adsabs/SciX_UAT_keywords huggingface dataset:
Magnetar Models of Superluminous Supernovae from the Dark Energy Survey: Exploring Redshift Evolution

Superluminous supernovae (SLSNe) are luminous transients that can be detected to high redshifts with upcoming optical time-domain surveys such as the Vera C. Rubin Observatory Legacy Survey of Space and Time. An interesting open question is whether the properties of SLSNe evolve through cosmic time. To address this question, in this paper we model the multicolor light curves of all 21 Type I SLSNe from the Dark Energy Survey (DES) with a magnetar spin-down engine, implemented in the Modular Open-Source Fitter for Transients (MOSFiT). With redshifts up to z ≈ 2, this sample includes some of the highest-redshift SLSNe. We find that the DES SLSNe span a similar range of ejecta and magnetar engine parameters as previous samples of mostly lower-redshift SLSNe (spin period P ≈ 0.79-13.61 ms, magnetic field B ≈ (0.03-7.33) × 1014 G, ejecta mass Mej ≈ 1.54-30.32 M⊙, and ejecta velocity vej ≈ (0.55-1.45) × 104 km s-1). The DES SLSN sample by itself exhibits the previously found negative correlation between Mej and P, with a pronounced absence of SLSNe with low ejecta mass and rapid spin. Combining our results for the DES SLSNe with 60 previous SLSNe modeled in the same way, we find no evidence for redshift evolution in any of the key physical parameters.

Keywords: supernovae
Minimal Conditions for Survival of Technological Civilizations in the Face of Stellar Evolution

The ease of interstellar rocket travel is an issue with implications for the long-term fate of our own and other civilizations and for the much-debated number of technological civilizations in the Galaxy. We show that the physical barrier to interstellar travel can be greatly reduced if voyagers are patient, and wait for the close passage of another star. For a representative time of ∼1 Gyr, characteristic of the remaining time that Earth will remain habitable, one anticipates a passage of another star within ∼1500 au. This lowers the travel time for interstellar migration by ∼two orders of magnitude compared with calculated travel times based on distances comparable to average interstellar separations (i.e., ∼1 pc) in the solar vicinity. We consider the implications for how long-lived civilizations may respond to stellar evolution, including the case of stars in wide binaries, and the difficulties of identifying systems currently undergoing a relevant close encounter. Assuming that life originates only around G-type stars, but migrates primarily to lower mass hosts when the original system becomes uninhabitable, the fraction of extant technological civilizations that exist as diaspora can be comparable to the fraction that still orbit their original host stars.

Keywords: astrobiology; stellar evolution; white dwarf stars; astrometric binary stars; visual binary stars; solar neighborhood; space vehicles
Diffuse Flux of Ultra-high-energy Photons from Cosmic-Ray Interactions in the Disk of the Galaxy and Implications for the Search for Decaying Super-heavy Dark Matter

An estimate of the expected photon flux above 1017 eV from the interactions of ultra-high-energy cosmic rays with the matter in the Galactic disk is presented. Uncertainties arising from the distribution of the gas in the disk, the absolute level of the cosmic-ray flux, and the composition of the cosmic rays are taken into account. Within these uncertainties, the integrated photon flux above 1017 eV is averaged out over Galactic latitude less than 5°, between ≃3.2 × 10-2 km-2 yr-1 sr-1 and ≃8.7 × 10-2 km-2 yr-1 sr-1. The all-sky average value amounts to ≃1.1 ×10-2 km-2 yr-1 sr-1 above 1017 eV and decreases roughly as E -2, making this diffuse flux the dominant one from cosmic-ray interactions for energy thresholds between 1017 and 1018 eV. Compared to the current sensitivities of detection techniques, a gain of between two and three orders of magnitude in exposure is required for a detection below ≃1018 eV. The implications for searches for photon fluxes from the Galactic center that would be indicative of the decay of super-heavy dark matter particles are discussed, as the photon flux presented in this study can be considered as a floor below which other signals would be overwhelmed.

