adsabs/SciX_UAT_keywords huggingface dataset:
Impact of Tides on the Potential for Exoplanets to Host Exomoons

Exomoons may play an important role in determining the habitability of worlds outside of our solar system. They can stabilize conditions, alter the climate by breaking tidal locking with the parent star, drive tidal heating, and perhaps even host life themselves. However, the ability of an exoplanet to sustain an exomoon depends on complex tidal interactions. Motivated by this, we make use of simplified tidal lag models to follow the evolution of the separations and orbital and rotational periods in planet, star, and moon systems. We apply these models to known exoplanet systems to assess the potential for these exoplanets to host exomoons. We find that there are at least 36 systems in which an exoplanet in the habitable zone may host an exomoon for longer than one gigayear. This includes Kepler-1625b, an exoplanet with an exomoon candidate, which we determine would be able to retain a Neptune-sized moon for longer than a Hubble time. These results may help provide potential targets for future observation. In many cases, there remains considerable uncertainty in the composition of specific exoplanets. We show the detection (or not) of an exomoon would provide an important constraint on the planet structure due to differences in their tidal response.

Keywords: natural satellites (extrasolar); exoplanet tides; habitable planets
Direct-imaging Discovery of a Substellar Companion Orbiting the Accelerating Variable Star HIP 39017

We present the direct-imaging discovery of a substellar companion (a massive planet or low-mass brown dwarf) to the young, γ Doradus (γ Dor)-type variable star HIP 39017 (HD 65526). The companion's SCExAO/CHARIS JHK (1.1–2.4 μm) spectrum and Keck/NIRC2 $L^{\prime} $ photometry indicate that it is an L/T transition object. A comparison of the JHK+L $^{\prime} $ spectrum to several atmospheric model grids finds a significantly better fit to cloudy models than cloudless models. Orbit modeling with relative astrometry and precision stellar astrometry from Hipparcos and Gaia yields a semimajor axis of ${23.8}_{-6.1}^{+8.7}$ au, a dynamical companion mass of ${30}_{-12}^{+31}$ M J, and a mass ratio of ∼1.9%, properties most consistent with low-mass brown dwarfs. However, its mass estimated from luminosity models is a lower ∼13.8 M J due to an estimated young age (≲115 Myr); using a weighted posterior distribution informed by conservative mass constraints from luminosity evolutionary models yields a lower dynamical mass of ${23.6}_{-7.4}^{+9.1}$ M J and a mass ratio of ∼1.4%. Analysis of the host star's multifrequency γ Dor-type pulsations, astrometric monitoring of HIP 39017 b, and Gaia Data Release 4 astrometry of the star will clarify the system age and better constrain the mass and orbit of the companion. This discovery further reinforces the improved efficiency of targeted direct-imaging campaigns informed by long-baseline, precision stellar astrometry.

Keywords: direct imaging; brown dwarfs; astrometry; coronagraphic imaging
Dissecting the Extended X-Ray Emission in the Merging Pair NGC 6240: Photoionization and Winds

We present a detailed spectral and imaging analysis of the central 15″ radius (~7.5 kpc) region of the merger galaxy NGC 6240 that makes use of all the available Chandra-ACIS data (0.3-3 keV effective exposure of ~190 ks). This region shows extended X-ray structures with lower-energy counterparts imaged in CO, [O III], and Hα line emission. We find both photoionized phases of possible nuclear excitation and thermal shock-excited emission in the different large-scale components: the northwest "loop" detected in Hα, the region surrounding the two nuclei, the large outflow region to the northeast detected in [O III], and the southern X-ray extensions. The latter could be the ionization cone of the northern nucleus, with the N counterpart being obscured by the galaxy disk. The radial distribution of the X-ray surface brightness suggests a confined hot interstellar medium at r < 2.5 kpc, with a free-flowing wind at larger radii; if the confinement is magnetic, we estimate B-field values of ~100 μG, similar to those measured in the halo of M82. The thermal gas of the extended halo at kT ~ 1 keV absorbs soft X-rays from the active galactic nucleus, but not the extreme ultraviolet radiation leading to a rapid increase in F [O III]/F X beyond ~3 kpc. The α-element to Fe abundance ratios of the thermal components in the different regions of the extended X-ray emission are generally compatible with Type II supernova yields, confirming the importance of active star formation in NGC 6240.

