adsabs/SciX_UAT_keywords huggingface dataset:
Improving Detection of Gravitational-wave Microlensing Using Repeated Signals Induced by Strong Lensing

Microlensing imprints by typical stellar-mass lenses on gravitational waves are challenging to identify in the LIGO-Virgo frequency band because such effects are weak. However, stellar-mass lenses are generally embedded in lens galaxies such that strong lensing accompanies microlensing. Therefore, events that are strongly lensed in addition to being microlensed may significantly improve the inference of the latter. We present a proof-of-principle demonstration of how one can use parameter estimation results from one strongly lensed signal to enhance the inference of the microlensing effects of the other signal with the Bayesian inference method currently used in gravitational-wave astronomy. We expect this to significantly enhance our future ability to detect the weak imprints from stellar-mass objects on gravitational-wave signals from colliding compact objects.

Keywords: gravitational wave astronomy; gravitational waves; astronomical methods; gravitational lensing; strong gravitational lensing; gravitational microlensing; bayesian statistics
Observational Constraints in Delta-gravity: CMB and Supernovae

Delta-gravity (DG) is a gravitational model based on an extension of general relativity given by a new symmetry called $\tilde{\delta }$ . In this model, new matter fields are added to the original matter fields, motivated by the additional symmetry. We call them $\tilde{\delta }$ matter fields. This model predicts an accelerating universe without the need to introduce a cosmological constant. In this work, we study the scalar cosmic microwave background (CMB) temperature (TT) power spectrum predicted by DG using an analytical hydrodynamic approach. To fit the Planck satellite's data with the DG model, we used a Markov Chain Monte Carlo analysis. We also include a study about the compatibility between Type Ia supernovae (SNe Ia) and CMB observations in the DG context. Finally, we obtain the scalar CMB TT power spectrum and the fitted parameters needed to explain both SN Ia data and CMB measurements. The results are in reasonable agreement with both observations considering the analytical approximation. We also discuss whether the Hubble constant and the accelerating universe are in concordance with the observational evidence in the DG context.

Keywords: dark energy; cosmology; cosmic microwave background radiation; cosmological perturbation theory; cosmological models
The Young and the Wild: What Happens to Protoclusters Forming at Redshift z ≈ 4?

Using one of the largest volumes of the hydrodynamical cosmological simulation suit Magneticum, we study the evolution of protoclusters identified at redshift ≈ 4, with properties similar to the well-observed protocluster SPT2349-56. We identify 42 protoclusters in the simulation as massive and equally rich in substructures as observed, confirming that these observed structures can already be virialized. The dynamics of the internally fast-rotating member galaxies within these protoclusters resemble observations, merging rapidly to form the cores of the brightest cluster galaxies of the assembling clusters. Half of the gas reservoir of these structures is in a hot phase, with the metal enrichment at a very early stage. These systems show a good agreement with the observed amount of cold star-forming gas, largely enriched to solar values. We predict that some of the member galaxies are already quenched at z ≈ 4, rendering them undetectable through measurements of their gas reservoirs. Tracing the evolution of protoclusters reveals that none of the typical mass indicators at high redshift are good tracers to predict the present-day mass of the system. We find that none of the simulated protoclusters at z = 4.3 are among the top ten most massive clusters at redshift z = 0.2, with some barely reaching masses of M ≈ 2 × 1014 M ⊙. Although the average star formation and mass growth rates in the simulated galaxies match observations at high redshift reasonably well, the simulation fails to reproduce the extremely high total star formation rates within the observed protoclusters, indicating that the subgrid models are lacking the ability to reproduce a higher star formation efficiency (or lower depletion timescales).