Keywords: cosmic rays; ultra-high-energy cosmic radiation; particle astrophysics
A Universal Equation to Predict Ωm from Halo and Galaxy Catalogs

We discover analytic equations that can infer the value of Ωm from the positions and velocity moduli of halo and galaxy catalogs. The equations are derived by combining a tailored graph neural network (GNN) architecture with symbolic regression. We first train the GNN on dark matter halos from Gadget N-body simulations to perform field-level likelihood-free inference, and show that our model can infer Ωm with ~6% accuracy from halo catalogs of thousands of N-body simulations run with six different codes: Abacus, CUBEP3M, Gadget, Enzo, PKDGrav3, and Ramses. By applying symbolic regression to the different parts comprising the GNN, we derive equations that can predict Ωm from halo catalogs of simulations run with all of the above codes with accuracies similar to those of the GNN. We show that, by tuning a single free parameter, our equations can also infer the value of Ωm from galaxy catalogs of thousands of state-of-the-art hydrodynamic simulations of the CAMELS project, each with a different astrophysics model, run with five distinct codes that employ different subgrid physics: IllustrisTNG, SIMBA, Astrid, Magneticum, SWIFT-EAGLE. Furthermore, the equations also perform well when tested on galaxy catalogs from simulations covering a vast region in parameter space that samples variations in 5 cosmological and 23 astrophysical parameters. We speculate that the equations may reflect the existence of a fundamental physics relation between the phase-space distribution of generic tracers and Ωm, one that is not affected by galaxy formation physics down to scales as small as 10 h -1 kpc.

Keywords: cosmology; cosmological parameters; hydrodynamical simulations
Fermi-LAT Observations of V549 Vel 2017: A Subluminous Gamma-Ray Nova?

We report on the Fermi Large Area Telescope detection (with ≈5.7σ significance) as well as the multiwavelength analysis of the 2017 nova eruption V549 Vel. Unlike the recent shock-powered novae ASASSN-16ma and V906 Car, the optical and γ-ray light curves of V549 Vel show no correlation, likely implying relatively weak shocks in the eruption. Gaia detected a candidate progenitor of V549 Vel and found a parallax measurement of ϖ = 1.91 ± 0.39 mas, equivalent to a mode distance of d ≈ 560 pc (90% credible interval of 380-1050 pc). The progenitor was also observed by the 2MASS and WISE surveys. When adopting the Gaia distance, the spectral energy distribution of the progenitor is close to that of a G-type star. The Swift X-Ray Telescope detected the supersoft X-ray emission of the nova (kT = 30-40 keV) since day 236, and the inferred blackbody size is comparable to that of other novae assuming d ≈ 560 pc (i.e., Rbb ∼ 5 × 108 cm). However, there is also an unknown astrometric excess noise of ɛi = 3.2 mas found in the Gaia data, and the inferred distance becomes controversial. If the Gaia distance is accurate, the γ-ray luminosity of V549 Vel will be as low as Lγ ∼ 4 × 1033 erg s-1, making it the least luminous γ-ray nova known so far. This may imply that the shock properties responsible for the γ-ray emission in V549 Vel are different from those of the more luminous events. If the nova is located farther away, it is likely a symbiotic system with a giant companion as the observed progenitor.

Keywords: classical novae; gamma-ray transient sources; high energy astrophysics
Element Abundances in Impulsive Solar Energetic Particle Events

We outline and discuss a model for the enhanced abundances of trans-Fe elements in impulsive solar energetic particle (SEP) events, where large mass-dependent abundance enhancements are frequently seen. It comes about as a variation of the ponderomotive force model for the first ionization potential (FIP) effect, i.e., the increase in coronal abundance of elements like Fe, Mg, and Si that are ionized in the solar chromosphere relative to those that are neutral. In this way, the fractionation region is placed in the chromosphere and is connected to the solar envelope, allowing the huge abundance variations to occur, which might otherwise be problematic with a coronal fractionation site. The principal mechanism behind the mass-independent FIP fractionation becoming the mass-dependent impulsive SEP fractionation is the suppression of acoustic waves in the chromosphere. The ponderomotive force causing the fractionation must be due to torsional Alfvén waves, which couple much less effectively to slow modes than do shear waves, and upward-propagating acoustic waves deriving from photospheric convection must be effectively mode-converted to fast modes at the chromospheric layer, where Alfvén and sound speeds are equal, and subsequently totally internally reflected. We further discuss observations of the environments thought to be the source of impulsive SEPs and the extent to which the real Sun might meet these conditions.

