nancy Grace Roman Space Telescope. By solely using constraints from the Roman lightcurves and images, pyLIMASS estimates the masses of the lens of the Roman catalog with a median precision of 20% with almost no bias.

Keywords: gravitational microlensing
The Colocation of Magnetic Reconnection and Current Disruption in Jovian Middle Magnetosphere

Magnetic reconnection and current disruption are two key processes in driving energy conversion and dissipation in planetary magnetospheres. At the Earth, the two processes usually occur at different locations: the current disruption process occurs more frequently in the near-Earth magnetotail ∼10 R E, while the magnetotail reconnection process is expected to take place in the more distant region where the current sheet is thinner. Occasionally, under very intense solar wind perturbations, reconnection could be located closer to the Earth where current disruption processes usually operate. But it is unclear what the situation is at giant planets, in which the plasma environment is very different from the Earth. In this study, we investigate a middle-Jupiter reconnection event at ∼43 R J. During the event, the inferred integrated cross-field currents were substantially reduced, which we argue is a signature of current disruption. In this case, we suggest that magnetic reconnection could be colocated with a current disruption process in the Jovian magnetosphere, which is roughly analogous to the situation in the extremely perturbed Earth's magnetosphere.

Keywords: planetary magnetospheres
Metal Mixing in the r-process Enhanced Ultrafaint Dwarf Galaxy Reticulum II

The ultrafaint dwarf galaxy Reticulum II was enriched by a single rare and prolific r-process event. The r-process content of Reticulum II thus provides a unique opportunity to study metal mixing in a relic first galaxy. Using multi-object high-resolution spectroscopy with VLT/GIRAFFE and Magellan/M2FS, we identify 32 clear spectroscopic member stars and measure abundances of Mg, Ca, Fe, and Ba where possible. We find ${72}_{-12}^{+10} \% $ of the stars are r-process-enhanced, with a mean $\left\langle [\mathrm{Ba}{\rm{/}}{\rm{H}}]\right\rangle =-1.68\,\pm \,0.07$ and unresolved intrinsic dispersion σ [Ba/H]<0.20. The homogeneous r-process abundances imply that Ret II's metals are well mixed by the time the r-enhanced stars form, which simulations have shown requires at least 100 Myr of metal mixing in between bursts of star formation to homogenize. This is the first direct evidence of bursty star formation in an ultrafaint dwarf galaxy. The homogeneous dilution prefers a prompt and high-yield r-process site, such as collapsar disk winds or prompt neutron star mergers. We also find evidence from [Ba/H] and [Mg/Ca] that the r-enhanced stars in Ret II formed in the absence of substantial pristine gas accretion, perhaps indicating that ≈70% of Ret II stars formed after reionization. *This paper includes data gathered with the 6.5 m Magellan Telescopes, located at Las Campanas Observatory, Chile.

Keywords: dwarf galaxies; local group; r-process; chemical abundances; galaxy chemical evolution
Deep Paβ Imaging of the Candidate Accreting Protoplanet AB Aur b

Giant planets grow by accreting gas through circumplanetary disks, but little is known about the timescale and mechanisms involved in the planet-assembly process because few accreting protoplanets have been discovered. Recent visible and infrared imaging revealed a potential accreting protoplanet within the transition disk around the young intermediate-mass Herbig Ae star, AB Aurigae (AB Aur). Additional imaging in Hα probed for accretion and found agreement between the line-to-continuum flux ratio of the star and companion, raising the possibility that the emission source could be a compact disk feature seen in scattered starlight. We present new deep Keck/NIRC2 high-contrast imaging of AB Aur to characterize emission in Paβ, another accretion tracer less subject to extinction. Our narrow band observations reach a 5σ contrast of 9.6 mag at 0.″6, but we do not detect significant emission at the expected location of the companion, nor from other any other source in the system. Our upper limit on Paβ emission suggests that if AB Aur b is a protoplanet, it is not heavily accreting or accretion is stochastic and was weak during the observations.

