Sazuna/UAT_keywords huggingface dataset:
Distortion of Magnetic Fields in the Dense Core CB81 (L1774, Pipe 42) in the Pipe Nebula. The detailed magnetic field structure of the starless dense core CB81 (L1774, Pipe 42) in the Pipe Nebula was determined based on near-infrared polarimetric observations of background stars to measure dichroically polarized light produced by magnetically aligned dust grains in the core. The magnetic fields pervading CB81 were mapped using 147 stars and axisymmetrically distorted hourglass-like fields were identified. On the basis of simple 2D and 3D magnetic field modeling, the magnetic inclination angles in the plane-of-sky and line-of-sight directions were determined to be 4° ± 8° and 20° ± 20°, respectively. The total magnetic field strength of CB81 was found to be 7.2 ± 2.3 μG. Taking into account the effects of thermal/turbulent pressure and magnetic fields, the critical mass of CB81 was calculated to be Mcr = 4.03 ± 0.40 M⊙, which is close to the observed core mass of Mcore = 3.37 ± 0.51 M⊙. We thus conclude that CB81 is in a condition close to the critical state. In addition, a spatial offset of 92″ was found between the center of the magnetic field geometry and the dust extinction distribution; this offset structure could not have been produced by self-gravity. The data also indicate a linear relationship between polarization and extinction up to AV ∼ 30 mag going toward the core center. This result confirms that near-infrared polarization can accurately trace the overall magnetic field structure of the core.

Keywords: Interstellar dust, Polarimetry, Infrared astronomy, Extinction, Magnetic fields
Detection of Late-time Optical Emission from SN 1941C in NGC 4136. We report the detection of broad, high-velocity oxygen emission lines from the site of SN 1941C nearly eight decades after outburst, making it the oldest optically detected historical core-collapse supernova (CCSN) and one of the youngest CCSN remnants with a well determined age. In contrast to the strongly blueshifted emission line profiles observed for other late-time CCSNe thought to be due to internal dust extinction of far-side hemisphere of expanding ejecta, SN 1941C's spectrum exhibits stronger redshifted than blueshifted emissions of [O I] 6300, 6364 Å, [O II] 7319, 7330 Å, and [O III] 4959, 5007 Å. These oxygen emissions exhibit rest-frame expansion velocities from -2200 to $+4400\,\,\mathrm{km}\,{{\rm{s}}}^{-1}$ . No other significant broad line emissions were detected including Hα emission. We discuss possible causes for this unusual spectrum and compare SN 1941C's optical and X-ray luminosities to other evolved CCSNe.

Keywords: Supernova remnants, Type II supernovae, Interstellar emissions, Core-collapse supernovae
Repeated State Change of Variable Gamma-Ray Pulsar PSR J2021+4026. PSR J2021+4026 is a radio-quiet gamma-ray pulsar and the first pulsar that shows state change of the gamma-ray emission and spindown rate. The state change of PSR J2021+4026 was first observed at 2011 October, at which the pulsar changes the state from high gamma-ray flux/low spindown rate state to low gamma-ray flux/high spindown rate state. In 2014 December, PSR J2021+4026 recovered the state before the 2011 state change over a timescale of a few months. We report that the long-term evolution of the gamma-ray flux and timing behavior suggests that PSR J2021+4026 changed the state near 2018 February 1 and entered a new low gamma-ray flux/high spindown rate state. At the 2018 state change, the averaged flux dropped from (1.29 ± 0.01) × 10-6 cts cm-2 s-1 to (1.12 ± 0.01) × 10-6 cts cm-2 s-1, which is behavior similar to that of the 2011 event. The spindown rate has increased by ∼3% in the new state since the 2018 state change. The shapes of pulse profile and spectrum in GeV bands also changed at the 2018 event, and they are consistent with behavior at the 2011 state change. Our results probably suggest that PSR J2021+4026 is switching between different states with a timescale of several years, like some radio pulsars (e.g., PSR B1828-11). PSR J2021+4026 will provide a unique opportunity to study the mechanism of the state switching.

