Sazuna/UAT_keywords huggingface dataset:
Long-term Variability of Class I Methanol Masers in the High-mass Star-forming Region DR21(OH). High-mass stars play an important role in the interstellar medium, but much remains to be known about their formation. Class I methanol masers may be unique tracers of an early stage of high-mass star formation, and a better understanding of such masers will allow them to be used as more effective probes of the high-mass star-forming process. We present an investigation of the long-term variability of Class I methanol masers at 44 GHz toward the high-mass star-forming region DR21(OH). We compare observations taken in 2017 to observations from 2012, and also to 2001 data from the literature. A total of 57 maser spots were found in the 2017 data, with center velocities ranging between -8.65 to +2.56 km s-1. The masers are arranged in a western and an eastern lobe with two arcs in each lobe that look like bow shocks, consistent with previous observations. The general trend is an increase in intensity from 2001 to 2012, and a decrease from 2012 to 2017. Variability appears to be more prevalent in the inner arc of the western lobe than in the outer arc. We speculate that this may be a consequence of episodic accretion, in which a later accretion event has resulted in ejection of material whose shock reached the inner arc at some point in time after 2001. We conclude that class I methanol masers are variable on long timescales (of the order of 5-10 yr).

Keywords: Massive stars, Star forming regions, Interferometers, Star formation, Astrophysical masers, Interstellar masers
NECOLA: Toward a Universal Field-level Cosmological Emulator. We train convolutional neural networks to correct the output of fast and approximate N-body simulations at the field level. Our model, Neural Enhanced COLA (NECOLA), takes as input a snapshot generated by the computationally efficient COLA code and corrects the positions of the cold dark matter particles to match the results of full N-body Quijote simulations. We quantify the accuracy of the network using several summary statistics, and find that NECOLA can reproduce the results of the full N-body simulations with subpercent accuracy down to k ≃ 1 hMpc-1. Furthermore, the model that was trained on simulations with a fixed value of the cosmological parameters is also able to correct the output of COLA simulations with different values of Ωm, Ωb, h, n  s , σ 8, w, and M  ν  with very high accuracy: the power spectrum and the cross-correlation coefficients are within ≃1% down to k = 1 hMpc-1. Our results indicate that the correction to the power spectrum from fast/approximate simulations or field-level perturbation theory is rather universal. Our model represents a first step toward the development of a fast field-level emulator to sample not only primordial mode amplitudes and phases, but also the parameter space defined by the values of the cosmological parameters.

Keywords: Large-scale structure of the universe, Neural networks, N-body simulations, Cosmological parameters
Detection of a Broad 8 μm UIR Feature in the Mid-infrared Spectrum of WR 125 Observed with Subaru/COMICS. We present the detection of a broad 8 μm feature in newly formed dust around the carbon-rich Wolf-Rayet (WC) binary WR 125 from N-band low-resolution (NL; R ~ 250) spectroscopy between 7.3 and 13.6 μm and N-band (11.7 μm) and Q-band (18.8 μm) imaging with Subaru/COMICS in 2019 October. WR 125 is a colliding-wind binary (WC7 + O9) that exhibited renewed dust formation starting in 2018, ~28 yr after its first dust formation episode had been observed. We also compare our infrared photometry with historical observations and revise the dust formation period of WR 125 to 28.1 yr. Archival infrared spectra of five dusty WC stars, WR 48a, WR 98a, WR 104, WR 112, and WR 118, obtained with Infrared Space Observatory/Short-Wavelength Spectrometer are reanalyzed and compared with the WR 125 spectrum to search for a similar feature. We analyze the dusty WC spectra using two different extinction curves to investigate the impact of interstellar extinction correction on the presence and/or properties of the 8 μm feature. All of the dusty WC spectra dereddened with the two different extinction curves show a broad feature around 8 μm (FWHM ~ 1-2 μm). We suggest that these 8 μm features seen in the dusty WC spectra are related to the Class C unidentified infrared features.

