Sazuna/UAT_keywords huggingface dataset:
Dynamical Evidence of a Spiral Arm-driving Planet in the MWC 758 Protoplanetary Disk. More than a dozen young stars host spiral arms in their surrounding protoplanetary disks. The excitation mechanisms of such arms are under debate. The two leading hypotheses—companion-disk interaction and gravitational instability (GI)—predict distinct motion for spirals. By imaging the MWC 758 spiral arm system at two epochs spanning ∼5 yr using the SPHERE instrument on the Very Large Telescope, we test the two hypotheses for the first time. We find that the pattern speeds of the spirals are not consistent with the GI origin. Our measurements further evince the existence of a faint "missing planet" driving the disk arms. The average spiral pattern speed is 0°22 ± 0°03 yr-1, pointing to a driver at ${172}_{-14}^{+18}$ au around a 1.9 M☉ central star if it is on a circular orbit. In addition, we witness time-varying shadowing effects on a global scale that are likely originating from an inner disk.

Keywords: Planetary system formation, Coronagraphic imaging, Protoplanetary disks, Orbital motion
Of Harbingers and Higher Modes: Improved Gravitational-wave Early Warning of Compact Binary Mergers. A crucial component to maximizing the science gain from the multi-messenger follow-up of gravitational-wave (GW) signals from compact binary mergers is the prompt discovery of the electromagnetic counterpart. Ideally, the GW detection and localization must be reported early enough to allow for telescopes to slew to the location of the GW event before the onset of the counterpart. However, the time available for early warning is limited by the short duration spent by the dominant (ℓ = m = 2) mode within the detector's frequency band. Nevertheless, we show that including higher modes—which enter the detector's sensitivity band well before the dominant mode—in GW searches can enable us to significantly improve the early warning ability for compact binaries with asymmetric masses (such as neutron star-black hole (NSBH) binaries). We investigate the reduction in the localization sky-area when the ℓ = m = 3 and ℓ = m = 4 modes are included in addition to the dominant mode, considering typical slew-times of electromagnetic telescopes (30-60 s). We find that, in LIGO's projected "O5" ("Voyager") network with five GW detectors, some of the NSBH mergers, located at a distance of 40 Mpc, can be localized to a few hundred sq. deg. ∼45 s prior to the merger, corresponding to a reduction-factor of 3-4 (5-6) in sky-area. For a third-generation network, we get gains of up to 1.5 min in early warning times for a localization area of 100 sq. deg., even when the source is placed at 100 Mpc.

Keywords: Gravitational wave astronomy, Compact binary stars, Gravitational waves
CTCV J2056-3014: An X-Ray-faint Intermediate Polar Harboring an Extremely Fast-spinning White Dwarf. We report on XMM-Newton X-ray observations that reveal CTCV J2056-3014 to be an unusual accretion-powered, intermediate polar (IP) system. It is a member of the class of X-ray-faint IPs whose space density remains unconstrained but potentially very high, with Lx,0.3-12 keV of 1.8 × 1031 erg s-1. We discovered a coherent 29.6 s pulsation in X-rays that was also revealed in our reanalysis of published optical data, showing that the system harbors the fastest-spinning, securely known white dwarf (WD) so far. There is no substantial X-ray absorption in the system. Accretion occurs at a modest rate (∼6 × 10-12 M☉ yr-1) in a tall shock above the WD, while the star seems to be spinning in equilibrium and to have low magnetic fields. Further studies of CTCV J2056-3014 potentially have broad implications on the origin of magnetic fields in WDs, on the population and evolution of magnetic cataclysmic variables, and also on the physics of matter around rapidly rotating magnetic WDs.

Keywords: DQ Herculis stars, Cataclysmic variable stars, X-ray binary stars
Collisionless Heat Flux Regulation via the Electron Firehose Instability in the Presence of a Core and Suprathermal Population in the Expanding Solar Wind. The evolution of the electron heat flux in the solar wind is regulated by the interplay between several effects: solar wind expansion, which can potentially drive velocity-space instabilities, turbulence, wave-particle interactions, and, possibly, collisions. Here we address the respective role played by the solar wind expansion and the electron firehose instability (EFI), developing in the presence of multiple electron populations, in regulating the heat flux. We carry out fully kinetic, expanding box model simulations and separately analyze the enthalpy, bulk, and velocity distribution function skewness contributions for each of the electron species. We observe that the key factor determining electron energy flux evolution is the reduction of the drift velocity of the electron populations in the rest frame of the solar wind. In our simulations, redistribution of the electron thermal energy from the parallel to the perpendicular direction after the onset of the EFI is observed. However, this process seems to impact energy flux evolution only minimally. Hence, reduction of the electron species drift velocity in the solar wind frame appears to directly correlate with efficiency for heat flux instabilities.

