adsabs/SciX_UAT_keywords huggingface dataset:
A Magnetic Disk-outflow Model for Changing Look Active Galactic Nuclei

The timescales of the variabilities in changing look (CL) active galactic nuclei (AGNs) are usually on the order of years to tens of years (some of them are even shorter than one year), which is much shorter than the viscous timescale of a standard thin accretion disk. This implies that the variabilities of CL AGNs cannot be reproduced by varying the mass accretion rate of the thin disk. In this work, we employ a magnetic accretion disk-outflow model to calculate the inflow time of the disk predominantly driven by magnetic outflows. In this model, most angular momentum of the gas in the disk is carried away by the outflows, and therefore its radial velocity can be substantially higher than that of a conventional viscous disk. Our calculations show that the inflow time of such a disk with outflows can be around several years to tens of years. The calculated spectra of the disk with outflows can fit the observed spectra of a CL AGN Mrk 1018 quite well both in the low and high states. The derived inflow time of such a disk with outflows is around 5 yr in the high state, while it becomes ~20 yr in the low state, which is roughly consistent with the observations of the variabilities in Mrk 1018.

Keywords: accretion; stellar accretion disks; magnetic fields; black hole physics; quasars; interstellar medium
Calibration of the IXPE Focal Plane X-Ray Polarimeters to Polarized Radiation

The Imaging X-ray Polarimetry Explorer (IXPE) is a NASA Small Explorer mission-in partnership with the Italian Space Agency-dedicated to X-ray polarimetry in the 2-8 keV energy band. The IXPE telescope comprises three grazing incidence mirror modules coupled to three detector units hosting each one a Gas Pixel Detector, a gas detector that allows measuring the polarization degree by using the photoelectric effect. A wide and accurate ground calibration was carried out on the IXPE Detector Units at INAF-IAPS, in Italy, where a dedicated facility was setup at this aim. In this paper, we present the results obtained from this calibration campaign to study the IXPE focal plane detector response to polarized radiation. In particular, we report on the modulation factor, which is the main parameter to estimate the sensitivity of a polarimeter.

Keywords: x-ray astronomy; polarimetry
Near-IR Observations of the Young Star [BHB2007]-1: A Substellar Companion Opening the Gap in the Disk

The presence of planets or substellar objects still embedded in their native protoplanetary disks is indirectly suggested by disk substructures like gaps, cavities, and spirals. However, these companions are rarely detected. We present Very Large Telescope/NACO high-contrast images in the J, H, KS, and $L^{\prime} $ bands of the young star [BHB2007]-1 probing the inclined disk in scattered light and revealing the probable presence of a companion. The point source is detected in the $L^{\prime} $ band in spatial correspondence with complementary Very Large Array observations. This object is constrained to have a mass in the range of 37-47 MJup and is located at 50 au from the central star, inside the 70 au-large disk cavity recently imaged by the Atacama Large Millimeter/submillimeter Array (ALMA), that is absent from our NACO data (down to 20 au). This mass range is compatible with the upper end derived from the size of the ALMA cavity. The NIR disk brightness is highly asymmetric around the minor axis, with the southern side 5.5 times brighter than the northern side. The constant amount of asymmetry across all wavelengths suggests that it is due to a shadow cast by a misaligned inner disk. The massive companion that we detect could, in principle, explain the possible disk misalignment, as well as the different cavity sizes inferred by the NACO and ALMA observations. The confirmation and characterization of the companion is entrusted to future observations.

Keywords: exoplanet astronomy; exoplanet systems; planet hosting stars; star formation
Numerical Modeling of Latitudinal Gradients for Galactic Cosmic-Ray Protons during Solar Minima: Comparing with Ulysses Observations

The latitudinal gradients of galactic cosmic-ray (GCR) protons measured by Ulysses during two successive minima provide a unique opportunity to study the modulation effects in polar regions of the heliosphere. In this work, a GCR modulation model based on numerically solving the Parker transport equation is used to study the latitudinal distribution of GCR protons in the inner heliosphere. Modifications of the standard Parker heliospheric magnetic field, the reduction of particle drifts, the latitudinal-dependent magnetic turbulence characteristics, and the anisotropic perpendicular diffusion coefficient are incorporated in the numerical model to investigate the corresponding modulation effects. It is found that the latitudinal-dependent magnetic turbulence magnitude, which makes the parallel diffusion coefficient decrease with the increasing of latitude, is crucial to obtain the negative latitude gradient in the inner heliosphere during the negative-polarity solar cycle. For the A > 0 period, on the other hand, the latitudinal diffusion coefficient in the inner heliosphere and the reduced drift velocity in the polar region are more important, while the anisotropic perpendicular diffusion coefficient at high latitude might be not essential. Finally, the proton latitudinal gradient and the corresponding differential intensity along the trajectory of Ulysses during its first and third fast latitude scans are computed, and the results show good agreement with the spacecraft observations.