Keywords: Infrared astronomy, Wolf-Rayet stars, Circumstellar dust, Astrochemistry
Identification of Coronal Holes on AIA/SDO Images Using Unsupervised Machine Learning. Through its magnetic activity, the Sun governs the conditions in Earth's vicinity, creating space weather events, which have drastic effects on our space- and ground-based technology. One of the most important solar magnetic features creating the space weather is the solar wind that originates from the coronal holes (CHs). The identification of the CHs on the Sun as one of the source regions of the solar wind is therefore crucial to achieve predictive capabilities. In this study, we used an unsupervised machine-learning method, k-means, to pixel-wise cluster the passband images of the Sun taken by the Atmospheric Imaging Assembly on the Solar Dynamics Observatory in 171, 193, and 211 Å in different combinations. Our results show that the pixel-wise k-means clustering together with systematic pre- and postprocessing steps provides compatible results with those from complex methods, such as convolutional neural networks. More importantly, our study shows that there is a need for a CH database where a consensus about the CH boundaries is reached by observers independently. This database then can be used as the "ground truth," when using a supervised method or just to evaluate the goodness of the models.

Keywords: Detection, Space weather, Gravitational waves
Wave-driven Outbursts and Variability of Low-mass Supernova Progenitors. In a substantial number of core-collapse supernovae (SNe), early-time interaction indicates a dense circumstellar medium (CSM) that may be produced by outbursts from the progenitor star. Wave-driven mass loss is a possible mechanism to produce these signatures, with previous work suggesting that this mechanism is most effective for low-mass (~11 M ☉) SN progenitors. Using one-dimensional hydrodynamic simulations with MESA, we study the effects of this wave heating in SN progenitors of masses M ZAMS = 10-13 M ☉. This range encompasses stars that experience semidegenerate central neon burning and more degenerate off-center neon ignition. We find that central Ne ignition at M ZAMS = 11 M ☉ produces a burst of intense wave heating that transmits ~1047 erg of energy at 10 yr before core collapse, whereas other masses experience smaller levels of wave heating. Wave heating does not hydrodynamically drive mass loss in any of our models and is unlikely to produce a very massive CSM on its own. However, wave heating can cause large radial expansion (by more than an order of magnitude), photospheric cooling, and luminosity brightening by up to ~106 L ☉ in hydrogen-poor stripped star models. Some Type Ib/c progenitors could drastically change their appearance in the final years of their lives, with brightness in the visual bands increasing by nearly 3 mag. Moreover, interaction with a close binary companion could drive intense mass loss, with implications for Type Ibn and other interaction-powered SNe.

Keywords: Stellar astronomy, Circumstellar matter, Supernovae, Stellar mass loss
Proton Heating by a Proton-Alpha Drift Instability with an Anisotropic Alpha-particle Temperature in a Turbulent Solar-wind Plasma. The proton-alpha drift instability is a possible mechanism of the alpha-particle deceleration and the resulting proton heating in the solar wind. We present hybrid numerical simulations of this instability with particle-in-cell ions and a quasi-neutralizing electron fluid for typical conditions at 1 au. For the parameters used in this paper, we find that fast magnetosonic unstable modes propagate only in the direction opposite to the alpha-particle drift and do not produce the perpendicular proton heating necessary to accelerate the solar wind. Alfvén modes propagate in both directions and heat the protons perpendicularly to the mean magnetic field. Despite being driven by the alpha temperature anisotropy, the Alfvén instability also extracts the energy from the bulk motion of the alpha particles. In the solar wind, the instabilities operate in a turbulent ambient medium. We show that the turbulence suppresses the Alfvén instability but the perpendicular proton heating persists. Unlike a static nonuniform background, the turbulence does not invert the sense of the proton heating associated with the fast magnetosonic instability and it remains preferentially parallel.

Keywords: Interplanetary turbulence, Space plasmas, Solar wind
Spectral Line Depth Variability in Radial Velocity Spectra. Stellar active regions, including spots and faculae, can create radial velocity (RV) signals that interfere with the detection and mass measurements of low-mass exoplanets. In doing so, these active regions affect each spectral line differently, but the origin of these differences is not fully understood. Here we explore how spectral line variability correlated with S-index (Ca H and K emission) is related to the atomic properties of each spectral line. Next, we develop a simple analytic stellar atmosphere model that can account for the largest sources of line variability with S-index. Then, we apply this model to HARPS spectra of α Cen B to explain Fe I line depth changes in terms of a disk-averaged temperature difference between active and quiet regions on the visible hemisphere of the star. This work helps establish a physical basis for understanding how stellar activity manifests differently in each spectral line and may help future work mitigating the impact of stellar activity on exoplanet RV surveys.

