adsabs/SciX_UAT_keywords huggingface dataset:
Latitude Variation of Flux and Impact Angle of Asteroid Collisions with Earth and the Moon

Flux and impact angles were calculated for asteroid collisions with Earth and the Moon, using the latest population models for the distribution of near-Earth objects (NEOs) and precession models to determine the impact probabilities. The calculations predict that the flux of impacts to the poles for Earth is 22% greater than the flux at the equator, and 55% greater for the Moon. Impacts near the equator typically have shallower impact angles with a mode near 30° above the horizontal. Conversely, impacts near the poles are typically steep with a mode close to 65°. Our new analysis updates the previously published results by Le Feuvre & Wieczorek incorporating: (1) an updated debiased distribution of NEOs, and (2) updated collision probabilities that account for Lidov-Kozai precession. The new impact distributions provide an important update to risk models, showing a 7% increase in average population risks from sub-300 m impactors, compared to previous atmospheric entry distributions, mostly due to faster impact velocities.

Keywords: near-earth objects; impact phenomena; meteor radiants; lunar craters; lunar impacts
The Hα Dots Survey. IV. A Fourth List of Faint Emission-line Objects

We present the fourth catalog of serendipitously discovered compact extragalactic emission-line sources—Hα Dots. A total of 454 newly discovered objects are included in the current survey list. These objects have been detected in searches of moderately deep narrowband images acquired for the ALFALFA Hα project. The catalog of Hα Dots presented in the current paper was derived from searches carried out using ALFALFA Hα images obtained with the KPNO 2.1 m telescope. This results in a substantially deeper sample of Dots compared to our previous lists, which were all discovered in images taken with the WIYN 0.9 m telescope. The median R-band magnitude of the current catalog is 21.59, more than 1.6 mag fainter than the median for the 0.9 m sample (a factor of 4.4× fainter). Likewise, the median emission-line flux of the detected sources is a factor of 4.3× fainter. The line flux completeness limit of the current sample is ~3 × 10-16 erg s-1 cm-2. We present accurate coordinates, apparent magnitudes, and narrowband line fluxes for each object in the sample. Unlike our previous lists of Hα Dots, the current sample does not include follow-up spectroscopy.

Keywords: emission line galaxies; seyfert galaxies; blue compact dwarf galaxies; dwarf galaxies; quasars; starburst galaxies; star formation
Recovering the Maya Constellations in the Highlands of Guatemala

For many generations, the Maya people of the highlands of Guatemala have been engaged in continual knowledge creation emerging from a deep and sustained relationship with the Earth and the sky. Maya elders and youth who are Calendar Keepers, or Ajq'ijab' in the K'iche' Mayan language, curate calendars with roots in pre-colonial times. The pressures of colonial invasion, civil war, and globalization have eroded the oral tradition and ancestral memory in the community, causing the loss of invaluable cultural information. Today, certain sectors of Maya youth are engaged in cultural revitalization and the recovery of ancestral astronomical knowledge. Our elders are extremely important for strengthening the oral tradition and the historical, scientific, and cultural understandings of the night sky. I describe a project of recovery of the Maya constellations, ancestral observation sites, and measurement techniques in the Guatemala highlands.

Keywords: a stars
Scaling of Magnetic Reconnection Electron Bulk Heating in the High-Alfvén-speed and Low-β Regime of Earth's Magnetotail

We have surveyed 21 reconnection exhaust events observed by Magnetospheric MultiScale in the low-plasma-β and high-Alfvén-speed regime of the Earth's magnetotail to investigate the scaling of electron bulk heating produced by reconnection. The ranges of inflow Alfvén speed and inflow electron β e covered by this study are 800-4000 km s-1 and 0.001-0.1, respectively, and the observed heating ranges from a few hundred electronvolts to several kiloelectronvolts. We find that the temperature change in the reconnection exhaust relative to the inflow, ΔT e, is correlated with the inflow Alfvén speed, V Ax,in, based on the reconnecting magnetic field and the inflow plasma density. Furthermore, ΔT e is linearly proportional to the inflowing magnetic energy per particle, ${{m}_{{\rm{i}}}{V}_{\mathrm{Ax},\mathrm{in}}}^{2}$ , and the best fit to the data produces the empirical relation ΔT e = 0.020 ${{m}_{{\rm{i}}}{V}_{\mathrm{Ax},\mathrm{in}}}^{2}$ , i.e., the electron temperature increase is on average ~2% of the inflowing magnetic energy per particle. This magnetotail study extends a previous magnetopause reconnection study by two orders of magnitude in both magnetic energy and electron β, to a regime that is comparable to the solar corona. The validity of the empirical relation over such a large combined magnetopause-magnetotail plasma parameter range of V A ~ 10-4000 km s-1 and β e ~ 0.001-10 suggests that one can predict the magnitude of the bulk electron heating by reconnection in a variety of contexts from the simple knowledge of a single parameter: the Alfvén speed of the ambient plasma.