Keywords: Space plasmas, Solar wind
High-resolution Spectra for a Wide Range of Habitable Zone Planets around Sun-like Stars. The search for life in the universe is currently focused on Earth-analog planets. However, we should be prepared to find a diversity of terrestrial exoplanets not only in terms of host star but also in terms of surface environment. Simulated high-resolution spectra of habitable planets covering a wide parameter space are essential in training retrieval tools, optimizing observing strategies, and interpreting upcoming observations. Ground-based extremely large telescopes like ELT, GMT, and TMT and future space-based mission concepts like Origins, HabEx, and LUVOIR are designed to have the capability of characterizing a variety of potentially habitable worlds. Some of these telescopes will use high-precision radial velocity techniques to obtain the required high-resolution spectra (R ≈ 100,000) needed to characterize potentially habitable exoplanets. Here we present a database of high-resolution (0.01 cm-1) reflection and emission spectra for simulated exoplanets with a wide range of surfaces, receiving similar irradiation as Earth around 12 different host stars from F0 to K7. Depending on surface type and host star, we show differences in spectral feature strength as well as overall reflectance, emission, and star-to-planet contrast ratio of terrestrial planets in the habitable zone of their host stars. Accounting for the wavelength-dependent interaction of the stellar flux and the surface will help identify the best targets for upcoming spectral observations in the visible and infrared. All of our spectra and model profiles are available online.

Keywords: Exoplanet catalogs, Exoplanet surface composition, Exoplanet astronomy, Habitable planets, Exoplanet atmospheres
Evolution of the Earth's Magnetosheath Turbulence: A Statistical Study Based on MMS Observations. Composed of shocked solar wind, the Earth's magnetosheath serves as a natural laboratory to study the transition of turbulence from low Alfvén Mach number, MA, to high MA. The simultaneous observations of magnetic field and plasma moments with unprecedented high temporal resolution provided by NASA's Magnetospheric Multiscale Mission (MMS) enable us to study the magnetosheath turbulence at both magnetohydrodynamics (MHD) and sub-ion scales. Based on 1841 burst-mode segments of MMS-1 from 2015 September to 2019 June, comprehensive patterns of the spatial evolution of magnetosheath turbulence are obtained: (1) from the subsolar region to the flanks, MA increases from &lt;1 to &gt;5. At MHD scales, the spectral indices of the magnetic-field and velocity spectra present a positive and negative correlation with MA. However, no obvious correlations between the spectral indices and MA are found at sub-ion scales. (2) From the bow shock to the magnetopause, the turbulent sonic Mach number, ${M}_{\mathrm{turb}}$ , generally decreases from &gt;0.4 to &lt;0.1. All spectra steepen at MHD scales and flatten at sub-ion scales, representing positive/negative correlations with Mturb. The break frequency increases by 0.1 Hz when approaching the magnetopause for the magnetic-field and velocity spectra, while it remains at 0.3 Hz for the density spectra. (3) In spite of minor differences, similar results are found for the quasi-parallel and quasi-perpendicular magnetosheath. In addition, such spatial evolution of magnetosheath turbulence is found to be independent of the upstream solar wind conditions, e.g., the averaged Z-component of the interplanetary magnetic field and solar wind speed.

Keywords: Interplanetary turbulence, Planetary magnetospheres
The Hα Emission Line Variations of HR 6819. The star system HR 6819 was recently proposed by Rivinius et al. as the site of the nearest example of a stellar-mass black hole. Their spectra show evidence of two components: a B3 III star in a 40 day orbit and a stationary B-emission line star. Based upon the orbital mass function and the lack of evidence of a spectral component with reflex orbital motion, Rivinius et al. suggested that HR 6819 is a triple system consisting of an inner B3 III star plus black hole binary orbited by a distant Be star. Here we present an alternative model based upon an examination of the Hα emission line in their spectra. We show that the emission line displays the small reflex motion expected for the companion in the inner orbit and shows variations in profile shape related to orbital phase. This indicates that HR 6819 is a binary system consisting of a massive Be star and a low-mass companion that is the stripped down remnant of a former mass donor star in a mass transfer binary.

