Sazuna/UAT_keywords huggingface dataset:
WASP-4 Is Accelerating toward the Earth. The orbital period of the hot Jupiter WASP-4b appears to be decreasing at a rate of -8.64 ± 1.26 ms yr-1, based on transit-timing measurements spanning 12 yr. Proposed explanations for the period change include tidal orbital decay, apsidal precession, and acceleration of the system along the line of sight. To investigate further, we performed new radial-velocity measurements and speckle imaging of WASP-4. The radial-velocity data show that the system is accelerating toward the Sun at a rate of -0.0422 ± 0.0028 m s-1 day-1. The associated Doppler effect should cause the apparent period to shrink at a rate of -5.94 ± 0.39 ms yr-1, comparable to the observed rate. Thus, the observed change in the transit period is mostly or entirely produced by the line-of-sight acceleration of the system. This acceleration is probably caused by a wide-orbiting companion of mass 10-300 MJup and orbital distance 10-100 au, based on the magnitude of the radial-velocity trend and the nondetection of any companion in the speckle images. We expect that the orbital periods of one out of three hot Jupiters will change at rates similar to WASP-4b, based on the hot-Jupiter companion statistics of Knutson et al. Continued radial-velocity monitoring of hot Jupiters is therefore essential to distinguish the effects of tidal orbital decay or apsidal precession from line-of-sight acceleration.

Keywords: Exoplanet dynamics, Radial velocity, Exoplanet tides, Transit timing variation method
Strong Near-infrared Spectral Variability of the Young Cloudy L Dwarf Companion VHS J1256-1257 b. Rotationally modulated variability of brown dwarfs and giant planets provides unique information about their surface brightness inhomogeneities, atmospheric circulation, cloud evolution, vertical atmospheric structure, and rotational angular momentum. We report results from Hubble Space Telescope/Wide Field Camera 3 near-infrared time-series spectroscopic observations of three companions with masses in or near the planetary regime: VHS J125601.92-125723.9 b, GSC 6214-210 B, and ROXs 42 B b. VHS J1256-1257 b exhibits strong total intensity and spectral variability with a brightness difference of 19.3% between 1.1 and 1.7 μm over 8.5 hr and even higher variability at the 24.7% level at 1.27 μm. The light curve of VHS J1256-1257 b continues to rise at the end of the observing sequence so these values represent lower limits on the full variability amplitude at this epoch. This observed variability rivals (and may surpass) the most variable brown dwarf currently known, 2MASS J21392676+0220226. The implied rotation period of VHS J1256-1257 b is ≈21-24 hr assuming sinusoidal modulations, which is unusually long for substellar objects. No significant variability is evident in the light curves of GSC 6214-210 B (&lt;1.2%) and ROXs 42 B b (&lt;15.6%). With a spectral type of L7, an especially red spectrum, and a young age, VHS J1256-1257 b reinforces emerging patterns between high variability amplitude, low surface gravity, and evolutionary phase near the L/T transition.

Keywords: Exoplanet atmospheric variability, Brown dwarfs
Orbit-induced Spin Precession as a Possible Origin for Periodicity in Periodically Repeating Fast Radio Bursts. FRB 180916.J0158+65 has been found to repeatedly emit fast radio bursts with a period of roughly 16 days. We propose that such periodicity comes from the orbit-induced spin precession of the emitter, which we assume to be a neutron star. Depending on the mass of the companion, the binary period ranges from several hundreds to thousands of seconds. Such tight binaries have relatively short lifetimes, and they are not likely to be products of gravitational decay from wide binaries. We comment on the relation of such binaries to GW190425 and the possibility of detecting them with LISA and LIGO.

