adsabs/SciX_UAT_keywords huggingface dataset:
Long-term Evolution of Relativistic Unmagnetized Collisionless Shocks

We study a relativistic collisionless electron–positron shock propagating into an unmagnetized ambient medium using 2D particle-in-cell simulations of unprecedented duration and size. The shock generates intermittent magnetic structures of increasingly larger size as the simulation progresses. Toward the end of our simulation, at around 26,000 plasma times, the magnetic coherence scale approaches λ ∼ 100 plasma skin depths, both ahead and behind the shock front. We anticipate a continued growth of λ beyond the time span of our simulation, as long as the shock accelerates particles to increasingly higher energies. The post-shock field is concentrated in localized patches, which maintain a local magnetic energy fraction ɛ B ∼ 0.1. Particles randomly sampling the downstream fields spend most of their time in low field regions (ɛ B ≪ 0.1) but emit a large fraction of the synchrotron power in the localized patches with strong fields (ɛ B ∼ 0.1). Our results have important implications for models of gamma-ray burst afterglows.

Keywords: high energy astrophysics; shocks; non-thermal radiation sources; plasma astrophysics; gamma-ray bursts
Early Initiation of Inner Solar System Formation at the Dead-zone Inner Edge

The inner solar system possesses a unique orbital structure in which there are no planets inside the Mercury orbit and the mass is concentrated around the Venus and Earth orbits. The origins of these features still remain unclear. We propose a novel concept that the building blocks of the inner solar system formed at the dead-zone inner edge in the early phase of the protosolar disk evolution, where the disk is effectively heated by the disk accretion. First, we compute the dust evolution in a gas disk with a dead zone and obtain the spatial distribution of rocky planetesimals. The disk is allowed to evolve both by a viscous diffusion and magnetically driven winds. We find that the rocky planetesimals are formed in concentrations around ~1 au with a total mass comparable to the mass of the current inner solar system in the early phase of the disk evolution within ≲0.1 Myr. Based on the planetesimal distribution and the gas-disk structure, we subsequently perform N-body simulations of protoplanets to investigate the dynamical configuration of the planetary system. We find that the protoplanets can grow into planets without significant orbital migration because of the rapid clearing of the inner disk by the magnetically driven disk winds. Our model can explain the origins of the orbital structure of the inner solar system. Several other features such as the rocky composition can also be explained by the early formation of rocky planetesimals.

Keywords: solar system formation; solar system terrestrial planets; protoplanetary disks
Detecting the Memory Effect from a Massive Black Hole Merger at the Galactic Center through Lunar Ranging

A gravitational wave pulse from a major merger of massive black holes at the Galactic center induces a permanent increase in the Earth-Moon separation. For black holes of mass ~106 M ⊙, the shift in the local gravitational potential is comparable to the Earth-Moon potential, leading to the Moon being perturbed relative to the Earth during the passage of the pulse. The permanent increase in the Earth-Moon separation is a fraction of a millimeter, measurable by lunar ranging for future merger events.

Keywords: gravitational waves
Investigating the Stability of Mass Transfer in Neutron Star-helium White Dwarf Binaries

Neutron star-helium white dwarf (NS+He WD) binaries are important evolutionary products of close-orbit binary star systems. They are often observed as millisecond pulsars and may continue evolving into ultracompact X-ray binaries (UCXBs) and continuous gravitational wave (GW) sources that will be detected by space-borne GW observatories, such as LISA, TianQin, and Taiji. Nevertheless, the stability of NS+He WD binaries undergoing mass transfer has not been well studied and is still under debate. In this paper, we model the evolution of NS+He WD binaries with WD masses ranging from 0.17-0.45 M ⊙, applying the detailed stellar evolution code MESA. Contrary to previous studies based on hydrodynamics, we find that apparently all NS+He WD binaries undergo stable mass transfer. We find for such UCXBs that the larger the WD mass, the larger the maximum mass-transfer rate and the smaller the minimum orbital period during their evolution. Finally, we demonstrate numerically and analytically that there is a tight correlation between WD mass and GW frequency for UCXBs, independent of NS mass.