Keywords: Radial velocity, Exoplanet detection methods, Stellar activity, Stellar faculae
Milli-Hertz Gravitational-wave Background Produced by Quasiperiodic Eruptions. Extreme-mass-ratio inspirals (EMRIs) are important targets for future space-borne gravitational-wave (GW) detectors, such as the Laser Interferometer Space Antenna (LISA). Recent works suggest that EMRIs may reside in a population of newly discovered X-ray transients called "quasiperiodic eruptions" (QPEs). Here, we follow this scenario and investigate whether LISA could in the future detect the QPEs. We consider two specific models, in which the QPEs are made of either stellar-mass objects moving on circular orbits around massive black holes (MBHs) or white dwarfs (WDs) on eccentric orbits around MBHs. We find that in either case the five QPEs detected so far are too weak to be resolvable by LISA. However, if QPEs are made of eccentric WD-MBH binaries, they radiate GWs over a wide range of frequencies. The broad spectra overlap to form a background that peaks in the milli-Hertz band and has a signal-to-noise ratio of 9-17 even in the most pessimistic scenario. The presence of this GW background in the LISA band could impact future searches for seed black holes at high redshift as well as stellar-mass binary black holes in the local universe.

Keywords: X-ray transient sources, Intermediate-mass black holes, White dwarf stars, Gravitational waves
Stumbling over Planetary Building Blocks: AU Microscopii as an Example of the Challenge of Retrieving Debris-disk Dust Properties. We explore whether assumptions about dust grain shape affect the resulting estimates of the composition and grain size distribution of the AU Microscopii (AU Mic) debris disk from scattered-light data collected by Lomax et al. The near edge-on orientation of the AU Mic debris disk makes it ideal for studying the effect of the scattering phase function on the measured flux ratios as a function of wavelength and projected distance. Previous efforts to model the AU Mic debris disk have invoked a variety of dust grain compositions and explored the effect of porosity, but did not undertake a systematic effort to explore a full range of size distributions and compositions to understand possible degeneracies in fitting the data. The degree to which modeling dust grains with more realistic shapes compounds these degeneracies has also not previously been explored. We find differences in the grain properties retrieved depending on the grain shape model used. We also present here our calculations of porous grains of size parameters x = 0.1 to 48 and complex refractive indices (m = n + iκ) ranging from n = 1.1 to 2.43 and k = 0 to 1.0, covering multiple compositions at visible and near-infrared wavelengths such as ice, silicates, amorphous carbon, and tholins.

Keywords: Circumstellar dust, Interplanetary dust, Debris disks, Circumstellar disks
Anatomy of Photoevaporation Base: Linking the Property of the Launched Wind to Irradiation Flux. Ultraviolet and X-rays from radiation sources disperse nearby gas clumps by driving winds due to heating associated with the photochemical processes. This dispersal process, photoevaporation, constrains the lifetimes of the parental bodies of stars and planets. To understand this process in a universal picture, we develop an analytical model that describes the fundamental physics in the vicinity of the wind-launching region. The model explicitly links the density and velocity of photoevaporative winds at the launch points to the radiation flux reaching the wind-launching base, using a jump condition. The model gives a natural boundary condition for the wind-emanating points. We compare the analytical model with the results of radiation hydrodynamic simulations, where a protoplanetary disk is irradiated by the stellar extreme-ultraviolet, and confirm good agreement of the base density and velocity, and radial profiles of mass-loss rates. We expect that our analytical model is applicable to other objects subject to photoevaporation not only by extreme-ultraviolet but by far-ultraviolet/X-rays with suitable modifications. Future self-consistent numerical studies can test the applicability.