Keywords: Radio bursts, Compact binary stars, Radio transient sources
Interpreting Solar Wind Turbulent Spectra beyond Taylor's Hypothesis. In this Letter we apply a methodology, recently proposed by Bourouaine &amp; Perez (BP19), to interpret solar wind turbulent power spectra beyond the Taylor approximation (TA). The turbulent power spectra were measured using Helios spacecraft data near 0.6 au. We use the model proposed in BP19 to reproduce the field-perpendicular power spectrum E(k⊥) of antisunward Alfvénic fluctuations in the plasma frame (where k⊥ is the field-perpendicular wavenumber) from the corresponding measured frequency power spectrum ${P}_{\mathrm{sc}}(\omega ,{\theta }_{b})$ along the sampling angle θb, which is the angle between the local magnetic field and the sampling direction. Here ω = 2πf and f is the frequency of the time signal. Interestingly enough, we found that for all corresponding measured frequency power spectrum ${P}_{\mathrm{sc}}(\omega ,{\theta }_{b})$ the reproduced field-perpendicular power spectrum E(k⊥) is the same and independent of the considered sampling angle θb. This finding is consistent with the fact that the analyzed turbulence is strong and highly anisotropic with ${k}_{\parallel }\ll {k}_{\perp }$ (where ${k}_{\parallel }$ is the field-parallel wavenumber). Furthermore, for this specific time signal we found that the commonly used TA is still approximately valid with the important difference that a broadening in k⊥ for each angular frequency ω is present. This broadening can be described in the context of the methodology proposed in BP19.

Keywords: Space plasmas, Fast solar wind, Interplanetary turbulence, Alfven waves, Solar magnetic fields
Measuring the Metallicity of Early-type Galaxies. We use data for 6048 early-type galaxies (ETGs) from Galaxy Zoo 1 that have been cross-matched with the catalog of the MPA-JHU emission-line measurements for the Sloan Digital Sky Survey Data Release 7. We measure the metallicity of these ETGs by excluding various ionization sources, and study other properties as well. We use the optimal division line of W2-W3 = 2.5 as a diagnostic tool, and for the first time derive metallicity measurements for 2218 ETGs. We find that these ETGs actually are closer to H II regions as defined by Kauffmann et al. in the Baldwin-Philips-Terevich diagram, and they display younger stellar populations. We present a full mass-metallicity relation and find that most ETGs have lower metallicities than star-forming galaxies (SFGs) at a given galaxy stellar mass. We use five metallicity calibrators to check our results. We find that these metallicity indicators (R23, O32, and O3S2) give consistent results. We suggest that the remaining two metallicity calibrators, which increase metallicity by N-enrichment, can be used to calibrate metallicities for SFGs, but not to estimate the metallicities of ETGs.

Keywords: Galaxy abundances, Galaxy evolution, Galaxy accretion
Clumpy AGN Outflows due to Thermal Instability. One of the main mechanisms that could drive mass outflows on parsec scales in active galactic nuclei (AGN) is thermal driving. The same X-rays that ionize and heat the plasma are also expected to make it thermally unstable. Indeed, it has been proposed that the observed clumpiness in AGN winds is caused by thermal instability (TI). While many studies employing time-dependent numerical simulations of AGN outflows have included the necessary physics for TI, none have so far managed to produce clumpiness. Here we present the first such clumpy wind simulations in 1D and 2D, obtained by simulating parsec-scale outflows irradiated by an AGN. By combining an analysis of our extensive parameter survey with physical arguments, we show that the lack of clumps in previous numerical models can be attributed to the following three effects: (I) insufficient radiative heating or other physical processes that prevent the outflowing gas from entering the TI zone; (II) the stabilizing effect of stretching (due to rapid radial acceleration) in cases where the gas enters the TI zone; and (III) a flow speed effect: in circumstances where stretching is inefficient, the flow can still be so fast that it passes through the TI zone too quickly for perturbations to grow. In addition to these considerations, we also find that a necessary condition to trigger TI in an outflow is for the pressure ionization parameter to decrease along a streamline once gas enters a TI zone.

Keywords: Hydrodynamical simulations, Active galactic nuclei
A New Helioseismic Constraint on a Cosmic-time Variation of G. The best available estimate of 8640 days of low-ℓ BiSON data is used to constrain the evolution of Newton's constant over cosmic time. The effect of different chemical compositions and the impact of the theoretical uncertainties on the efficiency of the proton-proton (pp) fusion cross-section have been considered within a Bayesian approach. The resulting new helioseismic limit on the variation of the gravitational constant turns out to be $| \dot{G}/G{| }_{t={t}_{0}}\lt 2\times {10}^{-13}$ ∣ G ˙ / G ∣ t = t 0 &lt; 2 × 10 - 13 yr-1.