Keywords: Observational astronomy, Gamma-ray astronomy, Magnetic fields, Rotation powered pulsars
Identification of the Nature of Electromagnetic Waves near the Proton-cyclotron Frequency in Solar-terrestrial Plasmas. Low-frequency (quasi-)monochromatic electromagnetic waves near the ion-cyclotron frequency always exhibit both left-hand (LH) and right-hand (RH) polarization in solar-terrestrial spacecraft observations. However, due to the Doppler frequency shift resulting from the bulk flow of charged particles, the nature of these waves in the plasma frame is still unclear. This paper proposes a useful method to directly identify the nature of the observed waves. Using three wave parameters including polarization, direction of the parallel Poynting flux, and correlation between perpendicular magnetic field and perpendicular ion/electron velocity, we could discriminate the wave mode (Alfvén/ion-cyclotron wave or fast-magnetosonic/whistler wave) and its propagation direction (along or against the magnetic field) in the plasma frame. Using Magnetospheric Multiscale spacecraft measurements, we analyze two wave events containing both LH- and RH-polarized low-frequency electromagnetic waves in the Earth's magnetosheath, and find that these waves correspond to counter-propagating Alfvén/ion-cyclotron waves in the plasma frame. Our method is helpful for studying low-frequency electromagnetic waves detected by satellites that have particle measurements with an adequate temporal resolution.

Keywords: Planetary magnetospheres, Solar wind, Space plasmas, Plasma physics
Globular Cluster Formation from Colliding Substructure. We investigate a scenario where the formation of globular clusters (GCs) is triggered by high-speed collisions between infalling atomic-cooling subhalos during the assembly of the main galaxy host, a special dynamical mode of star formation that operates at high gas pressures and is intimately tied to ΛCDM hierarchical galaxy assembly. The proposed mechanism would give origin to "naked" globular clusters as colliding dark matter subhalos and their stars will simply pass through one another while the warm gas within them clashes at highly supersonic speed and decouples from the collisionless component, in a process reminiscent of the Bullet galaxy cluster. We find that the resulting shock-compressed layer cools on a timescale that is typically shorter than the crossing time, first by atomic line emission and then via fine-structure metal-line emission, and is subject to gravitational instability and fragmentation. Through a combination of kinetic theory approximation and high-resolution N-body simulations, we show that this model may produce: (a) a GC number-halo mass relation that is linear down to dwarf galaxy scales and agrees with the trend observed over five orders of magnitude in galaxy mass; (b) a population of old globular clusters with a median age of 12 Gyr and an age spread similar to that observed; (c) a spatial distribution that is biased relative to the overall mass profile of the host; and (d) a bimodal metallicity distribution with a spread similar to that observed in massive galaxies.

Keywords: Globular star clusters, Galaxy formation, Hydrodynamics, Cold dark matter, N-body simulations
Thermal Regulation and the Star-forming Main Sequence. We argue that the interplay between cosmic rays, the initial mass function (IMF), and star formation plays a crucial role in regulating the star-forming "main sequence." To explore these phenomena we develop a toy model for galaxy evolution in which star formation is regulated by a combination of a temperature-dependent IMF and heating due to starlight, cosmic rays, and (at very high redshift) the cosmic microwave background. This produces an attractor, near-equilibrium solution which is consistent with observations of the star-forming main sequence over a broad redshift range. Additional solutions to the same equations may correspond to other observed phases of galaxy evolution, including quiescent galaxies. This model makes several falsifiable predictions, including higher metallicities and dust masses than anticipated at high redshift and isotopic abundances in the Milky Way. It also predicts that stellar mass-to-light ratios are lower than produced using a Milky Way-derived IMF, such that inferences of stellar masses and star formation rates for high redshift galaxies are overestimated. In some cases, this may also transform inferred dark matter profiles from core-like to cusp-like.

Keywords: Initial mass function, Cosmic microwave background radiation, Star formation, Galaxy evolution, Cosmic ray sources, Cosmic rays
Wave Reflection and Transmission at the Interface of Convective and Stably Stratified Regions in a Rotating Star or Planet. We use a simplified model to study wave reflection and transmission at the interface of the convective region and stably stratified region (e.g., radiative zone in a star or stratification layer in a gaseous planet). The inertial wave in the convective region and gravito-inertial wave in the stably stratified region are considered. We begin with the polar area and then extend to any latitude. Six cases are discussed (see Table 1), and in Case 2 both waves co-exist in both regions. Four configurations are further discussed for Case 2. The angles and energy ratios of wave reflection and transmission are calculated. It is found that wave propagation and transmission depend on the ratio of buoyancy frequency to rotational frequency. In a rapidly rotating star or planet, the wave propagates across the interface and most of the energy of the incident wave is transmitted to the other region, but in a slowly rotating star or planet, wave transmission is inhibited.

