adsabs/SciX_UAT_keywords huggingface dataset:
Quantifying the Influence of Jupiter on the Earth’s Orbital Cycles

A wealth of Earth-sized exoplanets will be discovered in the coming years, providing a large pool of candidates from which the targets for the search for life beyond the solar system will be chosen. The target selection process will require the leveraging of all available information in order to maximize the robustness of the target list and make the most productive use of follow-up resources. Here, we present the results of a suite of n-body simulations that demonstrate the degree to which the orbital architecture of the solar system impacts the variability of Earth’s orbital elements. By varying the orbit of Jupiter and keeping the initial orbits of the other planets constant, we demonstrate how subtle changes in solar system architecture could alter the Earth’s orbital evolution—a key factor in the Milankovitch cycles that alter the amount and distribution of solar insolation, thereby driving periodic climate change on our planet. The amplitudes and frequencies of Earth’s modern orbital cycles fall in the middle of the range seen in our runs for all parameters considered—neither unusually fast nor slow, neither large nor small. This finding runs counter to the “Rare Earth” hypothesis, which suggests that conditions on Earth are so unusual that life elsewhere is essentially impossible. Our results highlight how dynamical simulations of newly discovered exoplanetary systems could be used as an additional means to assess the potential targets of biosignature searches, and thereby help focus the search for life to the most promising targets.

Keywords: astrobiology; n-body simulations; gravitational interaction; exoplanet systems; dynamical evolution
Dust-enshrouded AGNs Can Dominate Host-galaxy-scale Cold Dust Emission

It is widely assumed that long-wavelength infrared (IR) emission from cold dust (T ~ 20-40 K) is a reliable tracer of star formation even in the presence of a bright active galactic nucleus (AGN). Based on radiative transfer (RT) models of clumpy AGN tori, hot dust emission from the torus contributes negligibly to the galaxy spectral energy distribution (SED) at λ ≳ 100 μm. However, these models do not include AGN heating of host-galaxy-scale diffuse dust, which may have far-IR (FIR) colors comparable to cold diffuse dust heated by stars. To quantify the contribution of AGN heating to host-galaxy-scale cold dust emission at λ ≳ 100 μm, we perform dust RT calculations on a simulated galaxy merger both including and excluding the bright AGN that it hosts. By differencing the SEDs yielded by RT calculations with and without AGNs that are otherwise identical, we quantify the FIR cold dust emission arising solely from reprocessed AGN photons. In extreme cases, AGN-heated host-galaxy-scale dust can increase galaxy-integrated FIR flux densities by factors of 2-4; star formation rates calculated from the FIR luminosity assuming no AGN contribution can overestimate the true value by comparable factors. Because the FIR colors of such systems are similar to those of purely star-forming galaxies and redder than torus models, broadband SED decomposition may be insufficient for disentangling the contributions of stars and heavily dust-enshrouded AGNs in the most IR-luminous galaxies. We demonstrate how kiloparsec-scale resolved observations can be used to identify deeply dust-enshrouded AGNs with cool FIR colors when spectroscopic and/or X-ray detection methods are unavailable.

Keywords: infrared galaxies; agn host galaxies; galaxy evolution; hydrodynamical simulations; radiative transfer simulations; ultraluminous infrared galaxies
Far-ultraviolet to Far-infrared Spectral Energy Distribution Modeling of the Star Formation History across M31

Our neighboring galaxy M31 has been recently surveyed at the far- and near-ultraviolet (FUV and NUV) with the UVIT telescope on AstroSat, which provides unprecedented sensitivity to young stellar populations. Here the UVIT data are supplemented with optical data, near-infrared (IR) data (Spitzer), and mid- and far-IR data (Herschel). The observations are processed to obtain the spectral energy distributions (SEDs) for 73 regions covering M31. The SEDs are modeled using the Cigale SED fitting code with old and young stellar populations. The old stellar population has an age of 12 Gyr across M31 but has longer formation times at further distances from the center. Significant dependences on the position of dust extinction, dust emission, and young stellar population properties are found. Across M31, there are regions with a low-age (≲100 Myr) young population and regions with an intermediate-age (∼1 Gyr) young population. The mass in the young population has declined by a factor of ∼10 for ages 800–100 Myr ago but has increased again for ages ≲100 Myr. This indicates that cold gas available for star formation has been changing over the past Gyr, whether it is caused by a changing merger rate, changing gas infall, or changes in the gas reservoir in M31. We find that the dust luminosity, based on far-IR observations, is driven by the youngest stars, which are primarily measured in the FUV and NUV bands.

