adsabs/SciX_UAT_keywords huggingface dataset:
A Layered Debris Disk around M Star TWA 7 in Scattered Light

We have obtained Hubble Space Telescope (HST) coronagraphic observations of the circumstellar disk around M star TWA 7 using the Space Telescope Imaging Spectrograph (STIS) instrument in visible light. Together with archival observations, including HST/NICMOS using the F160W filter and Very Large Telescope/SPHERE at the H-band in polarized light, we investigate the system in scattered light. By studying this nearly face-on system using geometric disk models and Henyey-Greenstein phase functions, we report a new discovery of a tertiary ring and a clump. We identify a layered architecture: three rings, a spiral, and an ≈150 au2 elliptical clump. The most extended ring peaks at 28 au, and the other components are on its outskirts. Our point-source detection-limit calculations demonstrate the necessity of disk modeling in imaging fainter planets. Morphologically, we witness a clockwise spiral motion, and the motion pattern is consistent with both solid body motion and local Keplerian motion; we also observe underdensity regions for the secondary ring that might result from mean-motion resonance or moving shadows: both call for re-observations to determine their nature. Comparing multi-instrument observations, we obtain blue STIS-NICMOS color, a STIS-SPHERE radial distribution peak difference for the tertiary ring, and a high SPHERE-NICMOS polarization fraction; these aspects indicate that TWA 7 could retain small dust particles. By viewing the debris disk around M star TWA 7 at a nearly face-on vantage point, our study allows for the understanding of such disks in scattered light in both system architecture and dust property.

Keywords: debris disks; coronagraphic imaging; planetary system formation; orbital motion
Fractal Aggregates of Submicron-sized Grains in the Young Planet-forming Disk around IM Lup

Despite rapidly growing disk observations, it remains a mystery what primordial dust aggregates look like and what the physical and chemical properties of their constituent grains (monomers) are in young planet-forming disks. Confrontation of models with observations to answer this mystery has been a notorious task because we have to abandon a commonly used assumption, perfectly spherical grains, and take into account particles with complex morphology. In this Letter, we present the first thorough comparison between near-infrared scattered light of the young planet-forming disk around IM Lup and the light-scattering properties of complex-shaped dust particles. The availability of scattering observations at multiple wavelengths and over a significant range of scattering angles allows for the first determination of the monomer size, fractal dimension, and size of dust aggregates in a planet-forming disk. We show that the observations are best explained by fractal aggregates with a fractal dimension of 1.5 and a characteristic radius larger than ~2 μm. We also determined the radius of the monomer to be ~200 nm, and monomers much smaller than this size can be ruled out on the premise that the fractal dimension is less than 2. Furthermore, dust composition comprising amorphous carbon is found to be favorable to simultaneously account for the faint scattered light and the flared disk morphology. Our results support that planet formation begins with fractal coagulation of submicron-sized grains. All the optical properties of complex dust particles computed in this study are publicly available.

Keywords: protoplanetary disks; near infrared astronomy; planet formation
Detection of Tidal Disruption Events around Direct-collapse Black Holes at High Redshifts with the James Webb Space Telescope

This is the third sequel in a series discussing the discovery of various types of extragalactic transients with the James Webb Space Telescope (JWST) in a narrow-field (∼0.1 deg2), moderately deep (mAB ∼ 27 mag) survey. In this part we focus on the detectability and observational characteristics of direct-collapse black holes (DCBHs) and tidal disruption events (TDEs) around them. We use existing models for DCBH accretion luminosities and spectra, as well as for TDE light curves, and find that accreting DCBH seeds may be bright enough for detection up to z ∼ 7 with JWST NIRCam imaging. TDEs of massive (M ≳ 50 M⊙) stars around them can enhance the chance for discovering them as transient objects, although the rate of such events is low, a few per survey time. TDEs around nonaccreting black holes of M ∼ 106 M⊙ may also be detected at z < 7 redshifts in the redder NIRCam bands between 3 and 5 μs. It is also shown that accreting DCBHs appear separate from supernovae on the NIRCam color-color plot, but TDEs from quiescent black holes fall in nearly the same color range as superluminous supernovae, which makes them more difficult to identify.

