adsabs/SciX_UAT_keywords huggingface dataset:
A Wideband Polarization Observation of Hydra A with the Jansky Very Large Array

We present the results of a wideband high-resolution polarization study of Hydra A, one of the most luminous FR I radio galaxies known and among the most well studied. The radio emission from this source displays extremely large Faraday rotation measures (RMs), ranging from -12,300 rad m-2 to 5000 rad m-2, the majority of which are believed to originate from magnetized thermal gas external to the radio tails. The radio emission from both tails strongly depolarizes with decreasing frequency. Depolarization, as a function of wavelength, is commonly nonmonotonic, often showing oscillatory behavior, with strongly nonlinear rotation of the polarization position angle with λ 2. A simple model, based on the RM screen derived from the high-frequency, high-resolution data, predicts the lower frequency depolarization remarkably well. The success of this model indicates the majority of the depolarization can be attributed to fluctuations in the magnetic field on scales <1500 pc, suggesting the presence of turbulent magnetic field/electron density structures on subkiloparsec scales within a Faraday rotating medium.

Keywords: extragalactic magnetic fields; extragalactic radio sources; extragalactic astronomy; radio galaxies; intracluster medium; galaxy clusters; magnetic fields
Cooling-induced Vortex Decay in Keplerian Disks

Vortices are readily produced by hydrodynamical instabilities, such as the Rossby wave instability, in protoplanetary disks. However, large-scale asymmetries indicative of dust-trapping vortices are uncommon in submillimeter continuum observations. One possible explanation is that vortices have short lifetimes. In this paper, we explore how radiative cooling can lead to vortex decay. Elliptical vortices in Keplerian disks go through adiabatic heating and cooling cycles. Radiative cooling modifies these cycles and generates baroclinicity that changes the potential vorticity of the vortex. We show that the net effect is typically a spin down, or decay, of the vortex for a subadiabatic radial stratification. We perform a series of two-dimensional shearing box simulations, varying the gas cooling (or relaxation) time, tcool, and initial vortex strength. We measure the vortex decay half-life, thalf, and find that it can be roughly predicted by the timescale ratio tcool/tturn, where tturn is the vortex turnaround time. Decay is slow in both the isothermal (tcool ≪ tturn) and adiabatic (tcool ≫ tturn) limits; it is fastest when tcool ~ 0.1 tturn, where thalf is as short as ~300 orbits. At tens of astronomical units where disk rings are typically found, tturn is likely much longer than tcool, potentially placing vortices in the fast decay regime.

Keywords: protoplanetary disks; circumstellar disks; planet formation; hydrodynamical simulations; planetary-disk interactions
Early Infrared and Visible Spectra from the 2022 Outburst of the Recurrent Novae U Scorpii

Spectroscopy from 0.46-2.5 μm is presented for the 2022 outburst of the recurrent nova U Scorpii from 2.54, 3.60, and 8.59 days after maximum light. During this period the spectra evolved from comparatively low excitation to the verge of displaying coronal lines. Between days 2.54 and 3.60, the nova showed a marked decrease in the low excitation lines of N I, O I, and Mg II , an increase in He I, the emergence of N III, and changes to the very broad line profiles. By day 8.59, the He I lines had been largely replaced by He II emission and most broad component were weak or undetectable. No optical coronal lines were observed during or immediately following the detection of infrared coronal lines by Banerjee et al.

Keywords: recurrent novae
Measuring the Obliquities of the TRAPPIST-1 Planets with MAROON-X

A star's obliquity with respect to its planetary system can provide us with insight into the system's formation and evolution, as well as hinting at the presence of additional objects in the system. However, M dwarfs, which are the most promising targets for atmospheric follow-up, are underrepresented in terms of obliquity characterization surveys due to the challenges associated with making precise measurements. In this paper, we use the extreme-precision radial velocity (RV) spectrograph MAROON-X to measure the obliquity of the late M dwarf TRAPPIST-1. With the Rossiter-McLaughlin effect, we measure a system obliquity of $-2{^\circ }_{-{19}^{\circ }}^{+{17}^{\circ }}$ and a stellar rotational velocity of 2.1 ± 0.3 km s-1. We were unable to detect stellar surface differential rotation, and we found that a model in which all planets share the same obliquity was favored by our data. We were also unable to make a detection of the signatures of the planets using Doppler tomography, which is likely a result of the both the slow rotation of the star and the low signal-to-noise ratio of the data. Overall, TRAPPIST-1 appears to have a low obliquity, which could imply that the system has a low primordial obliquity. It also appears to be a slow rotator, which is consistent with past characterizations of the system and estimates of the star's rotation period. The MAROON-X data allow for a precise measurement of the stellar obliquity through the Rossiter-McLaughlin effect, highlighting the capabilities of MAROON-X and its ability to make high-precision RV measurements around late, dim stars.