Keywords: active galaxies; interacting galaxies; x-ray active galactic nuclei
Milky Way's Eccentric Constituents with Gaia, APOGEE, and GALAH

We report the results of an unsupervised decomposition of the local stellar halo in the chemodynamical space spanned by the abundance measurements from APOGEE DR17 and GALAH DR3. In our Gaussian mixture model, only four independent components dominate the halo in the solar neighborhood, three previously known, Aurora, Splash, and Gaia-Sausage/Enceladus (GS/E), and one new, Eos. Only one of these four is of accreted origin, namely, the GS/E, thus supporting the earlier claims that the GS/E is the main progenitor of the Galactic stellar halo. We show that Aurora is entirely consistent with the chemical properties of the so-called Heracles merger. In our analysis in which no predefined chemical selection cuts are applied, Aurora spans a wide range of [Al/Fe] with a metallicity correlation indicative of a fast chemical enrichment in a massive galaxy, the young Milky Way. The new halo component dubbed Eos is classified as in situ given its high mean [Al/Fe]. Eos shows strong evolution as a function of [Fe/H], where it changes from being the closest to GS/E at its lowest [Fe/H] to being indistinguishable from the Galactic low-α population at its highest [Fe/H]. We surmise that at least some of the outer thin disk of the Galaxy started its evolution in the gas polluted by the GS/E, and Eos is evidence of this process.

Keywords: galaxy formation; galaxy evolution; galaxy stellar halos; stellar abundances; galaxy kinematics; galaxy dynamics; galaxy chemical evolution; galactic archaeology
Growth of Outward Propagating Fast-magnetosonic/Whistler Waves in the Inner Heliosphere Observed by Parker Solar Probe

The solar wind in the inner heliosphere has been observed by Parker Solar Probe (PSP) to exhibit abundant wave activities. The cyclotron wave modes responding to ions or electrons are among the most crucial wave components. However, their origin and evolution in the inner heliosphere close to the Sun remains a mystery. Specifically, it remains unknown whether it is an emitted signal from the solar atmosphere or an eigenmode growing locally in the heliosphere due to plasma instability. To address and resolve this controversy, we must investigate the key quantity of the energy change rate of the wave mode. We develop a new technique to measure the energy change rate of plasma waves, and apply this technique to the wave electromagnetic fields measured by PSP. We provide the wave Poynting flux in the solar wind frame, identify the wave nature to be the outward propagating fast-magnetosonic/whistler wave mode instead of the sunward propagating waves. We provide the first evidence for growth of the fast-magnetosonic/whistler wave mode in the inner heliosphere based on the derived spectra of the real and imaginary parts of the wave frequencies. The energy change rate rises and stays at a positive level in the same wavenumber range as the bumps of the electromagnetic field power spectral densities, clearly manifesting that the observed fast-magnetosonic/whistler waves are locally growing to a large amplitude.

Keywords: solar wind; interplanetary turbulence
Spitzer Phase-curve Observations and Circulation Models of the Inflated Ultrahot Jupiter WASP-76b

The large radii of many hot Jupiters can only be matched by models that have hot interior adiabats, and recent theoretical work has shown that the interior evolution of hot Jupiters has a significant impact on their atmospheric structure. Due to its inflated radius, low gravity, and ultrahot equilibrium temperature, WASP-76b is an ideal case study for the impact of internal evolution on observable properties. Hot interiors should most strongly affect the nonirradiated side of the planet, and thus full phase-curve observations are critical to ascertain the effect of the interior on the atmospheres of hot Jupiters. In this work, we present the first Spitzer phase-curve observations of WASP-76b. We find that WASP-76b has an ultrahot dayside and relatively cold nightside with brightness temperatures of 2471 ± 27 K/1518 ± 61 K at 3.6 μm and 2699 ± 32 K/1259 ± 44 K at 4.5 μm, respectively. These results provide evidence for a dayside thermal inversion. Both channels exhibit small phase offsets of 0.68 ± 0°48 at 3.6 μm and 0.67 ± 0°2 at 4.5 μm. We compare our observations to a suite of general circulation models (GCMs) that consider two endmembers of interior temperature along with a broad range of frictional drag strengths. Strong frictional drag is necessary to match the small phase offsets and cold nightside temperatures observed. From our suite of cloud-free GCMs, we find that only cases with a cold interior can reproduce the cold nightsides and large phase-curve amplitude at 4.5 μm, hinting that the hot interior adiabat of WASP-76b does not significantly impact its atmospheric dynamics or that clouds blanket its nightside.

