adsabs/SciX_UAT_keywords huggingface dataset:
DustPy: A Python Package for Dust Evolution in Protoplanetary Disks

Many processes during the evolution of protoplanetary disks and during planet formation are highly sensitive to the sizes of dust particles that are present in the disk: the efficiency of dust accretion in the disk and volatile transport on dust particles, gravoturbulent instabilities leading to the formation of planetesimals, or the accretion of pebbles onto large planetary embryos to form giant planets are typical examples of processes that depend on the sizes of the dust particles involved. Furthermore, radiative properties like absorption or scattering opacities depend on the particle sizes. To interpret observations of dust in protoplanetary disks, a proper estimate of the dust particle sizes is needed. We present DustPy: a Python package to simulate dust evolution in protoplanetary disks. DustPy solves gas and dust transport including viscous advection and diffusion as well as collisional growth of dust particles. DustPy is written with a modular concept, such that every aspect of the model can be easily modified or extended to allow for a multitude of research opportunities.

Keywords: protoplanetary disks; astronomy software; astronomical simulations; circumstellar dust; planet formation; planetesimals
Would SN1993J Have Been Detected by Next-generation Cerenkov Instruments?

Already in the first days after the explosion of a supernova, the strong shock expanding forward into the dense wind of the progenitor star can theoretically accelerate particles up to the ∼PeV (=1015 eV) range. These accelerated particles, interacting with the dense wind material, should lead to the production of gamma-rays in the 1-100 TeV range, through pion production. However, no supernova has yet been detected by current Cerenkov instruments, and the question of the detectability of extragalactic supernovae in nearby galaxies (within a few Mpc) by next generation instruments is still open. The detection in the TeV range is especially hindered by the two-photon annihilation process, in which high-energy gamma-rays interact with soft photons from the photosphere to produce electron/positron pairs, thereby degrading the gamma-ray signal from the system. We calculate the temporal evolution of the expected gamma-ray attenuation in the well-studied type IIb SN 1993J, accounting for both temporal and geometrical effects.

Keywords: gamma-ray astronomy; type ii supernovae
Gaia 18dvy: A New FUor in the Cygnus OB3 Association

We present optical-infrared photometric and spectroscopic observations of Gaia 18dvy, located in the Cygnus OB3 association at a distance of 1.88 kpc. Gaia 18dvy was noted by the Gaia alerts system when its light curve exhibited a ≳4 mag rise in 2018-2019. The brightening was also observable at mid-infared wavelengths. The infrared colors of Gaia 18dvy became bluer as the outburst progressed. Its optical and near-infrared spectroscopic characteristics in the outburst phase are consistent with those of bona fide FU Orionis-type young eruptive stars. The progenitor of the outburst is probably a low-mass K-type star with an optical extinction of ∼3 mag. A radiative transfer modeling of the circumstellar structure, based on the quiescent spectral energy distribution, indicates a disk with a mass of 4 × 10-3 M⊙. Our simple accretion disk modeling implies that the accretion rate had been exponentially increasing for more than 3 yr until mid-2019, when it reached a peak value of 6.9 × 10-6 M⊙ yr-1. In many respects, Gaia 18dvy is similar to the FU Ori-type object HBC 722.

Keywords: star formation; accretion; protoplanetary disks; eruptive variable stars
Revealing the Structure and Internal Rotation of the Sagittarius Dwarf Spheroidal Galaxy with Gaia and Machine Learning