Keywords: star formation; andromeda galaxy; ultraviolet astronomy
Doppler Boosting of the S-stars in the Galactic Center

Astrometry and spectroscopy of the S-stars in the Galactic Center provide a unique way to probe the properties of the central supermassive black hole, as well as the post-Newtonian effects caused by its gravity, e.g., gravitational redshift and general relativistic precession. It has also been suggested that the photometry of S-stars can be used for studying the properties of the gaseous environment of Sgr A*. Due to the high velocities of the S-stars, sometimes approaching 0.1c, their photometric signal should be considerably affected by the Doppler boosting. We calculate this relativistic effect for several S-stars closely approaching the central black hole (most of them recently announced) and show that the amplitude of the photometric variability due to the Doppler boosting for some of them (S62 and S4714) exceeds 6%; for the well-studied star S2 it is about 2%. Measurement of the Doppler boosting can confirm the existence and help refine orbital parameters of the S-stars with noisy spectroscopy and astrometry. This effect should be explicitly accounted for when the photometry of S-stars is used for probing the medium around the Sgr A*. We discuss the observability of the Doppler boosting given the complications typical for the Galactic Center and conclude, in particular, that the purely photometric detection of the higher-order relativistic corrections to the Doppler-boosting signal (due to the gravitational redshift and transverse Doppler shift, which we also calculate) is hardly possible for the S-stars.

Keywords: supermassive black holes; doppler shift; infrared photometry
The Circumstellar Gas of Phi Leonis in the UV

HST UV spectra were obtained to study whether the φ Leo system has one or more stellar companions, as shown for the A-star dwarf, HR10, stellar pulsation, or transiting exocomets. During five partial HST observation sets spread over 13 months, redshifted gas with radial velocities up to +245 km s-1 was observed on one occasion, with lower velocity infalling material seen twice. Blueshifted gas features with velocities as high as -150 km s-1 with up to three features in two spectra were also seen. Low-mass stellar companions to late A stars are coronal sources. Assuming an age of 450 Myr, G-K companions to φ Leo, and multiple M-star companions would have been detected in the ROSAT All-Sky Survey data, but are not seen. Further, the star shows only 1 major pulsation component, suggesting it is single, excluding an A- or early F-star companion. Low covering factor absorption features with ∣v∣ ≤ 200 km s-1 have been reported in optical spectra with variation on timescales consistent with nonradial pulsation. However, the highest velocity infall feature has a broader, continuous absorption profile extending from the stellar velocity to +245 km s-1, with a covering factor of ~25% which is more consistent with a transit by a body on a star-grazing orbit.

Keywords: stellar pulsations
Synchronous Rotation in the (136199) Eris-Dysnomia System

We combine photometry of Eris from a 6 month campaign on the Palomar 60 inch telescope in 2015, a 1 month Hubble Space Telescope WFC3 campaign in 2018, and Dark Energy Survey data spanning 2013-2018 to determine a light curve of definitive period 15.771 ± 0.008 days (1σ formal uncertainties), with nearly sinusoidal shape and peak-to-peak flux variation of 3%. This is consistent at part-per-thousand precision with the P = 15.785 90 ± 0.00005 day sidereal period of Dysnomia's orbit around Eris, strengthening the recent detection of synchronous rotation of Eris by Szakáts et al. with independent data. Photometry from Gaia are consistent with the same light curve. We detect a slope of 0.05 ± 0.01 mag per degree of Eris's brightness with respect to illumination phase averaged across g, V, and r bands, intermediate between Pluto's and Charon's values. Variations of 0.3 mag are detected in Dysnomia's brightness, plausibly consistent with a double-peaked light curve at the synchronous period. The synchronous rotation of Eris is consistent with simple tidal models initiated with a giant-impact origin of the binary, but is difficult to reconcile with gravitational capture of Dysnomia by Eris. The high albedo contrast between Eris and Dysnomia remains unexplained in the giant-impact scenario.