Keywords: Stellar interiors, Planetary interior
Tracking Cosmic-Ray Spectral Variation during 2007-2018 Using Neutron Monitor Time-delay Measurements. The energy spectrum of Galactic cosmic-ray (GCR) ions at Earth varies with solar activity as these ions cross the heliosphere. Thus, this "solar modulation" of GCRs provides remote sensing of heliospheric conditions throughout the ∼11 yr sunspot cycle and ∼22 yr solar magnetic cycle. A neutron monitor (NM) is a stable ground-based detector that measures cosmic-ray rate variations above a geomagnetic or atmospheric cutoff rigidity with high precision (∼0.1%) over such timescales. Furthermore, we developed electronics and analysis techniques to indicate variations in the cosmic-ray spectral index using neutron time-delay data from a single station. Here we study solar modulation using neutron time-delay histograms from two high-altitude NM stations: (1) the Princess Sirindhorn Neutron Monitor at Doi Inthanon, Thailand, with the world's highest vertical geomagnetic cutoff rigidity, 16.7 GV, from 2007 December to 2018 April; and (2) the South Pole NM, with an atmosphere-limited cutoff of ∼1 GV, from 2013 December to 2018 April. From these histograms, we extract the leader fraction L, I.e., inverse neutron multiplicity, as a proxy of a GCR spectral index above the cutoff. After correction for pressure and precipitable water vapor variations, we find that L roughly correlates with the count rate but also exhibits hysteresis, implying a change in spectral shape after a solar magnetic polarity reversal. Spectral variations due to Forbush decreases, 27 day variations, and a ground-level enhancement are also indicated. These methods enhance the high-precision GCR spectral information from the worldwide NM network and extend it to higher rigidity.

Keywords: Solar cycle, Solar-terrestrial interactions, Cosmic rays
Chromospheric Heating by Acoustic Waves Compared to Radiative Cooling. II. Revised Grid of Models. Acoustic and magnetoacoustic waves are considered to be possible agents of chromospheric heating. We present a comparison of deposited acoustic energy flux with total integrated radiative losses in the middle chromosphere of the quiet Sun and a weak plage. The comparison is based on a consistent set of high-resolution observations acquired by the Interferometric Bidimensional Spectrometer instrument in the Ca II 854.2 nm line. The deposited acoustic-flux energy is derived from Doppler velocities observed in the line core and a set of 1737 non-local thermodynamic equilibrium 1D hydrostatic semi-empirical models, which also provide the radiative losses. The models are obtained by scaling the temperature and column mass of five initial models by Vernazza et al. (1981; VAL) B-F to get the best fit of synthetic to observed profiles. We find that the deposited acoustic-flux energy in the quiet-Sun chromosphere balances 30%-50% of the energy released by radiation. In the plage, it contributes by 50%-60% in locations with vertical magnetic field and 70%-90% in regions where the magnetic field is inclined more than 50° to the solar surface normal.

Keywords: Solar chromosphere, Solar chromospheric heating, Plages
Current Population Statistics Do Not Favor Photoevaporation over Core-powered Mass Loss as the Dominant Cause of the Exoplanet Radius Gap. We search for evidence of the cause of the exoplanet radius gap, I.e., the dearth of planets with radii near 1.8 R⊕. If the cause were photoevaporation, the radius gap should trend with proxies for the early-life high-energy emission of the planet-hosting stars. If, alternatively, the cause were core-powered mass loss, no such trends should exist. Critically, spurious trends between the radius gap and stellar properties arise from an underlying correlation with instellation. After accounting for this underlying correlation, we find that no trends remain between the radius gap and stellar mass or present-day stellar activity as measured by near-UV emission. We dismiss the nondetection of a radius gap trend with near-UV emission because present-day near-UV emission is unlikely to trace early-life high-energy emission, but we provide a catalog of Galaxy Evolution Explorer near-UV and far-UV emission measurements for general use. We interpret the nondetection of a radius gap trend with stellar mass by simulating photoevaporation with mass-dependent evolution of stellar high-energy emission. The simulation produces an undetectable trend between the radius gap and stellar mass under realistic sources of error. We conclude that no evidence, from this analysis or others in the literature, currently exists that clearly favors either photoevaporation or core-powered mass loss as the primary cause of the exoplanet radius gap. However, repeating this analysis once the body of well-characterized &lt;4 R⊕ planets has roughly doubled could confirm or rule out photoevaporation.

