adsabs/SciX_UAT_keywords huggingface dataset:
Ocean Circulation on Enceladus with a High- versus Low-salinity Ocean

Previous studies that have considered the ocean circulation on Enceladus have generally assumed the salinity to be Earth-like. However, according to observations and geochemical constraints, the salinity of Enceladus's ocean is likely to be lower, and importantly, it is probably low enough to reverse the sign of thermal expansivity. We investigate the ocean circulation and stratification of Enceladus's ocean using a combination of theoretical arguments and simulations using the MITgcm. We find that if the salinity is high, the whole ocean is unstratified, and convection dominates the entire ocean. However, if the salinity is low enough, there exists a stratified layer in the upper ocean, whose thickness depends on the magnitude of the turbulent vertical diffusivity, which remains poorly constrained. Such a layer can suppress the vertical flux of heat and tracers, thereby affecting the heat flux to the ice shell and leading to a vertical tracer mixing timescale across the stratified layer of at least hundreds of years. This timescale is inconsistent with a previous estimate of vertical ocean mixing of several years, based on the size of detected silica nanoparticles in the plumes, leading us to conclude that either the salinity of Enceladus's ocean is higher than previously suggested or the interpretation of silica nanoparticle observations has to be reconsidered.

Keywords: planetary science
Estimating Aerodynamic Properties of Planetary Surfaces using Drone Attitude

Measuring the wind profile near a planet's surface provides a way to estimate friction velocity and the surface's aerodynamic roughness length, parameters key for understanding and predicting aeolian activity. In this study, we demonstrate the feasibility of measuring the wind profile using only the attitude of a small drone. Such an approach may be particularly advantageous in planetary exploration where instrument payload, data volume, and power are all limited. Indeed, estimates of Martian winds and the wind profile are likely already feasible with telemetry from Mars 2020 Ingenuity. Given the enormous influence of wind in energy and sediment redistribution on Mars, such measurements are critical to understanding aeolian processes and to constraining parameters used in geologic and climate models (such as dust lofting rates). Future work should explore how to expand on and improve the measurement approach discussed here and whether the already collected telemetry from Ingenuity might be used.

Keywords: planetary atmospheres
Tip of the Red Giant Branch Distances with JWST: An Absolute Calibration in NGC 4258 and First Applications to Type Ia Supernova Hosts

The tip of the red giant branch (TRGB) allows for the measurement of precise and accurate distances to nearby galaxies based on the brightest ascent of low-mass red giant branch stars before they undergo the helium flash. With the advent of JWST, there is great promise to utilize the technique to measure galaxy distances out to at least 50 Mpc, significantly further than the Hubble Space Telescope's (HST's) reach of 20 Mpc. However, with any standard candle, it is first necessary to provide an absolute reference. Here, we use Cycle 1 data to provide an absolute calibration in the F090W filter. F090W is most similar to the F814W filter commonly used for TRGB measurements with HST, which had been adopted by the community due to its minimal dependence on the underlying metallicities and ages of stars. The imaging we use was taken in the outskirts of NGC 4258, which has a direct geometrical distance measurement from the Keplerian motion of its water megamaser. Utilizing several measurement techniques, we find ${M}_{\mathrm{TRGB}}^{{\rm{F}}090{\rm{W}}}$ = ‑4.362 ± 0.033 (stat) ± 0.045 (sys) mag (Vega) for the metal-poor TRGB. We also perform measurements of the TRGB in two Type Ia supernova hosts, NGC 1559 and NGC 5584. We find good agreement between our TRGB distances and previous determinations of distances to these galaxies from Cepheids (Δ = 0.01 ± 0.06 mag), with these differences being too small to explain the Hubble tension (∼0.17 mag). In addition, we showcase the serendipitous discovery of a faint dwarf galaxy near NGC 5584.