Keywords: planetary magnetospheres; plasma physics; space plasmas; geomagnetic fields; magnetic fields
An Insight-HXMT Dedicated 33 day Observation of SGR J1935+2154. II. Burst Spectral Catalog

Since 2020 April 28, Insight-HXMT has implemented a dedicated observation on the magnetar SGR J1935+2154. Thanks to the wide energy band (1-250 keV) and high sensitivity of Insight-HXMT, we obtained 75 bursts from SGR J1935+2154 during a month-long activity episode after the emission of FRB 200428. Here we report the detailed time-integrated spectral analysis of these bursts and the statistical distribution of the spectral parameters. We find that for ~15% (11/75) of SGR J1935+2154 bursts, the CPL model is preferred, and most of them occurred in the later part of this active epoch. In the cumulative fluence distribution, we find that the fluence of bursts in our sample is about an order of magnitude weaker than that of Fermi/GBM, but it follows the same power-law distribution. Finally, we find a burst with similar peak energy to the time-integrated spectrum of the X-ray burst associated with FRB 200428 (FRB 200428-Associated Burst), but the low energy index is harder.

Keywords: magnetars
Laboratory Simulation of the Positron-Dust Interaction and its Implication for Interstellar Dark Clouds

We report the first laboratory experiment dealing with the interaction of a cosmic dust simulant with positrons emitted from a 22Na radioisotope. Measurements of a charge of micrometer SiO2 dust grains with an accuracy of one elementary charge e revealed +1 e steps due to positron annihilation inside the grain. The observed average rate of these charging events agrees well with prediction of a model based on the continuous slowing down approximation of energetic of positrons inside the grain. Less frequent charge steps larger than +1 e were attributed to emission of secondary electrons during positron slowing down. The determined coefficient of secondary electron emission is approximately inversely proportional to the grain radius. The experimental results led us to the formulation of a possible scenario of interstellar dark clouds charging.

Keywords: interstellar dust; laboratory astrophysics; nuclear physics; interdisciplinary astronomy
The COS CGM Compendium. IV. Effects of Varying Ionization Backgrounds on Metallicity Determinations in the z < 1 Circumgalactic Medium

Metallicity estimates of circumgalactic gas based on absorption-line measurements typically require photoionization modeling to account for unseen ionization states. We explore the impact of uncertainties in the extreme-ultraviolet background (EUVB) radiation on such metallicity determinations for the z < 1 circumgalactic medium. In particular, we study how uncertainties in the power-law slope of the EUV radiation, α EUVB, from active galactic nuclei affect metallicity estimates in a sample of 34 absorbers with H I column densities between $15.25\lt \mathrm{log}({N}_{{\rm{H}}\,{\rm\small{I}}}/{\mathrm{cm}}^{-2})\lt 17.25$ and measured metal ion column densities. We demonstrate the sensitivity of metallicity estimates to changes in the EUV power-law slope of active galactic nuclei, α EUVB, at low redshift (z < 1), showing that derived absorber metallicities increase on average by ≈0.3 dex as the EUV slope is hardened from α EUVB = -2.0 to -1.4. We use Markov Chain Monte Carlo sampling of photoionization models with α EUVB as a free parameter to derive metallicities for these absorbers. The current sample of absorbers does not provide a robust constraint on the slope α EUVB itself; we discuss how future analyses may provide stronger constraints. Marginalizing over the uncertainty in the slope of the background, we find that the average uncertainties in the metallicity determinations increase from 0.08 to 0.14 dex when switching from a fixed EUVB slope to one that freely varies. Thus, we demonstrate that EUVB uncertainties can be included in ionization models while still allowing for robust metallicity inferences.

Keywords: circumgalactic medium; intergalactic medium; lyman limit systems; quasar absorption line spectroscopy
Is It Possible to Know Cosmological Fine-tuning?

