Sazuna/UAT_keywords huggingface dataset:
Damping Mechanisms of the Solar Filament Longitudinal Oscillations in the Weak Magnetic Field. Longitudinal oscillations of the solar filament have been investigated via numerical simulations continuously, but mainly in one dimension, where the magnetic field line is treated as a rigid flux tube. Whereas those one-dimensional (1D) simulations can roughly reproduce the observed oscillation periods, implying that gravity is the main restoring force for filament longitudinal oscillations, the decay time in 1D simulations is generally longer than in observations. In this paper, we perform a two-dimensional (2D) nonadiabatic magnetohydrodynamic simulation of filament longitudinal oscillations, and compare it with the 2D adiabatic case and 1D adiabatic and nonadiabatic cases. It is found that, whereas both nonadiabatic processes (radiation and heat conduction) can significantly reduce the decay time, wave leakage is another important mechanism to dissipate the kinetic energy of the oscillating filament when the magnetic field is weak so that gravity is comparable to Lorentz force. In this case, our simulations indicate that the pendulum model might lead to an error of ∼100% in determining the curvature radius of the dipped magnetic field using the longitudinal oscillation period when the gravity to Lorentz force ratio is close to unity.

Keywords: Solar filaments, Solar prominences, Magnetohydrodynamical simulations
The Distribution of Dense Cores near H II Regions. An investigation of dust emission associated with a large sample of H II regions has been carried out. Stacked results from this sample suggest that each H II region is at or near the center of a cluster of dense cores that extends far beyond the H II region, and has a volume density that decreases as r -3. The data also show evidence for enhanced numbers of cores near the boundary of the H II regions. At the same time, a significant decrease in the number of cores, consistent with no cores, is observed in the interior of these H II regions. Neither these H II regions nor their associated massive OB stars were found to have a significant heating effect on their associated dusty clumps. “Clouds,” or the outermost layers of the clumps in which the cores are embedded, are found to exert a strong shielding effect against external heating sources. Despite this, a large portion of the identified cores were found to be warmer than their surrounding clouds and consequently may be in the initial stages of star formation. The star-formation efficiency of the 7 H II region systems with the most reliable mass budgets ranged between 1% and 9%.

Keywords: Massive stars, Young stellar objects, Dense interstellar clouds
Supernova Shocks in Molecular Clouds: Velocity Distribution of Molecular Hydrogen. Supernovae from core collapse of massive stars drive shocks into the molecular clouds from which the stars formed. Such shocks affect future star formation from the molecular clouds, and the fast-moving, dense gas with compressed magnetic fields is associated with enhanced cosmic rays. This paper presents new theoretical modeling, using the Paris-Durham shock model, and new observations at high spectral resolution, using the Stratospheric Observatory for Infrared Astronomy, of the H2 S(5) pure rotational line from molecular shocks in the supernova remnant IC 443. We generate MHD models for nonsteady-state shocks driven by the pressure of the IC 443 blast wave into gas of densities 103-105 cm-3. We present the first detailed derivation of the shape of the velocity profile for emission from H2 lines behind such shocks, taking into account the shock age, preshock density, and magnetic field. For preshock densities 103-105 cm-3, the H2 emission arises from layers that extend 0.01-0.0003 pc behind the shock, respectively. The predicted shifts of line centers, and the line widths, of the H2 lines range from 20-2 and 30-4 km s-1, respectively. The a priori models are compared to the observed line profiles, showing that clumps C and G can be explained by shocks into gas with density 103 to 2 × 104 cm-3 and strong magnetic fields. Two positions in clump B were observed. For clump B2 (a fainter region near clump B), the H2 spectrum requires a J-type shock into moderate-density gas (∼102 cm-3) with the gas accelerated to 100 km s-1 from its preshock location. Clump B1 requires both a magnetic-dominated C-type shock (like for clumps C and G) and a J-type shock (like for clump B2) to explain the highest observed velocities. The J-type shocks that produce high-velocity molecules may be locations where the magnetic field is nearly parallel to the shock velocity, which makes it impossible for a C-type shock (with ions and neutrals separated) to form.