Keywords: Hydrodynamical simulations, Hydrodynamics, Astrophysical fluid dynamics, Protoplanetary disks, Interdisciplinary astronomy, Interstellar medium wind, H II regions
Investigating Superdiffusive Shock Acceleration at a Parallel Shock with a Fractional Parker Equation for Energetic-particle Interaction with Small-scale Magnetic Flux Ropes. It has been suggested before that small-scale magnetic flux rope (SMFR) structures in the solar wind can temporarily trap energetic charged particles. We present the derivation of a new fractional Parker equation for energetic-particle interaction with SMFRs from our pitch-angle-dependent fractional diffusion-advection equation that can account for such trapping effects. The latter was derived previously in le Roux &amp; Zank from the first principles starting with the standard focused transport equation. The new equation features anomalous advection and diffusion terms. It suggests that energetic-particle parallel transport occurs with a decaying efficiency of advection effects as parallel superdiffusion becomes more dominant at late times. Parallel superdiffusion can be linked back to underlying anomalous pitch-angle transport, which might be subdiffusive during interaction with quasi-helical coherent SMFRs. We apply the new equation to time-dependent superdiffusive shock acceleration at a parallel shock. The results show that the superdiffusive-shock-acceleration timescale is fractional, the net fractional differential particle flux is conserved across the shock ignoring particle injection at the shock, and the accelerated particle spectrum at the shock converges to the familiar power-law spectrum predicted by standard steady-state diffusive-shock-acceleration theory at late times. Upstream, as parallel superdiffusion progressively dominates the advection of energetic particles, their spatial distributions decay on spatial scales that grow with time. Furthermore, superdiffusive parallel shock acceleration is found to be less efficient if parallel anomalous diffusion is more superdiffusive, while perpendicular particle escape from the shock, thought to be subdiffusive during SMFR interaction, is reduced when increasingly subdiffusive.

Keywords: Interplanetary turbulence, Interplanetary particle acceleration, Solar wind
The Low-redshift Lyman Continuum Survey. II. New Insights into LyC Diagnostics. The Lyman continuum (LyC) cannot be observed at the epoch of reionization (z ≳ 6) owing to intergalactic H I absorption. To identify LyC emitters (LCEs) and infer the fraction of escaping LyC, astronomers have developed various indirect diagnostics of LyC escape. Using measurements of the LyC from the Low-redshift Lyman Continuum Survey (LzLCS), we present the first statistical test of these diagnostics. While optical depth indicators based on Lyα, such as peak velocity separation and equivalent width, perform well, we also find that other diagnostics, such as the [O III]/[O II] flux ratio and star formation rate surface density, predict whether a galaxy is an LCE. The relationship between these galaxy properties and the fraction of escaping LyC flux suggests that LyC escape depends strongly on H I column density, ionization parameter, and stellar feedback. We find that LCEs occupy a range of stellar masses, metallicities, star formation histories, and ionization parameters, which may indicate episodic and/or different physical causes of LyC escape.

Keywords: Hubble Space Telescope, Emission line galaxies, Galactic and extragalactic astronomy, Ultraviolet astronomy, Reionization
Evolution of a Peculiar Type Ibn Supernova SN 2019wep. We present a high-cadence short term photometric and spectroscopic monitoring campaign of a type Ibn SN 2019wep, which is one of the rare SN Ibn after SNe 2010al and 2019uo to display signatures of flash ionization (He II, C III, N III). We compare the decline rates and rise time of SN 2019wep with other SNe Ibn and fast transients. The post-peak decline in all bands (0.1 mag day-1) are consistent with SNe Ibn but less than the fast transients. On the other hand, the Δm 15 values are slightly lower than the average values for SNe Ibn but consistent with the fast transients. The rise time is typically shorter than SNe Ibn but longer than fast transients. SN 2019wep lies at the fainter end of SNe Ibn but possesses an average luminosity among the fast transients sample. The peculiar color evolution places it between SNe Ib and the most extreme SNe Ibn. The bolometric light-curve modeling shows resemblance with SN 2019uo with ejecta masses consistent with SNe Ib. SN 2019wep belongs to the P cygni subclass of SNe Ibn and shows faster evolution in line velocities as compared to the emission subclass. The post-maximum spectra show close resemblance with ASASSN-15ed hinting it to be of SN Ib nature. The low He I CSM velocities and residual Hα further justifies it and provide evidence of an intermittent progenitor between Wolf-Rayet and LBV stars.