Keywords: Exoplanet evolution, Exoplanet catalogs, Stellar activity
The Properties of the Interstellar Medium of Galaxies across Time as Traced by the Neutral Atomic Carbon [C I]. We report Atacama Large Millimeter Array observations of the neutral atomic carbon transitions [C I] and multiple CO lines in a sample of ∼30 main-sequence galaxies at $z\sim 1$ , including novel information on [C I] ${(}^{3}{P}_{2}{\mbox{--}}^{3}{P}_{1})$ and CO $(7\mbox{--}6)$ for 7 of such normal objects. We complement our observations with a collection of &gt;200 galaxies with coverage of similar transitions, spanning the z = 0-4 redshift interval and a variety of ambient conditions from local to high-redshift starbursts. We find systematic variations in the [C I]/IR and [C I]/high-Jupper (Jupper = 7) CO luminosity ratios among the various samples. We interpret these differences as increased dense molecular gas fractions and star formation efficiencies in the strongest high-redshift starbursts with respect to normal main-sequence galaxies. We further report constant ${L}_{{[{\rm{C}}{\rm{I}}]}^{3}{P}_{2}\,-{}^{3}{P}_{1}}^{{\prime} }$ / ${L}_{{[{\rm{C}}{\rm{I}}]}^{3}{P}_{1}\,-{}^{3}{P}_{0}}^{{\prime} }$ ratios across the galaxy populations and redshifts, suggesting that gas temperatures Texc traced by [C I] do not strongly vary. We find only a mild correlation with Tdust and that, generally, Texc ≲ Tdust. We fit the line ratios with classical photodissociation region models, retrieving consistently larger densities and intensities of the UV radiation fields in submillimeter galaxies than in main-sequence and local objects. However, these simple models fall short in representing the complexity of a multiphase interstellar medium and should be treated with caution. Finally, we compare our observations with the Santa Cruz semi-analytical model of galaxy evolution, recently extended to simulate submillimeter emission. While we confirm the success in reproducing the CO lines, we find systematically larger [C I] luminosities at fixed IR luminosity than predicted theoretically. This highlights the necessity of improving our understanding of the mechanisms regulating the [C I] emission on galactic scales. We release our data compilation to the community.

Keywords: Starburst galaxies, Star formation, Galaxy evolution, Interstellar medium, Submillimeter astronomy, Ultraluminous infrared galaxies, High-redshift galaxies
Complementarity of Stacking and Multiplet Constraints on the Blazar Contribution to the Cumulative High-energy Neutrino Intensity. We investigate the blazar contribution to the cumulative neutrino intensity assuming a generic relationship between neutrino and gamma-ray luminosities, ${L}_{\nu }\propto {({L}_{\mathrm{ph}})}^{{\gamma }_{\mathrm{lw}}}$ L ν ∝ ( L ph ) γ lw . Using the gamma-ray luminosity functions for blazars, including flat-spectrum radio quasars (FSRQs) and BL Lac objects, as well as the Fermi-LAT detection efficiency, we estimate contributions from blazars resolved by Fermi-LAT as well as the unresolved counterpart. Combining the existing upper limits from stacking analyses, the cumulative neutrino flux from all blazars (including Fermi-LAT resolved and unresolved ones) are constrained in the range 0 ≲ γlw ≲ 2.5. We also evaluate the effects of the redshift evolution and the effective local number densities for each class of FSRQs, BL Lacs, and all blazars, on which we place another type of constraints on the blazar contribution using the nondetection of high-energy neutrino multiplets. We demonstrate that these two upper limits are complementary, and that the joint consideration of the stacking and multiplet analyses not only supports the argument that blazars are disfavored as the dominant sources of the 100 TeV neutrino background, but also extends it by including Fermi-LAT-unresolved blazars as well, for a more generic luminosity correlation ${L}_{\nu }\propto {({L}_{\mathrm{ph}})}^{{\gamma }_{\mathrm{lw}}}$ L ν ∝ ( L ph ) γ lw .