Keywords: compact binary stars; x-ray binary stars; neutron stars; white dwarf stars; gravitational wave sources
Alpha Particle Temperature Anisotropy in Earth's Magnetosheath

In magnetized plasmas, temperature anisotropy manifests as distinct temperatures (T ⊥j , T ∥j ). Numerous prior studies have demonstrated that as plasma beta (β ∥j ) increases, the range of temperature anisotropy (R j = T ⊥j /T ∥j ) narrows. This limiting effect is conventionally taken as evidence that kinetic microinstabilities are active in the plasma, and has been previously observed for protons in the magnetosheath. This study is the first to use data from the Magnetic Multiscale Mission to investigate these instability-driven limits on alpha particle (ionized helium) anisotropy in Earth's magnetosheath. The distribution of data over the (β ∥j , R j ) plane was plotted and shows the characteristic narrowing in the range of R j -values as β ∥j increases. The contours of the data distribution align well with the contours of the constant growth rate for the ion cyclotron, mirror, parallel firehose, and oblique firehose instabilities, which were calculated using linear Vlasov theory.

Keywords: space plasmas; solar wind; planetary magnetospheres
Explaining the Chemical Inventory of Orion KL through Machine Learning

The interplay of the chemistry and physics that exists within astrochemically relevant sources can only be fully appreciated if we can gain a holistic understanding of their chemical inventories. Previous work by Lee et al. demonstrated the capabilities of simple regression models to reproduce the abundances of the chemical inventory of the Taurus Molecular Cloud 1 (TMC-1), as well as to provide abundance predictions for new candidate molecules. It remains to be seen, however, to what degree TMC-1 is a "unicorn" in astrochemistry, where the simplicity of its chemistry and physics readily facilitates characterization with simple machine learning models. Here we present an extension in chemical complexity to a heavily studied high-mass star-forming region: the Orion Kleinmann-Low (Orion KL) nebula. Unlike TMC-1, Orion KL is composed of several structurally distinct environments that differ chemically and kinematically, wherein the column densities of molecules between these components can have nonlinear correlations that cause the unexpected appearance or even lack of likely species in various environments. This proof-of-concept study used similar regression models sampled by Lee et al. to accurately reproduce the column densities from the XCLASS fitting program presented by Crockett et al.

Keywords: astrochemistry; star forming regions; computational methods
A Linear Divider Between the Blue Sequence and Red Sequence in Color-Magnitude Space

We compute the optimal divider between the red sequence and blue sequence in the Sloan Digital Sky Survey Legacy Survey of galaxies. Within the luminosity range -18 > M r > -24, we find a good fit with a simple linear relation, u - r = 2.326-0.1305(M r + 21).

Keywords: galaxy classification systems; galaxy colors; galaxy luminosities; red sequence galaxies
COOL-LAMPS. I. An Extraordinarily Bright Lensed Galaxy at Redshift 5.04

We report the discovery of COOL J1241+2219, a strongly lensed galaxy at redshift z = 5.043 ± 0.002 with observed magnitude zAB = 20.47, lensed by a moderate-mass galaxy cluster at z = 1.001 ± 0.001. COOL J1241+2219 is the brightest lensed galaxy currently known at optical and near-infrared wavelengths at z ≳ 5; it is ∼5 times brighter than the prior record-holder lensed galaxy, and several magnitudes brighter than the brightest unlensed galaxies known at these redshifts. It was discovered as part of COOL-LAMPS, a collaboration initiated to find strongly lensed systems in recent public optical imaging data. We characterize the lensed galaxy, as well as the central galaxy of the lensing cluster using ground-based grizJH imaging and optical spectroscopy. We report model-based magnitudes, and derive stellar masses, dust content, metallicity, and star-formation rates via stellar-population synthesis modeling. Our lens mass modeling, based on ground-based imaging, implies a median source magnification of ∼30, which puts the stellar mass and star-formation rate (in the youngest age bin, closest to the epoch of observation) at logM* = ${10.11}_{-0.26}^{+0.21}$ and SFR = ${27}_{-9}^{+13}$ M⊙ yr-1, respectively. We constrain a star-formation history for COOL J1241+2219 consistent with constant star formation across ∼1 Gyr of cosmic time, and that places this galaxy on the high-mass end of the star-forming main sequence. COOL J1241+2219 is two to four times more luminous than a galaxy with the characteristic UV luminosity at these redshifts. The UV continuum slope β = -2.2 ± 0.2 places this galaxy on the blue side of the observed distribution of galaxies at z = 5, although the lack of Lyα emission indicates dust sufficient to suppress this emission. * This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

