Sazuna/UAT_keywords huggingface dataset:
Detection of Polarization due to Cloud Bands in the Nearby Luhman 16 Brown Dwarf Binary. Brown dwarfs exhibit patchy or spatially varying banded cloud structures that are inferred through photometric and spectroscopic variability modeling techniques. However, these methods are insensitive to rotationally invariant structures, such as the bands seen in Jupiter. Here, we present H-band Very Large Telescope/NaCo linear polarization measurements of the nearby Luhman 16 L/T transition binary, which suggest that Luhman 16A exhibits constant longitudinal cloud bands. The instrument was operated in pupil tracking mode, allowing us to unambiguously distinguish between a small astrophysical polarization and the ∼2% instrumental linear polarization. We measure the degree and angle of linear polarization of Luhman 16A and B to be pA = 0.031% ± 0.004% and ψA = -32° ± 4°, and pB = 0.010% ± 0.004% and ${\psi }_{B}={73}_{-11}^{+13\circ} $ , respectively. Using known physical parameters of the system, we demonstrate that an oblate homogeneous atmosphere cannot account for the polarization measured in Luhman 16A, but could be responsible for that of the B component. Through a nonexhaustive search of banded cloud morphologies, we demonstrate a two-banded scenario that can achieve a degree of linear polarization of p = 0.03% and conclude that the measured polarization of the A component must be predominantly due to cloud banding. For Luhman 16B, either oblateness or cloud banding could be the dominant source of the measured polarization. The misaligned polarization angles of the two binary components tentatively suggest spin-orbit misalignment. These measurements provide new evidence for the prevalence of cloud banding in brown dwarfs while at the same time demonstrating a new method—complementary to photometric and spectroscopic variability methods—for characterizing the cloud morphologies of substellar objects without signs of variability.

Keywords: Very Large Telescope, Polarimetry, Near infrared astronomy
The Late-time Afterglow Evolution of Long Gamma-Ray Bursts GRB 160625B and GRB 160509A. We present post-jet-break Hubble Space Telescope, Very Large Array, and Chandra observations of the afterglow of the long γ-ray bursts GRB 160625B (between 69 and 209 days) and GRB 160509A (between 35 and 80 days). We calculate the post-jet-break decline rates of the light curves and find the afterglow of GRB 160625B is inconsistent with a simple t-3/4 steepening over the break, expected from the geometric effect of the jet edge entering our line of sight. However, the favored optical post-break decline ( ${f}_{\nu }\propto {t}^{-1.96\pm 0.07}$ ) is also inconsistent with the fν ∝ t-p decline (where p ≈ 2.3 from the pre-break light curve), which is expected from exponential lateral expansion of the jet; perhaps suggesting lateral expansion that only affects a fraction of the jet. The post-break decline of GRB 160509A is consistent with both the t-3/4 steepening and with fν ∝ t-p. We also use BOXFIT to fit afterglow models to both light curves and find both to be energetically consistent with a millisecond magnetar central engine, but the magnetar parameters need to be extreme (I.e., E ∼ 3 × 1052 erg). Finally, the late-time radio light curves of both afterglows are not reproduced well by BOXFIT and are inconsistent with predictions from the standard jet model; instead, both are well represented by a single power-law decline (roughly fν ∝ t-1) with no breaks. This requires a highly chromatic jet break ( ${t}_{j,\mathrm{radio}}\gt 10\times {t}_{j,\mathrm{optical}}$ ) and possibly a two-component jet for both bursts.

Keywords: Gamma-ray bursts, Relativistic jets
The Impact of Type Ia Supernovae in Quiescent Galaxies. I. Formation of the Multiphase Interstellar Medium. A cool phase of the interstellar medium has been observed in many giant elliptical galaxies, but its origin remains unclear. We propose that uneven heating from Type Ia supernovae (SNe Ia), together with radiative cooling, can lead to the formation of the cool phase. The basic idea is that since SNe Ia explode randomly, gas parcels that are not directly heated by SN shocks will cool, forming multiphase gas. We run a series of idealized high-resolution numerical simulations and find that cool gas develops even when the overall SN heating rate H exceeds the cooling rate C by a factor as large as 1.4. We also find that the time for multiphase gas development depends on the gas temperature. When the medium has a temperature T = 3 × 106 K, the cool phase forms within one cooling time ${t}_{{\rm{c}},0}$ ; however, the cool phase formation is delayed to a few times ${t}_{{\rm{c}},0}$ for higher temperatures. The main reason for the delay is turbulent mixing. Cool gas formed this way would naturally have a metallicity lower than that of the hot medium. For constant H/C, there is more turbulent mixing for higher-temperature gas. We note that this mechanism of producing cool gas cannot be captured in cosmological simulations, which usually fail to resolve individual SN remnants.

