adsabs/SciX_UAT_keywords huggingface dataset:
Rogue Planets and Brown Dwarfs: Predicting the Populations Free-floating Planetary Mass Objects Observable with JWST

Free-floating (or rogue) planets are planets that are liberated (or ejected) from their host systems. Although simulations predict their existence in substantial numbers, direct observational evidence for free-floating planets with masses below ~5 M Jup is still lacking. Several cycle-1 observing programs with JWST aim to hunt for them in four different star-forming clusters. These surveys are designed to be sensitive to masses of 1-15 M Jup (assuming a hot-start formation), which corresponds to spectral types of early L to late T for the ages of these clusters. If the existing simulations are not wide off the mark, we show here that the planned programs are likely to find up to 10-20 giant rogue planets in moderate density clusters like NGC1333 or IC348, and several dozen to ~100 in high-density regions like NGC2024 and the Orion Nebula Cluster. These numbers correspond to 1%-5% of the total cluster population; they could be substantially higher if stars form multiple giant planets at birth. In contrast, the number of free-floating brown dwarfs, formed from core collapse (like stars) is expected to be significantly lower, only about 0.25% of the number of stars, or 1-7 for the clusters considered here. Below 10 M Jup that number drops further by an order of magnitude. We also show that the planned surveys are not at risk of being significantly contaminated by field brown dwarfs in the foreground or background, after spectroscopic confirmation. Taken together, our results imply that if a population of L and T dwarfs were to be found in these JWST surveys, it is expected to be predominantly made up of rogue planets.

Keywords: exoplanet formation; free floating planets; infrared observatories; brown dwarfs; initial mass function
Validation of the PDFI_SS Method for Electric Field Inversions Using a Magnetic Flux Emergence Simulation

Knowledge of electric fields in the photosphere is required to calculate the electromagnetic energy flux through the photosphere and set up boundary conditions for data-driven magnetohydrodynamic (MHD) simulations of solar eruptions. Recently, the PDFI_SS method for inversions of electric fields from a sequence of vector magnetograms and Doppler velocity measurements was improved to incorporate spherical geometry and a staggered-grid description of variables. The method was previously validated using synthetic data from anelastic MHD (ANMHD) simulations. In this paper, we further validate the PDFI_SS method, using approximately 1 hr long MHD simulation data of magnetic flux emergence from the upper convection zone into the solar atmosphere. We reconstruct photospheric electric fields and calculate the Poynting flux, and we compare those to the actual values from the simulations. We find that the accuracy of the PDFI_SS reconstruction is quite good during the emergence phase of the simulated ephemeral active region evolution and decreases during the shearing phase. Analyzing our results, we conclude that the more complex nature of the evolution (compared to the previously studied ANMHD case) that includes the shearing evolution phase is responsible for the obtained accuracy decrease.

Keywords: solar magnetic flux emergence; solar active region velocity fields; solar active region magnetic fields; solar active regions; solar photosphere; solar atmosphere
Fermi Large Area Telescope Detection of Gamma Rays from the NGC 6251 Radio Lobe

We report the detection of extended γ-ray emission from lobes in the radio galaxy NGC 6251 using observation data from the Fermi Large Area Telescope. The maximum likelihood analysis results show that a radio morphology template provides a better fit than a pointlike source description for the observational data at a confidence level of 8.1σ, and the contribution of lobes constitutes more than 50% of the total γ-ray flux. Furthermore, the γ-ray energy spectra show a significant disparity in shape between the core and lobe regions, with a curved log-parabola shape observed in the core region and a power-law form observed in the lobes. Neither the core region nor the northwest (NW) lobe displays significant flux variations in the long-term γ-ray light curves. The broadband spectral energy distributions of the core region and the NW lobe can be explained with a single-zone leptonic model. The γ-rays of the core region are due to the synchrotron-self-Compton process, while the γ-rays from the NW lobe are interpreted as inverse Compton emission of the cosmic microwave background.