Keywords: solar energetic particles; solar particle emission; chemical abundances; overabundances; alfven waves
Exomoons as Sources of White Dwarf Pollution

Polluted white dwarfs (WDs) offer a unique way to study the bulk compositions of exoplanetary material, but it is not always clear if this material originates from comets, asteroids, moons, or planets. We combine N-body simulations with an analytical model to assess the prevalence of extrasolar moons as WD polluters. Using a sample of observed polluted WDs, we find that the extrapolated parent body masses of the polluters are often more consistent with those of many solar system moons, rather than solar-like asteroids. We provide a framework for estimating the fraction of WDs currently undergoing observable moon accretion based on results from simulated WD planetary and moon systems. Focusing on a three-planet WD system of super-Earth to Neptune-mass bodies, we find that we could expect about one percent of such systems to be currently undergoing moon accretions as opposed to asteroid accretion.

Keywords: white dwarf stars; planetary dynamics
Creating the Radius Gap without Mass Loss

The observed exoplanet population features a gap in the radius distribution that separates the smaller super-Earths (≲1.7 Earth radii) from the larger sub-Neptunes (~1.7-4 Earth radii). While mass-loss theories can explain many of the observed features of this radius valley, it is difficult to reconcile them with the potentially rising population of terrestrials beyond orbital periods of ~30 days. We investigate the ability of gas accretion during the gas-poor phase of disk evolution to reproduce both the location of the observed radius gap and the existence of long-period terrestrial planets. Updating the analytic scaling relations of gas accretion rate accounting for the shrinking of the bound radius by hydrodynamic effects and deriving a more realistic disk temperature profile, we find that the late-stage gas accretion alone is able to carve out the observed radius gap, with slopes R gap ∝ P -0.096 and ${R}_{\mathrm{gap}}\propto {M}_{\star }^{0.15}$ for top-heavy; and R gap ∝ P -0.089 and ${R}_{\mathrm{gap}}\propto {M}_{\star }^{0.22}$ for bottom-heavy core mass distributions, in good agreement with observations. The general morphology of the primordial radius gap is stable against a range of disk gas density and disk accretion rate with the latter affecting mostly the population of large planets (≳3-4 R ⊕). The peaks and valleys in the radius distribution were likely set in place primordially while post-formation mass loss further tunes the exoplanetary population. We provide potential observational tests that may be possible with TESS, PLATO, and Roman Space Telescope.

Keywords: exoplanet astronomy; exoplanet formation; exoplanet evolution
Search for Gravitational Waves from the Coalescence of Subsolar Mass and Eccentric Compact Binaries

We present a search for gravitational waves from subsolar mass compact-binary mergers that allows for nonnegligible orbital eccentricity. Subsolar mass black holes are a signature of primordial origin black holes, which may be a component of dark matter. To produce binary coalescences, primordial black holes may form close binaries either in the early universe or more recently through dynamical interactions. A signature of dynamical formation would be the observation of noncircularized orbits. We search for black hole mergers where the primary mass is 0.1-7M⊙ and the secondary mass is 0.1-1M⊙. We allow for eccentricity up to ~0.3 at a dominant-mode gravitational-wave frequency of 10 Hz for binaries with component masses >0.5M⊙. We find no convincing candidates in the public LIGO data from 2015-2017. The two most promising candidates have a false alarm rate of 1 per 3 and 4 yr, respectively, which combined is only a ~2.4σ deviation from the expected Poisson rate. Given the marginal statistical significance, we place upper limits on the rate of subsolar mass mergers under the assumption of a null observation and compare how these limits may inform the possible dark matter contribution.

Keywords: primordial black holes; elliptical orbits; gravitational waves
CO and Atomic Line Emission from the Young Stellar Object V1331 Cygni

The infrared spectrum of the young disk star V1331 Cygni shows rare atomic emission lines from several species including C I, O I, Na I, Mg I, Al I, Si I, Ca I, Fe I, and probably S I. The presence of H I emission but the absence of N I recombination lines indicates excitation by a comparatively cool source unable to ionize nitrogen. Measurements of both the fundamental and first overtone emission of carbon monoxide indicate a hot (T ≈ 3000 K), optically thick (optical depth ≈100 in the strongest transitions of the fundamental) for the molecular gas.