Keywords: Hydrodynamical simulations, Core-collapse supernovae, Galaxy chemical evolution, Type Ia supernovae, Galaxy evolution, Interstellar medium, Shocks, Elliptical galaxies
Toward a Full MHD Jet Model of Spinning Black Holes. II. Kinematics and Application to the M87 Jet. In this paper, we investigate the magnetohydrodynamical structure of a jet powered by a spinning black hole, where electromagnetic fields and fluid motion are governed by the Grad-Shafranov equation and the Bernoulli equation, respectively. When a steady and axisymmetric jet structure is assumed, the global solution is uniquely determined with the prescribed plasma loading into the jet and the poloidal shape of the outmost magnetic field line. We apply this model to the jet in the center of the nearby radio galaxy M87, and we find that it can naturally explain the slow flow acceleration and the flow velocity stratification within 105 gravitational radii from the central black hole. In particular, we find that the extremal black hole spin is disfavored by the flow velocity measurements if the plasma loading into the jet is dominated by the electron-positron pair production at the jet base.

Keywords: Black hole physics, Magnetohydrodynamics, Relativistic jets, Galaxy jets, Magnetic fields
MEM_GE: A New Maximum Entropy Method for Image Reconstruction from Solar X-Ray Visibilities. Maximum Entropy is an image reconstruction method conceived to image a sparsely occupied field of view, therefore it is particularly effective at achieving super-resolution effects. Although widely used in image deconvolution, this method has been formulated in radio astronomy for the analysis of observations in the spatial frequency domain, and an Interactive Data Language code has been implemented for image reconstruction from solar X-ray Fourier data. However, this code relies on a non-convex formulation of the constrained optimization problem addressed by the Maximum Entropy approach, and this sometimes results in unreliable reconstructions characterized by unphysical shrinking effects. This paper introduces a new approach to Maximum Entropy based on the constrained minimization of a convex functional. In the case of observations recorded by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), the resulting code provides the same super-resolution effects of the previous algorithm, while also working properly when that code produces unphysical reconstructions. We also obtain results via testing the algorithm with synthetic data simulating observations of the Spectrometer/Telescope for Imaging X-rays (STIX) in Solar Orbiter. The new code is available in the HESSI folder of the Solar SoftWare (SSW) tree.

Keywords: Solar flares, The Sun, Experimental techniques, Astronomical techniques, Solar x-ray flares, Radio transient sources
Circular Polarization from Inhomogeneous Synchrotron Sources. Inhomogeneities can influence the polarization emerging from a synchrotron source. However, it is shown that the frequency distribution of circular polarization is only marginally affected, although its magnitude may change substantially. This is used to argue that the observed properties of compact radio sources imply a radiating plasma in which the characteristic waves are nearly circular. As a result, restrictions can be put on the low-energy part of the energy distribution of the relativistic electrons as well as the presence of electron-positron pairs. It is emphasized that this constrains theoretical modeling of the acceleration process for the relativistic electrons; for example, some of the currently popular scenarios seem to need modifications to become consistent with observations.

Keywords: Radio jets, Extragalactic radio sources, Active galaxies, Relativistic jets, Radiative transfer equation, Radio galaxies, Non-thermal radiation sources, Radio active galactic nuclei, Radiative transfer, Radiative processes, Radio continuum emission, Magnetic fields
Discovery of Tidal Tails around the Old Open Cluster NGC 2506. We report the discovery of tidal tails around the old open cluster NGC 2506 based on Gaia-DR2. A principal-component analysis and Gaussian mixture model are used to identify extra-tidal stars. We identify 2301 stars closely related to the cluster, 147 of which are likely extra-tidal stars. We find clear evidence for the existence of two well-defined tidal tails emerging from the cluster. The tidal tails extend out to projected distances of at least 54 pc, which is nearly three times as large as the tidal radius of the cluster. Furthermore, we find that the extra-tidal stars have a wide mass spectrum (∼0.6-1.4 M⊙), which cannot be completely explained by mass segregation and the preferential evaporation of low-mass stars. An extra dynamical process such as disk-shocking may also play an important role in forming these extra-tidal stars. A mass-loss rate of ∼5.3 M⊙ Myr-1 is estimated for the cluster. This reveals that NGC 2506 is currently undergoing heavy mass-loss due to star escapes.