We present a detailed study of the internal structure and kinematics of the core of the Sagittarius dwarf spheroidal galaxy (Sgr). Using machine-learning techniques, we have combined the information provided by 3300 RR Lyrae stars, more than 2000 spectroscopically observed stars, and the Gaia second data release to derive the full phase space, i.e., 3D positions and kinematics, of more than 1.2 × 105 member stars in the core of the galaxy. Our results show that Sgr has a bar structure ∼2.5 kpc long, and that tidal tails emerge from its tips to form what it is known as the Sgr stream. The main body of the galaxy, strongly sheared by tidal forces, is a triaxial (almost prolate) ellipsoid with its longest principal axis of inertia inclined 43° ± 6° with respect to the plane of the sky and axis ratios of 1:0.67:0.60. Its external regions are expanding mainly along its longest principal axis, yet the galaxy conserves an inner core of about 500×330×300 pc that shows no net expansion and is rotating at vrot = 4.13 ± 0.16 km s-1. The internal angular momentum of the galaxy forms an angle θ = 18° ± 6° with respect to its orbital angular momentum, meaning that Sgr is in an inclined prograde orbit around the Milky Way. We compared our results with predictions from N-body models with spherical, pressure-supported progenitors and a model whose progenitor is a flattened rotating disk. Only the rotating model, based on preexisting simulations aimed at reproducing the line-of-sight velocity gradients observed in Sgr, was able to reproduce the observed properties in the core of the galaxy.

Keywords: galaxy interactions; galaxy dynamics; galaxy evolution; sagittarius dwarf spheroidal galaxy
Is π Men c’s Atmosphere Hydrogen-dominated? Insights from a Non-detection of H I Lyα Absorption

Constraining the composition of super-Earth-to-sub-Neptune-sized planets is a priority in order to understand the processes of planetary formation and evolution. π Men c represents a unique target for the atmospheric and compositional characterization of such planets because it is strongly irradiated and its bulk density is consistent with abundant H2O. We searched for hydrogen from photodissociating H2/H2O in π Men c's upper atmosphere through H I Lyα transmission spectroscopy with the Hubble Space Telescope’s Space Telescope Imaging Spectrograph, but did not detect it. We set 1σ (3σ) upper limits for the effective planet-to-star size ratio R Lyα /R ⋆ = 0.13 (0.24) and 0.12 (0.20) at velocities [-215, -91] km s-1 and [+57, +180] km s-1, respectively. We reconstructed the stellar spectrum, and estimate that π Men c receives about 1350 erg cm-2 s-1 of 5-912 Å energy, enough to cause rapid atmospheric escape. An interesting scenario to explain the non-detection is that π Men c's atmosphere is dominated by H2O or other heavy molecules rather than H2/He. According to our models, abundant oxygen results in less extended atmospheres, which transition from neutral to ionized hydrogen closer to the planet. We compare our non-detection to other detection attempts, and tentatively identify two behaviors: planets with densities ≲2 g cm-3 (and likely hydrogen-dominated atmospheres) result in H I Lyα absorption, whereas planets with densities ≳3 g cm-3 (and plausibly non-hydrogen-dominated atmospheres) do not result in measurable absorption. Investigating a sample of strongly irradiated sub-Neptunes may provide some statistical confirmation if it is shown that they do not generally develop extended atmospheres.

Keywords: exoplanet atmospheres; aeronomy; ultraviolet astronomy; exoplanet atmospheric composition
X-Ray Emission Evolution of the Galactic Ultraluminous X-Ray Pulsar Swift J0243.6+6124 during the 2017-2018 Outburst Observed by the MAXI GSC

This paper reports on the X-ray emission evolution of the ultraluminous Galactic X-ray pulsar Swift J0243.6+6124 during the giant outburst from 2017 October to 2018 January as observed by the MAXI GSC all-sky survey. The 2-30 keV light curve and the energy spectra confirm the source luminosity LX assuming an isotropic emission reached 2.5 × 1039 erg s-1, 10 times higher than the Eddington limit for a 1.4 M⊙ neutron star. When the source was luminous with LX ≳ 0. 9 × 1038 erg s-1, it generally exhibited a negative correlation on a hardness-intensity diagram. However, two hardness ratios, a soft color (=4-10 keV/2-4 keV) and a hard color (=10-20 keV/4-10 keV), showed somewhat different behavior across a characteristic luminosity of Lc ≃ 5 × 1038 erg s-1. The soft color changed more than the hard color when LX < Lc, whereas the opposite was observed above Lc. The spectral change above Lc was represented by a broad enhanced feature at ∼6 keV on top of the canonical cutoff power-law continuum. The pulse profiles, derived daily, made the transition from a single-peak to a double-peak as the source brightened across Lc. These spectral and pulse-shape properties can be interpreted by a scenario in which the accretion columns on the neutron-star surface, producing the Comptonized X-ray emission, gradually became taller as LX increases. The broad 6 keV enhancement could be a result of cyclotron-resonance absorption at ∼10 keV, corresponding to a surface magnetic field Bs ≃ 1.1 × 1012 G. The spin-frequency derivatives calculated with the Fermi GBM data showed a smooth positive correlation with LX up to the outburst peak, and its linear coefficient is comparable to those of typical Be binary pulsars whose Bs are (1-8) × 1012 G. These results suggest that the Bs of Swift J0243.6+6124 is a few times 1012 G.

