adsabs/SciX_UAT_keywords huggingface dataset:
First Detection of Polarization in X-Rays for PSR B0540-69 and Its Nebula

We report on X-ray polarization measurements of the extragalactic Crab-like PSR B0540-69 and its Pulsar Wind Nebula (PWN) in the Large Magellanic Cloud, using a ∼850 ks Imaging X-ray Polarimetry Explorer (IXPE) exposure. The PWN is unresolved by IXPE. No statistically significant polarization is detected for the image-averaged data, giving a 99% confidence polarization upper limit (MDP99) of 5.3% in the 2–8 keV energy range. However, a phase-resolved analysis detects polarization for both the nebula and pulsar in the 4–6 keV energy range. For the PWN defined as the off-pulse phases, the polarization degree (PD) of (24.5 ± 5.3)% and polarization angle (PA) of (78.1 ± 6.2)° is detected at 4.6σ significance level, consistent with the PA observed in the optical band. In a single on-pulse window, a hint of polarization is measured at 3.8σ with PD of (50.0 ± 13.1)% and PA of (6.2 ± 7.4)°. A "simultaneous" PSR/PWN analysis finds two bins at the edges of the pulse exceeding 3σ PD significance, with PD of (68 ± 20)% and (62 ± 20)%; intervening bins at 2–3σ significance have lower PD, hinting at additional polarization structure.

Keywords: pulsars; pulsar wind nebulae; polarimetry
X-Ray and Ultraviolet Observations of the Eclipsing Binary V471 Tauri with XMM-Newton: X-Ray-Cycles, Eclipse Timings and Further Evidence of a Substellar Tertiary Companion

Few stars offer as much toward understanding fundamental aspects of stellar astrophysics and binary star evolution than the eclipsing binary V471 Tauri (DAZ+K2V; P = 12.52 hr). V471 Tauri (Tau) is the product of common-envelope binary evolution and a pre-cataclysmic variable. X-ray and UV (291 nm) observations were secured with XMM-Newton over ~ 62 ks during 2019 September. X-ray and UV photometry show variations over the binary's orbit as well as flares. A precise eclipse timing was obtained from the UV photometry with the Optical Monitor. The timing was added to prior measures and fit with a 35.6 yr Light-Travel-Time-Effect (LTTE) Keplerian orbit of a substellar, tentative brown dwarf companion. However, this companion was not detected by VLT/SPHERE. The LTTE third-body solution appears reliable, now covering ~50 yr of timings. The non-detection of the companion may be due to changes in its physical properties during the high-mass loss common envelope stage.

Keywords: x-ray bursts; eclipsing binary stars; stellar activity
Merger or Not: Accounting for Human Biases in Identifying Galactic Merger Signatures

Significant galaxy mergers throughout cosmic time play a fundamental role in theories of galaxy evolution. The widespread usage of human classifiers to visually assess whether galaxies are in merging systems remains a fundamental component of many morphology studies. Studies that employ human classifiers usually construct a control sample, and rely on the assumption that the bias introduced by using humans will be evenly applied to all samples. In this work, we test this assumption and develop methods to correct for it. Using the standard binomial statistical methods employed in many morphology studies, we find that the merger fraction, error, and the significance of the difference between two samples are dependent on the intrinsic merger fraction of any given sample. We propose a method of quantifying merger biases of individual human classifiers and incorporate these biases into a full probabilistic model to determine the merger fraction and the probability of an individual galaxy being in a merger. Using 14 simulated human responses and accuracies, we are able to correctly label a galaxy as merger or isolated to within 1% of the truth. Using 14 real human responses on a set of realistic mock galaxy simulation snapshots our model is able to recover the pre-coalesced merger fraction to within 10%. Our method can not only increase the accuracy of studies probing the merger state of galaxies at cosmic noon, but also can be used to construct more accurate training sets in machine-learning studies that use human classified data sets.