Keywords: Parallax, Hertzsprung Russell diagram, Stellar kinematics, Proper motions, Open star clusters
A Modified Spheromak Model Suitable for Coronal Mass Ejection Simulations. Coronal mass ejections (CMEs) are some of the primary drivers of extreme space weather. They are large eruptions of mass and magnetic field from the solar corona and can travel the distance between Sun and Earth in half a day to a few days. Predictions of CMEs at 1 au, in terms of both its arrival time and magnetic field configuration, are very important for predicting space weather. Magnetohydrodynamic modeling of CMEs, using flux rope-based models, is a promising tool for achieving this goal. In this study, we present one such model for CME simulations, based on spheromak magnetic field configuration. We have modified the spheromak solution to allow for independent input of poloidal and toroidal fluxes. The motivation for this is the possibility of estimating these fluxes from solar magnetograms and extreme ultraviolet data from a number of different approaches. We estimate the poloidal flux of CME using post-eruption arcades and toroidal flux from the coronal dimming. In this modified spheromak, we also have the option to control the helicity sign of flux ropes, which can be derived from the solar disk magnetograms using the magnetic tongue approach. We demonstrate the applicability of this model by simulating the 2012 July 12 CME in the solar corona.

Keywords: Solar wind, Solar coronal mass ejections, Magnetohydrodynamical simulations
Time Variability of Nonthermal X-Ray Stripes in Tycho's Supernova Remnant with Chandra. Analyzing Chandra data of Tycho's supernova remnant (SNR) taken in 2000, 2003, 2007, 2009, and 2015, we search for time-variable features of synchrotron X-rays in the southwestern part of the SNR, where stripe structures of hard X-ray emission were previously found. By comparing X-ray images obtained at each epoch, we discover a knot-like structure in the northernmost part of the stripe region became brighter particularly in 2015. We also find a bright filamentary structure gradually became fainter and narrower as it moves outward. Our spectral analysis reveals that not only the nonthermal X-ray flux but also the photon indices of the knot-like structure change from year to year. During the period from 2000 to 2015, the small knot shows a brightening of ∼70% and hardening of ΔΓ ∼ 0.45. The time variability can be explained if the magnetic field is amplified to $\sim 100\,\mu {\rm{G}}$ and/or if magnetic turbulence significantly changes with time.

Keywords: Supernova remnants, Galactic cosmic rays, Cosmic ray sources, X-ray sources, Interstellar medium, Magnetic fields
Evidence for Proton Acceleration up to TeV Energies Based on VERITAS and Fermi-LAT Observations of the Cas A SNR. We present a study of γ-ray emission from the core-collapse supernova remnant Cas A in the energy range from 0.1 GeV to 10 TeV. We used 65 hr of the Very Energetic Radiation Imaging Telescope Array System (VERITAS) data to cover 200 GeV-10 TeV, and 10.8 yr of Fermi-Large Area Telescope (LAT) data to cover 0.1-500 GeV. The spectral analysis of Fermi-LAT data shows a significant spectral curvature around 1.3 ± 0.4stat GeV that is consistent with the expected spectrum from pion decay. Above this energy, the joint spectrum from Fermi-LAT and VERITAS deviates significantly from a simple power law, and it is best described by a power law with a spectral index of 2.17 ± 0.02stat and a cutoff energy of 2.3 ± 0.5stat TeV. These results, along with radio, X-ray, and γ-ray data, are interpreted in the context of leptonic and hadronic models. Assuming a one-zone model, we exclude a purely leptonic scenario and conclude that proton acceleration up to at least 6 TeV is required to explain the observed γ-ray spectrum. From modeling of the entire multiwavelength spectrum, a minimum magnetic field inside the remnant of Bmin ≈ 150 μG is deduced.