Keywords: extrasolar rocky planets; m dwarf stars
Correlation of Structure and Stellar Properties of Galaxies in Stripe 82

Establishing a correlation (or lack thereof) between the bimodal color distribution of galaxies and their structural parameters is crucial to understand the origin of bimodality. To achieve that, we have performed a 2D mass-based structural decomposition (bulge+disk) of all disk galaxies (total = 1263) in the Herschel imaging area of the Stripe 82 region using Ks-band images from the VICS82 survey. The scaling relations thus derived are found to reflect the internal kinematics and are employed in combination to select an indubitable set of classical- and pseudo-bulge-hosting disk galaxies. The rest of the galaxies (<20%) are marked as disks with "ambiguous" bulges. Pseudo- and classical bulge-disk galaxies exhibit clear bimodality in terms of all stellar parameters (M*, specific star formation rate, r - Ks). All pseudo-bulge-disk galaxies are blue and star forming, and all classical bulge-disk galaxies are red and quiescent with less than 5% digressions. Ambiguous bulge-disk galaxies are intermediate to pseudo- and classical bulge-disk galaxies in the distribution of all structural and stellar parameters. ${\rm{\Delta }}\langle {\mu }_{\mathrm{eb}}\rangle $ —based on the placement of bulges on the Kormendy relation—is found to be the most efficient single structural indicator of both bulge type and stellar activity. The placement of ambiguous bulge-disk galaxies on scaling relations and the fundamental plane, in addition to their peculiar stellar properties, suggests that they are dominantly part of the green valley.

Keywords: galaxy bulges; star formation; galaxy structure; galaxy stellar content
Feasibility of High-resolution Transmission Spectroscopy for Low-velocity Exoplanets

In recent years, high-resolution transmission spectroscopy in the near-infrared has led to detections of prominent molecules in several giant exoplanets on close-in orbits. This approach has traditionally relied on the large Doppler shifts of the planetary spectral lines induced by the high velocities of close-in planets, which were considered necessary for separating them from the quasi-static stellar and telluric lines. In this work, we demonstrate the feasibility of high-resolution transmission spectroscopy for chemical detections in atmospheres of temperate low-mass exoplanets around M dwarfs with low radial velocity variation during transit. We pursue this goal using model injection and recovery tests with H- and K-band high-resolution spectroscopy of the temperate sub-Neptune TOI-732 c, observed using the IGRINS spectrograph on Gemini South. We show that planetary signals in transit may be recovered when the change in the planet's radial velocity is very small, down to subpixel velocities. This is possible due to the presence of the planetary signal in only a subset of the observed spectra. A sufficient number of out-of-transit spectra can create enough contrast between the planet signal and telluric/stellar contaminants that the planet signal does not constitute a principal component of the time-series spectra and can therefore be isolated using principal-component-analysis-based detrending without relying on a significant Doppler shift. We additionally explore novel metrics for finding such signals, and investigate trends in their detectability. Our work extends the scope of high-resolution transmission spectroscopy and creates a pathway toward the characterization of habitable sub-Neptune worlds with ground-based facilities.

Keywords: exoplanets; atmospheric composition; infrared spectroscopy
Implications from Late-time X-Ray Detections of Optically Selected Tidal Disruption Events: State Changes, Unification, and Detection Rates