Keywords: distance indicators; galaxy distances; hubble constant; red giant tip
Discovery of a Gamma-Ray Black Widow Pulsar by GPU-accelerated Einstein@Home

We report the discovery of 1.97 ms period gamma-ray pulsations from the 75 minute orbital-period binary pulsar now named PSR J1653-0158. The associated Fermi Large Area Telescope gamma-ray source 4FGL J1653.6-0158 has long been expected to harbor a binary millisecond pulsar. Despite the pulsar-like gamma-ray spectrum and candidate optical/X-ray associations—whose periodic brightness modulations suggested an orbit—no radio pulsations had been found in many searches. The pulsar was discovered by directly searching the gamma-ray data using the GPU-accelerated Einstein@Home distributed volunteer computing system. The multidimensional parameter space was bounded by positional and orbital constraints obtained from the optical counterpart. More sensitive analyses of archival and new radio data using knowledge of the pulsar timing solution yield very stringent upper limits on radio emission. Any radio emission is thus either exceptionally weak, or eclipsed for a large fraction of the time. The pulsar has one of the three lowest inferred surface magnetic-field strengths of any known pulsar with Bsurf ≈ 4 × 107 G. The resulting mass function, combined with models of the companion star's optical light curve and spectra, suggests a pulsar mass ≳2 M⊙. The companion is lightweight with mass ∼0.01 M⊙, and the orbital period is the shortest known for any rotation-powered binary pulsar. This discovery demonstrates the Fermi Large Area Telescope's potential to discover extreme pulsars that would otherwise remain undetected.

Keywords: gamma-ray sources; millisecond pulsars; neutron stars; binary pulsars
Closure Traces: Novel Calibration-insensitive Quantities for Radio Astronomy

Closure phases and closure amplitudes have proven critical to modern radio interferometry due to their insensitivity to the uncertain station gains. We present the first set of closure quantities constructed from parallel-hand and cross-hand visibilities that are insensitive to both station gains and to polarimetric leakage. These complex "closure traces" are a natural extension of closure amplitudes and closure phases, are independent of all station-based linear corruptions of the polarized visibilities, and are complete in the sense that they contain all remaining information present in the visibility data. Products of closure traces on so-called "conjugate" quadrangles are sensitive only to structure in the source polarization fraction—independent of variations in the Stokes I structure—and thereby provide unambiguous probes of polarization in astronomical sources.

Keywords: radio interferometers; very long baseline interferometers; polarimetry
Photometric Selection of Unobscured QSOs at the Ecliptic Poles: KMTNet in the South Field and Pan-STARRS in the North Field

We search for quasi-stellar objects (QSOs) in a wide area of the south ecliptic pole (SEP) field, which has been and will continue to be intensively explored through various space missions. For this purpose, we obtain deep broadband optical images of the SEP field covering an area of ∼14.5 × 14.5 deg2 with the Korea Microlensing Telescope Network (KMTNet). The 5σ detection limits for point sources in the BVRI bands are estimated to be ∼22.59, 22.60, 22.98, and 21.85 mag, respectively. Utilizing data from the Wide-field Infrared Survey Explorer, unobscured QSO candidates are selected among the optically pointlike sources using mid-infrared (MIR) and optical–MIR colors. To refine our selection further and eliminate any contamination not adequately removed by the color-based selection, we perform spectral energy distribution fitting with archival photometric data ranging from optical to MIR. As a result, we identify a total of 2383 unobscured QSO candidates in the SEP field. We also apply a similar method to the north ecliptic pole field using Pan-STARRS data and obtain a similar result of identifying 2427 candidates. The differential number count per area of our QSO candidates is in good agreement with those measured from spectroscopically confirmed ones in other fields. Finally, we compare the results with the literature and discuss how this work will impact future studies, especially upcoming space missions.

Keywords: quasars; photometry; catalogs; galaxies
Isolated Massive Star Formation in G28.20-0.05