Keywords: black holes; reionization; early universe; surveys
UOCS. XIII. Study of the Far-ultraviolet Bright Stars in the Open Cluster NGC 2420 Using AstroSat

We present the study of four far-ultraviolet (FUV) bright stars in the field of the open cluster NGC 2420 using the Ultra Violet Imaging Telescope mounted on AstroSat. The three stars 525, 527, and 560 are members, while star 646 is a nonmember of the cluster. To characterize and determine the parameters of these stars, multiwavelength spectral energy distributions (SEDs) are analyzed using UV, optical, and IR data sets. For all four FUV bright stars, a two-component SED model fits well. Our findings indicate that two stars, 525 and 560, are binary blue straggler star (BSS) systems. These BSS systems may have formed in a tertiary system due to mass transfer from an evolved outer tertiary companion. Star 527 is a binary system of a BSS and an extremely low-mass (ELM) white dwarf, while star 646 is a binary system of a horizontal branch star and an ELM white dwarf. The effective temperatures, radii, luminosities, and masses of the two ELMs are (10250, 11500) K (0.42, 0.12) R ⊙, (1.61, 0.23) L ⊙, and (0.186, 0.170) M ⊙, respectively. The star 527 could be a post-mass-transfer system and may have originated through the Case A/B mass-transfer process in a low-density environment. The cooling age of the ELMs is < 1 Myr, indicating that they have only recently formed.

Keywords: star clusters; open star clusters
Connecting Atmospheric Properties and Synthetic Emission of Shock Waves Using 3D RMHD Simulations of the Quiet Sun

We analyze the evolution of shock waves in high-resolution 3D radiative MHD simulations of the quiet Sun and their synthetic emission characteristics. The simulations model the dynamics of a 12.8 × 12.8 × 15.2 Mm quiet-Sun region (including a 5.2 Mm layer of the upper convection zone and a 10 Mm atmosphere from the photosphere to corona) with an initially uniform vertical magnetic field of 10 G, naturally driven by convective flows. We synthesize the Mg II and C II spectral lines observed by the Interface Region Imaging Spectrograph (IRIS) satellite and extreme ultraviolet emission observed by the Solar Dynamics Observatory (SDO)/AIA telescope. Synthetic observations are obtained using the RH1.5D radiative transfer code and temperature response functions at both the numerical and instrumental resolutions. We found that the Doppler velocity jumps of the C II 1334.5 Å IRIS line and a relative enhancement of the emission in the 335 Å SDO/AIA channel are the best proxies for the enthalpy deposited by shock waves into the corona (with Kendall's τ correlation coefficients of 0.59 and 0.38, respectively). The synthetic emission of the lines and the extreme ultraviolet passbands are correlated with each other during the shock-wave propagation. All studied shocks are mostly hydrodynamic (i.e., the magnetic energy carried by horizontal fields is ≤2.6% of the enthalpy for all events) and have Mach numbers >1.0-1.2 in the low corona. The study reveals the possibility of diagnosing energy transport by shock waves into the solar corona, as well as their other properties, by using IRIS and SDO/AIA sensing observations.

Keywords: solar atmosphere; solar corona; solar transition region; radiative transfer; spectroscopy
Moderately High Obliquity Promotes Biospheric Oxygenation

Planetary obliquity is a first-order control on planetary climate and seasonal contrast, which has a number of cascading consequences for life. How moderately high obliquity (obliquities greater than Earth's current obliquity up to 45°) affects a planet's surface physically has been studied previously, but we lack an understanding of how marine life will respond to these conditions. We couple the ROCKE-3D general circulation model to the cGENIE 3D biogeochemical model to simulate the ocean biosphere's response to various planetary obliquities, bioessential nutrient inventories, and biospheric structure. We find that the net rate of photosynthesis increased by 35% and sea-to-air flux of biogenic oxygen doubled between the 0° and 45° obliquity scenarios, which is an equivalent response to doubling bioessential nutrients. Our results suggest that moderately high obliquity planets have higher potential for biospheric oxygenation than their low-obliquity counterparts and that life on moderately high obliquity habitable planets may be easier to detect with next-generation telescopes. These moderately high obliquity habitable planets may also be more conducive to the evolution of complex life.