Keywords: Theoretical models, Supernova remnants, Infrared astronomy, Non-thermal radiation sources, Cosmic ray sources, Shocks
Type IIn Supernova Light Curves Powered by Forward and Reverse Shocks. We present a bolometric light-curve model of Type IIn supernovae powered by supernova ejecta colliding with a circumstellar medium. We estimate the conversion efficiency of the ejecta’s kinetic energy to radiation at the reverse and forward shocks and find that a large density contrast makes a difference in the efficiency. The emission from the reverse shock can maintain high efficiency for a long time, and becomes important at the late phase of the light curve. We first construct a semi-analytical model that is applicable to the late phase of the light curve when the diffusion time of photons in the shocked region becomes negligible. We further develop radiation transfer simulations that incorporate these physical processes into the light curve. The numerical calculations predict light curves at early phases, which are testable by present and future short-cadence surveys. We compare our model with the bolometric light curve constructed from observations for a type IIn supernova 2005ip. Due to the reduced efficiency at the forward shock, we find from our model that the mass-loss rate of the progenitor star was ≈ 1× {10}-2 {M}⊙  {yr}}-1 for a wind velocity of 100 km s-1, an order of magnitude higher compared to previous work that used simple assumptions of the efficiency. This highlights the importance of taking these two components into account when extracting the physical parameters from observations.

Keywords: Type II supernovae, Light curves, Stellar mass loss
Regime Transition between Eddy-driven and Moist-driven Circulation on High Obliquity Planets. We investigate how the meridional circulation and baroclinic eddies change with insolation and rotation rate, under high and zero-obliquity setups, using a general circulation model. The total circulation is considered as superposition of circulations driven by different physics processes, such as diabatic and adiabatic processes. We decompose the meridional circulation into diabatic and adiabatic components, in order to understand their different responses to changes of insolation and rotation rate. As insolation or rotation period increases, the meridional circulation tends to become more diabatically dominant, regardless of the obliquity. The low obliquity circulation is always dominated by diabatic processes, while the high obliquity configuration has two circulation regimes: an adiabatic-dominant regime in the limit of low insolation and fast rotation, and a diabatic-dominant regime in the opposite limit. This regime transition may be observable via its signature on the upper atmospheric zonal wind and the column cloud cover. The momentum-driven circulation, the dominant circulation component in the weak-insolation and fast-rotating regimes is found to resemble that in a dry dynamic model forced by a reversed meridional temperature gradient, indicating the relevance of using a dry dynamic model to understand planetary general circulations under high obliquity.

Keywords: Exoplanet atmospheric variability, Planetary atmospheres, Exoplanet atmospheres
Characteristics of a Gradual Filament Eruption and Subsequent CME Propagation in Relation to a Strong Geomagnetic Storm. An unexpected strong geomagnetic storm occurred on 2018 August 26, which was caused by a slow coronal mass ejection (CME) from a gradual eruption of a large quiet-region filament. We investigate the eruption and propagation characteristics of this CME in relation to the strong geomagnetic storm with remote sensing and in situ observations. Coronal magnetic fields around the filament are extrapolated and compared with extreme ultraviolet observations. We determine the propagation direction and tilt angle of the CME flux rope near the Sun using a graduated cylindrical shell (GCS) model and the Sun-to-Earth kinematics of the CME with wide-angle imaging observations from STEREO A. We reconstruct the flux-rope structure using a Grad-Shafranov technique based on the in situ measurements at the Earth and compare it with those from solar observations and the GCS results. Our conclusions are as follows: (1) the eruption of the filament was unusually slow and occurred in the regions with relatively low critical heights of the coronal field decay index; (2) the axis of the CME flux rope rotated in the corona as well as in interplanetary space, which tended to be aligned with the local heliospheric current sheet; (3) the CME was bracketed between slow and fast solar winds, which enhanced the magnetic field inside the CME at 1 au; (4) the geomagnetic storm was caused by the enhanced magnetic field and a southward orientation of the flux rope at 1 au from the rotation of the flux rope.