Keywords: bayesian statistics; galaxy mergers; astronomical methods
Cosmological Parameter Estimation from the Two-dimensional Genus Topology—Measuring the Expansion History Using the Genus Amplitude as a Standard Ruler

We measure the genus of the galaxy distribution in two-dimensional slices of the SDSS-III BOSS catalog to constrain the cosmological parameters governing the expansion history of the universe. The BOSS catalogs are divided into 12 concentric shells over the redshift range 0.25 < z < 0.6, and we repeatedly measure the genus from the two-dimensional galaxy density fields, each time varying the cosmological parameters used to infer the distance-redshift relation to the shells. We also indirectly reconstruct the two-dimensional genus amplitude using the three-dimensional genus measured from SDSS Main Galaxy Sample with galaxies at low redshift z < 0.12. We combine the low- and high-redshift measurements, finding the cosmological model that minimizes the redshift evolution of the genus amplitude, using the fact that this quantity should be conserved. Being a distance measure, the test is sensitive to the matter density parameter (Ωm) and equation of state of dark energy (wde). We find a constraint of ${w}_{\mathrm{de}}=-{1.05}_{-0.12}^{+0.13}$ , Ωm = 0.303 ± 0.036 after combining the high- and low-redshift measurements and combining with Planck CMB data. Higher-redshift data and combining data sets at low redshift will allow for stronger constraints.

Keywords: cosmology; observational cosmology; dark energy; cosmological parameters; cosmological parameters from large-scale structure; large-scale structure of the universe
On Icy Ocean Worlds, Size Controls Ice Shell Geometry

The ice shell and subsurface ocean on icy worlds are strongly coupled together-heat and salinity flux from the ice shell induced by the ice thickness gradient drives circulation in the ocean, and in turn, the heat transport by ocean circulation shapes the ice shell. Since measurements in the near future are likely to remain constrained to above the ice shell, understanding this ocean-ice interaction is crucial. Using an ocean box model and a series of experiments simulating the 2D ocean circulation, we find that large icy moons with strong gravity tend to have stronger ocean heat transport under the same ice shell topography. As a result, the equilibrium ice shell geometry is expected to be flatter on moons with larger size, and vice versa. This finding is broadly consistent with the observed ice shell geometry for Enceladus and Europa.

Keywords: natural satellites (solar system); jovian satellites; saturnian satellites; habitable planets
Did the Event Horizon Telescope Detect the Base of the Submilliarsecond Tubular Jet in M87?

A high-sensitivity, 7 mm Very Long Baseline Array image of M 87 was previously analyzed in order to estimate the bulk flow jet velocity between 0.4 and 0.65 mas from the point of origin using the asymmetry between the well-characterized double-ridged counter-jet (unique to this image) and the double-ridged jet. We use this same image to estimate the cross-sectional area of this tubular stream. The velocity, acceleration, cross-sectional area, and flux density along this stream determine a unique, perfect magnetohydrodynamic jet solution that satisfies conservation of energy, angular momentum, and mass (a monotonic conversion of Poynting flux to kinetic energy flux along the jet). The solution is protonic and magnetically dominated. The bilateral jet transports ≈1.2 × 10-4M⊙ yr-1 and ≈1.1 × 1042 erg s-1, placing strong constraints on the central engine. A Keplerian disk source that also produces the Event Horizon Telescope (EHT) annulus of emission can supply the energy and mass if the vertical magnetic field at the equator is ~1-3.5 G (depending on location). A Parker spiral magnetic field, characteristic of a wind or jet, is consistent with the observed EHT polarization pattern. Even though there is no image of the jet connecting with the annulus, it is argued that these circumstances are not coincidental and the polarized portion of the EHT emission is mainly jet emission in the top layers of the disk that is diluted by emission from an underlying turbulent disk. This is a contributing factor to the relatively low polarization levels that were detected.

Keywords: active galactic nuclei; radio active galactic nuclei; low-luminosity active galactic nuclei
Evaluating and Enhancing Candidate Clocking Systems for CHIME/FRB VLBI Outriggers

As the Canadian Hydrogen Intensity Mapping Experiment (CHIME) has become the leading instrument for detecting Fast Radio Bursts (FRBs), CHIME/FRB Outriggers will use very-long-baseline interferometry (VLBI) to localize FRBs with milliarcsecond precision. The CHIME site uses a passive hydrogen maser frequency standard in order to minimize localization errors due to clock delay. However, not all outrigger stations will have access to a maser. This report presents techniques used to evaluate clocks for use at outrigger sites without a maser. More importantly, the resulting algorithm provides calibration methods for clocks that do not initially meet the stability requirements for VLBI, thus allowing CHIME/FRB Outriggers to remain true to the goal of having milliarcsecond precision.