Keywords: Observational astronomy, Supernova remnants, Galactic cosmic rays, Ground-based astronomy, Gamma-ray astronomy
Magnetar as Central Engine of Gamma-Ray Bursts: Quasi-universal Jet, Event Rate, and X-Ray Luminosity Function of Dipole Radiations. Early shallow-decaying X-ray afterglows of gamma-ray bursts (GRBs) may be attributed to the dipole radiations of newly born magnetars. Assuming that the GRB jets powered by magnetars are quasi-universal, we find that the jet structure can be parameterized as a uniform jet with a luminosity of $\mathrm{log}{L}_{{\rm{j}}}/\mathrm{erg}\ {{\rm{s}}}^{-1}={52.68}_{-0.33}^{+0.76}$ (1σ) and an opening angle ${\theta }_{{\rm{j}}}={2.10}_{-1.28}^{+1.90}$ (50% confidence level), surrounding by a power-law decay component with an index of $-{4.00}_{-0.37}^{+0.27}$ (1σ). The inferred local GRB rate is ρ = 9.6 Gpc-3 yr-1 by including both the typical GRBs and LL-GRBs as the same population. The typical viewing angle is 3.3°, and may be 20° ∼ 30° for LL-GRBs. The X-ray luminosity function of the dipole radiation wind can be empirically described by a broken power-law function with indices ${\beta }_{1}={0.78}_{-0.15}^{+0.16}$ and ${\beta }_{2}\gt 1.6$ broken at $\mathrm{log}{L}_{{\rm{b}},{\rm{w}}}/\mathrm{erg}\ {{\rm{s}}}^{-1}={48.51}_{-0.65}^{+0.53}$ . In the case where the wind outflow is collimated and coaxial with the GRB jet, we find that the wind structure is similar to the GRB jet, I.e., $\mathrm{log}{L}_{{\rm{c}},{\rm{w}}}/\mathrm{erg}\,{{\rm{s}}}^{-1}={48.38}_{-0.48}^{+0.30}$ , ${\theta }_{{\rm{c}},{\rm{w}}}={{2.65}^{o}}_{-{1.19}^{o}}^{+1.{73}^{o}}$ , and ${k}_{{\rm{w}}}={4.57}_{-0.75}^{+1.21}$ . The observed correlation between the prompt gamma-ray luminosity and X-ray luminosity of the wind may result from the viewing angle effect in such a jet-wind system. A discussion on surveys using the X-ray instruments on board the Einstein Probe mission in the soft X-ray band for the jet and wind emission is also presented.

Keywords: Luminosity function, Magnetars, Gamma-ray bursts, Relativistic jets
The ELM Survey South. I. An Effective Search for Extremely Low Mass White Dwarfs. We begin the search for extremely low mass (M ≤ 0.3M☉, ELM) white dwarfs (WDs) in the southern sky based on photometry from the VST ATLAS and SkyMapper surveys. We use a similar color selection method as the Hypervelocity star survey. We switched to an astrometric selection once Gaia Data Release 2 became available. We use the previously known sample of ELM white dwarfs to demonstrate that these objects occupy a unique parameter space in parallax and magnitude. We use the SOAR 4.1 m telescope to test the Gaia-based selection, and identify more than two dozen low mass white dwarfs, including six new ELM white dwarf binaries with periods as short as 2 h. The better efficiency of the Gaia-based selection enables us to extend the ELM Survey footprint to the southern sky. We confirm one of our candidates, J0500-0930, to be the brightest (G = 12.6 mag) and closest (d = 72 pc) ELM white dwarf binary currently known. Remarkably, the Transiting Exoplanet Survey Satellite (TESS) full-frame imaging data on this system reveals low-level (&lt;0.1%) but significant variability at the orbital period of this system (P = 9.5 hr), likely from the relativistic beaming effect. TESS data on another system, J0642-5605, reveals ellipsoidal variations due to a tidally distorted ELM WD. These demonstrate the power of TESS full-frame images in confirming the orbital periods of relatively bright compact object binaries.

Keywords: Radial velocity, White dwarf stars, Spectroscopy, Compact objects
Cosmological Model Insensitivity of Local H<SUB>0</SUB> from the Cepheid Distance Ladder. The observed tension (∼9% difference) between the local distance ladder measurement of the Hubble constant, H0, and its value inferred from the cosmic microwave background could hint at new, exotic, cosmological physics. We test the impact of the assumption about the expansion history of the universe ( $0.01\lt z\lt 2.3$ ) on the local distance ladder estimate of H0. In the fiducial analysis, the Hubble flow Type Ia supernova (SN Ia) sample is truncated to z &lt; 0.15, and the deceleration parameter (q0) is fixed to -0.55. We create realistic simulations of the calibrator and Pantheon samples, and account for a full systematics covariance between these two sets. We fit several physically motivated dark-energy models, and derive combined constraints from calibrator and Pantheon SNe Ia and simultaneously infer H0 and dark-energy properties. We find that the assumption on the dark-energy model does not significantly change the local distance ladder value of H0, with a maximum difference (ΔH0) between the inferred value for different models of 0.47 km ${{\rm{s}}}^{-1}\,{\mathrm{Mpc}}^{-1}$ , I.e., a 0.6% shift in H0, significantly smaller than the observed tension. Additional freedom in the dark-energy models does not increase the error in the inferred value of H0. Including systematics covariance between the calibrators, low-redshift SNe, and high-redshift SNe can induce small shifts in the inferred value for H0. The SN Ia systematics in this study contribute ≲0.8% to the total uncertainty of H0.