Keywords: trans-neptunian objects; small solar system bodies; tidal friction; dwarf planets; asteroid rotation
Diverse Molecular Structures across the Whole Star-forming Disk of M83: High-fidelity Imaging at 40 pc Resolution

We present Atacama Large Millimeter/submillimeter Array (ALMA) imaging of molecular gas across the full star-forming disk of the barred spiral galaxy M83 in CO(J = 1-0). We jointly deconvolve the data from ALMA's 12 m, 7 m, and Total Power arrays using the MIRIAD package. The data have a mass sensitivity and resolution of 104 M ⊙ (3σ) and 40 pc-sufficient to detect and resolve a typical molecular cloud in the Milky Way with a mass and diameter of 4 × 105 M ⊙ and 40 pc, respectively. The full disk coverage shows that the characteristics of molecular gas change radially from the center to outer disk, with the locally measured brightness temperature, velocity dispersion, and integrated intensity (surface density) decreasing outward. The molecular gas distribution shows coherent large-scale structures in the inner part, including the central concentration, offset ridges along the bar, and prominent molecular spiral arms. However, while the arms are still present in the outer disk, they appear less spatially coherent, and even flocculent. Massive filamentary gas concentrations are abundant even in the interarm regions. Building up these structures in the interarm regions would require a very long time (≳100 Myr). Instead, they must have formed within stellar spiral arms and been released into the interarm regions. For such structures to survive through the dynamical processes, the lifetimes of these structures and their constituent molecules and molecular clouds must be long (≳100 Myr). These interarm structures host little or no star formation traced by Hα. The new map also shows extended CO emission, which likely represents an ensemble of unresolved molecular clouds.

Keywords: interstellar medium; molecular gas; molecular clouds; star formation; spiral galaxies; millimeter astronomy; co line emission
Testing Blandford-Znajek Mechanism in Black Hole Hyperaccretion Flows for Long-duration Gamma-Ray Bursts

Long-duration gamma-ray bursts (GRBs) are generally related to the core-collapse of massive stars. In the collapsar scenario, a rotating stellar-mass black hole (BH) surrounded by a hyperaccretion disk has been considered as one of the plausible candidates of GRB central engines. In this paper, we work on a sample including 146 long GRBs with significant jet break features in the multiband afterglows. The jet opening angles can then be obtained by the jet break time. By assuming GRB jets powered by the Blandford-Znajek (BZ) mechanism in the BH hyperaccretion system, we analyze the distributions of the long GRB luminosities and durations in the samples, and constrain the accretion rates for the different BH spins. As a result, we find that the BZ mechanism is so powerful that it is possible to interpret the long GRB prompt emissions within reasonable accretion rates.

Keywords: gamma-ray bursts; accretion; black hole physics; magnetic fields; massive stars
3D MHD Modeling of the Impact of Subsurface Stratification on the Solar Dynamo

Various models of solar subsurface stratification are tested in the global EULAG-MHD solver to simulate diverse regimes of near-surface convective transport. Sub- and superadiabacity are altered at the surface of the model (r > 0.95R ⊙) to either suppress or enhance convective flow speeds in an effort to investigate the impact of the near-surface layer on global dynamics. A major consequence of increasing surface convection rates appears to be a significant alteration of the distribution of angular momentum, especially below the tachocline where the rotational frequency predominantly increases at higher latitudes. These hydrodynamic changes correspond to large shifts in the development of the current helicity in this stable layer (r < 0.72R ⊙), significantly altering its impact on the generation of poloidal and toroidal fields at the tachocline and below, acting as a major contributor toward transitions in the dynamo cycle. The enhanced near-surface flow speed manifests in a global shift of the toroidal field (B ϕ ) in the butterfly diagram, from a north-south symmetric pattern to a staggered antisymmetric emergence.