Fine-tuning studies whether some physical parameters, or relevant ratios between them, are located within so-called life-permitting intervals of small probability outside of which carbon-based life would not be possible. Recent developments have found estimates of these probabilities that circumvent previous concerns of measurability and selection bias. However, the question remains whether fine-tuning can indeed be known. Using a mathematization of the concepts of learning and knowledge acquisition, we argue that most examples that have been touted as fine-tuned cannot be formally assessed as such. Nevertheless, fine-tuning can be known when the physical parameter is seen as a random variable and it is supported in the nonnegative real line, provided the size of the life-permitting interval is small in relation to the observed value of the parameter.

Keywords: anthropic principle; bayesian statistics; analytical mathematics; cosmological constant; cosmological parameters
Turbulent Regimes in Collisions of 3D Alfvén-wave Packets

Using three-dimensional gyrofluid simulations, we revisit the problem of Alfvén-wave (AW) collisions as building blocks of the Alfvénic turbulent cascade and their interplay with magnetic reconnection at magnetohydrodynamic (MHD) scales. Depending on the large-scale value of the nonlinearity parameter χ 0 (the ratio between the AW linear propagation time and nonlinear turnover time), different regimes are observed. For strong nonlinearities (χ 0 ~ 1), turbulence is consistent with a dynamically aligned, critically balanced cascade-fluctuations exhibit a scale-dependent alignment $\sin {\theta }_{{k}_{\perp }}\propto {k}_{\perp }^{-1/4}$ , resulting in a ${k}_{\perp }^{-3/2}$ spectrum and ${k}_{\parallel }\propto {k}_{\perp }^{1/2}$ spectral anisotropy. At weaker nonlinearities (small χ 0), a spectral break marking the transition between a large-scale weak regime and a small-scale ${k}_{\perp }^{-11/5}$ tearing-mediated range emerges, implying that dynamic alignment occurs also for weak nonlinearities. At χ 0 < 1 the alignment angle ${\theta }_{{k}_{\perp }}$ shows a stronger scale dependence than in the χ 0 ~ 1 regime, namely $\sin {\theta }_{{k}_{\perp }}\propto {k}_{\perp }^{-1/2}$ at χ 0 ~ 0.5, and $\sin {\theta }_{{k}_{\perp }}\propto {k}_{\perp }^{-1}$ at χ 0 ~ 0.1. Dynamic alignment in the weak regime also modifies the large-scale spectrum, scaling approximately as ${k}_{\perp }^{-3/2}$ for χ 0 ~ 0.5 and as ${k}_{\perp }^{-1}$ for χ 0 ~ 0.1. A phenomenological theory of dynamically aligned turbulence at weak nonlinearities that can explain these spectra and the transition to the tearing-mediated regime is provided; at small χ 0, the strong scale dependence of the alignment angle combines with the increased lifetime of turbulent eddies to allow tearing to onset and mediate the cascade at scales that can be larger than those predicted for a critically balanced cascade by several orders of magnitude. Such a transition to tearing-mediated turbulence may even supplant the usual weak-to-strong transition.

Keywords: plasma astrophysics; space plasmas; interplanetary turbulence; alfven waves; magnetohydrodynamical simulations; magnetohydrodynamics; ccd photometry
Ultra-steep-spectrum Radio "Jellyfish" Uncovered in A2877

We report on the discovery of a mysterious ultra-steep-spectrum (USS) synchrotron source in the galaxy cluster A2877. We have observed the source with the Murchison Widefield Array at five frequencies across 72-231 MHz and found the source to exhibit strong spectral curvature over this range, as well as the steepest known spectra of a synchrotron cluster source, with a spectral index across the central three frequency bands of $\alpha =-{5.97}_{-0.48}^{+0.40}$ <!-- --> . Higher-frequency radio observations, including a deep observation with the Australia Telescope Compact Array, fail to detect any of the extended diffuse emission. The source is approximately 370 kpc wide and bears an uncanny resemblance to a jellyfish with two peaks of emission and long tentacles descending south toward the cluster center. While the "USS Jellyfish" defies easy classification, we here propose that the phenomenon is caused by the reacceleration and compression of multiple aged electron populations from historic active galactic nucleus (AGN) activity, a so-called "radio phoenix," by an as yet undetected weak cluster-scale mechanism. The USS Jellyfish adds to a growing number of radio phoenix in cool-core clusters with unknown reacceleration mechanisms; as the first example of a polyphoenix, however, this implies that the mechanism is on the scale of the cluster itself. Indeed, we show that in simulations, emission akin to the USS Jellyfish can be produced as a short-lived transient phase in the evolution of multiple interacting AGN remnants when subject to weak external shocks.