Keywords: neutron stars; binary pulsars; accretion; high mass x-ray binary stars
CMR Exploration. II. Filament Identification with Machine Learning

We adopt magnetohydrodynamic simulations that model the formation of filamentary molecular clouds via the collision-induced magnetic reconnection (CMR) mechanism under varying physical conditions. We conduct radiative transfer using RADMC-3D to generate synthetic dust emission of CMR filaments. We use the previously developed machine-learning technique CASI-2D along with the diffusion model to identify the location of CMR filaments in dust emission. Both models show a high level of accuracy in identifying CMR filaments in the test data set, with detection rates of over 80% and 70%, respectively, at a false detection rate of 5%. We then apply the models to real Herschel dust observations of different molecular clouds, successfully identifying several high-confidence CMR filament candidates. Notably, the models are able to detect high-confidence CMR filament candidates in Orion A from dust emission, which have previously been identified using molecular line emission.

Keywords: interstellar medium; interstellar filaments; convolutional neural networks; molecular clouds; interstellar magnetic fields; magnetohydrodynamics
Anisotropic Ionizing Illumination from an M-type Pre-main-sequence Star, DM Tau

The powerful, high-energy magnetic activities of young stars play important roles in the magnetohydrodynamics in the innermost parts of the protoplanetary disks. In addition, the associated UV and X-ray emission dictates the photochemistry; moreover, the corona activities can affect the atmosphere of a newborn extrasolar planet. How the UV and X-ray photons are generated and how they illuminate the disks are not well understood. Here we report the analyses of the optical and infrared (OIR) photometric monitoring observations and the high angular resolution centimeter-band images of the low-mass (M1-type) pre-main-sequence star DM Tau. We found that the OIR photometric light curves present periodic variations, which suggests that the host young star is rotating in the same direction as the natal disk and is hosting at least one giant cold spot. In addition, we resolved that the ionized gas in the DM Tau disk is localized and its spatial distribution is varying with time. All the present observations can be coherently interpreted, if the giant cold spot is the dominant anisotropic UV and/or X-ray source that illuminates the ambient cone-like region. These results indicate that a detailed theoretical model of the high-energy protostellar emission is essential in understanding the space weather around extrasolar planets and the origin of life.

Keywords: starspots; protoplanetary disks; star-planet interactions; stellar accretion disks; t tauri stars; observational astronomy
The 450 Day X-Ray Monitoring of the Changing-look AGN 1ES 1927+654

1ES 1927+654 is a nearby active galactic nucleus (AGN) that underwent a changing-look event in early 2018, developing prominent broad Balmer lines that were absent in previous observations. We have followed up this object in the X-rays with an ongoing campaign that started in 2018 May and that includes 265 NICER (for a total of 678 ks) and 14 Swift/XRT (26 ks) observations, as well as three simultaneous XMM-Newton/NuSTAR (158/169 ks) exposures. In the X-rays, 1ES 1927+654 shows a behavior unlike any previously known AGN. The source is extremely variable both in spectral shape and flux and does not show any correlation between X-ray and UV flux on timescales of hours or weeks/months. After the outburst, the power-law component almost completely disappeared, and the source showed an extremely soft continuum dominated by a blackbody component. The temperature of the blackbody increases with the luminosity, going from kT ~ 80 eV (for a 0.3-2 keV luminosity of L0.3-2 ~ 1041.5 erg s-1) to ~200 eV (for L0.3-2 ~ 1044 erg s-1). The spectra show evidence of ionized outflows and of a prominent feature at ~1 keV, which can be reproduced by a broad emission line. The unique characteristics of 1ES 1927+654 in the X-ray band suggest that it belongs to a new type of changing-look AGN. Future X-ray surveys might detect several more objects with similar properties.