Keywords: Stellar structures, Bayesian statistics, Helioseismology, Gravitation, Fundamental parameters of stars, Non-standard theories of gravity
Asymmetric Lunar Magnetic Perturbations Produced by Reflected Solar Wind Particles. Magnetic perturbations characterize the solar wind interaction of the Moon. The solar wind plasma absorption on the dayside surface produces large-scale field perturbations behind, I.e., the field enhancement in the central wake and reduction on the wake boundary. The solar wind repellence over local lunar magnetic anomalies (LMAs) leads to small-scale magnetic compressions ahead. In this study, the magnetic perturbations around the Moon are examined by using the observations from a near-Moon satellite mission, the Lunar Prospector, and they exhibit a clear left-right asymmetry in a coordinate system related to the solar wind convection electric field ( ${{\boldsymbol{E}}}_{\mathrm{SW}}$ ). The magnetic field is observed to enhance before the left terminator that ${{\boldsymbol{E}}}_{\mathrm{SW}}$ points to, while on the opposite side, it is not. The test particle simulations show that ${{\boldsymbol{E}}}_{\mathrm{SW}}$ can divert the particles reflected over the LMAs to the left and then the solar wind pickup of these particles leads to the field enhancement observed before the left terminator. Behind the lunar terminator, the wake field reduction is also asymmetric. On the left, the field reduction is more remarkable and located closer to the central wake. The denser plasma, consisting of the background as well as the reflected solar wind particles, may produce a stronger diamagnetic current and thus more significant field reduction there. The asymmetric plasma and magnetic perturbations associated with the reflected particles may be a common and nonnegligible element during the solar wind interaction of a small-scale magnetic field, such as that of an asteroid or a comet.

Keywords: Lunar magnetic fields, Pickup ions, Solar wind
The Binary Mass Ratio in the Black Hole Transient MAXI J1820+070. We present intermediate-resolution spectroscopy of the optical counterpart to the black hole X-ray transient MAXI J1820+070 (=ASASSN-18ey) obtained with the OSIRIS spectrograph on the 10.4 m Gran Telescopio Canarias. The observations were performed with the source close to the quiescent state and before the onset of renewed activity in 2019 August. We make use of these data and K-type dwarf templates taken with the same instrumental configuration to measure the projected rotational velocity of the donor star. We find Vrot sin I = 84 ± 5 km s-1 (1σ), which implies a donor to the black hole mass ratio $q={M}_{2}/{M}_{1}=0.072\pm 0.012$ for the case of a tidally locked and Roche-lobe filling donor star. The derived dynamical masses for the stellar components are ${M}_{1}=(5.95\pm 0.22){\sin }^{-3}I\,{M}_{\odot }$ and ${M}_{2}=(0.43\pm 0.08){\sin }^{-3}I\,{M}_{\odot }$ . The use of q, combined with estimates of the accretion disk size at the time of the optical spectroscopy, allows us to revise our previous orbital inclination constraints to 66° &lt; I &lt; 81°. These values lead to 95% confidence level limits on the masses of 5.73 &lt; M1(M⊙) &lt; 8.34 and 0.28 &lt; M2(M⊙) &lt; 0.77. Adopting instead the 63° ± 3° orientation angle of the radio jet as the binary inclination leads to ${M}_{1}={8.48}_{-0.72}^{+0.79}{M}_{\odot }$ and ${M}_{2}={0.61}_{-0.12}^{+0.13}\,{M}_{\odot }$ (1σ).

Keywords: Low-mass x-ray binary stars, Stellar mass black holes
A Numerical Model for the Multiwavelength Lightcurves of PSR J0030+0451. Recent modeling of Neutron Star Interior Composition Explorer (NICER) observations of the millisecond pulsar PSR J0030+0451 suggests that the magnetic field of the pulsar is non-dipolar. We construct a magnetic field configuration where foot points of the open field lines closely resemble the hotspot configuration from NICER observations. Using this magnetic field as input, we perform force-free simulations of the magnetosphere of PSR J0030+0451, showing the three-dimensional structure of its plasma-filled magnetosphere. Making simple and physically motivated assumptions about the emitting regions, we are able to construct the multiwavelength lightcurves that qualitatively agree with the corresponding observations. The agreement suggests that multipole magnetic structures are the key to modeling this type of pulsar, and can be used to constrain the magnetic inclination angle and the location of radio emission.