Keywords: galaxy clusters; spectral index; radio astronomy; plasma physics; intracluster medium
Using Stereoscopic Observations of Cometary Plasma Tails to Infer Solar Wind Speed

Detection of the solar wind speed near the Sun is significant in understanding the heating and acceleration of the solar wind. Cometary plasma tails have long been used as natural probes for solar wind speed; previous solar wind speed estimates via plasma tails, however, were based on comet images from a single viewpoint, and the projection effect may influence the result. Using stereoscopic observations from the Solar Terrestrial Relations Observatory and the Solar and Heliospheric Observatory, we three-dimensionally reconstruct the plasma tails of three comets C/2012 S1 (ISON), C/2010 E6, and C/2011 W3 (Lovejoy) and infer the ambient solar wind speed. The first comet is located between 3.5 and 6 solar radii (Rs) away from the Sun at high latitudes; the estimated solar wind speed is about 300-500 km s-1. The second comet is located within 10 Rs and about 20° away from the ecliptic; the estimated solar wind speed is about 200-320 km s-1. The third comet is also located at low latitudes but farther (>20 Rs) away from the Sun; the estimated solar wind speed is about 100-600 km s-1. For comets near the ecliptic, our results are close to those predicted by MHD models, whereas for the comet at high latitudes, the deviation between our estimate and the model results is notable. This consistency and difference could be used to constrain and improve solar wind models. We will seek opportunities to apply the method to comet 322P, whose tail may sweep the Parker Solar Probe.

Keywords: solar wind; comet tails
The Young Supernova Experiment: Survey Goals, Overview, and Operations

Time-domain science has undergone a revolution over the past decade, with tens of thousands of new supernovae (SNe) discovered each year. However, several observational domains, including SNe within days or hours of explosion and faint, red transients, are just beginning to be explored. Here we present the Young Supernova Experiment (YSE), a novel optical time-domain survey on the Pan-STARRS telescopes. Our survey is designed to obtain well-sampled griz light curves for thousands of transient events up to z ≈ 0.2. This large sample of transients with four-band light curves will lay the foundation for the Vera C. Rubin Observatory and the Nancy Grace Roman Space Telescope, providing a critical training set in similar filters and a well-calibrated low-redshift anchor of cosmologically useful SNe Ia to benefit dark energy science. As the name suggests, YSE complements and extends other ongoing time-domain surveys by discovering fast-rising SNe within a few hours to days of explosion. YSE is the only current four-band time-domain survey and is able to discover transients as faint as ∼21.5 mag in gri and ∼20.5 mag in z, depths that allow us to probe the earliest epochs of stellar explosions. YSE is currently observing approximately 750 deg2 of sky every 3 days, and we plan to increase the area to 1500 deg2 in the near future. When operating at full capacity, survey simulations show that YSE will find ∼5000 new SNe per year and at least two SNe within 3 days of explosion per month. To date, YSE has discovered or observed 8.3% of the transient candidates reported to the International Astronomical Union in 2020. We present an overview of YSE, including science goals, survey characteristics, and a summary of our transient discoveries to date.

Keywords: supernovae; cosmology; sky surveys; transient detection
An Unambiguous Separation of Gamma-Ray Bursts into Two Classes from Prompt Emission Alone

The duration of a gamma-ray burst (GRB) is a key indicator of its physical origin, with long bursts perhaps associated with the collapse of massive stars and short bursts with mergers of neutron stars. However, there is substantial overlap in the properties of both short and long GRBs and neither duration nor any other parameter so far considered completely separates the two groups. Here we unambiguously classify every GRB using a machine-learning dimensionality reduction algorithm, t-distributed stochastic neighborhood embedding, providing a catalog separating all Swift GRBs into two groups. Although the classification takes place only using prompt emission light curves, every burst with an associated supernova is found in the longer group and bursts with kilonovae in the short, suggesting along with the duration distributions that these two groups are truly long and short GRBs. Two bursts with a clear absence of a supernova belong to the longer class, indicating that these might have been direct-collapse black holes, a proposed phenomenon that may occur in the deaths of more massive stars.