Keywords: solar physics; magnetohydrodynamical simulations; solar dynamo
Stellar Halos from the The Dragonfly Edge-on Galaxies Survey

We present the primary results from the Dragonfly Edge-on Galaxies Survey, an exploration of the stellar halos of twelve nearby (d < 25 Mpc) edge-on disk galaxies with the Dragonfly Telephoto Array. The edge-on orientation of these galaxies allows their stellar halos to be explored with minimal obscuration by or confusion with the much brighter disk light. Galaxies in the sample span a range of stellar masses from 109.68 to 1010.88 M ⊙. We confirm that the wide range of stellar halo mass fractions previously seen for Milky Way-mass galaxies is also found among less massive spiral galaxies. The scatter in stellar halo mass fraction is large, but we do find a significant positive correlation between stellar halo mass fraction and total stellar mass when the former is measured beyond five half-mass radii. Reasonably good agreement is found with predictions from cosmological hydrodynamical simulations, although observed stellar halo fractions appear to be somewhat lower than expected from these simulations.

Keywords: galaxy structure; galaxy stellar halos; spiral galaxies; galaxy photometry
The Relative Emission from Chromospheres and Coronae: Dependence on Spectral Type and Age

Extreme-ultraviolet and X-ray emission from stellar coronae drives mass loss from exoplanet atmospheres, and ultraviolet emission from stellar chromospheres drives photochemistry in exoplanet atmospheres. Comparisons of the spectral energy distributions of host stars are, therefore, essential for understanding the evolution and habitability of exoplanets. The large number of stars observed with the MUSCLES, Mega-MUSCLES, and other recent Hubble Space Telescope observing programs has provided for the first time a large sample (79 stars) of reconstructed Lyα fluxes that we compare with X-ray fluxes to identify significant patterns in the relative emission from these two atmospheric regions as a function of stellar age and effective temperature. We find that as stars age on the main sequence, the emissions from their chromospheres and coronae follow a pattern in response to the amount of magnetic heating in these atmospheric layers. A single trend-line slope describes the pattern of X-ray versus Lyα emission for G and K dwarfs, but the different trend lines for M dwarf stars show that the Lyα fluxes of M stars are significantly smaller than those of warmer stars with the same X-ray flux. The X-ray and Lyα luminosities divided by the stellar bolometric luminosities show different patterns depending on stellar age. The L(Lyα)/L(bol) ratios increase smoothly to cooler stars of all ages, but the L(X)/L(bol) ratios show different trends. For older stars, the increase in coronal emission with decreasing ${T}_{\mathrm{eff}}$ is much steeper than that of chromospheric emission. We suggest a fundamental link between atmospheric properties and trend lines relating coronal and chromospheric heating, * Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Mikulski Archive for Space Telescopes (MAST) at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS AR-09525.01A. These observations are associated with program Nos. 12475, 12596, 13650, 14640, and 15071.

Keywords: ultraviolet sources; x-ray stars; stellar chromospheres; stellar coronae; exoplanet atmospheres; exoplanet evolution
Transmission Spectroscopy of the Earth-Sun System to Inform the Search for Extrasolar Life

Upcoming NASA astrophysics missions such as the James Webb Space Telescope will search for signs of life on planets transiting nearby stars. Doing so will require coadding dozens of transmission spectra to build up sufficient signal to noise while simultaneously accounting for challenging systematic effects such as surface/weather variability, atmospheric refraction, and stellar activity. To determine the magnitude and impacts of both stellar and planet variability on measured transmission spectra, we must assess the feasibility of stacking multiple transmission spectra of exo-Earths around their host stars. Using our own solar system, we can determine if current methodologies are sufficient to detect signs of life in Earth's atmosphere and measure the abundance of habitability indicators, such as H2O and CO2, and biosignature pairs, such as O2 and CH4. We assess the impact on transmission spectra of Earth transiting across the Sun from solar and planetary variability and identify remaining unknowns for understanding exoplanet transmission spectra. We conclude that a satellite observing Earth transits across the Sun from beyond L2 is necessary to address these long-standing concerns about the reliability of coadding planet spectra at UV, optical, and infrared wavelengths from multiple transits in the face of relatively large astrophysical systematics.