Keywords: Magnetospheric radio emissions, Rotation powered pulsars, Millisecond pulsars, Gamma-ray sources, X-ray sources
FRB Periodicity: Mild Pulsars in Tight O/B-star Binaries. Periodicities observed in two fast radio burst (FRB) sources (16 days in FRB 180916.J0158+65 and 160 days in FRB 121102) are consistent with that of tight, stellar-mass binary systems. In the case of FRB 180916.J0158+65 the primary is an early OB-type star with the mass-loss rate $\dot{M}\sim {10}^{-8}\mbox{--}{10}^{-7}{M}_{\odot }$ yr-1, and the secondary is a neutron star. The observed periodicity is not intrinsic to the FRB's source, but is due to the orbital phase-dependent modulation of the absorption conditions in the massive star's wind. The observed relatively narrow FRB activity window implies that the primary's wind dynamically dominates that of the pulsar, $\eta ={L}_{\mathrm{sd}}/(\dot{M}{V}_{w}c)\leqslant 1$ , where Lsd is the pulsar spin-down, $\dot{M}$ is the primary's wind mass-loss rate, and Vw is its velocity. The condition η ≤ 1 requires a mildly powerful pulsar with Lsd ≲ 1037 erg s-1. The observations are consistent with magnetically powered radio emission originating in the magnetospheres of young, strongly magnetized neutron stars, the classical magnetars.

Keywords: Close binary stars, Magnetars, Stellar winds, Radio transient sources
NuSTAR Observation of a Minuscule Microflare in a Solar Active Region. We present X-ray imaging spectroscopy of one of the weakest active region (AR) microflares ever studied. The microflare occurred at ∼11:04 UT on 2018 September 9 and we studied it using the Nuclear Spectroscopic Telescope ARray (NuSTAR) and the Solar Dynamic Observatory's Atmospheric Imaging Assembly (SDO/AIA). The microflare is observed clearly in 2.5-7 keV with NuSTAR and in Fe XVIII emission derived from the hotter component of the 94 Å SDO/AIA channel. We estimate the event to be three orders of magnitude lower than a GOES A class microflare with an energy of 1.1 × 1026 erg. It reaches temperatures of 6.7 MK with an emission measure of 8.0 × 1043 cm-3. Non-thermal emission is not detected but we instead determine upper limits to such emission. We present the lowest thermal energy estimate for an AR microflare in literature, which is at the lower limits of what is still considered an X-ray microflare.

Keywords: Solar activity, Solar flares, Solar corona, Solar x-ray flares
Distinguishing Binary Neutron Star from Neutron Star-Black Hole Mergers with Gravitational Waves. The gravitational-wave signal from the merger of two neutron stars cannot be easily differentiated from the signal produced by a comparable-mass mixed binary of a neutron star and a black hole. Indeed, both binary types can account for the gravitational-wave signal GW170817 even if its electromagnetic counterpart emission is taken into account. We propose a method that requires neither information from the post-inspiral phase of the binary nor an electromagnetic counterpart to identify mixed binaries of neutron stars merging with low-mass black holes using gravitational waves alone. This method is based on the fact that certain neutron star properties that can be measured with gravitational waves are common or similar for all neutron stars. For example all neutron stars share the same equation of state, and if the latter is hadronic, neutron stars have similar radii. If a mixed binary is misidentified as a neutron star binary, the inferred neutron star properties will be misestimated and appear as outliers in a population of low-mass binaries. We show that as few as ∼5 low-mass events will allow for the identification of the type of one event at the 80% confidence level. We model the population of low-mass binaries with a hierarchical mixture model and show that we can constrain the existence of mixed binaries or measure their abundance relative to neutron star binaries to ∼0.1 at the 68% credible level with 100 events.