Keywords: exoplanets; exoplanet formation; direct imaging; protoplanetary disks
On the Stellar Populations of Galaxies at z = 9-11: The Growth of Metals and Stellar Mass at Early Times

We present a detailed stellar population analysis of 11 bright (H < 26.6) galaxies at z = 9-11 (three spectroscopically confirmed) to constrain the chemical enrichment and growth of stellar mass of early galaxies. We use the flexible Bayesian spectral energy distribution (SED) fitting code Prospector with a range of star formation histories (SFHs), a flexible dust attenuation law, and a self-consistent model of emission lines. This approach allows us to assess how different priors affect our results and how well we can break degeneracies between dust attenuation, stellar ages, metallicity, and emission lines using data that probe only the rest-frame ultraviolet (UV) to optical wavelengths. We measure a median observed UV spectral slope $\beta =-{1.87}_{-0.43}^{+0.35}$ for relatively massive star-forming galaxies ( $9\lt \mathrm{log}({M}_{\star }/{M}_{\odot })\lt 10$ ), consistent with no change from z = 4 to z = 9-10 at these stellar masses, implying rapid enrichment. Our SED-fitting results are consistent with a star-forming main sequence with sublinear slope (0.7 ± 0.2) and specific star formation rates of 3-10 Gyr-1. However, the stellar ages and SFHs are less well constrained. Using different SFH priors, we cannot distinguish between median mass-weighted ages of ~ 50-150 Myr, which corresponds to 50% formation redshifts of z 50 ~ 10-12 at z ~ 9 and is of the order of the dynamical timescales of these systems. Importantly, models with different SFH priors are able to fit the data equally well. We conclude that the current observational data cannot tightly constrain the mass-buildup timescales of these z = 9-11 galaxies, with our results consistent with SFHs implying both a shallow and steep increase in the cosmic SFR density with time at z > 10.

Keywords: early universe; galaxy formation; galaxy evolution; high-redshift galaxies; star formation
Neural Stellar Population Synthesis Emulator for the DESI PROVABGS

The Probabilistic Value-Added Bright Galaxy Survey (PROVABGS) catalog will provide the posterior distributions of physical properties of >10 million DESI Bright Galaxy Survey galaxies. Each posterior distribution will be inferred from joint Bayesian modeling of observed photometry and spectroscopy using Markov Chain Monte Carlo sampling and the Hahn et al. stellar population synthesis (SPS) model. To make this computationally feasible, PROVABGS will use a neural emulator for the SPS model to accelerate the posterior inference. In this work, we present how we construct the emulator using the Alsing et al. approach and verify that it can be used to accurately infer galaxy properties. We confirm that the emulator is in excellent agreement with the original SPS model with ≪1% error and is 100× faster. In addition, we demonstrate that the posteriors of galaxy properties derived using the emulator are also in excellent agreement with those inferred using the original model. The neural emulator presented in this work is essential in bypassing the computational challenge posed in constructing the PROVABGS catalog. Furthermore, it demonstrates the advantages of emulation for scaling sophisticated analyses to millions of galaxies.

Keywords: galaxies; astronomy data modeling; neural networks; spectral energy distribution
The Rise and Emergence of Untwisted Toroidal Flux Ropes on the Sun

Magnetic flux ropes (MFRs) rising buoyantly through the Sun's convection zone are thought to be subject to viscous forces preventing them from rising coherently. Numerous studies have suggested that MFRs require a minimum twist in order to remain coherent during their rise. Furthermore, even MFRs that get to the photosphere may be unable to successfully emerge into the corona unless they are at least moderately twisted, since the magnetic pressure gradient needs to overcome the weight of the photospheric plasma. To date, however, no lower limit has been placed on the critical minimum twist required for an MFR to rise coherently through the convection zone or emerge through the photosphere. In this paper, we simulate an untwisted toroidal MFR that is able to rise from the convection zone and emerge through the photosphere as an active region that resembles those observed on the Sun. We show that untwisted MFRs can remain coherent during their rise and then pile up near the photosphere, triggering undular instability, allowing the MFR to emerge through the photosphere. We propose that the toroidal geometry of our MFR is critical for its coherent rise. Upon emergence, a pair of lobes rises into the corona. The two lobes then interact and reconnect, resulting in a localized high speed jet. The resulting photospheric magnetogram displays the characteristic salt-and-pepper structure often seen in observations. Our major result is that MFRs need not be twisted to rise coherently through the convection zone and emerge through the photosphere.