Keywords: high-redshift galaxies; galaxies; ultraviolet astronomy; astronomical methods; star formation; gravitational lensing; strong gravitational lensing; surveys; spectral energy distribution; photometry; spectroscopy; galaxy properties
Anticipating the DART Impact: Orbit Estimation of Dimorphos Using a Simplified Model

We used the times of occultations and eclipses between the components of the 65803 Didymos binary system observed in its light curves from 2003 to 2021 to estimate the orbital parameters of Dimorphos relative to Didymos. We employed a weighted least-squares approach and a modified Keplerian orbit model in order to accommodate the effects from nongravitational forces such as binary YORP that could cause a linear change in mean motion over time. We estimate that the period of the mutual orbit at the epoch 2022 September 26.0 TDB, the day of the DART impact, is 11.921 487 ± 0.000028 hr (1σ) and that the mean motion of the orbit is changing at a rate of (5.0 ± 1.0) × 10-18 rad s-2 (1σ). The formal 3σ uncertainty in orbital phase of Dimorphos during the planned Double Asteroid Redirection Test (DART) mission is 5.°4. Observations from 2022 July to September, a few months to days prior to the DART impact, should provide modest improvements to the orbital phase uncertainty and reduce it to about 4.°2. These results, generated using a relatively simple model, are consistent with those generated using the more sophisticated model of Scheirich & Pravec, which demonstrates the reliability of our method and adds confidence to these mission-critical results.

Keywords: near-earth objects; orbit determination; asteroid satellites
Catalog of Magnetic White Dwarfs with Hydrogen Dominated Atmospheres

White dwarfs are excellent research laboratories as they reach temperatures, pressures, and magnetic fields that are unattainable on Earth. To better understand how these three physical parameters interact with each other and with other stellar features, we determined the magnetic field strength for a total of 804 hydrogen-rich white dwarfs (WDs) of which 287 are not in the literature. We fitted the spectra observed with the Sloan Digital Sky Survey using atmospheric models that consider the Zeeman effect due to the magnetic field at each point in the stellar disk. Comparing magnetic and nonmagnetic WDs, the literature already shows that the magnetic ones have on average higher mass than the nonmagnetic. In addition to that, magnetic fields are more common in cooler WDs than in hotter WDs. In consonance, we found that those with higher magnetic field strengths tend to have higher masses, and lower temperatures, for which models indicate the crystallization process has already started. This reinforces the hypothesis that the field is being generated and/or amplified in the cooling process of the white dwarf. Our sample constitutes the largest number of white dwarfs with determined magnetic fields to date.

Keywords: white dwarf stars; da stars
Asteroseismology of the Pulsating Extremely Low-mass White Dwarf SDSS J111215.82 + 111745.0: A Model with p-mode Pulsations Consistent with the Observations

SDSS J111215.82+111745.0 is the second pulsating extremely low-mass white dwarf discovered. Two short-period pulsations, 107.56 and 134.275 s, were detected on this star, which would be the first observed pressure mode (p-mode) pulsations observed on a white dwarf. While the two potential p-modes have yet to be confirmed, they make SDSS J111215.82+111745.0 an interesting object. In this work, we analyzed the whole set of seven periods observed on SDSS J111215.82+111745.0. We adopt three independent period-spacing tests to reveal a roughly 93.4 s mean period spacing of ℓ = 1 g-modes, which gives added credence to the ℓ = 1 identifications. Then we perform asteroseismic modeling for this star, in which the H chemical profile is taken as a variable. The stellar parameters M = 0.1650 ± 0.0137 M ☉ and T eff = 9750 ± 560 K are determined from the best-fit model, and the H/He chemical profiles are also defined. The two suspected p-modes are also well represented in the best-fit model, and both the stellar parameters and the pulsation frequencies are in good agreement with the values derived from spectroscopy.