Keywords: early universe; large-scale structure of the universe; high-redshift galaxy clusters; galaxy clusters; computational methods
The Impact of Cosmic Ray Injection on Magnetic Flux Tubes in a Galactic Disk

In a seminal paper, Parker showed the vertical stratification of the interstellar medium (ISM) is unstable if magnetic fields and cosmic rays provide too large a fraction of pressure support. Cosmic ray acceleration is linked to star formation, so Parker's instability and its nonlinear outcomes are a type of star formation feedback. Numerical simulations have shown the instability can significantly restructure the ISM, thinning the thermal gas layer and thickening the magnetic field and cosmic ray layer. However, the timescale on which this occurs is rather long (~0.4 Gyr). Furthermore, the conditions for instability depend on the model adopted for cosmic ray transport. In this work, we connect the instability and feedback problems by examining the effect of a single, spatially and temporally localized cosmic ray injection on the ISM over ~1 kpc3 scales. We perform cosmic ray magnetohydrodynamic simulations using the Athena++ code, varying the background properties, dominant cosmic ray transport mechanism, and injection characteristics between our simulation runs. We find robust effects of buoyancy for all transport models, with disruption of the ISM on timescales as short as 100 Myr when the background equilibrium is dominated by cosmic ray pressure.

Keywords: galaxy structure; magnetohydrodynamical simulations; cosmic rays
Lyman Continuum Escape Fraction from Low-mass Starbursts at z = 1.3

We present a new constraint on the Lyman continuum (LyC) escape fraction at $z\sim 1.3$ . We obtain deep, high sensitivity far-UV imaging with the Advanced Camera for Surveys Solar Blind Channel on the Hubble Space Telescope, targeting 11 star-forming galaxies at 1.2 < z < 1.4. The galaxies are selected from the 3D-HST survey to have high Hα equivalent width (EW) with an EW > 190 Å, low stellar mass (M* < 1010 M⊙), and U-band magnitude of U < 24.2. These criteria identify young, low metallicity star-bursting populations similar to the early star-forming galaxies believed to have reionized the universe. We do not detect any LyC signal (with a signal-to-noise ratio > 3) in the individual galaxies or in the stack in the far-UV images. We place 3σ limits on the relative escape fraction of individual galaxies to be ${f}_{\mathrm{esc},\mathrm{rel}}\lt [0.10\mbox{--}0.22]$ and a stacked 3σ limit of ${f}_{\mathrm{esc},\mathrm{rel}}\lt 0.07$ . Measuring various galaxy properties, including stellar mass, dust attenuation, and star formation rate, we show that our measured values fall within the broad range of values covered by the confirmed LyC emitters from the literature. In particular, we compare the distribution of Hα and [O III] EWs of confirmed LyC emitters and non-detections, including the galaxies in this study. Finally, we discuss if a dichotomy seen in the distribution of Hα EWs can perhaps distinguish the LyC emitters from the non-detections. * Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555.

Keywords: galaxy evolution; reionization; starburst galaxies; ultraviolet astronomy; intergalactic medium; emission line galaxies; high-redshift galaxies
Network Jets as the Driver of Counter-streaming Flows in a Solar Filament/Filament Channel

Counter-streaming flows in a small (100″ long) solar filament/filament channel are directly observed in high-resolution Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) extreme-ultraviolet (EUV) images of a region of enhanced magnetic network. We combine images from SDO/AIA, SDO/Helioseismic and Magnetic Imager (HMI), and the Interface Region Imaging Spectrograph (IRIS) to investigate the driving mechanism of these flows. We find that: (I) counter-streaming flows are present along adjacent filament/filament channel threads for ∼2 hr, (II) both ends of the filament/filament channel are rooted at the edges of magnetic network flux lanes along which there are impinging fine-scale opposite-polarity flux patches, (III) recurrent small-scale jets (known as network jets) occur at the edges of the magnetic network flux lanes at the ends of the filament/filament channel, (IV) the recurrent network jet eruptions clearly drive the counter-streaming flows along threads of the filament/filament channel, (V) some of the network jets appear to stem from sites of flux cancelation, between network flux and merging opposite-polarity flux, and (VI) some show brightening at their bases, analogous to the base brightening in coronal jets. The average speed of the counter-streaming flows along the filament/filament channel threads is 70 km s-1. The average widths of the AIA filament/filament channel and the Hα filament are 4″ and 2"5, respectively, consistent with the earlier findings that filaments in EUV images are wider than in Hα images. Thus, our observations show that the continually repeated counter-streaming flows come from network jets, and these driving network jet eruptions are possibly prepared and triggered by magnetic flux cancelation.