Keywords: Neutron stars, Nuclear astrophysics, Gravitational waves
Gamma-Ray and X-Ray Observations of the Periodic-repeater FRB 180916 during Active Phases. FRB 180916 is a most intriguing source capable of producing repeating fast radio bursts with a periodic 16.3 day temporal pattern. The source is well positioned in a star-forming region in the outskirts of a nearby galaxy at 150 Mpc distance. In this Letter we report on the X-ray and γ-ray observations of FRB 180916 obtained by AGILE and Swift. We focused especially on the recurrent 5 day time intervals of enhanced radio bursting. In particular, we report on the results obtained in the time intervals 2020 February 3-8, 2020 February 25, 2020 March 5-10, and 2020 March 22-28 during a multiwavelength campaign involving high-energy and radio observations of FRB 180916. We also searched for temporal coincidences at millisecond timescales between the 32 known radio bursts of FRB 180916 and X-ray and MeV events detectable by AGILE. We do not detect any simultaneous event or any extended X-ray and γ-ray emission on timescales of hours/days/weeks. Our cumulative X-ray (0.3-10 keV) flux upper limit of 5 × 10-14 erg cm-2 s-1 (obtained during 5 day active intervals from several 1-2 ks integrations) translates into an isotropic luminosity upper limit of LX,UL ∼ 1.5 × 1041 erg s-1. Deep γ-ray observations above 100 MeV over a many-year timescale provide an average luminosity upper limit one order of magnitude larger. These results provide the so-far most stringent upper limits on high-energy emission from the FRB 180916 source. Our results constrain the dissipation of magnetic energy from a magnetar-like source of radius Rm, internal magnetic field Bm, and dissipation timescale τd to satisfy the relation ${R}_{m,6}^{3}\,{B}_{m,16}^{2}\,{\tau }_{d,8}^{-1}\lesssim 1$ , where Rm,6 is Rm in units of 106 cm, Bm,16 is Bm in units of 1016 G, and τd,8 in units of 108 s.

Keywords: X-ray astronomy, Radio bursts, Gamma-ray astronomy, Gamma-ray transient sources, Radio transient sources
Why Is it So Cold in Here? Explaining the Cold Temperatures Retrieved from Transmission Spectra of Exoplanet Atmospheres. Transmission spectroscopy is a powerful technique widely used to probe exoplanet terminators. Atmospheric retrievals of transmission spectra are enabling comparative studies of exoplanet atmospheres. However, the atmospheric properties inferred by retrieval techniques display a significant anomaly: most retrieved temperatures are far colder than expected. In some cases, retrieved temperatures are $\sim 1000\,{\rm{K}}$ colder than ${T}_{\mathrm{eq}}$ . Here, we provide an explanation for this conundrum. We demonstrate that erroneously cold temperatures result when 1D atmospheric models are applied to spectra of planets with differing morning-evening terminator compositions. Despite providing an acceptable fit, 1D retrieval techniques artificially tune atmospheric parameters away from terminator-averaged properties. Retrieved temperature profiles are hundreds of degrees cooler and have weaker temperature gradients than reality. Retrieved abundances are mostly biased by $\gt 1\sigma $ and sometimes by $\gt 3\sigma $ , with the most extreme biases for ultra-hot Jupiters. When morning-evening compositional differences manifest for prominent opacity sources, H2O abundances retrieved by 1D models can be biased by over an order of magnitude. Finally, we demonstrate that these biases provide an explanation for the cold retrieved temperatures reported for WASP-17b and WASP-12b. To overcome biases associated with 1D atmospheric models, there is an urgent need to develop multidimensional retrieval techniques.

Keywords: Exoplanet atmospheric composition , Bayesian statistics, Hot Jupiters, Exoplanets, Astronomy data analysis, Transmission spectroscopy, Spectroscopy, Exoplanet atmospheres
Solar Disk Center Shows Scattering Polarization in the Sr I 4607 Å Line. Magnetic fields in turbulent, convective high-β plasma naturally develop highly tangled and complex topologies - the solar photosphere being the paradigmatic example. These fields are mostly undetectable by standard diagnostic techniques with finite spatio-temporal resolution due to cancellations of Zeeman polarization signals. Observations of resonance scattering polarization have been considered to overcome these problems. But up to now, observations of scattering polarization lack the necessary combination of high sensitivity and high spatial resolution in order to directly infer the turbulent magnetic structure at the resolution limit of solar telescopes. Here, we report the detection of clear spatial structuring of scattering polarization in a magnetically quiet solar region at disk center in the Sr I 4607 Å spectral line on granular scales, confirming theoretical expectations. We find that the linear polarization presents a strong spatial correlation with the local quadrupole of the radiation field. The result indicates that polarization survives the dynamic and turbulent magnetic environment of the middle photosphere and is thereby usable for spatially resolved Hanle observations. This is an important step toward the long-sought goal of directly observing turbulent solar magnetic fields at the resolution limit and investigating their spatial structure.

Keywords: Spectropolarimetry, Solar photosphere, Quiet sun, Solar magnetic fields, Polarimeters