Keywords: active galaxies; galaxy jets; gamma-rays; non-thermal radiation sources
Distances to Local Group Galaxies via Population II, Stellar Distance Indicators. II. The Fornax Dwarf Spheroidal

We determine three independent Population II distance moduli to the Fornax dwarf spheroidal (dSph) galaxy, using wide-field, ground-based VI imaging acquired with the Magellan-Baade telescope at Las Campanas Observatory. After subtracting foreground stars using Gaia EDR3 proper motions, we measure an I-band tip of the red giant branch (TRGB) magnitude of ${I}_{0}^{\mathrm{TRGB}}=16.753\pm {0.03}_{\mathrm{stat}}\pm {0.037}_{\mathrm{sys}}$ mag, with a calibration based in the LMC giving a distance modulus of ${\mu }_{0}^{\mathrm{TRGB}}=20.80\pm {0.037}_{\mathrm{stat}}\pm {0.057}_{\mathrm{sys}}$ mag. We determine an RR Lyrae (RRL) distance from template mean magnitudes, with periods adopted from the literature. Adopting a Gaia DR2 calibration of first overtone RRL period-luminosity and period-Wesenheit relations, we find ${\mu }_{0}^{\mathrm{PLZ}}=20.74\pm {0.01}_{\mathrm{stat}}\pm {0.12}_{\mathrm{sys}}$ mag and ${\mu }_{0}^{\mathrm{PWZ}}=20.68\pm {0.02}_{\mathrm{stat}}\pm {0.07}_{\mathrm{sys}}$ mag. Finally, we determine a distance from Fornax's horizontal branch (HB) and two galactic globular cluster calibrators, giving ${\mu }_{0}^{\mathrm{HB}}=20.83\pm {0.03}_{\mathrm{stat}}\pm {0.09}_{\mathrm{sys}}$ mag. These distances are each derived from homogeneous IMACS photometry, are anchored to independent geometric zero-points, and utilize different classes of stars. We therefore average over independent uncertainties and report the combined distance modulus <μ 0> =20.770 ± 0.042stat ± 0.024sys mag (corresponding to a distance of 143 ± 3 kpc). * Based in part on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555. These observations are associated with program No. 13691. Additional observations are credited to the Observatories of the Carnegie Institution of Science for the use of Magellan-Baade IMACS.

Keywords: fornax dwarf spheroidal galaxy; population ii stars; distance measure; rr lyrae variable stars; red giant tip; horizontal branch; local group
Mapping the Galactic Disk with the LAMOST and Gaia Red Clump Sample. V. On the Origin of the "Young" [α/Fe]-enhanced Stars

Using a sample of nearly 140,000 primary red-clump stars selected from the LAMOST and Gaia surveys, we have identified a large sample of "young" [α/Fe]-enhanced stars with stellar ages younger than 6.0 Gyr and [α/Fe] ratios greater than 0.15 dex. The stellar ages and [α/Fe] ratios are measured from LAMOST spectra, using a machine-learning method trained with common stars in the LAMOST-APOGEE fields (for [α/Fe]) and in the LAMOST-Kepler fields (for stellar age). The existence of these "young" [α/Fe]-enhanced stars is not expected from the classical Galactic chemical evolution models. To explore their possible origins, we have analyzed the spatial distribution, and the chemical and kinematic properties of those stars and compared the results with those of the chemically thin and thick disk populations. We find that those "young" [α/Fe]-enhanced stars have distributions in number density, metallicity, [C/N] abundance ratio, velocity dispersion, and orbital eccentricity that are essentially the same as those of the chemically thick disk population. Our results clearly show those so-called "young" [α/Fe]-enhanced stars are not really young but genuinely old. Although other alternative explanations can not be fully ruled out, our results suggest that the most possible origin of these old stars is the result of stellar mergers or mass transfer.