We present Chandra X-ray observations of four optically selected tidal disruption events (TDEs) obtained 4-9 yr after discovery. Three sources were detected with luminosities between 9 × 1040 and 3 × 1042 erg s-1. The spectrum of PTF09axc is consistent with a power law of index 2.5 ± 0.1, whereas the spectrum of PTF09ge is very soft. The power-law spectrum of PTF09axc and prior literature findings provide evidence that TDEs transition from an early-time soft state to a late-time hard state many years after disruption. We propose that the time to peak luminosity for optical and X-ray emission may differ substantially in TDEs, with X-rays being produced or becoming observable later. This delay helps explain the differences in observed properties such as Lopt/LX of optically and X-ray-selected TDEs. We update TDE rate predictions for the eROSITA instrument: it ranges from 3 to 990 yr-1, depending sensitively on the distribution of black hole spins and the time delay between disruption and peak X-ray brightness. We further predict an asymmetry in the number of retrograde and prograde disks in samples of optically and X-ray-selected TDEs. The details of the observational biases can contribute to observed differences between optically and X-ray-selected TDEs (with optically selected TDEs being fainter in X-rays for retrograde TDE disks).

Keywords: astrophysical black holes; tidal disruption; active galactic nuclei; high energy astrophysics; x-ray transient sources
On the Cooling Flow Problem in the Gaseous Halo of the Milky Way

Theoretical and observational arguments suggest that there is a large amount of hot (∼106 K) diffuse gas residing in the Milky Way (MW) halo, but its total mass and spatial distribution are still unclear. In this work, we present a general model for the gas density distribution in the Galactic halo, and investigate the gas evolution under radiative cooling with a series of 2D hydrodynamic simulations. We find that the mass inflow rate in the developed cooling flow increases with gas metallicity and the total gas mass in the halo. For a fixed halo gas mass, the spatial gas distribution affects the onset time of the cooling catastrophe, which starts earlier when the gas distribution is more centrally peaked, but does not substantially affect the final mass inflow rate. The gravity from the Galactic bulge and disk affects gas properties in the inner regions, but has little effect on the final inflow rate either. We confirm our results by investigating cooling flows in several density models adopted from the literature, including the Navarro-Frenk-White (NFW) model, the cored-NFW model, the Maller & Bullock model, and the β model. Typical mass inflow rates in our simulations range from ∼5 M⊙ yr-1 to ∼60 M⊙ yr-1, and are much higher than the observed star formation rate in our Galaxy, suggesting that stellar and active galactic nucleus feedback processes may play important roles in the evolution of the MW and MW-type galaxies.

Keywords: circumgalactic medium; hydrodynamical simulations; galaxy physics; milky way galaxy; plasma astrophysics; galaxy evolution; cooling flows; galaxy processes
X-Ray Constraints on the Spectral Energy Distribution of the z = 5.18 Blazar SDSS J013127.34-032100.1

We report on X-ray measurements constraining the spectral energy distribution (SED) of the high-redshift z = 5.18 blazar SDSS J013127.34-032100.1 with new XMM-Newton and NuSTAR exposures. The blazar's X-ray spectrum is well fit by a power law with Γ = 1.9 and ${N}_{{\rm{H}}}=1.1\times {10}^{21}\,{\mathrm{cm}}^{-2}$ , or a broken power law with ${{\rm{\Gamma }}}_{l}=0.7$ , ${{\rm{\Gamma }}}_{h}=1.8$ , and a break energy ${E}_{b}=0.7\,\mathrm{keV}$ for an expected absorbing column density of ${N}_{{\rm{H}}}=3.6\times {10}^{20}\ {\mathrm{cm}}^{-2}$ , supported by spectral fitting of a nearby bright source. No additional spectral break is found at higher X-ray energies (1-30 keV). We supplement the X-ray data with lower-energy radio-to-optical measurements and Fermi-LAT gamma-ray upper limits, construct broadband SEDs of the source, and model the SEDs using a synchro-Compton scenario. This modeling constrains the bulk Doppler factor of the jets to ≥7 and ≥6 (90%) for the low- and high-NH SEDs, respectively. The corresponding beaming implies ≥130 (low NH) or $\geqslant 100$ (high NH) high-spin supermassive black holes similar to J0131 exist at similar redshifts.