Keywords: White dwarf stars, Binary stars, Circumstellar disks
Low Water Outgassing from (24) Themis and (65) Cybele: 3.1 μm Near-IR Spectral Implications. Asteroids (24) Themis and (65) Cybele have an absorption feature at 3.1 μm reported to be directly linked to surface water ice. We searched for water vapor escaping from these asteroids with the Herschel Space Observatory Heterodyne Instrument for the Far Infrared. While no H2O line emission was detected, we obtain sensitive 3σ water production rate upper limits of Q(H2O) &lt; 4.1 × 1026 molecules s-1 for Themis and Q(H2O) &lt; 7.6 × 1026 molecules s-1 for Cybele. Using a thermophysical model, we merge data from the Subaru/Cooled Mid-Infrared Camera and Spectrometer and the Herschel/Spectral and Photometric Imaging Receiver with the contents of a multi-observatory database to derive new radiometric properties for these two asteroids. For Themis, we find a thermal inertia ${\rm{\Gamma }}={{20}^{+25}}_{-10}$ J m-2 s-1/2 K-1, a diameter ${{192}^{+10}}_{-7}$ km, and a geometric V-band albedo pV = 0.07 ± 0.01. For Cybele, we obtain a thermal inertia ${\rm{\Gamma }}={{25}^{+28}}_{-19}$ J m-2 s-1/2 K-1, a diameter 282 ± 9 km, and an albedo pV = 0.042 ± 0.005. Using all inputs, we estimate that water ice intimately mixed with the asteroids' dark surface material would cover &lt;0.0017% (for Themis) and &lt;0.0033% (for Cybele) of their surfaces, while an areal mixture with very clean ice (Bond albedo 0.8 for Themis and 0.7 for Cybele) would cover &lt;2.2% (for Themis) and &lt;1.5% (for Cybele) of their surfaces. While surface (and subsurface) water ice may exist in small localized amounts on both asteroids, it is not the reason for the observed 3.1 μm absorption feature.

Keywords: Astronomy data modeling, Small Solar System bodies, Asteroids, Main-belt comets, Main belt asteroids, Comets
Interactions among Noninteracting Particles in Planet Formation Simulations. Over the course of recent decades, N-body simulations have become a standard tool for quantifying the gravitational perturbations that ensue in planet-forming disks. Within the context of such simulations, massive non-central bodies are routinely classified into "big" and "small" particles, where big objects interact with all other objects self-consistently, while small bodies interact with big bodies but not with each other. Importantly, this grouping translates to an approximation scheme where the orbital evolution of small bodies is dictated entirely by the dynamics of the big bodies, yielding considerable computational advantages with little added cost in terms of astrophysical accuracy. Here we point out, however, that this scheme can also yield spurious dynamical behavior where, even in the absence of big bodies within a simulation, indirect coupling among small bodies can lead to excitation of the constituent "non-interacting" orbits. We demonstrate this self-stirring by carrying out a sequence of numerical experiments, and confirm that this effect is largely independent of the time-step or the integration algorithm employed. Furthermore, adopting the growth of angular momentum deficit as a proxy for dynamical excitation, we explore its dependence on time, the cumulative mass of the system, as well as the total number of particles present in the simulation. Finally, we examine the degree of such indirect excitation within the context of conventional terrestrial planet formation calculations, and conclude that although some level of caution may be warranted, this effect plays a negligible role in driving the simulated dynamical evolution.