Keywords: galaxy chemical evolution; galaxy structure; stellar abundances; galaxy stellar disks; stellar kinematics
Unsupervised Learning for Thermophysical Analysis on the Lunar Surface

We investigate the use of unsupervised machine learning to understand and extract valuable information from thermal measurements of the lunar surface. We train a variational autoencoder (VAE) to reconstruct observed variations in lunar surface temperature from over 9 yr of Diviner Lunar Radiometer Experiment data and in doing so learn a fully data-driven thermophysical model of the lunar surface. The VAE defines a probabilistic latent model that assumes the observed surface temperature variations can be described by a small set of independent latent variables and uses a deep convolutional neural network to infer these latent variables and to reconstruct surface temperature variations from them. We find it is able to disentangle five different thermophysical processes from the data, including (1) the solar thermal onset delay caused by slope aspect, (2) effective albedo, (3) surface thermal conductivity, (4) topography and cumulative illumination, and (5) extreme thermal anomalies. Compared to traditional physics-based modeling and inversion, our method is extremely efficient, requiring orders of magnitude less computational power to invert for underlying model parameters. Furthermore our method is physics-agnostic and could therefore be applied to other space exploration data sets, immediately after the data is collected and without needing to wait for physical models to be developed. We compare our approach to traditional physics-based thermophysical inversion and generate new, VAE-derived global thermal anomaly maps. Our method demonstrates the potential of artificial intelligence-driven techniques to complement existing physical models as well as for accelerating lunar and space exploration in general.

Keywords: the moon; lunar composition; convolutional neural networks
Common Envelope Wind Tunnel: Range of Applicability and Self-similarity in Realistic Stellar Envelopes

Common envelope evolution, the key orbital tightening phase of the traditional formation channel for close binaries, is a multistage process that presents many challenges to the establishment of a fully descriptive, predictive theoretical framework. In an approach complementary to global 3D hydrodynamical modeling, we explore the range of applicability for a simplified drag formalism that incorporates the results of local hydrodynamic "wind tunnel" simulations into a semi-analytical framework in the treatment of the common envelope dynamical inspiral phase using a library of realistic giant branch stellar models across the low, intermediate, and high-mass regimes. In terms of a small number of key dimensionless parameters, we characterize a wide range of common envelope events, revealing the broad range of applicability of the drag formalism as well its self-similar nature across mass regimes and ages. Limitations arising from global binary properties and local structural quantities are discussed together with the opportunity for a general prescriptive application for this formalism.

Keywords: binary stars; common envelope binary stars; close binary stars; common envelope evolution; stellar evolution; late stellar evolution; stellar interiors
Applying the Tremaine-Weinberg Method to Nearby Galaxies: Stellar-mass-based Pattern Speeds and Comparisons with ISM Kinematics

We apply the Tremaine-Weinberg method to 19 nearby galaxies using stellar mass surface densities and velocities derived from the PHANGS-MUSE survey, to calculate (primarily bar) pattern speeds (ΩP). After quality checks, we find that around half (10) of these stellar-mass-based measurements are reliable. For those galaxies, we find good agreement between our results and previously published pattern speeds, and we use rotation curves to calculate major resonance locations (corotation radii and Lindblad resonances). We also compare these stellar-mass-derived pattern speeds with Hα (from MUSE) and CO(J = 2 - 1) emission from the PHANGS-ALMA survey. We find that in the case of these clumpy interstellar medium (ISM) tracers, this method erroneously gives a signal that is simply the angular frequency at a representative radius set by the distribution of these clumps (Ωclump), and that this Ωclump is significantly different from ΩP (∼20% in the case of Hα, and ∼50% in the case of CO). Thus, we conclude that it is inadvisable to use "pattern speeds" derived from ISM kinematics. Finally, we compare our derived pattern speeds and corotation radii, along with bar properties, to the global parameters of these galaxies. Consistent with previous studies, we find that galaxies with a later Hubble type have a larger ratio of corotation radius to bar length, more molecular-gas-rich galaxies have higher ΩP, and more bulge-dominated galaxies have lower ΩP. Unlike earlier works, however, there are no clear trends between the bar strength and ΩP, nor between the total stellar mass surface density and the pattern speed.