Keywords: radio astronomy; radio transient sources; radio pulsars; astronomical instrumentation; very long baseline interferometry
GW170817 4.5 Yr After Merger: Dynamical Ejecta Afterglow Constraints

GW170817 is the first binary neutron star (NS) merger detected in gravitational waves (GWs) and photons, and so far remains the only GW event of its class with a definitive electromagnetic counterpart. Radio emission from the structured jet associated with GW170817 has faded below the sensitivity achievable via deep radio observations with the most sensitive radio arrays currently in operation. Hence, we now have the opportunity to probe the radio re-brightening that some models predict, which should emerge at late times from the interaction of the dynamically stripped merger ejecta with the interstellar medium. Here we present the latest results from our deep radio observations of the GW170817 field with the Karl G. Jansky Very Large Array (VLA), 4.5 yr after the merger. Our new data at 3 GHz do not show any compelling evidence for emission in excess to the tail of the jet afterglow (<3.3 μJy), confirming our previous results. We thus set new constraints on the dynamical ejecta afterglow models. These constraints favor single-speed ejecta with energies ≲1050 erg (for an ejecta speed of β 0 = 0.5), or steeper energy-speed distributions of the kilonova ejecta. Our results also suggest larger values of the cold, nonrotating maximum NS mass in equal-mass scenarios. However, without a detection of the dynamical ejecta afterglow, obtaining precise constraints on the NS equation of state remains challenging.

Keywords: radio continuum emission; radio transient sources; x-ray transient sources
Transport, Destruction, and Growth of Pebbles in the Gas Envelope of a Protoplanet

We analyze the size evolution of pebbles accreted into the gaseous envelope of a protoplanet growing in a protoplanetary disk, taking into account collisions driven by the relative sedimentation speed as well as the convective gas motion. Using a simple estimate of the convective gas speed based on the pebble accretion luminosity, we find that the speed of the convective gas is higher than the sedimentation speed for all particles smaller than 1 mm. This implies that both pebbles and pebble fragments are strongly affected by the convective gas motion and will be transported by large-scale convection cells both toward and away from the protoplanet's surface. We present a simple scheme for evolving the characteristic size of the pebbles, taking into account the effects of erosion, mass transfer, and fragmentation. Including the downwards motion of convective cells for the transport of pebbles with an initial radius of 1 mm, we find pebble sizes between 100 μm and 1 mm near the surface of the protoplanet. These sizes are generally amenable to accretion at the base of the convection flow. Small protoplanets far from the star (>30 au) nevertheless erode their pebbles to sizes below 10 μm; future hydrodynamical simulations will be needed to determine whether such small fragments can detach from the convection flow and become accreted by the protoplanet.

Keywords: planetary system formation; exoplanet formation
Plasma Emission versus Electron Cyclotron Maser Emission due to Power-law Energetic Electrons in Differently Magnetized Coronal Plasmas

By using self-consistent 2.5-dimensional particle-in-cell simulations, we study the excitation efficiency of electromagnetic waves by power-law energetic electrons with an anisotropic pitch-angle velocity distribution, which can simultaneously trigger the Langmuir and electron cyclotron maser instabilities, in differently magnetized coronal plasmas. It is found that the (transverse) electromagnetic waves can be excited much more efficiently in the case of strongly magnetized plasmas with ω ce > ω pe than that of weakly magnetized plasmas with ω ce < ω pe, where ω ce and ω pe are the electron cyclotron frequency and the electron plasma frequency, respectively. In particular, in a weakly magnetized plasma the electromagnetic wave is hardly excited effectively via the nonlinear coupling of Langmuir waves; although the Langmuir waves can be generated by the power-law energetic electrons, implying that the so-called plasma emission does not effectively work. These results can be helpful for us to better understand the physical mechanism of solar radio bursts.

Keywords: plasma physics; solar radio emission; solar corona
New Active Asteroid (588045) 2007 FZ18

We present evidence that, on UT 2018 February 15, main-belt asteroid (588045) 2007 FZ18 displayed cometary activity in the form of two tails, one each in the anti-solar and anti-motion directions. Activity was first identified by volunteers of the NASA Partner program Active Asteroids, a Citizen Science program hosted on the Zooniverse platform, in an image acquired with the Dark Energy Camera on the Blanco 4 m telescope at the Cerro Tololo Inter-American Observatory in Chile. Notably, (588045) 2007 FZ18 is inbound toward perihelion, so telescope observations are timely to detect a possible second activity outburst.