We report high-resolution 1.3 mm continuum and molecular line observations of the massive protostar G28.20-0.05 with Atacama Large Millimeter/submillimeter Array. The continuum image reveals a ring-like structure with 2000 au radius, similar to morphology seen in archival 1.3 cm Very Large Array observations. Based on its spectral index and associated H30α emission, this structure mainly traces ionized gas. However, there is evidence for ~30 M ⊙ of dusty gas near the main millimeter continuum peak on one side of the ring, as well as in adjacent regions within 3000 au. A virial analysis on scales of ~2000 au from hot core line emission yields a dynamical mass of ~80 M ⊙. A strong velocity gradient in the H30α emission is evidence for a rotating, ionized disk wind, which drives a larger-scale molecular outflow. An infrared spectral energy distribution (SED) analysis indicates a current protostellar mass of m * ~ 40 M ⊙ forming from a core with initial mass M c ~ 300 M ⊙ in a clump with mass surface density of Σcl ~ 0.8 g cm-2. Thus the SED and other properties of the system can be understood in the context of core accretion models. A structure-finding analysis on the larger-scale continuum image indicates G28.20-0.05 is forming in a relatively isolated environment, with no other concentrated sources, i.e., protostellar cores, above ~1 M ⊙ found from ~0.1 to 0.4 pc around the source. This implies that a massive star can form in relative isolation, and the dearth of other protostellar companions within the ~1 pc environs is a strong constraint on massive star formation theories that predict the presence of a surrounding protocluster.

Keywords: massive stars; interstellar medium; star formation; star forming regions
Prompt Emission of γ-Ray Bursts in the High-density Environment of Active Galactic Nucleus Accretion Disks

Long and short γ-ray bursts (GRBs) are traditionally associated with galactic environments, where circumburst densities are small or moderate (few to hundreds of protons per cubic centimeter). However, both are also expected to occur in the disks of active galactic nuclei, where the ambient medium density can be much larger. In this work we study, via semianalytical methods, the propagation of the GRB outflow, its interaction with the external material, and the ensuing prompt radiation. In particular, we focus on the case in which the external shock develops early in the evolution at a radius that is smaller than the internal shock one. We find that bursts in such high-density environments are likely characterized by a single, long emission episode that is due to the superposition of individual pulses, with a characteristic hard-to-soft evolution irrespective of the light-curve luminosity. While multipulse light curves are not impossible, they would require the central engine to go dormant for a long time before reigniting. In addition, short GRB engines would produce bursts with prompt duration that would exceed the canonical 2 s separation threshold and likely be incorrectly classified as long events, even though they would not be accompanied by a simultaneous supernova. Finally, these events have a large dynamical efficiency, which would produce a bright prompt emission followed by a somewhat dim afterglow.

Keywords: gamma-ray bursts; galaxy accretion disks; special relativity
Molecular Gas and Star Formation in Nearby Starburst Galaxy Mergers

We employ the Feedback In Realistic Environments (FIRE-2) physics model to study how the properties of giant molecular clouds (GMCs) evolve during galaxy mergers. We conduct a pixel-by-pixel analysis of molecular gas properties in both the simulated control galaxies and galaxy major mergers. The simulated GMC pixels in the control galaxies follow a similar trend in a diagram of velocity dispersion (σ v ) versus gas surface density (Σmol) to the one observed in local spiral galaxies in the Physics at High Angular resolution in Nearby GalaxieS (PHANGS) survey. For GMC pixels in simulated mergers, we see a significant increase of a factor of 5-10 in both Σmol and σ v , which puts these pixels above the trend of PHANGS galaxies in the σ v versus Σmol diagram. This deviation may indicate that GMCs in the simulated mergers are much less gravitationally bound compared with simulated control galaxies with virial parameters (α vir) reaching 10-100. Furthermore, we find that the increase in α vir happens at the same time as the increase in global star formation rate, which suggests that stellar feedback is responsible for dispersing the gas. We also find that the gas depletion time is significantly lower for high-α vir GMCs during a starburst event. This is in contrast to the simple physical picture that low-α vir GMCs are easier to collapse and form stars on shorter depletion times. This might suggest that some other physical mechanisms besides self-gravity are helping the GMCs in starbursting mergers collapse and form stars.

Keywords: giant molecular clouds; galaxy mergers; molecular gas; star formation; starburst galaxies
Magnetic Discontinuities in the Inner Heliosphere: Do Intermediate Shocks Exist?