Keywords: Solar-terrestrial interactions, Solar wind, Solar coronal mass ejections
Opposite Polarity Magnetic Fields and Convective Downflows in a Simulated Sunspot Penumbra. Recent numerical simulations and observations of sunspots show a significant amount of opposite polarity magnetic fields within the sunspot penumbra. Most of the opposite polarity fields are associated with convective downflows. We present an analysis of 3D MHD simulations through forward modeling of synthetic Stokes profiles of the Fe I 6301.5 Å and Fe I 6302.5 Å lines. The synthetic Stokes profiles are spatially and spectrally degraded considering typical instrument properties. Line bisector shifts of the Fe I 6301.5 Å line are used to determine line-of-sight velocities. Far wing magnetograms are constructed from the Stokes V profiles of the Fe I 6302.5 Å line. While we find an overall good agreement between observations and simulations, the fraction of opposite polarity magnetic fields, the downflow filling factor, and the opposite polarity-downflow association are strongly affected by spatial smearing and presence of strong gradients in the line-of-sight magnetic fields and velocity. A significant fraction of opposite polarity magnetic fields and downflows is hidden in the observations due to typical instrumental noise. Comparing simulations that differ by more than a factor of two in grid spacing, we find that these quantities are robust within the simulations.

Keywords: Solar magnetic fields, Solar physics, Solar photosphere
Serendipitous Discovery of PSR J1431-6328 as a Highly Polarized Point Source with the Australian SKA Pathfinder. We identified a highly polarized, steep-spectrum radio source in a deep image with the Australian Square Kilometre Array Pathfinder (ASKAP) telescope at 888 MHz. After considering and rejecting a stellar origin for this source, we discovered a new millisecond pulsar (MSP) using observations from the Parkes radio telescope. This pulsar has period 2.77 ms and dispersion measure 228.27 pc cm-3. Although this pulsar does not yet appear to be particularly remarkable, its short spin period, wide profile, and high dispersion measure make it relatively hard to discover through traditional blind periodicity searches. Over the course of several weeks we see changes in the barycentric period of this pulsar that are consistent with orbital motion in a binary system, but the properties of any binary need to be confirmed by further observations. While even a deep ASKAP survey may not identify large numbers of new MSPs compared with the existing population, it would be competitive with existing all-sky surveys and could discover interesting new MSPs at high Galactic latitude without the need for computationally expensive all-sky periodicity searches.

Keywords: Late-type dwarf stars, Radio interferometry, Polarimetry, Millisecond pulsars
The Inside-out Growth of the Galactic Disk. We quantify the inside-out growth of the Milky Way’s low-α stellar disk, modeling the ages, metallicities, and Galactocentric radii of APOGEE red clump stars with 6 kpc &lt; R &lt; 13 kpc. The current stellar distribution differs significantly from that expected from the star formation history due to the redistribution of stars through radial orbit mixing. We propose and fit a global model for the Milky Way disk, specified by an inside-out star formation history, radial orbit mixing, and an empirical, parametric model for its chemical evolution. We account for the spatially complex survey selection function, and find that the model fits all data well. We find distinct inside-out growth of the Milky Way disk; the best-fit model implies that the half-mass radius of the Milky Way disk has grown by 43% over the last 7 Gyr. Yet, such inside-out growth still results in a present-day age gradient weaker than 0.1 Gyr kpc-1. Our model predicts the half-mass and half-light sizes of the Galactic disk at earlier epochs, which can be compared to the observed redshift-size relations of disk galaxies. We show that radial orbit migration can reconcile the distinct disk-size evolution with redshift, also expected from cosmological simulations, with the modest present-day age gradients seen in the Milky Way and other galaxies.

Keywords: Galaxy formation, Milky Way disk, Milky Way formation
Medium-band Photometry Reverberation Mapping of Nearby Active Galactic Nuclei. Reverberation mapping (RM) is one of the most efficient ways to investigate the broad-line region around the central supermassive black holes of active galactic nuclei (AGNs). A common way of performing the RM is to perform a long term spectroscopic monitoring of AGNs, but the spectroscopic monitoring campaign of a large number of AGNs requires an extensive amount of observing time of medium to large size telescopes. As an alternative way, we present the results of photometric RM with medium-band photometry. As the widths of medium-band filters match well with the widths of AGN broad emission lines, the medium-band observation with small telescopes can be a cost-effective way to perform RM. We monitored five nearby AGNs with available spectroscopic RM results showing days to weeks scale variability. Observations were performed for ∼3 months with an average of 3 days cadence using three medium-band filters on a 0.43 m telescope. The time lags between the continuum and the Hα emission line light curves are calculated using the JAVELIN software and the discrete correlation function. We find time lags of 1.5-15.9 days for these AGNs, which are consistent with the time lags derived from previous spectroscopic RM measurements. This result demonstrates that even a 0.5 m class telescope can perform RM with medium-bands. Furthermore, we show that RM for tens of thousands AGNs is possible with a dedicated 1 m class telescope.