Keywords: exoplanet atmospheres; exoplanet astronomy; hot jupiters
Electric Currents through J-shaped and Non-J-shaped Flare Ribbons

Increasing attention has recently been paid to solar flares exhibiting double-J-shaped ribbons in the lower solar atmosphere, in the context of extending the two-dimensional standard flare model to three dimensions, as motivated by the spatial correlation between photospheric current channels and flare ribbons. Here, we study the electric currents through the photospheric area swept by flare ribbons (termed the synthesized ribbon area (SRA)), with a sample of 71 two-ribbon flares, of which 36 are J-shaped. Electric currents flowing through one ribbon are highly correlated with those flowing through the other, and they therefore belong to the same current system. The nonneutrality factor of this current system is independent of the flare magnitude, implying that both direct and return currents participate in flares. J-shaped flares are distinct from non-J-shaped flares in the following ways: (1) electric-current densities within the J-shaped SRA are significantly smaller than those within the non-J-shaped SRA, but the J-shaped SRA and its associated magnetic flux is also significantly larger. (2) Electric currents through the SRA are positively correlated with the flare magnitude, but J-shaped flares show a stronger correlation than non-J-shaped flares. (3) The majority (75%) of J-shaped flares are eruptive, while the majority (86%) of non-J-shaped flares are confined; accordingly, hosting active regions of J-shaped flares are more likely to be sigmoidal than non-J-shaped flares. Thus, J-shaped flares constitute a distinct subset of two-ribbon flares, probably representative of eruptive ones. Further, we found that combining the SRA and its associated magnetic flux has the potential to differentiate eruptive from confined flares.

Keywords: solar flares; solar active regions; solar storm; solar coronal mass ejections; magnetic fields
Spatial Distribution of Electromagnetic Waves near the Proton Cyclotron Frequency in ICME Sheath Regions Associated with Quasi-perpendicular Shocks: Wind Observations

Electromagnetic waves (EMWs) near the proton cyclotron frequency fcp are transverse left-handed (LH) or right-handed (RH) polarized waves, and are ubiquitous in the solar wind. However, the characteristics of these waves in the sheath regions of interplanetary coronal mass ejections (ICMEs) are poorly understood. Through a comprehensive survey of Wind magnetic field and plasma data using dynamic spectra and repeated filtering analyses, 700 EMW events (7.1% of the analysis time) are identified in the 62 ICME sheath regions associated with quasi-perpendicular shocks involved with a low shock Mach number Mf and low upstream β1. In the ICME sheath regions, outward (inward)-propagating LH (RH) EMWs have relatively higher counts and longer duration than inward (outward)-propagating LH (RH) EMWs in the plasma frame, consistent with previous STEREO observations. The spatial distributions of the magnetic field, plasma, and frequency parameters of EMWs are also presented in both spacecraft and plasma frames, especially the proton (alpha) temperature anisotropy Tp(α)\perp}/Tp(α)\parallel, α abundance Nα/Np, and normalized differential alpha-proton speed Vd/VA. After removing the Doppler shift, 81.1% (59%) of all outward (inward)-propagating LH EMWs have a frequency below (above) 0.5fcp, while 68.3% (64%) of all outward (inward)-propagating RH EMWs have a frequency smaller (greater) than 0.5fcp. Further investigations of local plasma parameters reveal that different excitation mechanisms for EMWs are in different subregions of the ICME sheath regions. These results are helpful in understanding the important role of EMWs in the solar wind-ICME coupling process with different sheath regions.

Keywords: interplanetary magnetic fields; solar coronal mass ejection shocks; solar wind; space plasmas
Gamma-Ray Absorption by the Cosmic Lyman Continuum from Star-forming Galaxies

Motivated by the discovery of the ultra-strong emission-line starburst galaxies (EELGs) known as "green pea galaxies," in this work we consider their contribution to the intergalactic flux of ionizing UV at high redshifts. Most galaxies that have been observed show a precipitous drop in the flux blueward of their Lyman limit. However, recent observations of EELGs have discovered that many more Lyman continuum photons escape from them into intergalactic space than previously suspected. We calculate their contribution to the extragalactic background light. We also calculate the effect of these photons on the absorption of high-energy γ-rays. For the more distant γ-ray sources, particularly at z ≥ 3, an intergalactic opacity above a few GeV is significantly higher than previous estimates which ignored the Lyman continuum photons. We calculate the results of this increased opacity on observed γ-ray spectra, which produce a high-energy turnover starting at lower energies than previously thought, and a gradual spectral steepening that may also be observable.