Keywords: gamma-ray bursts; astronomy data analysis; astronomy data visualization; light curve classification; supernovae; high energy astrophysics
MINDS: The JWST MIRI Mid-INfrared Disk Survey

The study of protoplanetary disks has become increasingly important with the Kepler satellite finding that exoplanets are ubiquitous around stars in our galaxy and the discovery of enormous diversity in planetary system architectures and planet properties. High-resolution near-IR and ALMA images show strong evidence for ongoing planet formation in young disks. The JWST MIRI mid-INfrared Disk Survey (MINDS) aims to (1) investigate the chemical inventory in the terrestrial planet-forming zone across stellar spectral type, (2) follow the gas evolution into the disk dispersal stage, and (3) study the structure of protoplanetary and debris disks in the thermal mid-IR. The MINDS survey will thus build a bridge between the chemical inventory of disks and the properties of exoplanets. The survey comprises 52 targets (Herbig Ae stars, T Tauri stars, very low-mass stars and young debris disks). We primarily obtain MIRI/MRS spectra with high signal-to-noise ratio (∼100–500) covering the complete wavelength range from 4.9 to 27.9 μm. For a handful of selected targets we also obtain NIRSpec IFU high resolution spectroscopy (2.87–5.27 μm). We will search for signposts of planet formation in thermal emission of micron-sized dust—information complementary to near-IR scattered light emission from small dust grains and emission from large dust in the submillimeter wavelength domain. We will also study the spatial structure of disks in three key systems that have shown signposts for planet formation, TW Hya and HD 169142 using the MIRI coronagraph at 15.5 μm and 10.65 μm respectively and PDS 70 using NIRCam imaging in the 1.87 μm narrow and the 4.8 μm medium band filter. We provide here an overview of the MINDS survey and showcase the power of the new JWST mid-IR molecular spectroscopy with the TW Hya disk spectrum where we report the detection of the molecular ion ${{\mathrm{CH}}_{3}}^{+}$ and the robust confirmation of HCO+ earlier detected with Spitzer.

Keywords: pre-main sequence stars; protoplanetary disks; t tauri stars; low mass stars; herbig ae/be stars
The Abundance of Phosphorus in the HgMn Star 14 Sge

The abundances of several elements in the atmosphere of the HgMn star 14 Sge (HR 7664) are derived from the analysis of high-resolution spectra obtained recently with the spectropolarimeter NeoNarval. A large phosphorus overabundance, about 60 times the solar abundance, is found. This study is the beginning of a systematic survey of all northern HgMn stars aiming at deriving their abundances in a consistent manner.

Keywords: chemically peculiar stars
The Van Hoof Effect over the Blazhko Cycle

We provide the first detection of the Van Hoof effect over a complete Blazhko cycle in the variations of H β, neutral, and ionized metallic lines, measurable on 2782 high-resolution line profiles obtained during the course of a 41 day continuous and unprecedented survey of RR ab star, RR Lyr. We detect phase-lag variations in the velocity-velocity diagrams during the Blazhko period. The Van Hoof effect is maximum at the Blazhko modulation maximum and minimum at the Blazhko modulation minimum. Both turbulent velocities and equivalent widths are correlated with the Van Hoof and Blazhko effects. We investigate the differential motion between the upper and lower photosphere and between the photosphere and high atmosphere in the RR Lyr star. The differential radial velocity and differential acceleration curves show bulges and dents, respectively, during the inward moving atmosphere, but at the pulsation amplitude maximum, the differential acceleration curve is double peaked with a high differential radial-velocity gradient. Correlations between differential radial velocity, separating distance, and differential acceleration are monotonous during the Blazhko cycle, but the double-peak structure, left peak and right peak, is strongly Blazhko antiphased and phased, respectively. We explain the physical mechanisms driving the modulation of these quantities by the ShPM1, ShPM, ShPM2, and ShPM3 receding shocks, and the ShH+He outwarding main shock. The 3D interplay between the Van Hoof, Blazhko, and hypersonic-hydrodynamical effects provides a powerful tool for stellar pulsation and evolution challenges.

Keywords: radial velocity; ground-based astronomy; high resolution spectroscopy; stellar evolution; astronomy data analysis; stellar pulsations; stellar convection envelopes; shocks; hydrodynamics; blazhko effect; rr lyrae variable stars; pulsating variable stars