Keywords: Neutrino astronomy, Active galaxies, High energy astrophysics
Interpreting the Equatorially Antisymmetric Gravitational Field of Saturn Measured by the Cassini Grand Finale. The equatorially antisymmetric gravitational field of Saturn, represented by the four gravitational coefficients J3, J5, J7, and J9, has been measured by the Cassini Grand Finale. Since the rotational distortion and the internal structure do not contribute to the asymmetric gravity field, the spectrum of the odd coefficients offers a direct window into the structure and amplitude of fluid motion in Saturn. We show that the observed cloud-top asymmetric winds extending into Saturn's interior cannot produce the measured gravity field, suggesting that the cloud-top winds are confined within a thin weather layer and hence do not contribute to the observed gravity. We interpret the asymmetric gravitational field by searching for an a priori unknown zonal circulation taking place in the molecular envelope. We find that a zonal circulation confined in the 20,000 km thick molecular layer produces the coefficients J3, J5, J7, J9 in agreement with measurements. The depth of the circulation is consistent with that inferred from the equatorially symmetric gravitational field of Saturn.

Keywords: Deep space probes, Saturn, Hydrodynamics, Gravitational fields, Planetary atmospheres, Solar system gas giant planets, Gravity anomaly, Magnetohydrodynamical simulations
Local Group Analogs in ΛCDM Cosmological Simulations. We use semi-analytic galaxy catalogs based on two high-resolution cosmological N-body simulations, Millennium-WMAP7 and Millennium-II, to investigate the formation of Local Group (LG) analogs. Unlike previous studies, we use the observed stellar masses to select the LG member (Milky Way (MW) and M31) analogs, and then impose constraints using the observed separation, isolation, and kinematics of the two main member galaxies. By comparing radial and low-ellipticity orbits between the MW and M31, we find higher tangential velocity results in higher total mass, which are ${4.4}_{-1.5}^{+2.4}\,\times $ 10 ${}^{12}{M}_{\odot }$ and ${6.6}_{-1.5}^{+2.7}\,\times $ 10 ${}^{12}{M}_{\odot }$ for radial and low-ellipticity orbits. The orbits also influence the individual mass distribution of MW and M31 analogs. For radial orbits, typical host halo masses of the MW and M31 are ${1.5}_{-0.7}^{+1.4}\,\times $ 10 ${}^{12}{M}_{\odot }$ and ${2.5}_{-1.1}^{+1.3}\,\times $ 10 ${}^{12}{M}_{\odot };$ for low-ellipticity orbits, the masses are ${2.5}_{-1.4}^{+2.2}\,\times $ 10 ${}^{12}{M}_{\odot }$ and ${3.8}_{-1.8}^{+2.8}\,\times $ 10 ${}^{12}{M}_{\odot }$ . The LG is located primarily in filaments with tails extending toward higher densities up to $\delta \sim 4.5$ . The dark matter velocity anisotropy parameters β of both the MW and M31 analogs are close to zero in the center, increasing to 0.2-0.3 at 50-80 kpc and decreasing slowly outward. The slope is much flatter than computed from the MW satellites, and the amplitude is smaller than traced by halo stars. Values of β from different tracers agree at ∼120 kpc where β ∼ 0.2. We also find that model predictions agree broadly with observations in the radial distribution and luminosity function of satellites around the MW and M31.

Keywords: Local Group, Cold dark matter, Cosmology
A Simple Unified Spectroscopic Indicator of Stellar Luminosity: The Extended Flux-weighted Gravity-Luminosity Relationship. We show that for a wide range of stellar masses, from 0.3 to 20 M⊙, and for evolutionary phases from the main sequence to the beginning of the red giant stage, the stellar flux-weighted gravity, gF ≅ g/ ${T}_{\mathrm{eff}}^{4}$ , is tightly correlated with absolute bolometric magnitude ${M}_{\mathrm{bol}}$ . Such a correlation is predicted by stellar evolution theory. We confirm this relation observationally, using a sample of 445 stars with precise stellar parameters. It holds over 17 stellar magnitudes from ${M}_{\mathrm{bol}}$ = 9.0 to -8.0 mag with a scatter of 0.17 mag above ${M}_{\mathrm{bol}}$ = -3.0 and 0.29 mag below this value. We then test the relation with 2.2 million stars with 6.5 mag ≥ ${M}_{\mathrm{bol}}$ ≥ 0.5 mag, where "mass-produced" but robust $\mathrm{log}\,g$ , ${T}_{{\rm{e}}{\rm{f}}{\rm{f}}},$ and ${M}_{\mathrm{bol}}$ from LAMOST DR5 and Gaia DR2 are available. We find that the same relation holds with a scatter of ∼0.2 mag for single stars offering a simple spectroscopic distance estimate good to ∼10%.

Keywords: Fundamental parameters of stars, Stellar physics, Stellar evolution