Keywords: Medium band photometry, Reverberation mapping, Active galactic nuclei, Time series analysis
Mitigating Internal Instrument Coupling for 21 cm Cosmology. I. Temporal and Spectral Modeling in Simulations. We study the behavior of internal signal chain reflections and antenna cross coupling as systematics for 21 cm cosmological surveys. We outline the mathematics for how these systematics appear in interferometric visibilities and describe their phenomenology. We then describe techniques for modeling and removing these systematics without attenuating the 21 cm signal in the data. This has critical implications for low-frequency radio surveys aiming to characterize the 21 cm signal from the Epoch of Reionization (EoR) and Cosmic Dawn, as systematics can cause bright foreground emission to contaminate the EoR window and prohibit a robust detection. We also quantify the signal loss properties of the systematic modeling algorithms, and show that our techniques demonstrate resistance against EoR signal loss. In a companion paper, we demonstrate these methods on data from the Hydrogen Epoch of Reionization Array as a proof-of-concept.

Keywords: Cosmology, Reionization, Astronomy data analysis
A NICER Look at Strong X-Ray Obscuration in the Seyfert-2 Galaxy NGC 4388. We present an analysis of the time-averaged spectrum of the Seyfert-2 active galaxy NGC 4388, obtained by NICER. The intrinsic strength of the reflection spectrum in NGC 4388, the large collecting area and favorable passband of NICER, and a net exposure of 105.6 ks yielded an exceptionally sensitive spectrum. Using two independent families of models, the intrinsic spectrum from the central engine is found to be highly obscured but not Compton-thick. Enforcing physical self-consistency within each model, the independent treatments give formally consistent results: {N}{{H}}={2.67}-0.03+0.02× {10}23 {cm}}-2 or {N}{{H}}={2.64}-0.03+0.03× {10}23 {cm}}-2. Past measurements made with Suzaku and XMM-Newton are in broad agreement with these column density values. A more recent measurement with NuSTAR (in late 2013) recorded a column density about twice as large; the robustness of this variability is reinforced by the use of consistent models and procedures. The neutral Fe Kα line in the NICER spectrum is nominally resolved and consistent with an origin in the optical broad-line region). The data also require ionized absorption in the Fe K band, similar to the “warm absorbers” detected in Seyfert-1 active galactic nuclei. The low-energy spectrum is consistent with a set of ionized plasma components. We discuss these findings and note that the geometric inferences that derive from this analysis can be tested with XRISM and Athena.

Keywords: Accretion, Black hole physics, Active galactic nuclei, X-ray active galactic nuclei
The Bayesian Asteroseismology Data Modeling Pipeline and Its Application to K2 Data. We present the Bayesian Asteroseismology data Modeling (BAM) pipeline, an automated asteroseismology pipeline that returns global oscillation parameters and granulation parameters from the analysis of photometric time series. BAM also determines whether a star is likely to be a solar-like oscillator. We have designed BAM to specially process K2 light curves, which suffer from unique noise signatures that can confuse asteroseismic analysis, though it may be used on any photometric time series—including those from Kepler and TESS. We demonstrate that the BAM oscillation parameters are consistent within ∼1.53% (random) ± 0.2% (systematic) and 1.51% (random) ± 0.6% (systematic) for {ν }\max  and {{Δ }}ν with benchmark results for typical K2 red giant stars in the K2 Galactic Archaeology Program’s (GAP) Campaign 1 sample. Application of BAM to 13,016 K2 Campaign 1 targets not in the GAP sample yields 104 red giant solar-like oscillators. Based on the number of serendipitous giants we find, we estimate an upper limit on the average purity in dwarf selection among C1 proposals of ≈99%, which could be lower when considering incompleteness in BAM detection efficiency and proper-motion cuts specific to C1 Guest Observer proposals.