Keywords: astrophysical black holes; x-ray quasars; active galactic nuclei; supermassive black holes
Formation of Inner Planets in the Presence of a Cold Jupiter: Orbital Evolution and Relative Velocities of Planetesimals

We investigate the orbital evolution of planetesimals in the inner disk in the presence of nebula gas and a (proto-) cold Jupiter. By varying the mass, eccentricity, and semimajor axis of the planet, we study the dependence of the relative velocities of the planetesimals on these parameters. For classic small planetesimals (1016-1020 g) whose mutual gravitational interaction is negligible, gas drag introduces a size-dependent alignment of orbits and keeps the relative velocity low for similar-sized bodies, while preventing orbital alignment for different-sized planetesimals. Regardless of the location and the mass ratio of the planetesimals, increasing the mass and eccentricity or decreasing the orbital distance of the planet always lead to higher relative velocities of the planetesimals. However, for massive planetesimals, the interplay of viscous stirring, gas damping, and secular perturbation results in the lower velocity dispersion of equal-sized planetesimals when the planet is more massive or when it is located on a closer or more eccentric orbit. The random velocities of such planetesimals remain almost unperturbed when the planet is located beyond Jupiter's current orbit or when it is less massive or less eccentric than Jupiter. Unlike small planetesimals, such large planetesimals can grow in a runaway fashion, as in the unperturbed case. Our results imply that the presence of a cold Jupiter does not impede the formation of inner rocky planets through planetesimal accretion, provided that the planetesimals are initially large.

Keywords: planetesimals; planet formation; orbital evolution; planetary dynamics
About One-point Statistics of the Ratio of Two Fourier-transformed Cosmic Fields and an Application

The Fourier transformation is an effective and efficient operation of Gaussianization at the one-point level. Using a set of N-body simulation data, we verified that the one-point distribution functions of the dark matter momentum divergence and density fields closely follow complex Gaussian distributions. The one-point distribution function of the quotient of two complex Gaussian variables is introduced and studied. Statistical theories are then applied to model one-point statistics about the growth of individual Fourier modes of the dark matter density field, which can be obtained by the ratio of two Fourier-transformed cosmic fields. Our simulation results proved that the models based on the Gaussian approximation are impressively accurate, and our analysis revealed many interesting aspects of the growth of dark matter's density fluctuation in Fourier space.

Keywords: large-scale structure of the universe; dark matter distribution; n-body simulations; astrostatistics distributions
Linking Circumstellar Disk Lifetimes to the Rotational Evolution of Low-mass Stars

The high-energy radiation emitted by young stars can have a strong influence on their rotational evolution at later stages. This is because internal photoevaporation is one of the major drivers of the dispersal of circumstellar disks, which surround all newly born low-mass stars during the first few million years of their evolution. Employing an internal EUV/X-ray photoevaporation model, we have derived a simple recipe for calculating realistic inner disk lifetimes of protoplanetary disks. This prescription was implemented into a magnetic-morphology-driven rotational evolution model and is used to investigate the impact of disk locking on the spin evolution of low-mass stars. We find that the length of the disk locking phase has a profound impact on the subsequent rotational evolution of a young star, and the implementation of realistic disk lifetimes leads to an improved agreement of model outcomes with observed rotation period distributions for open clusters of various ages. However, for both young star-forming regions tested in our model, the strong bimodality in rotation periods that is observed in h Per could not be recovered. h Per is only successfully recovered if the model is started from a double-peaked distribution with an initial disk fraction of 65%. However, at an age of only ~1 Myr, such a low disk fraction can only be achieved if an additional disk dispersal process, such as external photoevaporation, is invoked. These results therefore highlight the importance of including realistic disk dispersal mechanisms in rotational evolution models of young stars.