Keywords: active galactic nuclei; high energy astrophysics; blazars; spectral energy distribution; early universe; quasars; supermassive black holes
The ESA Hera Mission: Detailed Characterization of the DART Impact Outcome and of the Binary Asteroid (65803) Didymos

Hera is a planetary defense mission under development in the Space Safety and Security Program of the European Space Agency for launch in 2024 October. It will rendezvous in late 2026 December with the binary asteroid (65803) Didymos and in particular its moon, Dimorphos, which will be impacted by NASA's DART spacecraft on 2022 September 26 as the first asteroid deflection test. The main goals of Hera are the detailed characterization of the physical properties of Didymos and Dimorphos and of the crater made by the DART mission, as well as measurement of the momentum transfer efficiency resulting from DART's impact. The data from the Hera spacecraft and its two CubeSats will also provide significant insights into asteroid science and the evolutionary history of our solar system. Hera will perform the first rendezvous with a binary asteroid and provide new measurements, such as radar sounding of an asteroid interior, which will allow models in planetary science to be tested. Hera will thus provide a crucial element in the global effort to avert future asteroid impacts at the same time as providing world-leading science.

Keywords: near-earth objects; asteroid satellites; impact phenomena; asteroid dynamics; asteroid surfaces
Evolution of Large-amplitude Alfvén Waves and Generation of Switchbacks in the Expanding Solar Wind

Motivated by recent Parker Solar Probe (PSP) observations of "switchbacks" (abrupt, large-amplitude reversals in the radial magnetic field, which exhibit Alfvénic correlations), we examine the dynamics of large-amplitude Alfvén waves in the expanding solar wind. We develop an analytic model that makes several predictions: switchbacks should preferentially occur in regions where the solar wind plasma has undergone a greater expansion, the switchback fraction at radii comparable to PSP should be an increasing function of radius, and switchbacks should have their gradients preferentially perpendicular to the mean magnetic field direction. The expansion of the plasma generates small compressive components as part of the wave's nonlinear evolution: these are maximized when the normalized fluctuation amplitude is comparable to $\sin \theta $ , where θ is the angle between the propagation direction and the mean magnetic field. These compressive components steepen the primary Alfvénic waveform, keeping the solution in a state of nearly constant magnetic field strength as its normalized amplitude δB/B grows due to expansion. The small fluctuations in the magnetic field strength are minimized at a particular θ-dependent value of β, usually of order unity, and the density and magnetic-field-strength fluctuations can be correlated or anticorrelated depending on β and θ. Example solutions of our dynamical equation are presented; some do indeed form magnetic-field reversals. Our predictions appear to match some previously unexplained phenomena in observations and numerical simulations, providing evidence that the observed switchbacks result from the nonlinear evolution of the initially small-amplitude Alfvén waves already known to be present at the coronal base.

Keywords: alfven waves; magnetohydrodynamics; solar wind; space plasmas
Switchbacks in the Young Solar Wind: Electron Evolution Observed inside Switchbacks between 0.125 au and 0.25 au

Switchbacks are localized deviations from the nominal Parker spiral field in the solar wind. In this study, we investigate the electron distributions inside switchbacks, focusing primarily on the suprathermal (halo and strahl) populations. We explore electron parameters in relation to the angle of rotation of the magnetic field from radial to determine whether electron distributions observed within switchbacks have any differences from those outside of switchbacks. Our observations reveal several trends in the suprathermal electron populations inside switchbacks. We find that the sunward deficit in the electron velocity distribution function typically observed near the Sun is filled in at larger rotation angles. This results in the suprathermal electron density and heat flux in the antistrahl direction changing from a negative to a positive value. On many days, we also observe a positive correlation between the halo density and rotation angle, and this may suggest that the growth of the halo may fill in the sunward deficit. We also find that strahl distributions have an increased average angular spread at large magnetic field rotation angles. The increase in suprathermal electron flux in the antistrahl direction, and the increase in strahl width, together could suggest that enhanced scattering occurs inside switchbacks. Electron core beta values tend to increase with the magnetic field rotation angle, mainly due to a decrease in magnetic pressure. An increase in electron beta may favor the growth of instabilities inside switchbacks. The Parker Solar Probe observations therefore support an enhanced role for wave-particle interactions in switchbacks.