Keywords: solar chromosphere; solar filaments; solar magnetic fields; solar magnetic reconnection; jets; solar chromospheric heating; solar corona
2-OGC: Open Gravitational-wave Catalog of Binary Mergers from Analysis of Public Advanced LIGO and Virgo Data

We present the second Open Gravitational-wave Catalog (2-OGC) of compact-binary coalescences, obtained from the complete set of public data from Advanced LIGO's first and second observing runs. For the first time we also search public data from the Virgo observatory. The sensitivity of our search benefits from updated methods of ranking candidate events including the effects of nonstationary detector noise and varying network sensitivity; in a separate targeted binary black hole merger search we also impose a prior distribution of binary component masses. We identify a population of 14 binary black hole merger events with probability of astrophysical origin >0.5 as well as the binary neutron star merger GW170817. We confirm the previously reported events GW170121, GW170304, and GW170727 and also report GW151205, a new marginal binary black hole merger with a primary mass of {67}-17+28 M⊙ that may have formed through hierarchical merger. We find no additional significant binary neutron star merger or neutron star-black hole merger events. To enable deeper follow-up as our understanding of the underlying populations evolves, we make available our comprehensive catalog of events, including the subthreshold population of candidates and posterior samples from parameter inference of the 30 most significant binary black hole candidates.

Keywords: gravitational waves; compact objects; black holes; neutron stars
The Mass Accretion Rate and Stellar Properties in Class I Protostars

Stars collect most of their mass during the protostellar stage, yet the accretion luminosity and stellar parameters, which are needed to compute the mass accretion rate, are poorly constrained for the youngest sources. The aim of this work is to fill this gap, computing the stellar properties and the accretion rates for a large sample of Class I protostars located in nearby (<500 pc) star-forming regions and analyzing their interplay. We used a self-consistent method to provide accretion and stellar parameters by modeling the spectral energy distribution and using veiling information from near-IR observations when possible. We calculated accretion and stellar properties for the first time for 50 young stars. We focused our analysis on the 39 confirmed protostars, finding that their mass accretion rate varies between ~10-8 and ~10-4 M ⊙ yr-1 in a stellar mass range between ~0.1 and 3 M ⊙. We find systematically larger mass accretion rates for our Class I sample than for Class II objects. Although the mass accretion rate we found is high, it still suggests that either stars collect most of their mass before the Class I stage, or eruptive accretion is needed during the overall protostellar phase. Indeed, our results suggest that for a large number of protostars the disk can be unstable, which can result in accretion bursts and disk fragmentation in the past or in the future.

Keywords: star formation; stellar accretion disks; stellar properties; protostars; low mass stars; circumstellar disks; circumstellar dust
Search for Off-pulse Emission in Long-period Pulsars

We have revisited the problem of off-pulse emission in pulsars, where a detailed search for the presence of low-level radio emission outside the pulse window is carried out. The presence of off-pulse emission was earlier reported in two long-period pulsars, PSR B0525+21 and B2046-16, at frequencies below 1 GHz using the Giant Metrewave Radio Telescope (GMRT). However, subsequent studies did not detect off-pulse emission from these pulsars at higher radio frequencies (>1 GHz). We have carefully inspected the analysis scheme used in the earlier detections and found an anomaly with data editing routines used, which resulted in leakage of signal from the on-pulse to the off-pulse region. We show that the earlier detections from PSR B0525+21 and B2046-16 were a result of this leakage. The above analysis scheme has been modified and offline gating has been used to search for off-pulse emission in 21 long-period pulsars (P > 1.2 s) at different observing frequencies of GMRT. The presence of low-level off-pulse emission of the peak flux 0.5 mJy was detected in the brightest pulsar in this list, PSR 0B0628-28, with an off-pulse to average pulsar flux ratio of 0.25%. We suggest that coherent radio emission resulting due to cyclotron resonance near the light cylinder can be a possible source for the off-pulse emission in this pulsar.