Keywords: stellar evolutionary models; stellar rotation; circumstellar disks; protoplanetary disks
The Control of Lava Rheology on the Formation of Lunar Sinuous Rilles by Substrate Thermal Erosion: Topographic and Morphometric Relationships with Eruption Rates, Erosion Rates, Event Durations, and Erupted Magma Volumes

We describe a model of the fluid mechanics and thermodynamics of turbulent lava flows capable of thermally eroding sinuous rille channels on bodies without atmospheres. The model assumes Bingham plastic rheology for the lava and shows how the effects of radiant cooling and consequent crystallization change the rheology and control the point at which turbulence ceases. A correlation is found between magma volume eruption rate and the length and width of the eroded rille channel. Thus, simple measurements of rille length and width in images can provide reliable estimates of magma eruption rates. The model also predicts rille floor erosion rates, so that if rille depths are measured, eruption durations and erupted magma volumes can also be found. The model is applied in detail to six well-preserved lunar rilles and more generally to a published catalog of 214 lunar rilles. We find that rille-forming eruptions have magma volume eruption rates of a few times 104 m3 s-1, durations of up to 3 months, and erupted magma volumes up to ~200 km3, consistent with theoretical predictions of basaltic magma ascent and eruption from deep mantle sources. The key requirement for rille formation, rather than mare lava flow deposit formation, is the turbulent eruption of a sufficiently large volume of low-viscosity magma at a sufficiently low eruption rate.

Keywords: planetary surfaces
Quasiperiodic Velocity Fluctuations in Eruptive Prominences Observed by AIA/SDO

The current study presents an investigation of the behavior of prominences during eruptions. Variations in the distribution of their velocities are detected at altitudes <0.6 R⊙. Detailed analyses are carried out for 304 Å Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) observations. To track the behavior of prominences during eruptions, 41 events in the period 2010-2017 are studied. To follow the rise of a filament on higher altitudes (up to 32 R⊙), Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph (SOHO/LASCO) data are also inspected. They are used to obtain kinematic profiles of eruptions. Obtained height-time and speed-time plots of the eruptions show velocity fluctuations in 83% of the explored cases, detected only in the SDO/AIA field of view, and not in any of the prominences observed at higher altitudes by SOHO/LASCO. Time intervals between fluctuations and heights at which they are detected are estimated. Strong periodicity cannot be determined.

Keywords: solar prominences; solar filament eruptions
Near-IR Spectral Observations of the Didymos System: Daily Evolution Before and After the DART Impact Indicates that Dimorphos Originated from Didymos

Ejecta from Dimorphos following the DART mission impact significantly increased the brightness of the Didymos-Dimorphos system, allowing us to examine subsurface material. We report daily near-IR spectroscopic observations of the Didymos system using NASA's IRTF that follow the evolution of the spectral signature of the ejecta cloud over 1 week, from 1 day before the impact. Overall, the spectral features remained fixed (S-type classification) while the ejecta dissipated, confirming that both Didymos and Dimorphos are constructed from the same silicate material. This novel result strongly supports binary asteroid formation models that include the breaking up of a single body due to rotational breakup of kilometer-wide bodies. At impact time +14 and +38 hr, the spectral slope decreased, but the following nights presented an increasing spectral slope that almost returned to the preimpact slope. However, the parameters of the 1 μm band remained fixed, and no "fresh"/Q-type-like spectrum was measured. We interpret this as follows. (1) The ejecta cloud is the main contributor (60%-70%) to the overall light during the ~40 hr after impact. (2) Coarser debris (≥100 μm) dominated the ejecta cloud, decreasing the spectral slope (after radiation pressure removed the fine grains ≤10 hr after impact). (3) After approximately 1 week, the ejecta cloud dispersed enough to make the fine grains on Didymos's surface the dominant part of the light, increasing the spectral slope to the preimpact level. (4) A negligible amount of nonweathered material was ejected from Dimorphos's subsurface, suggesting that Dimorphos was accumulated from weathered material ejected from Didymos's surface.

Keywords: near-earth objects; asteroid satellites; infrared spectroscopy; asteroid surfaces; asteroids