Keywords: exoplanet detection methods; exoplanet atmospheres; exoplanet atmospheric variability; exoplanet surface characteristics; exoplanet surface variability; active sun; stellar activity; stellar granulation; stellar faculae; starspots; transmission spectroscopy
The Near Infrared Imager and Slitless Spectrograph for the James Webb Space Telescope. I. Instrument Overview and In-flight Performance

The Near-Infrared Imager and Slitless Spectrograph (NIRISS) is the science module of the Canadian-built Fine Guidance Sensor onboard the James Webb Space Telescope (JWST). NIRISS has four observing modes: (1) broadband imaging featuring seven of the eight NIRCam broadband filters, (2) wide-field slitless spectroscopy at a resolving power of ~150 between 0.8 and 2.2 μm, (3) single-object cross-dispersed slitless spectroscopy (SOSS) enabling simultaneous wavelength coverage between 0.6 and 2.8 μm at R ~ 700, a mode optimized for exoplanet spectroscopy of relatively bright (J < 6.3) stars and (4) aperture masking interferometry (AMI) between 2.8 and 4.8 μm enabling high-contrast (~10-3 - 10-4) imaging at angular separations between 70 and 400 mas for relatively bright (M < 8) sources. This paper presents an overview of the NIRISS instrument, its design, its scientific capabilities, and a summary of in-flight performance. NIRISS shows significantly better response shortward of ~2.5 μm resulting in 10%-40% sensitivity improvement for broadband and low-resolution spectroscopy compared to pre-flight predictions. Two time-series observations performed during instrument commissioning in the SOSS mode yield very stable spectro-photometry performance within ~10% of the expected noise. The first space-based companion detection of the tight binary star AB Dor AC through AMI was demonstrated.

Keywords: space vehicle instruments; astronomical instrumentation
Confirmation of Subsolar Metallicity for WASP-77Ab from JWST Thermal Emission Spectroscopy

We present the dayside thermal emission spectrum of WASP-77Ab from 2.8 to 5.2 μm as observed with the NIRSpec instrument on the James Webb Space Telescope (JWST). WASP-77Ab was previously found to have a subsolar metallicity and a solar carbon-to-oxygen (C/O) ratio from H2O and CO absorption lines detected using high-resolution spectroscopy. By performing atmospheric retrievals on the JWST spectrum assuming chemical equilibrium, we find a subsolar metallicity [M/H] = $-{0.91}_{-0.16}^{+0.24}$ and C/O ratio ${0.36}_{-0.09}^{+0.10}$ . We identify H2O and CO and constrain their abundances, and we find no CO2 in the spectrum. The JWST and high-resolution spectroscopy results agree within ~1σ for the metallicity and within 1.8σ for the C/O ratio. However, our results fit less well in the picture painted by the shorter wavelength spectrum measured by Hubble Space Telescope Wide Field Camera 3. Comparing the JWST thermal emission spectra of WASP-77Ab and HD 149026b shows that both hot Jupiters have nearly identical brightness temperatures in the near-infrared but distinctly different atmospheric compositions. Our results reaffirm high-resolution spectroscopy as a powerful and reliable method to measure molecular abundances. Our results also highlight the incredible diversity of hot Jupiter atmospheric compositions.

Keywords: exoplanets; exoplanet atmospheres; james webb space telescope
Strategies for Determining the Cascade Rate in MHD Turbulence: Isotropy, Anisotropy, and Spacecraft Sampling

Exact laws for evaluating cascade rates, tracing back to the Kolmogorov "4/5" law, have been extended to many systems of interest including magnetohydrodynamics (MHD), and compressible flows of the magnetofluid and ordinary fluid types. It is understood that implementations may be limited by the quantity of available data and by the lack of turbulence symmetry. Assessment of the accuracy and feasibility of such third-order (or Yaglom) relations is most effectively accomplished by examining the von Kármán-Howarth equation in increment form, a framework from which the third-order laws are derived as asymptotic approximations. Using this approach, we examine the context of third-order laws for incompressible MHD in some detail. The simplest versions rely on the assumption of isotropy and the presence of a well-defined inertial range, while related procedures generalize the same idea to arbitrary rotational symmetries. Conditions for obtaining correct and accurate values of the dissipation rate from these laws based on several sampling and fitting strategies are investigated using results from simulations. The questions we address are of particular relevance to sampling of solar wind turbulence by one or more spacecraft.

Keywords: interplanetary turbulence; space plasmas; plasma physics; magnetohydrodynamics; magnetohydrodynamical simulations