Keywords: solar magnetic fields; solar magnetic flux emergence; solar active regions; solar physics
The Effects of Tilt on the Images of Black Hole Accretion Flows

We analyze two 3D general-relativistic magnetohydrodynamic accretion simulations in the context of how they would manifest in Event Horizon Telescope (EHT) observations of supermassive black holes. The two simulations differ only in whether the initial angular momentum of the plasma is aligned with the rapid (a = 0.9) spin of the black hole. Both have low net magnetic flux. Ray tracing is employed to generate resolved images of the synchrotron emission. When using parameters appropriate for Sgr A* and assuming a viewing angle aligned with the black hole spin, we find the most prominent difference is that the central shadow in the image is noticeably eccentric in tilted models, with the ring of emission relatively unchanged. Applying this procedure to M87 with a viewing angle based on the large-scale jet, we find that adding tilt increases the angular size of the ring for fixed black hole mass and distance, while at the same time increasing the number of bright spots in the image. Our findings illustrate observable features that can distinguish tilted from aligned flows. They also show that tilted models can be viable for M87, and that not accounting for tilt can bias inferences of physical parameters. Future modeling of horizon-scale observations should account for potential angular momentum misalignment, which is likely generic at the low accretion rates appropriate for EHT targets.

Keywords: accretion; magnetohydrodynamics; magnetohydrodynamical simulations; relativistic disks; relativistic fluid dynamics; general relativity; supermassive black holes; low-luminosity active galactic nuclei
Quijote-PNG: The Information Content of the Halo Power Spectrum and Bispectrum

We investigate how much can be learnt about four types of primordial non-Gaussianity (PNG) from small-scale measurements of the halo field. Using the QUIJOTE-PNG simulations, we quantify the information content accessible with measurements of the halo power spectrum monopole and quadrupole, the matter power spectrum, the halo-matter cross spectrum, and the halo bispectrum monopole. This analysis is the first to include small, nonlinear scales, up to ${k}_{\max }=0.5\,{\rm{h}}\,{\mathrm{Mpc}}^{-1}$ , and to explore whether these scales can break degeneracies with cosmological and nuisance parameters making use of thousands of N-body simulations. We perform all the halo measurements in redshift space with a single sample comprised of all halos with mass >3.2 × 1013 h -1 M ⊙. For local PNG, measurements of the scale-dependent bias effect from the power spectrum using sample variance cancellation provide significantly tighter constraints than measurements of the halo bispectrum. In this case measurements of the small scales add minimal additional constraining power. In contrast, the information on equilateral and orthogonal PNG is primarily accessible through the bispectrum. For these shapes, small-scale measurements increase the constraining power of the halo bispectrum by up to 4×, though the addition of scales beyond k ≈ 0.3 h Mpc-1 improves constraints largely through reducing degeneracies between PNG and the other parameters. These degeneracies are even more powerfully mitigated through combining power spectrum and bispectrum measurements. However, even with combined measurements and small-scale information, equilateral non-Gaussianity remains highly degenerate with σ 8 and our bias model.

Keywords: cosmology; non-gaussianity; observational cosmology; large-scale structure of the universe
Far-ultraviolet Variables in M31: Concentration in Spiral Arms and Association with Young Stars

The Andromeda galaxy (M31) is an object of ongoing study with the Ultraviolet Imaging Telescope (UVIT) on AstroSat. Field 2, which is 6.4 kpc in diameter at the distance of M31, includes a substantial part of the NE spiral arms of the galaxy. We have obtained a second observation of Field 2 with the far-ultraviolet (FUV) F148W (148 nm) filter, separated from the first observation by 1465 days. Both observations are analyzed to detect sources that are variable at a >3σ confidence level. For sources with less than ~2″ separation, we apply multi-Gaussian fits, to obtain reliable magnitudes in the presence of source crowding. The variable sources are found to be concentrated in the spiral arms, with fraction of variable to nonvariable sources ~2 times higher than for interarm regions, indicating an association of FUV variables with young stellar populations. UVIT FUV-NUV color-magnitude diagrams confirm the association of FUV variables with young massive/hot stars. Using existing catalogs, we obtain counterparts for 64 of the 82 most variable sources (>5σ). The counterparts include 13 star clusters, three ionized hydrogen (H II) regions, three novae, one S Doradus star, eight eclipsing binaries, 20 foreground sources, two regular variables, and 14 unspecified variables.