Keywords: radio pulsars
EPIC 219511354, A Binary Pair of Active K-stars: Modeling Activity-induced Radius Inflation by Magneto-convection

Magnetically active low-mass stars are observed to have their empirical radii R "inflated" and their empirical T eff reduced relative to standard predictions. Models which have been proposed to replicate these discrepancies include magneto-convection (M-C), and/or star-spots (S-S). Here we raise the question: is there any reason to prefer a dominant role for either M-C or S-S in order to replicate the data? In the binary EPIC 219511354, the empirical M and R values have remarkably high (1%-2%) precision. To replicate these data, the S-S model requires almost the entire (88%-94%) secondary surface to be spotted. Here, we report that our M-C model fits the empirical R and T eff values for both members of the binary within 1σ error bars without needing spots. If an areal spot coverage of 94% is regarded as physically implausible, the M-C model could be considered preferable over S-S in EPIC 219511354.

Keywords: magnetic stars; k dwarf stars; stellar evolutionary models; stellar magnetic fields
Life in a Random Universe: Sciama's Argument Reconsidered

Random sampling in high dimensions has successfully been applied to phenomena as diverse as nuclear resonances, neural networks, and black hole evaporation. Here we revisit an elegant argument by the British physicist Dennis Sciama, who demonstrated that were our Universe random, it would almost certainly have a negligible chance for life. Under plausible assumptions, we show that a random universe can masquerade as "intelligently designed," with the fundamental constants instead appearing to be fined tuned to achieve the highest probability for life to occur. For our Universe, this mechanism may only require there to be around a dozen currently unknown fundamental constants. We speculate on broader applications for the mechanism we uncover.

Keywords: anthropic principle; cosmology; astrobiology; search for extraterrestrial intelligence
TESS Giants Transiting Giants. III. An Eccentric Warm Jupiter Supports a Period-Eccentricity Relation for Giant Planets Transiting Evolved Stars

The fate of planets around rapidly evolving stars is not well understood. Previous studies have suggested that, relative to the main-sequence population, planets transiting evolved stars (P < 100 days) tend to have more eccentric orbits. Here we present the discovery of TOI-4582 b, a ${0.94}_{-0.12}^{+0.09}$ R J , 0.53 ± 0.05 M J planet orbiting an intermediate-mass subgiant star every 31.034 days. We find that this planet is also on a significantly eccentric orbit (e = 0.51 ± 0.05). We then compare the population of planets found transiting evolved (log g < 3.8) stars to the population of planets transiting main-sequence stars. We find that the rate at which median orbital eccentricity grows with period is significantly higher for evolved star systems than for otherwise similar main-sequence systems. In general, we observe that mean planet eccentricity <e> = a+blog10(P) for the evolved population with significant orbital eccentricity where a = -0.18 ± 0.08 and b = 0.38 ± 0.06, significantly distinct from the main-sequence planetary system population. This trend is seen even after controlling for stellar mass and metallicity. These systems do not appear to represent a steady evolution pathway from eccentric, long-period planetary orbits to circular, short-period orbits, as orbital model comparisons suggest that inspiral timescales are uncorrelated with orbital separation or eccentricity. Characterization of additional evolved planetary systems will distinguish effects of stellar evolution from those of stellar mass and composition.