Magnetic discontinuities are fundamental structures in space and laboratory plasmas where the changes in magnetic and velocity fields are constrained by Rankine-Hugoniot relations. Due to the absence of precise measurements for particles, some issues therein are hardly investigated. The nature of discontinuities driven by the magnetohydrodynamics (MHD) turbulence, and the intermediate shock are two puzzles to be solved. The MHD turbulence generates numerous discontinuities with both small normal magnetic fields and nearly constant magnetic field magnitudes in statistics. By utilizing the data from the Parker Solar Probe, we identify among the turbulence-driven discontinuities two components that exhibit diverse statistical characteristics of the plasma density, and reveal that these discontinuities comprise 80.2% rotational and 19.8% tangential discontinuities. Then, we note a special class of discontinuities within 0.35 au that have jump conditions similar to that of the rotational discontinuity and the shock simultaneously, including (1) positively correlated jumps in the plasma density and temperature, (2) a small change in the magnetic field magnitude, and (3) opposite tangential magnetic fields on two sides. These features conform to the theoretical intermediate shock, which previous studies have found to not practically exist due to the breakdown of the evolutionary condition. By the conservation law of the mass flux across a boundary, we calculate their propagation speeds and find three intermediate shock candidates with super-Alfvénic upstream and sub-Alfvénic downstream flows. This work can improve our understanding of plasma intermittencies and suggests reassessing conclusions based on ideal MHD Rankine-Hugoniot relations.

Keywords: interplanetary shocks; interplanetary discontinuities; solar wind; magnetohydrodynamics
On the Use of Naked-eye Sunspot Observations during the Maunder Minimum

Naked-eye sunspot observations (NESOs) have been recorded for the past two millennia, approximately. These kinds of records were made around the world, mainly in Asian civilizations, and they are compiled in several catalogs. In this work, we analyze solar activity on days of the 19th century when NESOs were recorded. We found that only more than five sunspot groups were recorded in 39% of days corresponding to these NESO events. Furthermore, regarding the largest groups observed on days when NESOs were reported, we show that the uncorrected areas of these groups were below 200 millionths of solar disk (msd) in 3.2% of total cases, while it is 12.9% for areas between 200 and 499 msd. Thus, NESO records do not necessarily imply high solar activity and big sunspot groups. Therefore, these results contradict the interpretations of recent works that, using the same NESO set, suggest the solar activity level during the Maunder Minimum is still an open question. NESO records support the Maunder Minimum as a very low solar activity period.

Keywords: sunspots; solar activity; maunder minimum
Discussions on the Nature of GLEAM-X J162759.5-523504.3

The nature of the long-period radio transient GLEAM-X J162759.5-523504.3 (hereafter GLEAM-X J1627) is discussed. We try to understand both its radio emission and pulsation in the neutron star scenario as an alternative to the white dwarf model. We think that (1) from the radio emission point of view, GLEAM-X J1627 can be a radio-loud magnetar; (2) from the rotational evolution point of view, GLEAM-X J1627 is unlikely to be an isolated magnetar; (3) the 1091 s period is unlikely to be the precession period; (4) GLEAM-X J1627 may be a radio-loud magnetar spun down by a fallback disk; (5) the pulsar death line is modified due to the presence of a fallback disk or a twisted magnetic field. In both cases, a higher maximum acceleration potential can be obtained. This may explain why GLEAM-X J1627 is still radioactive with such a long pulsation period; and (6) general constraints on the neutron star magnetic field and initial disk mass are given analytically. Possible ways to discriminate between different modelings are also discussed.

Keywords: magnetars; pulsars; radio pulsars
Classifying Optical (Out)bursts in Cataclysmic Variables: The Distinct Observational Characteristics of Dwarf Novae, Micronovae, Stellar Flares, and Magnetic Gating

Cataclysmic variables can experience short optical brightenings, which are commonly attributed to phenomena such as dwarf novae outbursts, micronovae, donor flares, or magnetic gating bursts. Since these events exhibit similar observational characteristics, their identification has often been ambiguous. In particular, magnetic gating bursts and micronovae have been suggested as alternative interpretations of the same phenomena. Here we show that the timescales and energies separate the optical brightenings into separate clusters consistent with their different classifications. This suggests that micronovae and magnetic gating bursts are in fact separate phenomena. Based on our findings, we develop diagnostic diagrams that can distinguish between these bursts/flares based on their properties. We demonstrate the effectiveness of this approach on observations of a newly identified intermediate polar, CTCV J0333-4451, which we classify as a magnetic gating system. CTCV J0333-4451 is the third highest spin-to-orbital period ratio intermediate polar with magnetic gating, suggesting that these bursts are common among these rare systems.