Keywords: asteroids; comae; comet tails; main belt asteroids
Thermal Variations of Extremely Close-in Exoplanets

Modern exoplanet light curves allow for detailed parameter characterization and are now employed to estimate parameters such as reflectivity and temperature to provide information about planet composition and potential habitability. Currently, exoplanet heat maps are in active development, but a simple model of temperature distribution assumes that the exoplanet has only a dayside and nightside temperature, where each side of the exoplanet emits thermal radiation like a blackbody at constant temperature. Presented here is a new method of characterizing the thermal emissions of exoplanets that considers N temperature zones. The zones make up a series of rings axially symmetric about the substellar point and each will be treated as a blackbody of constant temperature. The hottest zone will be centered about the substellar point. Here I will outline the differences between the N-zone and the dayside/nightside models.

Keywords: exoplanet astronomy; exoplanets
Applications of Fast Magnetic Reconnection Models to the Atmospheres of the Sun and Protoplanetary Disks

Partially ionized plasmas consist of charged and neutral particles whose mutual collisions modify magnetic reconnection compared with the fully ionized case. The collisions alter the rate and locations of the magnetic dissipation heating and the distribution of energies among the particles accelerated into the nonthermal tail. We examine the collisional regimes for the onset of fast reconnection in two environments: the partially ionized layers of the solar atmosphere, and the protoplanetary disks that are the birthplaces for planets around young stars. In both these environments, magnetic nulls readily develop into resistive current sheets in the regime where the charged and neutral particles are fully coupled by collisions, but the current sheets quickly break down under the ideal tearing instability. The current sheets collapse repeatedly, forming magnetic islands at successively smaller scales, until they enter a collisionally decoupled regime where the magnetic energy is rapidly turned into heat and charged-particle kinetic energy. Small-scale, decoupled fast reconnection in the solar atmosphere may lead to preferential heating and energization of ions and electrons that escape into the corona. In protoplanetary disks such reconnection causes localized heating in the atmospheric layers that produce much of the infrared atomic and molecular line emission observed with the Spitzer and James Webb Space Telescopes.

Keywords: solar magnetic reconnection; protoplanetary disks; space plasmas; plasma astrophysics
Organic Carbonyls Are Poor Biosignature Gases in Exoplanet Atmospheres but May Generate Significant CO

The search for signs of life beyond Earth is a crucial driving motivation of exoplanet science, fueling new work on biosignature gases in habitable exoplanet atmospheres. We study carbonyls, a category of molecules containing the C=O double bond, following our proposal to systematically identify plausible biosignature gas candidates from a list of all small volatile molecules. We rule out carbonyls as biosignature gases due to both their high water solubility and their high photolysis rate, despite their ubiquitous production by life on Earth, their critical importance in Earth's life biochemistry, and their uniquely identifiable molecular spectral features in mid- to low-resolution spectroscopy. Even in scenarios where life is a large net source of carbonyls, we demonstrate that detection of carbonyls is not possible on even the most ideal habitable exoplanet, because only 10 ppb of carbonyls can accumulate under our most optimistic assumptions. Moreover, high biological fluxes of organic carbon gases, while mathematically possible, are likely biologically unattainable due to the resulting huge waste of carbon-a main building block for life. Our simulations show that photochemical processing of carbonyls leads to generation of CO in quantities that can reengineer the atmosphere, affirming the ambiguity of CO as an antibiosignature. Overall, we find that the expression of a carbonyl-producing biosphere by CO, though potentially detectable by the James Webb Space Telescope, is unable to be uniquely traced back to carbonyls. While carbonyls fail as a bioindicator, by investigating them we have made a significant step toward systematically assessing the biosignature gas potential of all small volatile molecules.