Keywords: young stellar objects
Termination Shocks and the Extended X-Ray Emission in Mrk 78

Subarcsecond imaging of the X-ray emission in the type 2 active galactic nucleus (AGN) Mrk 78 with Chandra shows complex structure with spectral variations on scales from ~200 pc to ~2 kpc. Overall the X-ray emission is aligned E-W with the radio (3.6 cm) and narrow emission line region as mapped in [O III], with a marked E-W asymmetry. The eastern X-ray emission is mostly in a compact knot coincident with the location where the radio source is deflected, while the western X-ray emission forms a loop or shell ~2 kpc from the nucleus with radius ~0.7 kpc. There is suggestive evidence of shocks in both the eastern knot and the western arc. Both these positions coincide with large changes in the velocities of the [O III] outflow. We discuss possible reasons why the X-ray shocks on the western side occur ~1 kpc farther out than on the eastern side. We estimate that the thermal energy injected by the shocks into the interstellar medium corresponds to 0.05%-0.6% of the AGN bolometric luminosity.

Keywords: active galaxies; active galactic nuclei; markarian galaxies; seyfert galaxies; x-ray active galactic nuclei
G0.481-0.037, an Isolated Compact H II Region in Sgr B1

We present a near-infrared spectrum of the isolated compact H II region G0.481-0.037 taken with SpeX on the Infrared Telescope Facility. This spectrum shows strong lines of hydrogen Brγ, Brδ, Pα, and He I 2.059 μm. The radial velocity observed from the strongest line, Brγ, is V LSR = 77 ± 6 km s-1, significantly larger than the velocities of other ionized components of Sgr B1. We modeled the observed He I 2.059/Brγ ratio, 0.353 ± 0.075, with Cloudy C22.01 using model stellar atmospheres representing both dwarfs and giants. Our model ratios agree with the observed ratio for stellar effective temperatures of ~34,500 K for dwarfs and ~33,000 K for giants, from which we estimate late O spectral types for both luminosity classes. These values are consistent with the observed radio fluxes, given that the ionizing star of G0.481-0.037 is probably no longer embedded in its natal molecular cloud.

Keywords: galactic center; h ii regions; compact h ii region
Delay-weighted Calibration: Precision Calibration for 21 cm Cosmology with Resilience to Sky Model Error

One of the principal challenges of 21 cm cosmology experiments is overcoming calibration error. Established calibration approaches in the field require an exquisitely accurate sky model, and low-level sky model errors introduce calibration errors that corrupt the cosmological signal. We present a novel calibration approach called delay-weighted calibration, or DWCal, which enables precise calibration even in the presence of sky model error. Sky model error does not affect all power spectrum modes equally, and DWCal fits calibration solutions preferentially from error-free modes. We apply this technique to simulated data, showing that it substantially reduces calibration error in the presence of realistic levels of sky model error and can improve 21 cm power spectrum sensitivity by approximately 2 orders of magnitude.

Keywords: observational cosmology; reionization; radio astronomy; calibration; h i line emission; radio interferometry
Standard Cooling of Rapidly Rotating Isolated Neutron Stars in 2D

We study the long-term thermal evolution of axisymmetric rotating neutron stars in full general relativity. To this aim, we develop NSCool 2D Rot, a major upgrade to the 1D neutron stars thermal evolution code NSCool by Page. As a first application of our new code, we address the standard cooling of isolated neutron stars with rotation frequencies up to the mass shedding limit. We investigate the effects of the equation of state (EOS) by considering different combinations of core and crust EOSs. The results indicate complex time-dependent evolution of temperature distribution throughout the whole volume of the star, and in particular, in the crust. We show that most of that complexity can be attributed to the formation of a heat blob in the crust and the latitude dependence of the heat diffusion timescale through the crust.

Keywords: neutron stars; neutron star cores; x-ray point sources
WIYN Open Cluster Study. LXXXII. Radial-velocity Measurements and Spectroscopic Binary Orbits in the Open Cluster NGC 7789

We present an extensive time-series radial-velocity (RV) survey of stars in the rich open cluster NGC 7789 (1.6 Gyr, [Fe/H] = +0.02). The stellar sample lies within an 18' circular radius from the cluster center (10 pc in projection, or about 2 core radii), and includes giants, red clump stars, blue stragglers, red stragglers, sub-subgiants, and main-sequence stars down to 1 mag below the turnoff. Our survey began in 2005 and comprises more than 9000 RV measurements from the Hydra Multi-Object Spectrograph on the WIYN 3.5 m telescope. We identify 624 likely cluster members and present the orbital solutions for 81 cluster binary stars with periods between 1.45 and 4200 days. From the main-sequence binary solutions we fit a circularization period of ${7.2}_{-1.1}^{+0.6}\,$ days. We calculate an incompleteness-corrected main-sequence binary frequency of 31% ± 4% for binaries with periods less than 104 days, similar to other WIYN Open Cluster Survey (WOCS) open clusters of all ages. We detect a blue straggler binary frequency of 33% ± 17%, consistent with the similarly aged open cluster NGC 6819. We also find one secure, rapidly rotating sub-subgiant and one red straggler candidate in our sample.