Keywords: white dwarf stars; asteroseismology; stellar pulsations; pulsation modes
Resolving Decades of Periodic Spirals from the Wolf-Rayet Dust Factory WR 112

WR 112 is a dust-forming carbon-rich Wolf-Rayet (WC) binary with a dusty circumstellar nebula that exhibits a complex asymmetric morphology, which traces the orbital motion and dust formation in the colliding winds of the central binary. Unraveling the complicated circumstellar dust emission around WR 112 therefore provides an opportunity to understand the dust formation process in colliding-wind WC binaries. In this work, we present a multi-epoch analysis of the circumstellar dust around WR 112 using seven high spatial resolution (FWHM ∼ 0"3-0"4) N-band (λ ∼ 12 μm) imaging observations spanning almost 20 yr and that includes images obtained from Subaru/COMICS in 2019 October. In contrast to previous interpretations of a face-on spiral morphology, we observe clear evidence of proper motion of the circumstellar dust around WR 112 consistent with a nearly edge-on spiral with a θs = 55° half-opening angle and a ∼20 yr period. The revised near edge-on geometry of WR 112 reconciles previous observations of highly variable nonthermal radio emission that was inconsistent with a face-on geometry. We estimate a revised distance to WR 112 of $d={3.39}_{-0.84}^{+0.89}$ kpc based on the observed dust expansion rate and a spectroscopically derived WC terminal wind velocity of ${v}_{\infty }=1230\pm 260$ km s-1. With the newly derived WR 112 parameters, we fit optically thin dust spectral energy distribution models and determine a dust production rate of ${\dot{M}}_{{\rm{d}}}={2.7}_{-1.3}^{+1.0}\times {10}^{-6}$ M⊙ yr-1, which demonstrates that WR 112 is one of the most prolific dust-making WC systems known.

Keywords: circumstellar dust; wc stars; dust shells; dust nebulae; binary stars
Future Prospects on Constraining Neutrino Cosmology with the Ali CMB Polarization Telescope

We forecast the constraints on the parameters of neutrino physics with the constructions of Cosmic Microwave Background (CMB) temperature, E-mode polarization, and lensing spectra for the ground-based Ali Cosmic Microwave Background Polarization Telescope (AliCPT). To implement the forecast calculations, we perform numerical simulations which show that AliCPT would yield the result σ(N eff) = 0.56 and M ν < 1.10 eV (95% CL.) with TT, TE, EE, and CMB lensing power spectra for the first year of observation. Moreover, we investigate how the instrumental parameters, such as noise level, FWHM, and sky coverage can affect the constraints on these two parameters. Our forecasting results find that a larger aperture telescope with a larger sky survey strategy would significantly improve the current constraints for AliCPT.

Keywords: cosmic microwave background radiation; cosmological neutrinos; telescopes
On the Detection of Exomoons Transiting Isolated Planetary-mass Objects

All-sky imaging surveys have identified several dozen isolated planetary-mass objects (IPMOs) far away from any star. Here we examine the prospects for detecting transiting moons around these objects. We expect transiting moons to be common, occurring around 10%-15% of IPMOs, given that close-orbiting moons have a high geometric transit probability and are expected to be a common outcome of giant planet formation. The IPMOs offer an advantage over other directly imaged planets in that high-contrast imaging is not necessary to detect the photometric transit signal. For at least 30 (>50%) of the currently known IPMOs, observations of a single transit with the James Webb Space Telescope would have low enough forecast noise levels to allow for the detection of an Io- or Titan-like moon. The intrinsic variability of the IPMOs will be an obstacle. Using archival time-series photometry of IPMOs with the Spitzer Space Telescope as a proof of concept, we found evidence for a fading event of 2MASS J1119-1137 AB that might have been caused by intrinsic variability but is also consistent with a single transit of a habitable-zone 1.7 R⊕ exomoon. Although the interpretation of this particular event is inconclusive, the characteristics of the data and the candidate signal suggest that Earth-sized habitable-zone exomoons around IPMOs are detectable with existing instrumentation.

Keywords: natural satellites (extrasolar); free floating planets; transits; exoplanets; habitable zone
Is the Expansion of the Universe Accelerating? All Signs Still Point to Yes: A Local Dipole Anisotropy Cannot Explain Dark Energy

Type Ia supernovae (SNe Ia) provided the first strong evidence that the expansion of the universe is accelerating. With SN samples now more than ten times larger than those used for the original discovery, and joined by other cosmological probes, this discovery is on even firmer ground. Two recent, related, studies (N16 and C19) have claimed to undermine the statistical significance of the SN Ia constraints. Rubin & Hayden (RH16) showed N16 made an incorrect assumption about the distributions of SN Ia light-curve parameters, while C19 also fails to remove the impact of the motion of the solar system from the SN redshifts, interpreting the resulting errors as evidence of a dipole in the deceleration parameter. Building on RH16, we outline the errors C19 make in their treatment of the data and inference on cosmological parameters. Reproducing the C19 analysis with our proposed fixes, we find that the dipole parameters have little effect on the inferred cosmological parameters. We thus affirm the conclusion of RH16: the evidence for acceleration is secure.