Keywords: astrobiology; biosignatures; exoplanets; habitable planets; ocean-atmosphere interactions
Photoevaporation of Grain-depleted Protoplanetary Disks around Intermediate-mass Stars: Investigating the Possibility of Gas-rich Debris Disks as Protoplanetary Remnants

Debris disks are classically considered to be gas-less systems, but recent (sub)millimeter observations have detected tens of those with rich gas content. The origin of the gas component remains unclear, but it could be protoplanetary remnants and/or secondary products from large bodies. In order to be protoplanetary in origin, the gas component of the parental protoplanetary disk is required to survive for $\gtrsim 10\,\mathrm{Myr}$ . However, previous models predict $\lesssim 10\,\mathrm{Myr}$ lifetimes because of efficient photoevaporation at the late stage of disk evolution. We investigate photoevaporation of gas-rich, optically-thin disks around intermediate-mass stars at a late stage of the disk evolution. The evolved system is modeled like those devoid of small grains ( $\lesssim 4\,\mu {\rm{m}}$ ). We find that grain depletion reduces photoelectric heating so that far-ultraviolet photoevaporation is not excited. Extreme-ultraviolet (EUV) photoevaporation is dominant and yields a mass-loss rate of the order of $1\times {10}^{-11}{({{\rm{\Phi }}}_{\mathrm{EUV}}/{10}^{38}{{\rm{s}}}^{-1})}^{1/2}\,{M}_{\odot }\,{\mathrm{yr}}^{-1}$ , where ${{\rm{\Phi }}}_{\mathrm{EUV}}$ is the EUV emission rate of the host star. The estimated gas-disk lifetimes are $\sim 100{({M}_{\mathrm{disk}}/{10}^{-3}{M}_{\odot })({{\rm{\Phi }}}_{\mathrm{EUV}}/{10}^{38}{{\rm{s}}}^{-1})}^{1/2}\,\mathrm{Myr}$ and depend on the "initial" disk mass at the point small grains have been depleted in the system. We show that the gas component can survive for a much longer time around A-type stars than lower-mass (F-, G-, K-type) stars owing to their atypical low EUV (and X-ray) luminosities. This trend is consistent with the higher frequency of gas-rich debris disks around A-type stars, implying the possibility of the gas component being protoplanetary remnants.

Keywords: protoplanetary disks; debris disks; hydrodynamical simulations; star formation; planetary system formation
The Turbulent Stress Spectrum in the Inertial and Subinertial Ranges

For velocity and magnetic fields, the turbulent pressure and, more generally, the squared fields such as the components of the turbulent stress tensor, play important roles in astrophysics. For both one and three dimensions, we derive the equations relating the energy spectra of the fields to the spectra of their squares. We solve the resulting integrals numerically and show that for turbulent energy spectra of Kolmogorov type, the spectral slope of the stress spectrum is also of Kolmogorov type. For shallower turbulence spectra, the slope of the stress spectrum quickly approaches that of white noise, regardless of how blue the spectrum of the field is. For fully helical fields, the stress spectrum is elevated by about a factor of two in the subinertial range, while that in the inertial range remains unchanged. We discuss possible implications for understanding the spectrum of primordial gravitational waves from causally generated magnetic fields during cosmological phase transitions in the early universe. We also discuss potential diagnostic applications to the interstellar medium, where polarization and scintillation measurements characterize the square of the magnetic field.