Keywords: Asteroseismology, Astronomy data analysis, Astronomy software, Giant stars
New Millimeter CO Observations of the Gas-rich Debris Disks 49 Cet and HD 32297. Previous observations revealed the existence of CO gas at nearly protoplanetary level in several dust-rich debris disks around young A-type stars. Here we used the Atacama Large Millimeter/submillimeter Array (ALMA) 7 m Array to measure 13CO and C18O emission toward two debris disks, 49 Cet and HD 32297, and detected similarly high CO content (&gt;0.01 M ⊕). These high CO masses imply a highly efficient shielding of CO molecules against stellar and interstellar ultraviolet photons. Adapting a recent secondary gas disk model that considers both shielding by carbon atoms and self-shielding of CO, we can explain the observed CO level in both systems. Based on the derived gas densities we suggest that, in the HD 32297 disk, dust and gas are coupled and the dynamics of small grains is affected by the gaseous component. For 49 Cet, the question of coupling remains undecided. We found that the main stellar and disk properties of 49 Cet and HD 32297 are very similar to those of previously identified debris disks with high CO content. These objects constitute together the first known representatives of shielded debris disks.

Keywords: A dwarf stars, Circumstellar gas, Debris disks, Circumstellar disks
An ALMA/HST Study of Millimeter Dust Emission and Star Clusters. We present results from a joint ALMA/HST study of the nearby spiral galaxy NGC 628. We combine the Hubble Space Telescope (HST) Legacy ExtraGalactic UV Survey (LEGUS) database of over 1000 stellar clusters in NGC 628 with ALMA Cycle 4 mm/submillimeter observations of the cold dust continuum that span ∼15 kpc2 including the nuclear region and western portions of the galaxy’s disk. The resolution—1.″1 or approximately 50 pc at the distance of NGC 628—allows us to constrain the spatial variations in the slope of the millimeter dust continuum as a function of the ages and masses of the nearby stellar clusters. Our results indicate an excess of dust emission in the millimeter, assuming a typical cold dust model for a normal star-forming galaxy, but little correlation of the dust continuum slope with stellar cluster age or mass. For the depth and spatial coverage of these observations, we cannot substantiate the millimeter/submillimeter excess arising from the processing of dust grains by the local interstellar radiation field. We detect a bright unknown source in NGC 628 in ALMA bands 4 and 7 with no counterparts at other wavelengths from ancillary data. We speculate this is possibly a dust-obscured supernova.

Keywords: Interstellar medium, Spiral galaxies, Star clusters
Hubble Space Telescope Spectroscopy of a Planetary Nebula in an M31 Open Cluster: Hot-bottom Burning at 3.4 M <SUB>⊙</SUB>. We use imaging and spectroscopy from the Hubble Space Telescope (HST) to examine the properties of a bright planetary nebula (PN) projected within M31's young open cluster B477-D075. We show that the probability of a chance superposition of the PN on the cluster is small, ≲2%. Moreover, the radial velocity of the PN is the same as that of the cluster within the measurement error of ∼10 km s-1. Given the expected ∼70 km s-1 velocity dispersion in this region, ∼8 kpc from M31's nucleus, the velocity data again make it extremely likely that the PN belongs to the cluster. Applying isochrone fitting to archival color-magnitude photometric data from the HST Advanced Camera for Surveys, we determine the cluster age and metallicity to be 290 Myr and Z = 0.0071, respectively, implying an initial mass of {3.38}-0.02+0.03 {M}⊙  for any PN produced by the cluster. From HST’s Space Telescope Imaging Spectrograph observations and CLOUDY photoionization modeling, we find that the PN is likely a Type I planetary, with a nitrogen abundance that is enhanced by ∼5-6 times over the solar value scaled to the cluster metallicity. If the PN is indeed a cluster member, these data present strong empirical evidence that hot-bottom burning occurs in asymptotic giant branch stars with initial masses as low as 3.4 M ⊙. Based on observations with the NASA/ESA Hubble Space Telescope obtained at Space Telescope Science Institute, operated by Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

Keywords: Asymptotic giant branch, Post-asymptotic giant branch, Galaxy stellar content, Planetary nebulae, Andromeda Galaxy