Keywords: cataclysmic variable stars; optical bursts; dwarf novae; flare stars; time domain astronomy; dq herculis stars
Disentangling Stellar Age Estimates from Galactic Chemodynamical Evolution

Stellar ages are key for determining the formation history of the Milky Way, but are difficult to measure precisely. Furthermore, methods that use chemical abundances to infer ages may entangle the intrinsic evolution of stars with the chemodynamical evolution of the Galaxy. In this paper, we present a framework for making probabilistic predictions of stellar ages, and then quantify the contribution of both stellar evolution and Galactic chemical evolution to those predictions using SHapley Additive exPlanations. We apply this interpretable prediction framework to both a simulated Milky Way sample containing stars in a variety of evolutionary stages and an APOGEE-mocked sample of red clump stars. We find that in the former case, stellar evolution is the dominant driver for age estimates, while in the latter case, the more restricted evolutionary information causes the model to proxy ages through the chemical evolution model. We show that as a result of the use of nonintrinsic Galactic chemical information, trends estimated with the predicted ages, such as the age-metallicity relation, can deviate from the truth.

Keywords: astrostatistics; galactic archaeology; milky way disk; milky way evolution; stellar ages
Nature, Generation, and Dissipation of Alfvénic Kinks/Switchbacks Observed by Parker Solar Probe and WIND

The discovery of very prominent magnetic kinks/switchbacks in the solar wind within 0.3 au has become a scientific highlight of the Parker Solar Probe (PSP) mission. This discovery points at the promising impact of small-scale solar activity on the inner heliosphere. To address the nature, generation, and dissipation of these kinks, we perform a statistical analysis of the plasma and boundary properties of the kinks using PSP multi-encounter observations and WIND measurements at 1 au. The kinks show strong Alfvénicity and velocity fluctuations of the order of the local Alfvén speed. These findings suggest that the nature of the kinks is consistent with large-amplitude Alfvén pulses, and the steepening of these Alfvén pulses is likely the formation mechanism of these kinks. Based on the angle between the normal direction of the kinks' boundaries and the background magnetic field vector, PSP kinks and WIND kinks can be divided into two groups: quasi-parallel and quasi-perpendicular kinks. We speculate that quasi-parallel kinks form through the coupling of Alfvén and fast waves as launched from coronal interchange magnetic reconnection. In contrast, quasi-perpendicular kinks may come from the steepening of Alfvén waves launched from both coronal interchange magnetic reconnection and from the more inhomogeneous lower solar atmosphere. We find that the kink velocity perturbation gradually decreases during outward propagation and is much lower than expected from WKB theory, suggesting a progressive dissipation of the kinks. Comparing PSP kinks and WIND kinks, we conjecture that the kinks dissipate through merging with the turbulent energy cascade within 0.25 au.

Keywords: solar wind; interplanetary turbulence; interplanetary discontinuities
Investigation of Stellar Kinematics and Ionized Gas Outflows in Local (U)LIRGs

We explore the properties of stellar kinematics and ionized gas in a sample of 1106 local (U)LIRGs from the AKARI telescope. We combine data from Wide-field Infrared Survey Explorer and Sloan Digital Sky Survey Data Release 13 to fit the spectral energy distribution (SED) of each source to constrain the contribution of active galactic nuclei (AGNs) to the total IR luminosity and estimate physical parameters such as stellar mass and star formation rate (SFR). We split our sample into AGNs and weak/non-AGNs. We find that our sample is considerably above the main sequence. The highest SFRs and stellar masses are associated with ULIRGs. We also fit the Hβ and Hα regions to characterize the outflows. We find that the incidence of ionized gas outflows in AGN (U)LIRGs (~72%) is much higher than that in weak/non-AGN ones (~39%). The AGN ULIRGs have extreme outflow velocities (up to ~2300 km s-1) and high mass-outflow rates (up to ~60 M ⊙ yr-1). Our results suggest that starbursts are insufficient to produce such powerful outflows. We explore the correlations of SFR and specific SFR (sSFR) with ionized gas outflows. We find that AGN hosts with the highest SFRs exhibit a negative correlation between outflow velocity and sSFR. Therefore, in AGNs containing large amounts of gas, the negative feedback scenario might be suggested.

Keywords: active galactic nuclei