Keywords: interplanetary turbulence; gravitational waves; magnetohydrodynamics; hydrodynamics
Measuring the Stellar Population Parameters of the Early-type Galaxy NGC 3923: The Challenging Measurement of the Initial Mass Function

Recent studies of early-type galaxies have suggested that the initial mass function (IMF) slope is bottom-heavy; that is, they contain a larger fraction of low-mass stars than the Milky Way. However, measurements of the IMF remain challenging in unresolved galaxies because features in their observed spectra are sensitive to a number of factors, including the stellar age, metallicity, and elemental abundances, in addition to the IMF. In this paper, we use new high signal-to-noise IMACS (Magellan) spectra to study the elliptical shell galaxy NGC 3923 at optical (3700-6600 Å) and near-infrared (7900-8500 Å) wavelengths, as a function of radius. We have undertaken a number of independent approaches to better understand the uncertainties in our results. (1) We compare two different stellar population model libraries; (2) we undertake spectral index fitting as well as full spectral fitting; (3) we have performed simulations for which we a priori know the input IMF and that closely match our data; (4) we also investigate the effects of including a two-component rather than a single stellar population. We show that our results are sensitive to the assumptions we make and to the methods we use. In addition, we evaluate the accuracy and precision of our results based on simulated mock data. We find some indication (although assumption dependent) for a bottom-heavy IMF in the mass range 0.5-1.0 M⊙, while the IMF in the mass range 0.08-0.5 M⊙ appears to be Milky Way-like and constant. Including near-infrared data in our analysis gives consistent results and improves the precision. * "This paper includes data gathered with the 6.5 meter Magellan Telescopes located at Las Campanas Observatory, Chile." following the Las Campanas guidelines (http://www.lco.cl/?page_id=4409).

Keywords: elliptical galaxies; initial mass function; galaxy abundances; galaxy stellar content
Luminous Optical and X-Ray Flaring of the Putative Redback Millisecond Pulsar 1FGL J0523.5-2529

Several redback and black widow millisecond pulsar binaries have episodes of flaring in X-rays and optical. We initially detected such behavior from the Fermi selected redback candidate 1FGL J0523.5-2529 during optical time-series monitoring. Triggered observations with the Neil Gehrels Swift Observatory over the next ≈100 days showed episodic flaring in X-rays with luminosity up to 8 × 1033 erg s-1 (~100 times the minimum), and a comparable luminosity in the optical/UV, with similar power-law spectra of f ν ∝ ν -0.7. These are the most luminous flares seen in any nonaccreting "spider" pulsar system, which may be related to the large size of the companion through the fraction of the pulsar wind that it or its ablated wind intercepts. Simultaneously with an optical flare, we see Balmer line and He I emission, not previously known in this object, which is evidence of a stellar wind that may also inhibit detection of radio pulsations. The quiescent optical light curves, while dominated by ellipsoidal modulation, show evidence of variable nonuniform temperature that could be due either to large starspots or asymmetric heating of the companion by the pulsar. This may explain a previous measurement of unusual nonzero orbital eccentricity as, alternatively, distortion of the radial-velocity curve by the surface temperature distribution of the large companion.

Keywords: millisecond pulsars; gamma-ray sources
Massive Black Hole Binaries from the TNG50-3 Simulation. II. Using Dual AGNs to Predict the Rate of Black Hole Mergers

Dual active galaxy nuclei (dAGNs) trace the population of post-merger galaxies and are the precursors to massive black hole (MBH) mergers, an important source of gravitational waves that may be observed by the Laser Interferometer Space Antenna (LISA). In Paper I of this series, we used the population of ≈2000 galaxy mergers predicted by the TNG50-3 simulation to seed semi-analytic models of the orbital evolution and coalescence of MBH pairs with initial separations of ≈1 kpc. Here, we calculate the dAGN luminosities and separations of these pairs as they evolve in post-merger galaxies, and show how the coalescence fraction of dAGNs changes with redshift. We find that because of the several gigayear-long dynamical friction timescale for orbital evolution, the fraction of dAGNs that eventually end in an MBH merger grows with redshift and exceeds 50% beyond z dAGN ≈ 1. Dual AGNs in galaxies with bulge masses ≲1010 M ⊙, or consisting of near-equal-mass MBHs, evolve more quickly and have higher than average coalescence fractions. At any redshift, dAGNs observed with small separations (≲0.7 kpc) have a higher probability of merging before z = 0 than more widely separated systems. Radiation feedback effects can significantly reduce the number of MBH mergers, and this could be manifested as a larger than expected number of widely separated dAGNs. We present a method to estimate the MBH coalescence rate as well as the potential LISA detection rate given a survey of dAGNs. Comparing these rates to the eventual LISA measurements will help determine the efficiency of dynamical friction in post-merger galaxies.