Keywords: galaxies; galaxy dynamics; galaxy structure
Turbulent Viscosity Acting on the Equilibrium Tidal Flow in Convective Stars

Convection is thought to act as a turbulent viscosity in damping tidal flows and in driving spin and orbital evolution in close convective binary systems. This turbulent viscosity should be reduced, compared to mixing-length predictions, when the forcing (tidal) frequency $| {\omega }_{t}| $ exceeds the turnover frequency ωcv of the dominant convective eddies. However, two contradictory scaling laws have been proposed and this issue remains highly disputed. To revisit this controversy, we conduct the first direct numerical simulations of convection interacting with the equilibrium tidal flow in an idealized global model of a low-mass star. We present direct computations of the turbulent effective viscosity, νE, acting on the equilibrium tidal flow. We unexpectedly report the coexistence of the two disputed scaling laws, which reconciles previous theoretical (and numerical) findings. We recover the universal quadratic scaling ${\nu }_{E}\propto {(| {\omega }_{t}| /{\omega }_{{cv}})}^{-2}$ in the high-frequency regime $| {\omega }_{t}| /{\omega }_{{cv}}\gg 1$ . Our results also support the linear scaling ${\nu }_{E}\propto {(| {\omega }_{t}| /{\omega }_{{cv}})}^{-1}$ in an intermediate regime with $1\leqslant | {\omega }_{t}| /{\omega }_{{cv}}\lesssim { \mathcal O }(10)$ . Both regimes may be relevant to explain the observed properties of close binaries, including spin synchronization of solar-type stars and the circularization of low-mass stars. The robustness of these two regimes of tidal dissipation, and the transition between them, should be explored further in more realistic models. A better understanding of the interaction between convection and tidal flows is indeed essential to correctly interpret observations of close binary stars and short-period planetary orbits.

Keywords: close binary stars; stellar convective zones; hydrodynamics; astrophysical fluid dynamics; planet hosting stars; stellar convection envelopes
Solar Atmospheric Heating Due to Small-scale Events in an Emerging Flux Region

We investigate the thermal, kinematic, and magnetic structure of small-scale heating events in an emerging flux region (EFR). We use high-resolution multiline observations (including Ca II 8542 Å, Ca II K, and the Fe I 6301 Å line pair) of an EFR located close to the disk center from the CRISP and CHROMIS instruments at the Swedish 1 m Solar Telescope. We perform non-LTE inversions of multiple spectral lines to infer the temperature, velocity, and magnetic field structure of the heating events. Additionally, we use the data-driven Coronal Global Evolutionary Model to simulate the evolution of the 3D magnetic field configuration above the events and understand their dynamics. Furthermore, we analyze the differential emission measure to gain insights into the heating of the coronal plasma in the EFR. Our analysis reveals the presence of numerous small-scale heating events in the EFR, primarily located at polarity inversion lines of bipolar structures. These events not only heat the lower atmosphere but also significantly heat the corona. The data-driven simulations, along with the observed enhancement of currents and Poynting flux, suggest that magnetic reconnection in the lower atmosphere is likely responsible for the observed heating at these sites.

Keywords: magnetic fields; solar chromospheric heating; spectropolarimetry; solar atmosphere
Discovery of Faint Double-peak Hα Emission in the Halo of Low Redshift Galaxies

Aimed at the detection of cosmological gas being accreted onto galaxies in the local universe, we examined the Hα emission in the halo of 164 galaxies in the field of view of the Multi-Unit Spectroscopic Explorer Wide survey (MUSE-Wide) with observable Hα (redshift <0.42). An exhaustive screening of the corresponding Hα images led us to select 118 reliable Hα emitting gas clouds. The signals are faint, with a surface brightness of ${10}^{-17.3\pm 0.3}\,\mathrm{erg}\,{{\rm{s}}}^{-1}\,{\mathrm{cm}}^{-2}\,{\mathrm{arcsec}}^{-2}$ . Through statistical tests and other arguments, we ruled out that they are created by instrumental artifacts, telluric line residuals, or high-redshift interlopers. Around 38% of the time, the Hα line profile shows a double peak with the drop in intensity at the rest frame of the central galaxy, and with a typical peak-to-peak separation of the order of ±200 km s-1. Most line emission clumps are spatially unresolved. The mass of emitting gas is estimated to be between 1 and 10-3 times the stellar mass of the central galaxy. The signals are not isotropically distributed; their azimuth tends to be aligned with the major axis of the corresponding galaxy. The distances to the central galaxies are not random either. The counts drop at a distance >50 galaxy radii, which roughly corresponds to the virial radius of the central galaxy. We explore several physical scenarios to explain this Hα emission, among which accretion disks around rogue intermediate-mass black holes fit the observations best.