Keywords: Solar system formation, Dynamical friction, N-body simulations, Planet formation
Starbursting Nuclei in Old Dwarf Galaxies. Nuclei of early-type dwarf galaxies (dEs) are usually younger than the galaxy main body, and this discrepancy in age has been a puzzle. To explore the origin of young nuclei in dEs, we study a sample of dEs having compact star-forming blobs that are visually similar to dEs' nuclei but by far bluer. We find that (1) the compact star-forming blobs have a typical stellar mass of one percent of the host galaxy stellar mass; (2) some of the blobs are positioned slightly off from the center of the galaxies; (3) the Hα equivalent width measured from the publicly available Sloan Digital Sky Survey fiber spectroscopy shows their formation ages being an order of few megayear; (4) their emission line metallicities, 12 + log(O/H), are as high as the solar value, while the underlying galaxies have the typical stellar populations of dEs, i.e., log(Z/Z ${}_{\odot }$ ) ∼ -0.8. Based on the results, we argue that the central star-forming blobs can provide a caught-in-the-act view of nuclei formation in dEs, and discuss possible formation mechanisms of young nuclei in old dEs. We particularly propose that these off-centered compact star-forming regions may act as seeds of nuclei as proposed in the "wet migration" scenario of Guillard et al.

Keywords: Nucleated dwarf galaxies, Dwarf galaxies, Vilnius photometry, Star formation, Early-type galaxies
Probing the Intergalactic Turbulence with Fast Radio Bursts. The turbulence in the diffuse intergalactic medium (IGM) plays an important role in various astrophysical processes across cosmic time, but it is very challenging to constrain its statistical properties both observationally and numerically. Via the statistical analysis of turbulence along different sight lines toward a population of fast radio bursts (FRBs), we demonstrate that FRBs provide a unique tool to probe the intergalactic turbulence. We measure the structure function (SF) of dispersion measures (DMs) of FRBs to study the multiscale electron density fluctuations induced by the intergalactic turbulence. The SF has a large amplitude and a Kolmogorov power-law scaling with angular separations, showing large and correlated DM fluctuations over a range of length scales. Given that the DMs of FRBs are IGM dominated, our result tentatively suggests that the intergalactic turbulence has a Kolmogorov power spectrum and an outer scale on the order of 100 Mpc.

Keywords: Intergalactic medium, Hydrodynamics, Radio transient sources
The Minimal Helicity of Solar Coronal Magnetic Fields. Potential field extrapolations are widely used as minimum-energy models for the Sun's coronal magnetic field. As the reference to which other magnetic fields are compared, they have—by any reasonable definition—no global (signed) magnetic helicity. Here we investigate the internal topological structure that is not captured by the global helicity integral, by splitting it into individual field line helicities. These are computed using potential field extrapolations from magnetogram observations over Solar Cycle 24, as well as for a simple illustrative model of a single bipolar region in a dipolar background. We find that localized patches of field line helicity arise primarily from linking between strong active regions and their overlying field, so that the total unsigned helicity correlates with the product of photospheric and open fluxes. Within each active region, positive and negative helicity may be unbalanced, but the signed helicity is only around a tenth of the unsigned helicity. Interestingly, in Cycle 24, there is a notable peak in unsigned helicity caused by a single large active region. On average, the total unsigned helicity at the resolution considered is approximately twice the typical signed helicity of a single real active region, according to non-potential models in the literature.

Keywords: Solar cycle, Solar magnetic fields, Solar corona
Evidence of Runaway Gas Cooling in the Absence of Supermassive Black Hole Feedback at the Epoch of Cluster Formation. Cosmological simulations, as well as mounting evidence from observations, have shown that supermassive black holes play a fundamental role in regulating the formation of stars throughout cosmic time. This has been clearly demonstrated in the case of galaxy clusters in which powerful feedback from the central black hole is preventing the hot intracluster gas from cooling catastrophically, thus reducing the expected star formation rates by orders of magnitude. These conclusions, however, have been almost entirely based on nearby clusters. Based on new Chandra X-ray observations, we present the first observational evidence for massive, runaway cooling occurring in the absence of supermassive black hole feedback in the high-redshift galaxy cluster SpARCS104922.6 + 564032.5 (z = 1.709). The hot intracluster gas appears to be fueling a massive burst of star formation (≈900 M⊙ yr-1) that is offset by dozens of kpc from the central galaxy. The burst is co-spatial with the coolest intracluster gas but not associated with any galaxy in the cluster. In less than 100 million years, such runaway cooling can form the same amount of stars as in the Milky Way. Therefore, intracluster stars are not only produced by tidal stripping and the disruption of cluster galaxies, but can also be produced by runaway cooling of hot intracluster gas at early times. Overall, these observations show the dramatic impact when supermassive black hole feedback fails to operate in clusters. They indicate that in the highest overdensities, such as clusters and protoclusters, runaway cooling may be a new and important mechanism for fueling massive bursts of star formation in the early universe.