Keywords: exoplanets; stellar evolution; star-planet interactions; transits; extrasolar gaseous giant planets
Multiepoch Spectroscopy of Mg II Broad Absorption Line Transitions

Built upon a sample of 134 quasars that was dedicated to a systematic study of Mg II-BAL variability from Yi et al., we investigate these quasars, showing Mg II-BAL disappearance or emergence with the aid of at least three epoch optical spectra sampled more than 15 yr in the observed frame. We identified 3/3 quasars undergoing pristine/tentative BAL transformations. The incidence of pristine BAL transformations in the sample is therefore derived to be ${2.2}_{-1.2}^{+2.2}$ %, consistent with that of high-ionization BAL transformations from the literature. Adopting an average Mg II-BAL disappearance timescale of rest frame 6.89 yr among the six quasars, the average characteristic lifetime of Mg II BALs in the sample is constrained to be >160 yr along our line of sight. There is a diversity of BAL profile variability observed in the six quasars, probably reflecting a variety of mechanisms at work. Our investigations of Mg II-BAL transitions, combined with observational studies of BAL transitions from the literature, imply an overall FeLoBAL/LoBAL → HiBAL/non-BAL transformation sequence, along with a decrease in reddening. This sequence is consistent with the evacuation models for the origin of commonly seen blue quasars, in which LoBAL quasars are in a short-lived blowout phase.

Keywords: quasars; broad-absorption line quasar
Probing the Extent of Vertical Mixing in Brown Dwarf Atmospheres with Disequilibrium Chemistry

Evidence of disequilibrium chemistry due to vertical mixing in the atmospheres of many T- and Y-dwarfs has been inferred due to enhanced mixing ratios of CO and reduced NH3. Atmospheric models of planets and brown dwarfs typically parameterize this vertical mixing phenomenon with the vertical eddy diffusion coefficient, K zz . While K zz can perhaps be approximated in the convective regions in the atmosphere with mixing length theory, in radiative regions, the strength of vertical mixing is uncertain by many orders of magnitude. With a new grid of self-consistent 1D model atmospheres from T eff of 400-1000 K, computed with a new radiative-convective equilibrium python code PICASO 3.0, we aim to assess how molecular abundances and corresponding spectra can be used as a probe of depth-dependent K zz . At a given surface gravity, we find nonmonotonic behavior in the CO abundance as a function of T eff, as chemical abundances are sometimes quenched in either of two potential atmospheric convective zones, or quenched in either of two possible radiative zones. The temperature structure and chemical quenching behavior also change with gravity. We compare our models with available near-infrared and M-band spectroscopy of several T- and Y-dwarfs and assess their atmospheric vertical mixing profiles. We also compare to color-magnitude diagrams and make predictions for James Webb Space Telescope spectra. This work yields new constraints, and points the way to significant future gains, in determining K zz , a fundamental atmospheric parameter in substellar atmospheres, with significant implications for chemistry and cloud modeling.

Keywords: brown dwarfs; t dwarfs; y dwarfs; atmospheric composition
Optical Detection of the 1.1 day Variability at the White Dwarf GD 394 with TESS

Recent discoveries have demonstrated that planetary systems routinely survive the post-main-sequence evolution of their host stars, leaving the resulting white dwarf with a rich circumstellar environment. Among the most intriguing of such hosts is the hot white dwarf GD 394, exhibiting a unique 1.150 ± 0.003 day flux variation detected in Extreme Ultraviolet Explorer (EUVE) observations in the mid-1990s. The variation has eluded a satisfactory explanation, but hypotheses include channeled accretion producing a dark spot of metals, occultation by a gas cloud from an evaporating planet, or heating from a flux tube produced by an orbiting iron-cored planetesimal. We present observations obtained with the Transiting Exoplanet Survey Satellite (TESS) of GD 394. The space-based optical photometry demonstrates a 0.12 ± 0.01% flux variation with a period of 1.146 ± 0.001 days, consistent with the EUVE period and the first re-detection of the flux variation outside of the extreme ultraviolet. We describe the analysis of the TESS light curve and measurement of the optical variation, and discuss the implications of our results for the various physical explanations put forward for the variability of GD 394.

Keywords: white dwarf stars; variable stars; exoplanets