Keywords: binary stars; spectroscopic binary stars; close binary stars
Anisotropic Infall and Substructure Formation in Embedded Disks

The filamentary nature of accretion streams found around embedded sources suggests that protostellar disks experience heterogenous infall from the star-forming environment, consistent with the accretion behavior onto star-forming cores in top-down star-cluster formation simulations. This may produce disk substructures in the form of rings, gaps, and spirals that continue to be identified by high-resolution imaging surveys in both embedded Class 0/I and later Class II sources. We present a parameter study of anisotropic infall, informed by the properties of accretion flows onto protostellar cores in numerical simulations, and varying the relative specific angular momentum of incoming flows as well as their flow geometry. Our results show that anisotropic infall perturbs the disk and readily launches the Rossby wave instability. It forms vortices at the inner and outer edges of the infall zone where material is deposited. These vortices drive spiral waves and angular momentum transport, with some models able to drive stresses corresponding to a viscosity parameter on the order of α ~ 10-2. The resulting azimuthal shear forms robust pressure bumps that act as barriers to radial drift of dust grains, as demonstrated by postprocessing calculations of drift-dominated dust evolution. We discuss how a self-consistent model of anisotropic infall can account for the formation of millimeter rings in the outer disk as well as producing compact dust disks, consistent with observations of embedded sources.

Keywords: hydrodynamics; hydrodynamical simulations; planetary system formation; pre-solar nebulae; protoplanetary disks
Estimates of Proton and Electron Heating Rates Extended to the Near-Sun Environment

A central problem of space plasma physics is how protons and electrons are heated in a turbulent, magnetized plasma. The differential heating of charged species due to dissipation of turbulent fluctuations plays a key role in solar wind evolution. Measurements from previous heliophysics missions have provided estimates of proton and electron heating rates beyond 0.27 au. Using Parker Solar Probe (PSP) data accumulated during the first 10 encounters, we extend the evaluation of the individual rates of heat deposition for protons and electrons to a distance of 0.063 au (13.5 R ⊙) in the newly formed solar wind. The PSP data in the near-Sun environment show different behavior of the electron heat conduction flux from what was predicted from previous fits to Helios and Ulysses data. Consequently, the empirically derived proton and electron heating rates exhibit significantly different behavior than previous reports, with the proton heating becoming increasingly dominant over electron heating at decreasing heliocentric distances. We find that the protons receive about 80% of the total plasma heating at ≈13 R ⊙, slightly higher than the near-Earth values. This empirically derived heating partition between protons and electrons will help to constrain theoretical models of solar wind heating.

Keywords: solar wind; interplanetary physics; interplanetary turbulence; solar coronal heating; magnetohydrodynamics
Molecular Oxygen in the Nearest QSO Mrk 231

We report the detection of an emission feature at the 12σ level with FWHM line width of about 450 km s-1 toward the nearest quasi-stellar object, QSO Mrk 231. Based on observations with the IRAM 30 m telescope and the Northern Extended Millimeter Array Interferometer, the 11-10 transition of molecular oxygen is the likely origin of the line with rest frequency close to 118.75 GHz. The velocity of the O2 emission in Mrk 231 coincides with the red wing seen in CO emission, suggesting that it is associated with the outflowing molecular gas, located mainly at about 10 kpc away from the central active galactic nucleus (AGN). This first detection of extragalactic molecular oxygen provides an ideal tool to study AGN-driven molecular outflows on dynamic timescales of tens of megayears. O2 may be a significant coolant for molecular gas in such regions affected by AGN-driven outflows. New astrochemical models are needed to explain the implied high molecular oxygen abundance in such regions several kiloparsecs away from the center of galaxies.

Keywords: interstellar medium; quasars