Keywords: galaxies; galaxy evolution; galaxy dynamics; galaxy kinematics; galaxy nuclei; supermassive black holes
Reflection Features in the X-Ray Spectrum of Fairall 9 and Implications for Tests of General Relativity

X-ray reflection spectroscopy is potentially a powerful tool to probe the spacetime geometry around astrophysical black holes and test general relativity in the strong field regime. However, precision tests of general relativity are only possible if we employ the correct astrophysical model and if we can limit the systematic uncertainties. It is thus crucial to select the sources and the observations most suitable for these tests. In this work, we analyze simultaneous observations of XMM-Newton and NuSTAR of the supermassive black hole in Fairall 9. This source has a number of properties that make it a promising candidate for tests of general relativity using X-ray reflection spectroscopy. Nevertheless, we find that with the available data there is not a unique interpretation of the spectrum of Fairall 9, which prevents, for the moment, the use of this source for robust tests of general relativity. This issue may be solved by future X-ray missions with a higher energy resolution near the iron line.

Keywords: astrophysical black holes; general relativity; x-ray astronomy
Universal Protoplanetary Disk Size under Complete Nonideal Magnetohydrodynamics: The Interplay between Ion-neutral Friction, Hall Effect, and Ohmic Dissipation

The role of nonideal magnetohydrodynamics has been proven critical during the formation of protoplanetary disks, particularly in regulating their sizes. We provide a simple model to predict the disk size under the interplay among ambipolar diffusion, the Hall effect, and ohmic dissipation. The model predicts a small disk size of around 20 au that depends only sublinearly on disk parameters, for a wide range of initial conditions of subsolar mass and moderate magnetization. It is able to explain phenomena manifested in existing numerical simulations, including the bimodal disk behavior under parallel and antiparallel alignment between the rotation and magnetic field. In the parallel configuration, the disk size decreases and eventually disappears. In the antiparallel configuration, the disk has an outer partition (or pseudodisk), which is flat, shrinking, and short-lived, as well as an inner partition, which grows slowly with mass and is long-lived. Even with significant initial magnetization, the vertical field in the disk can only dominate at the early stage when the mass is low, and the toroidal field eventually dominates in all disks.

Keywords: protoplanetary disks; interstellar magnetic fields; magnetohydrodynamics; gravitation
2003-2019 Monitoring of the Crab Emission through INTEGRAL SPI, or Vice Versa

The Crab Nebula is used by many instruments as a calibration source, in particular at high energy, where it is one of the brightest celestial objects. The spectrometer INTEGRAL SPI (20 keV-8 MeV), in operation since 2002 October, offers a large data set dedicated to this source, with regular campaigns planned twice per year. We have analyzed the available data to quantify the source behavior on a long-term scale and examine the stability level on timescales from hours to years. As a result, the source flux variability appears to be contained within less than ±5% around an ∼20 yr mean value for broad bands covering the 20-400 keV energy domain, above which statistics limits any firm conclusion. In terms of spectral shape, the Band model provides a good description of the observed emission between 20 keV and 2.2 MeV. The averaged spectrum best-fit parameters correspond to a low-energy slope of 1.99 ± 0.01, a high-energy slope of -2.32 ± 0.02, and a characteristic energy Ec of 531 ± 50 keV to describe the curvature joining both power laws. The spectral parameters have then been determined on the revolution timescale (∼1-2 days), and their steadiness confirms the source emission stability. As a complementary result, this study demonstrates that the SPI instrument efficiency remains within 5% of its initial value after 17 yr of operation.

Keywords: space observatories; x-ray sources; gamma-ray sources; astronomical radiation sources