Keywords: exoplanet atmospheric composition; habitable planets; biosignatures; markov chain monte carlo
VMC J021140.41-735320.4—An Extremely Red L Dwarf Candidate Member of the AB Doradus Young Moving Group

We report the discovery of VMC J021140.41-735320.4, a faint ($J=19.9$ mag) and extremely red ($J-K_s=3.0$ mag, $W1-W2=0.45$ mag, $J-W2=4.7$ mag) high proper motion object in front of the Magellanic Bridge region. It is even redder in the near-infrared than the reddest L7 dwarfs ($J-K_s \gtrsim 2.8$ mag) found in the survey of Schneider et al. (2017) and its colours do also not match exactly those of other peculiar red L7.5 dwarfs. Therefore, we consider its photometric distance estimate of about 73 pc as uncertain. A preliminary combined proper motion and parallax solution involving 20 epochs from the Visible and Infrared Survey Telescope for Astronomy (VISTA) survey of the Magellanic Clouds (VMC), the VISTA hemisphere survey (VHS), and the Wide-field Infrared Survey Explorer (WISE) yields $\mu_{\alpha}\cos{\delta}=+74.3\pm3.4$ mas/yr, $\mu_{\delta}=+22.3\pm3.4$ mas/yr, and $\pi=21.0\pm7.1$ mas. Applying the BANYAN tool (http://www.exoplanetes.umontreal.ca/banyan/) to these results we find a $\approx$68% membership probability of this object in the AB Doradus young moving group (YMG). With its trignometric distance of $\approx$48 pc, VMC J021140.41-735320.4 has a similar absolute magnitude of $M_{K_s}\approx13.4$ mag as the planetary mass companion of another AB Doradus YMG member candidate, 2MASS J22362452+4751425. Follow-up classification spectroscopy and astrometric monitoring are recommended.

Keywords: proper motions; brown dwarfs
Supernova-driven Mechanism of Cusp-core Transformation: an Appraisal

We present and test an effective model for N-body simulations that aims at mimicking the impact of supernova (SN) feedback on the dark matter (DM) distribution of isolated halos hosting dwarf galaxies. Although the model is physically decoupled from the cosmological history of both the DM halo and the dwarf galaxy, it allows us to study the impact of different macroscopic parameters such as galaxy concentration, feedback energy, and energy injection time in the process of SN-driven core formation in a physically clear way. Using our effective model in a suite of N-body simulations of an isolated halo with different SN feedback parameters, we find that whether or not a DM core forms is determined by the total amount of SN feedback energy that is transferred to the DM particles. At a fixed injected energy, transfer of energy to the DM is more efficient the faster the energy is injected and the more compact the galaxy is, leading to an increased size of the formed DM core as a result. Analyzing the orbital evolution of kinematic tracers, we demonstrate that a core forms through SN feedback only if the energy injection is impulsive relative to the dynamical timescale of particles in the inner halo. However, there is no fundamental link between the total amount of injected energy and the injection rate. Consequently, the presence of signatures of impulsive changes of the gravitational potential is not a sufficient condition for dwarf-sized halos to have cored density profiles.

Keywords: stellar feedback; dwarf galaxies; stellar dynamics
Vitreous Magnesium Sulfate Hydrate as a Potential Mechanism for Preservation of Microbial Viability on Europa

Europa's subsurface ocean is postulated to contain appreciable amounts of Mg2+ and ${{\mathrm{SO}}_{4}}^{2-}$ ions, among other species. Recent laboratory experiments have shown that when solutions containing these species freeze to Europa-relevant temperatures, they can form vitreous MgSO4 hydrate, which can remain stable at these temperatures. Since vitreous phases can protect cells from physical damage that can occur during crystallization, their presence on Europa could potentially preserve entrained microorganisms from the ocean below. However, to date, it remains unclear whether such materials actually impact microbial survival. In this work, experiments were performed in which the motile nonspore-forming Antarctic isolate Pseudoalteromonas haloplanktis in solutions of 0.1 M MgSO4 were frozen to Europa surface temperatures (100 K) under conditions that resulted in the formation of either vitreous or crystalline salt hydrates. We found that cells survived in both cases, exhibiting a 3-log reduction in viable cells in the crystalline salt hydrate case while only a 1.5-log reduction in the vitreous salt hydrate case. Scanning electron microscopy accordingly showed much higher degrees of membrane lysis and cellular damage in the crystalline salt hydrate than the vitreous case. Our results demonstrate the ability of a terrestrial oceanic microorganism to survive in MgSO4 solutions frozen to Europa surface temperatures, with enhanced viability in vitreous salt-hydrate-producing conditions versus crystalline. These findings suggest that future missions should target vitrified salt-rich environments for life detection due to this potential for preserving viable microorganisms that may be present and trapped in ocean world ices.

Keywords: natural satellites (solar system); europa; astrobiology; biosignatures