Keywords: extragalactic astronomy; circumgalactic medium; galaxy accretion; galaxy winds; galaxy fountains; galaxy formation; cool intergalactic medium; astrophysical black holes; intermediate-mass black holes
Rocky Histories: The Effect of High Excitations on the Formation of Rocky Planets

Rocky planets both in and outside of our solar system are observed to have a range of core-mass fractions (CMFs). Imperfect collisions can preferentially strip mantle material from a planet, changing its CMF, and are therefore thought to be the most likely cause of this observed CMF variation. However, previous work that implements these collisions into N-body simulations of planet formation has struggled to reliably form high CMF super-Earths. In this work, we specify our initial conditions and simulation parameters to maximize the prevalence of high-energy, CMF-changing collisions in order to form planets with highly diverse CMFs. High-energy collisions have a large v imp/v esc ratio, so we maximize this ratio by starting simulations with high eccentricity and inclination disks to increase the difference in their orbital velocities, maximizing v imp. Additionally, we minimize v esc by starting with small embryos. The final planets undergo more high-energy, debris-producing collisions, and experience significant CMF change over their formation. However, we find that a number of processes work together to average out the CMF of a planet over time; therefore, we do not consistently form high CMF, high-mass planets. We do form high CMF planets below 0.5 M ⊕. Additionally, we find, in these highly eccentric environments, loss of debris mass due to collisional grinding has a significant effect on final planet masses and CMFs, resulting in smaller planets and a higher average planet CMF. This work highlights the importance of improving measurements of high-density planets to better constrain their CMFs.

Keywords: super earths; extrasolar rocky planets; exoplanet formation
The Large Superfast Rotators Discovered by the Zwicky Transient Facility

Two high-cadence surveys aiming for rotation period measurements of asteroids have been conducted in 2019 January and October using the Zwicky Transient Facility. From the surveys, 25 large superfast rotators (SFRs) were discovered and they are all main-belt asteroids (MBAs), except for one Mars crosser. These large SFRs have a diameter ranging from 0.43 to 7.87 km and a rotation period between 0.48 and 1.95 hr. Considering their diameters and fast rotations, they cannot be explained by rubble-pile structure unless using extraordinary high bulk densities. Cohesion, if available, can conserve these large SFRs. The estimated cohesion for these large SFRs could be up to thousands of pascals, much higher than the currently estimated cohesion for asteroids and that generated by the regolith of Moon and Mars. Such high-level cohesion can be produced from fine-grain regolith, like clay. However, the availability of such fine-grain regolith for asteroids is still unknown. Although the possibility of these large SFRs being large monolithic objects cannot be ruled out, this scenario is very unlikely given that the timescale of disruptive impact for MBAs in a similar diameter range is 107-108 yr.

Keywords: asteroids; asteroid rotation; light curves; time series analysis; time domain astronomy
Life in Elliptical Galaxies: Hot Spheroids, Fast Stars, Deadly Comets?

Elliptical galaxies have dynamically hot (σ1D ~100-300 km s-1) populations of stars, and presumably, smaller objects like comets. Because interstellar minor bodies are moving much faster, they hit planets harder and more often than in the local Galaxy. I estimate the rates for Chicxulub-scale impacts on an Earth-size planet in elliptical galaxies as a potential habitability constraint on intelligent life. Around most stars in a normal elliptical galaxy, these planets receive only ~0.01-0.1 Gyr-1, although hazardous rates may be common in certain compact early-type galaxies and red nuggets. About ~5% of the stellar mass is in a region where the rate is > 10 Gyr-1, large enough to dominate the mass extinction rate. This suggests that elliptical galaxies have an exclusion zone of order one hundred parsecs in radius around their centers for the evolution of intelligent life.

Keywords: habitable planets; elliptical galaxies; astrobiology; search for extraterrestrial intelligence