Keywords: Hubble constant, Cosmological parameters, Type Ia supernovae, Dark energy
SOFIA/FORCAST Galactic Center Legacy Survey: Overview. The Galactic Center contains some of the most extreme conditions for star formation in our Galaxy, as well as many other phenomena that are unique to this region. Given our relative proximity to the Galactic Center, we are able to study details of physical processes to a level that is simply not yet possible for more distant galaxies, yielding an otherwise inaccessible view of the nuclear region of a galaxy. We recently carried out a targeted imaging survey of mid-infrared bright portions of the Galactic Center at 25 and 37 μm using the FORCAST instrument on the Stratospheric Observatory for Infrared Astronomy (SOFIA). This survey was one of the inaugural Legacy Programs from SOFIA cycle 7, observing a total area of 403 arcmin2 (2180 pc2), including the Sgr A, B, and C complexes. Here we present an overview of the survey strategy, observations, and data reduction as an accompaniment to the initial public release of the survey data. We discuss interesting regions and features within the data, including extended features near the circumnuclear disk, structures in the Arched Filaments and Sickle H II regions, and signs of embedded star formation in Sgr B2 and Sgr C. We also feature a handful of less well studied mid-infrared sources located between Sgr A and Sgr C that could be sites of relatively isolated star formation activity. Last, we discuss plans for subsequent publications and future data releases from the survey.

Keywords: Star formation, Star forming regions, Galactic center, H II regions
Environmental Influences on Star Formation in Low-mass Galaxies Observed by the SDSS-IV/MaNGA Survey. We explore the environmental influences on the star formation (SF) in low-mass galaxies with stellar mass 8 ≤ log(M⋆/M⊙) ≤ 10 at a redshift of 0.01 &lt; z &lt; 0.07. We identify the neighboring galaxies for our sample using the spectroscopically observed galaxies in the Sloan Digital Sky Survey (SDSS). Our 287 selected pair candidates have a neighboring galaxy with a stellar mass ratio of MNeighbor/MCandidate ≤ 4 at a projected separation within dproj ≤ 1500 kpc and a line-of-sight kinematic separation of ΔVLOS ≤ 300 km s-1. Our control galaxies are isolated from other galaxies within a projected radius of 1500 kpc. All selected galaxies in our sample are spectroscopically observed by the fourth generation of SDSS/Mapping Nearby Galaxies at Apache Point Observatory (SDSS-IV/MaNGA) integral field spectroscopy survey. We radially bin our selected galaxies into three regions with a radial distance of 0 ≤ R/Re ≤ 0.5 (inner), 0.5 ≤ R/Re ≤ 1.0 (middle), and 1.0 ≤ R/Re ≤ 1.5 (outer), in which Re is the effective radius at where the galaxy emit half of its light. We conclude that the SF activities in low-mass galaxies are affected by their environmental conditions when ΔVLOS ≤ 100 km s-1 at dproj ≤ 400 kpc. We use stellar-mass-weighted SF rate surface density ( ${\rm{\Sigma }}\mathrm{SFR}/{M}_{\star }$ ) to describe the SF strength in each radially binned region. For the pair candidates with 0.25 ≤ MNeighbor/MCandidate ≤ 4 at dproj ≤ 100 kpc and ${\rm{\Delta }}{V}_{\mathrm{LOS}}\leqslant 100\,\mathrm{km}\,{{\rm{s}}}^{-1}$ , we observe an SF enhancement of ${f}_{{\rm{\Delta }}\mathrm{SF}}=1.75\pm 0.96$ ( ${f}_{{\rm{\Delta }}\mathrm{SF}}$ = $[{({\rm{\Sigma }}\mathrm{SFR}/{M}_{\star })}_{\mathrm{Pair}}-{({\rm{\Sigma }}\mathrm{SFR}/{M}_{\star })}_{\mathrm{Control},\mathrm{mean}}]$ / ${({\rm{\Sigma }}\mathrm{SFR}/{M}_{\star })}_{\mathrm{Control},\mathrm{mean}}$ ) in their inner regions, which decreases with increasing galactic radii.

Keywords: Star formation, Galaxy interactions, Dwarf galaxies, Galaxy evolution