Keywords: galaxy evolution; high-redshift galaxies; primordial galaxies; compact dwarf galaxies; cool intergalactic medium; intergalactic medium; gamma-ray sources; gamma-ray observatories
Twin Extreme Ultraviolet Waves in the Solar Corona

Solar extreme ultraviolet (EUV) waves are spectacular propagating disturbances with EUV enhancements in annular shapes in the solar corona. These EUV waves carry critical information about the coronal magnetized plasma that can shed light on the elusive physical parameters (e.g., the magnetic field strength) by global solar coronal magnetoseismology. EUV waves are closely associated with a wide range of solar atmospheric eruptions, from violent flares and coronal mass ejections to less energetic plasma jets or mini-filament eruptions. However, the physical nature and driving mechanism of EUV waves are still controversial. Here, we report the unique discovery of twin EUV waves (TEWs) that were formed in a single eruption with observations from two different perspectives. In all earlier studies, a single eruption was associated at most with a single EUV wave. The newly found TEWs urge us to revisit our theoretical understanding of the underlying formation mechanism(s) of coronal EUV waves. Two distinct scenarios of TEWs were found. In the first scenario, the two waves were separately associated with a filament eruption and a precursor jet, while in another scenario, the two waves were successively associated with a filament eruption. Hence, we label these distinguished scenarios as "fraternal TEWs" and "identical TEWs," respectively. Further, we also suggest that impulsive lateral expansions of two distinct groups of coronal loops are critical to the formation of TEWs in a single eruption.

Keywords: solar activity; solar corona; solar coronal mass ejections; solar coronal waves
Spectral Properties of Quasars from Sloan Digital Sky Survey Data Release 14: The Catalog

We present measurements of the spectral properties for a total of 526,265 quasars, out of which 63% have a continuum signal-to-noise ratio > 3 pixel-1, selected from the fourteenth data release of the Sloan Digital Sky Survey (SDSS-DR14) quasar catalog. We performed a careful and homogeneous analysis of the SDSS spectra of these sources to estimate the continuum and line properties of several emission lines such as Hα, Hβ, Hγ, Mg II, C III], C IV, and Lyα. From the derived emission line parameters, we estimated single-epoch virial black hole masses (MBH) for the sample using Hβ, Mg II, and C IV emission lines. The sample covers a wide range in bolometric luminosity ( $\mathrm{log}{L}_{\mathrm{bol}};$ erg s-1) between 44.4 and 47.3 and $\mathrm{log}{M}_{\mathrm{BH}}$ between 7.1 and 9.9 M⊙. Using the ratio of Lbol to the Eddington luminosity as a measure of the accretion rate, the logarithm of the accretion rate is found to be in the range between -2.06 and 0.43. We performed several correlation analyses between different emission line parameters and found them to match the correlation known earlier using smaller samples. We note that strong Fe II sources with a large Balmer line width and highly accreting sources with large MBH are rare in our sample. We make an extended and complete catalog available online that contains various spectral properties of 526,265 quasars derived in this work along with other properties culled from the SDSS-DR14 quasar catalog.

Keywords: quasars; supermassive black holes; spectroscopy
Ions Measured by Voyager 1 Outside the Heliopause to 28 au and Implications Thereof

We report 40-139 keV in situ ion measurements from the Voyager 1/Low Energy Charged Particle (LECP) instrument, over the time period from 2000 to the first 3 months of 2020, toward assessing energetic ion flow properties inside the heliosheath (HS) and upstream of the heliopause (HP). We identify an average radial outflow of ions at ~46, 67, and 109 keV of ~2.33 × 10-3, ~1.37 × 10-3, and ~7.27 × 10-4 $({\mathrm{cm}}^{2}\,\mathrm{sr}\,{\rm{s}}\,\mathrm{keV})$ -1, respectively, from the beginning of 2013 up to 2020, i.e., over a spatial range of ~28 au past the HP. The raw 40-139 keV rates, uncorrected for background, show distinct intensity dropouts for particles with 90° pitch angles, in concert with the >211 MeV Galactic cosmic-ray anisotropy events, reported after Voyager 1 exited the HS in 2012 August. The intensity spectrum is consistent with a power-law form in energy with a spectral index of ~-1.4, similar to energy spectra measured by both Voyager 1 and 2/LECP inside the HS, providing strong indication that these particles correspond to an ion population leaking from the HS into interstellar space, most likely due to the flux tube interchange instability at the boundary. Future modeling efforts should incorporate this ion population, which provides the framework for establishing a communication between the HS and the very local interstellar medium.