Keywords: cosmological parameters; dark energy; deceleration parameter; type ia supernovae
The Habitable-zone Planet Finder Detects a Terrestrial-mass Planet Candidate Closely Orbiting Gliese 1151: The Likely Source of Coherent Low-frequency Radio Emission from an Inactive Star

The coherent low-frequency radio emission detected by LOFAR from Gliese 1151, a quiescent M4.5 dwarf star, has radio emission properties consistent with theoretical expectations of star-planet interactions for an Earth-sized planet on a 1- to 5-day orbit. New near-infrared radial velocities from the Habitable-zone Planet Finder (HPF) spectrometer on the 10 m Hobby-Eberly Telescope at McDonald Observatory, combined with previous velocities from HARPS-N, reveal a periodic Doppler signature consistent with an $m\sin i=2.5\pm 0.5{M}_{\oplus }$ exoplanet on a 2.02-day orbit. Precise photometry from the Transiting Exoplanet Survey Satellite (TESS) shows no flares or activity signature, consistent with a quiescent M dwarf. While no planetary transit is detected in the TESS data, a weak photometric modulation is detectable in the photometry at a ~2-day period. This independent detection of a candidate planet signal with the Doppler radial velocity technique adds further weight to the claim of the first detection of star-exoplanet interactions at radio wavelengths and helps validate this emerging technique for the detection of exoplanets.

Keywords: radial velocity; exoplanet detection methods; high resolution spectroscopy; m dwarf stars; exoplanet astronomy
Mapping the Galactic Disk with the LAMOST and Gaia Red Clump Sample. IV. The Kinematic Signature of the Galactic Warp

Using a sample of nearly 140,000 red clump stars selected from the LAMOST and Gaia Galactic surveys, we have mapped mean vertical velocity $\overline{{V}_{z}}$ in the X-Y plane for a large volume of the Galactic disk (6 < R < 16 kpc; -20 < φ < 50°; $| Z| \lt 1$ kpc). A clear signature where $\overline{{V}_{z}}$ increases with R is detected for the chemically thin disk. The signature for the thick disk, however, is not significant, in line with the hot nature of this disk component. For the thin disk, the warp signature shows significant variations in both the radial and azimuthal directions, in excellent agreement with the previous results of star counts. Fitting the two-dimensional distribution of $\overline{{V}_{z}}$ with a simple long-lived static warp model yields a line-of-node angle for this kinematic warp of about 12°5, again consistent with the previous results.

Keywords: milky way disk; milky way dynamics; stellar kinematics; red giant branch
An Insight into the Coupling of CME Kinematics in Inner and Outer Corona and the Imprint of Source Regions

Despite studying coronal mass ejections (CMEs) for several years, we do not yet have a complete understanding of their kinematics. To this end, it is essential to understand the change in kinematics of the CMEs as they travel from the inner corona (<3 R⊙) up to the higher heights of the outer corona. We conduct a follow-up statistical study of several 3D kinematic parameters of 59 CMEs previously studied by Majumdar et al. (2020). The source regions of these CMEs are identified and classified as active regions (ARs), active prominences (APs), or prominence eruptions (PEs). We study several statistical correlations between different kinematic parameters of the CMEs. We show that the CMEs' average kinematic parameters change as they propagate from the inner to the outer corona, indicating the importance of a region where the common practice is to perform averaging. We also find that the CME parameters in the outer corona are highly influenced by those in the inner corona, indicating the importance of the inner corona in the understanding of the kinematics. Furthermore, we find that the source regions of the CMEs tend to have a distinct imprint on the statistical correlations between different kinematic parameters, and that an overall correlation tends to wash away this crucial information. The results of this work supports the possibility of different dynamical classes for the CMEs from ARs and prominences, which gets manifested in their kinematics.

Keywords: solar coronal mass ejections