Keywords: CCD photometry, Core-collapse supernovae, Spectroscopy, Supernovae, Supernova dynamics
The Galaxy Starburst/Main-sequence Bimodality over Five Decades in Stellar Mass at z ≍ 3-6.5. We study the relation between stellar mass (M *) and star formation rate (SFR) for star-forming galaxies over approximately five decades in stellar mass ( $5.5\ \lesssim \ {\mathrm{log}}_{10}({M}_{* }/{M}_{\odot })\lesssim 10.5$ ) at z ≍ 3-6.5. This unprecedented coverage has been possible thanks to the joint analysis of blank non-lensed fields (COSMOS/SMUVS) and cluster lensing fields (Hubble Frontier Fields) that allow us to reach very low stellar masses. Previous works have revealed the existence of a clear bimodality in the SFR-M * plane with a star formation Main Sequence and a starburst cloud at z ≍ 4-5. Here we show that this bimodality extends to all star-forming galaxies and is valid in the whole redshift range z ≍ 3-6.5. We find that starbursts constitute at least ≍20% of all star-forming galaxies with M * ≳ 109 M ☉ at these redshifts and reach a peak of 40% at z = 4-5. More importantly, 60%-90% of the total SFR budget at these redshifts is contained in starburst galaxies, indicating that the starburst mode of star formation is dominant at high redshifts. Almost all the low stellar mass starbursts with ${\mathrm{log}}_{10}({M}_{* }/{M}_{\odot })\lesssim 8.5$ have ages comparable to the typical timescales of a starburst event, suggesting that these galaxies are being caught in the process of formation. Interestingly, galaxy formation models fail to predict the starburst/main-sequence bimodality and starbursts overall, suggesting that the starburst phenomenon may be driven by physical processes occurring at smaller scales than those probed by these models.

Keywords: Starburst galaxies, Galaxy formation, High-redshift galaxies, Galaxy evolution
High-frequency Waves in Chromospheric Spicules. Using high-cadence observations from the Hydrogen-alpha Rapid Dynamics camera imaging system on the Dunn Solar Telescope, we present an investigation of the statistical properties of transverse oscillations in spicules captured above the solar limb. At five equally separated atmospheric heights, spanning approximately 4900-7500 km, we have detected a total of 15,959 individual wave events, with a mean displacement amplitude of 151 ± 124 km, a mean period of 54 ± 45 s, and a mean projected velocity amplitude of 21 ± 13 km s-1. We find that both the displacement and velocity amplitudes increase with height above the solar limb, ranging from 132 ± 111 km and 17.7 ± 10.6 km s-1 at ≈4900 km, and 168 ± 125 km and 26.3 ± 14.1 km s-1 at ≈7500 km, respectively. Following the examination of neighboring oscillations in time and space, we find 45% of the waves to be upwardly propagating, 49% to be downwardly propagating, and 6% to be standing, with mean absolute phase velocities for the propagating waves on the order of 75-150 km s-1. While the energy flux of the waves propagating downwards does not appear to depend on height, we find the energy flux of the upwardly propagating waves decreases with atmospheric height at a rate of -13,200 ± 6500 W m-2/Mm. As a result, this decrease in energy flux as the waves propagate upwards may provide significant thermal input into the local plasma.

Keywords: Solar spicules, Solar atmosphere, Solar chromosphere, Solar oscillations
Apparent Footpoint Rotation and Writhe of Double Hot Channels in a Solar Flare. We investigate the M6.5 class flare (SOL2015-06-22T18:23) occurring in NOAA Active Region 12371 on 2015 June 22. This eruptive flare is associated with a halo coronal mass ejection with a speed of 1200 km s-1. The 94 Å observations by Atmospheric Image Assembly onboard Solar Dynamics Observatory show that one hot channel first rises up, then forms a kinking structure with negative crossing and erupts, which is followed by the eruption of another kinking hot channel with negative crossing at a similar location between the start and peak times of the flare. Consistent with the standard flare model, footpoint drifting of the two hot channels is observed during the eruption. More interestingly, the two footpoints of the first hot channel continue to drift and display an apparent clockwise rotation after leaving the area of the hook-shaped flare ribbons. This apparent rotation is along the high-Q region of the log Q map derived from the nonlinear force-free field extrapolation. Our analysis suggests that the apparent rotational motion is likely caused by magnetic reconnection between the first hot channel and the surrounding magnetic fields at the high-Q region during the unwrithing process. The unwrithing of the second hot channel is accompanied by a significant slipping motion of its right footpoint.

Keywords: Solar magnetic reconnection, Solar extreme ultraviolet emission, Solar x-ray flares