Keywords: heliosphere; heliopause; heliosheath; termination shock; interstellar medium; interstellar magnetic fields
Cloud Properties and Correlations with Star Formation in Self-consistent Simulations of the Multiphase ISM

We apply gravity- and density-based methods to identify clouds in self-consistent numerical simulations of the star-forming, multiphase interstellar medium (ISM) and compare their properties and global correlation with the star formation rate (SFR) over time. The gravity-based method identifies bound objects, which have masses $M\sim {10}^{3}\mbox{--}{10}^{4}\,{M}_{\odot }$ at densities ${n}_{{\rm{H}}}\sim 100\,{\mathrm{cm}}^{-3}$ , and virial parameters αv ∼ 0.5-5. For clouds defined by a density threshold ${n}_{{\rm{H}},\min }$ , the average virial parameter decreases, and the fraction of material that is genuinely bound increases, with increasing ${n}_{{\rm{H}},\min }$ . Surprisingly, clouds defined by density thresholds can be unbound even when αv < 2, and high-mass clouds ( ${10}^{4}\mbox{--}{10}^{6}\,{M}_{\odot }$ ) are generally unbound. This suggests that the traditional αv is at best an approximate measure of boundedness in the ISM. All clouds have internal turbulent motions increasing with size as $\sigma \sim 1\,\mathrm{km}\,{{\rm{s}}}^{-1}{(R/\mathrm{pc})}^{1/2}$ , similar to observed relations. Bound structures comprise a small fraction of the total simulation mass and have a star formation efficiency per freefall time ${\varepsilon }_{\mathrm{ff}}$ ∼ 0.4. For ${n}_{{\rm{H}},\min }=10\mbox{--}100\,{\mathrm{cm}}^{-3}$ , ${\varepsilon }_{\mathrm{ff}}$ ∼ 0.03-0.3, increasing with density threshold. A temporal correlation analysis between $\mathrm{SFR}(t)$ and aggregate mass $M({n}_{{\rm{H}},\min };t)$ at varying ${n}_{{\rm{H}},\min }$ shows that time delays to star formation are ${t}_{\mathrm{delay}}\sim {t}_{\mathrm{ff}}({n}_{{\rm{H}},\min })$ . The correlation between $\mathrm{SFR}(t)$ and $M({n}_{{\rm{H}},\min };t)$ systematically tightens at higher ${n}_{{\rm{H}},\min }$ . Considering moderate-density gas, selecting against high virial parameter clouds improves correlation with the SFR, consistent with previous work. Even at high ${n}_{{\rm{H}},\min }$ , the temporal dispersion in $(\mathrm{SFR}-{\varepsilon }_{\mathrm{ff}}M/{t}_{\mathrm{ff}})/\langle \mathrm{SFR}\rangle $ is ∼50%, due to the large-amplitude variations and inherent stochasticity of the system.

Keywords: star formation; giant molecular clouds; interstellar medium
Zodiacal Exoplanets in Time (ZEIT). IX. A Flat Transmission Spectrum and a Highly Eccentric Orbit for the Young Neptune K2-25b as Revealed by Spitzer

Transiting planets in nearby young clusters offer the opportunity to study the atmospheres and dynamics of planets during their formative years. To this end, we focused on K2-25b—a close-in (P = 3.48 days), Neptune-sized exoplanet orbiting a M4.5 dwarf in the 650 Myr Hyades cluster. We combined photometric observations of K2-25 covering a total of 44 transits and spanning >2 yr, drawn from a mix of space-based telescopes (Spitzer Space Telescope and K2) and ground-based facilities (Las Cumbres Observatory Global Telescope network and MEarth). The transit photometry spanned 0.6-4.5 μm, which enabled our study of K2-25b’s transmission spectrum. We combined and fit each data set at a common wavelength within a Markov Chain Monte Carlo framework, yielding consistent planet parameters. The resulting transit depths ruled out a solar-composition atmosphere for K2-25b for the range of expected planetary masses and equilibrium temperature at a >4σ confidence level, and are consistent with a flat transmission spectrum. Mass constraints and transit observations at a finer grid of wavelengths (e.g., from the Hubble Space Telescope) are needed to make more definitive statements about the presence of clouds or an atmosphere of high mean molecular weight. Our precise measurements of K2-25b’s transit duration also enabled new constraints on the eccentricity of K2-25's orbit. We find K2-25b’s orbit to be eccentric (e > 0.20) for all reasonable stellar densities and independent of the observation wavelength or instrument. The high eccentricity is suggestive of a complex dynamical history and motivates future searches for additional planets or stellar companions.

Keywords: exoplanet atmospheres; exoplanets; transit photometry; open star clusters; exoplanet evolution; starspots; m dwarf stars; markov chain monte carlo; light curves