Keywords: solar wind; space plasmas; solar corona; solar magnetic fields; solar physics
A Multiwavelength Study of the Hard and Soft States of MAXI J1820+070 During Its 2018 Outburst

We present a comprehensive multiwavelength spectral analysis of the black hole (BH) X-ray binary MAXI J1820+070 during its 2018 outburst, utilizing AstroSat far-UV, soft X-ray, and hard X-ray data, along with (quasi-)simultaneous optical and X-ray data from the Las Cumbres Observatory and NICER, respectively. In the soft state, we detect soft X-ray and UV/optical excess components over and above the intrinsic accretion disk emission (kT in ∼ 0.58 keV) and a steep X-ray power-law component. The soft X-ray excess is consistent with a high-temperature blackbody (kT ∼ 0.79 keV), while the UV/optical excess is described by UV emission lines and two low-temperature blackbody components (kT ∼ 3.87 and ∼0.75 eV). Employing continuum spectral fitting, we determine the BH spin parameter (a = 0.77 ± 0.21), using the jet inclination angle of 64° ± 5° and a mass spanning 5–10 M ☉. In the hard state (HS), we observe a significantly enhanced optical/UV excess component, indicating a stronger reprocessed emission in the outer disk. Broadband X-ray spectroscopy in the HS reveals a two-component corona, each associated with its reflection component, in addition to the disk emission (kT in ∼ 0.19 keV). The softer coronal component dominates the bolometric X-ray luminosity and produces broader relativistic reflection features, while the harder component gets reflected far from the inner disk, yielding narrow reflection features. Furthermore, our analysis in the HS suggests a substantial truncation of the inner disk (≳51 gravitational radii) and a high disk density (∼1020 cm‑3).

Keywords: accretion; black hole physics; astronomy data analysis; low-mass x-ray binary stars; x-ray astronomy
Penumbral Brightening Events Observed in AR NOAA 12546

Penumbral transient brightening events have been attributed to magnetic reconnection episodes occurring in the low corona. We investigated the trigger mechanism of these events in active region NOAA 12546 by using multiwavelength observations obtained with the Interferometric Bidimensional Spectrometer, by the Solar Dynamics Observatory, the Interface Region Imaging Spectrograph, and the Hinode satellites. We focused on the evolution of an area of the penumbra adjacent to two small-scale emerging flux regions (EFRs), which manifested three brightening events detected from the chromosphere to the corona. Two of these events correspond to B-class flares. The same region showed short-lived moving magnetic features (MMFs) that streamed out from the penumbra. In the photosphere, the EFRs led to small-scale penumbral changes associated with a counter-Evershed flow and to a reconfiguration of the magnetic fields in the moat. The brightening events had one of the footpoints embedded in the penumbra and seemed to result from the distinctive interplay between the preexisting penumbral fields, MMFs, and the EFRs. The IRIS spectra measured therein reveal enhanced temperature and asymmetries in spectral lines, suggestive of event triggering at different heights in the atmosphere. Specifically, the blue asymmetry noted in C II and Mg II h&k lines suggests the occurrence of chromospheric evaporation at the footpoint located in the penumbra as a consequence of the magnetic reconnection process at higher atmospheric heights.

Keywords: solar magnetic reconnection; solar magnetic fields; active solar chromosphere; solar photosphere; solar x-ray emission
Effects of Superthermal Plasmas on the Linear Growth of Multiband EMIC Waves

Observations show that particle velocity distributions in space plasmas generally exhibit a non-Maxwellian high-energy tail that can be well fitted with kappa distributions. To better understand the correlation between realistic particle velocity distributions and plasma wave excitation, we investigate the linear cyclotron instability of multiband electromagnetic ion cyclotron (EMIC) waves in a kappa plasma containing hot anisotropic protons, which provides the free energy for the wave growth. We find that the effects of superthermal plasmas on EMIC wave instability have a strong dependence on the emission band, temperature anisotropy Ahp, and parallel beta βhp of hot protons. For H+ and He+ band EMIC waves, the maximum growth rates exhibit distinct behaviors with the variation of the spectral index κ of kappa distributions for different Ahp values. The maximum growth rates decrease with increasing κ-value for low Ahp and increase with increasing κ-value for high Ahp. For O+ band waves, the effects of superthermal plasmas on the maximum growth rate are strongly controlled by βhp. For low βhp, the growth rate decreases monotonically with increasing κ-value for all Ahp. For high βhp, increase of κ-value tends to enhance the wave growth for intermediate Ahp and to suppress the wave growth otherwise. Our results also indicate that the presence of a high-energy tail tends to decrease the real frequency corresponding to the maximum growth rate for all three bands. While the minimum electron resonant energy for O+ band EMIC waves decreases as the κ-value increases, the minimum electron resonant energies for H+ and He+ band waves remain unaffected.

Keywords: planetary magnetospheres; space plasmas