Keywords: Supermassive black holes, Cooling flows, High-redshift galaxy clusters, X-ray observatories, Intracluster medium
RGS Observations of Ejecta Knots in Tycho's Supernova Remnant. We present results from XMM-Newton/Reflection Grating Spectrometer (RGS) observations of prominent knots in the southernmost portion of Tycho's supernova remnant, known to be the remnant of a Type Ia supernova in 1572 C.E. By dispersing the photons from these knots out of the remnant with very little emission in front of or behind them, we obtained the nearly uncontaminated spectra of the knots. In the southernmost knot, the RGS successfully resolved numerous emission lines from Si, Ne, O Heα and Lyα, and Fe L-shell. This is the first clear detection of O lines in Tycho's supernova remnant. Line broadening was measured to be ∼3 eV for the O Heα and ∼4.5 eV for the Fe L lines. If we attribute the broadening to pure thermal Doppler effects, then we obtain kTO and kTFe to be ∼400 keV and 1.5 MeV, respectively. These temperatures can be explained by heating in a reverse shock with a shock velocity of ∼3500 km s-1. The abundances obtained from fitting the RGS and MOS data together imply substantially elevated amounts of these materials, confirming previous studies that the knots are heated by a reverse shock, and thus contain ejecta material from the supernova. We are unable to find a Type Ia explosion model that reproduces these abundances, but this is likely the result of this knot being too small to extrapolate to the entire remnant.

Keywords: Ejecta, Plasma astrophysics, Supernova remnants, Shocks, Supernovae
An Experimental Study of Chemical Desorption for Phosphine in Interstellar Ice. Phosphine (PH3), an important molecule for the chemistry of phosphorus (P)-bearing species in the interstellar medium (ISM) is considered to form primarily on interstellar grains. However, no report exists on the processes of PH3 formation on grains. Here, we experimentally studied the reactions of hydrogen (H) atoms and PH3 molecules on compact amorphous solid water, with a particular focus on the chemical desorption of PH3 at 10-30 K. After exposure to H atoms for 120 minutes, up to 50% of solid PH3 was lost from the icy surface. On the basis of experiments using deuterium atoms, it was concluded that the loss of PH3 resulted from chemical desorption through the reactions PH3 + H → PH2 + H2 and/or PH2 + H → PH3. The effective desorption cross-section was ∼5 × 10-17 cm2, which is three times larger than that of hydrogen sulfide measured under similar experimental conditions. The present results suggest that the formation of PH3, and possibly PH2 and PH, followed by their desorption from icy grains, may contribute to the formation of PN and PO in the gas phase, and thus may play a role in the P chemistry of the ISM.

Keywords: Interstellar dust processes, Astrochemistry, Pre-biotic astrochemistry, Dense interstellar clouds
Induced Metal-free Star Formation around a Massive Black Hole Seed. The direct formation of a massive black hole is a potential seeding mechanism of the earliest observed supermassive black holes. We investigate how the existence of a massive black hole seed impacts the ionization and thermal state of its pre-galactic host halo and subsequent star formation. We show that its X-ray radiation ionizes and heats the medium, enhancing H2 formation in shielded regions, within the nuclear region in the span of a million years. The enhanced molecular cooling triggers the formation of a ∼104 M⊙ metal-free stellar cluster at a star formation efficiency of ∼0.1% in a single event. Star formation occurs near the edges of the H II region that is partially ionized by X-rays; thus, the initial size depends on the black hole properties and surrounding environment. The simulated metal-free galaxy has an initial half-light radius of ∼10 pc but expands to ∼50 pc after 10 million years because of the outward velocities of their birth clouds. Supernova feedback then quenches any further star formation for tens of millions of years, allowing the massive black hole to dominate the spectrum once the massive metal-free stars die.

Keywords: Supermassive black holes, Radiative transfer simulations, Star formation, Galaxy evolution