Keywords: andromeda galaxy; ultraviolet astronomy; ultraviolet surveys; early-type variable stars
Design and Performance of a 30/40 GHz Diplexed Focal Plane for the BICEP Array

We demonstrate a wideband diplexed focal plane suitable for observing low-frequency foregrounds that are important for cosmic microwave background polarimetry. The antenna elements are composed of slotted bowtie antennas with 60% bandwidth that can be partitioned into two bands. Each pixel is composed of two interleaved 12 × 12 pairs of linearly polarized antenna elements forming a phased array, designed to synthesize a symmetric beam with no need for focusing optics. The signal from each antenna element is captured in-phase and uniformly weighted by a microstrip summing tree. The antenna signal is diplexed into two bands through the use of two complementary, six-pole Butterworth filters. This filter architecture ensures a contiguous impedance match at all frequencies, and thereby achieves minimal reflection loss between both bands. Subsequently, out-of-band rejection is increased with a bandpass filter and the signal is then deposited on a transition-edge sensor bolometer island. We demonstrate the performance of this focal plane with two distinct bands, 30 and 40 GHz, each with a bandwidth of ∼20 and 15 GHz, respectively. The unequal bandwidths between the two bands are caused by an unintentional shift in diplexer frequency from its design values. The end-to-end optical efficiency of these detectors is relatively modest, at 20%–30%, with an efficiency loss due to an unknown impedance mismatch in the summing tree. Far-field beam maps show good optical characteristics, with edge pixels having no more than ∼5% ellipticity and ∼10%–15% peak-to-peak differences for A–B polarization pairs.

Keywords: astronomical instrumentation; cmbr detectors; polarimeters
The Most Metal-poor Stars in the Magellanic Clouds Are r-process Enhanced

The chemical abundances of a galaxy's metal-poor stellar population can be used to investigate the earliest stages of its formation and chemical evolution. The Magellanic Clouds are the most massive of the Milky Way's satellite galaxies and are thought to have evolved in isolation until their recent accretion by the Milky Way. Unlike the Milky Way's less massive satellites, little is known about the Magellanic Clouds' metal-poor stars. We have used the mid-infrared metal-poor star selection of Schlaufman & Casey and archival data to target nine LMC and four SMC giants for high-resolution Magellan/MIKE spectroscopy. These nine LMC giants with -2.4 ≲ [Fe/H] ≲ -1.5 and four SMC giants with -2.6 ≲ [Fe/H] ≲ -2.0 are the most metal-poor stars in the Magellanic Clouds yet subject to a comprehensive abundance analysis. While we find that at constant metallicity these stars are similar to Milky Way stars in their α, light, and iron-peak elemental abundances, both the LMC and SMC are enhanced relative to the Milky Way in the r-process element europium. These abundance offsets are highly significant, equivalent to 3.9σ for the LMC, 2.7σ for the SMC, and 5.0σ for the complete Magellanic Cloud sample. We propose that the r-process enhancement of the Magellanic Clouds' metal-poor stellar population is a result of the Magellanic Clouds' isolated chemical evolution and long history of accretion from the cosmic web combined with r-process nucleosynthesis on a timescale longer than the core-collapse supernova timescale but shorter than or comparable to the thermonuclear (i.e., Type Ia) supernova timescale. * This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

Keywords: galaxy accretion; galaxy chemical evolution; galaxy environments; magellanic clouds; population ii stars; stellar abundances
On the Importance of Wave-Planet Interactions for the Migration of Two Super-Earths Embedded in a Protoplanetary Disk

We investigate a repulsion mechanism between two low-mass planets migrating in a protoplanetary disk, for which the relative migration switches from convergent to divergent. This mechanism invokes density waves emitted by one planet transferring angular momentum to the coorbital region of the other and then directly to it through the horseshoe drag. We formulate simple analytical estimates, which indicate when the repulsion mechanism is effective. One condition for a planet to be repelled is that it forms a partial gap in the disk and another is that this should contain enough material to support angular momentum exchange with it. Using two-dimensional hydrodynamical simulations, we obtain divergent migration of two super-Earths embedded in a protoplanetary disk because of repulsion between them and verify these conditions. To investigate the importance of resonant interaction, we study the migration of planet pairs near first-order commensurabilities. It appears that proximity to resonance is significant but not essential. In this context we find repulsion still occurs when the gravitational interaction between the planets is removed, suggesting the importance of angular momentum transfer through waves excited by another planet. This may occur through the scattering of coorbital material (the horseshoe drag), or material orbiting close by. Our results indicate that if conditions favor the repulsion between two planets described above, we expect to observe planet pairs with their period ratios greater, often only slightly greater, than resonant values or possibly rarity of commensurability.

Keywords: planetary system formation; exoplanet dynamics; exoplanet evolution