Keywords: galactic cosmic rays; heliosphere; interplanetary magnetic fields; interplanetary turbulence; solar wind
Investigation of the Long-term Variation of Solar Ca II K Intensity. II. Reconstruction of Solar UV Irradiance

Reconstruction of long-term solar UV variations during the entire 20th century is reported. The sunspot number has been used for this purpose so far. By using the full-disk Ca K intensity as an additional solar UV proxy, the range of allowed values for the reconstructed UV irradiance becomes more restricted. We use long-term archival data of the photographic Ca K plates digitized at the Kodaikanal Solar Observatory. The photographic calibration method developed in our previous paper (Paper I) is applied. Various long-term proxy data of solar activity have been used to estimate past UV irradiance. In light of this context, some issues using the historical Ca K data are commented on.

Keywords: astronomy data analysis; photoheliographs; solar chromosphere; solar cycle; solar ultraviolet emission; solar-terrestrial interactions
Detecting Gravitational Scattering of Interstellar Objects Using Pulsar Timing

Gravitational scattering events, in which the path of an interstellar object is deflected by a pulsar or the solar system, give rise to reflex motion that can potentially be detected using pulsar timing. We determine the form of the timing signal expected from a gravitational scattering event, which is ramp-like and resembles the signal produced by a glitch or a gravitational wave burst with memory (BWM), and investigate the prospects for detecting such a signal using a pulsar timing array. The level of timing precision currently achieved for some millisecond pulsars makes it possible to detect objects as small as 10-10 M⊙, less than the mass of the dwarf planet Ceres, at impact parameters as large as $1\,\mathrm{au}$ . The signals produced by gravitational scattering could provide independent constraints on models of dark matter involving asteroid-mass objects or subhalos, and should be considered as potential false positives in searches for BWMs.

Keywords: pulsar timing method; millisecond pulsars; pulsars; free floating planets; dark matter; hyperbolic orbit
Gaia GraL: Gaia DR2 Gravitational Lens Systems. VII. XMM-Newton Observations of Lensed Quasars

We present XMM-Newton X-ray observations of nine confirmed lensed quasars at 1 ≲ z ≲ 3 identified by the Gaia Gravitational Lens program. Eight systems are strongly detected, with 0.3-8.0 keV fluxes F 0.3-8.0 ≳ 5 ×10-14 erg cm-2 s-1. Modeling the X-ray spectra with an absorbed power law, we derive power-law photon indices and 2-10 keV luminosities for the eight detected quasars. In addition to presenting sample properties for larger quasar population studies and for use in planning for future caustic-crossing events, we also identify three quasars of interest: a quasar that shows evidence of flux variability from previous ROSAT observations, the most closely separated individual lensed sources resolved by XMM-Newton, and one of the X-ray brightest quasars known at z > 3. These sources represent the tip of the discoveries that will be enabled by SRG/eROSITA.

Keywords: quasars; strong gravitational lensing; x-ray astronomy; x-ray quasars; scaling relations
Using Cosmic Rays Detected by HST as Geophysical Markers. I. Detection and Characterization of Cosmic Rays

The Hubble Space Telescope (HST) has been operational for over 30 years, and throughout that time it has been bombarded by high-energy charged particles colloquially referred to as cosmic rays. In this paper, we present a comprehensive study of more than 1.2 billion cosmic rays observed with HST using a custom-written Python package, HSTcosmicrays, that is available to the astronomical community. We analyzed 75,908 dark calibration files taken as part of routine calibration programs for five different CCD imagers with operational coverage of Solar Cycle 23 and 24. We observe the expected modulation of galactic cosmic rays by solar activity. We model the observed energy-loss distributions to derive an estimate of 534 ± 117 MeV for the kinetic energy of the typical cosmic ray impacting HST. For the three imagers with the largest nonuniformity in thickness, we independently confirm the overall structure produced by fringing analyses by analyzing cosmic ray strikes across the detector field of view. We analyze STIS/CCD observations taken as HST crosses over the South Atlantic Anomaly and find a peak cosmic ray particle flux of ~1100 particle s-1 cm-2. We find strong evidence for two spatially confined regions over North America and Australia that exhibit increased cosmic ray particle fluxes at the 5σ level.

Keywords: geomagnetic fields; cosmic rays; hubble space telescope; galactic cosmic rays
On the Number of Independent Parameters of Interstellar Extinction Curves

The number of independent parameters that ultraviolet interstellar extinction curves depend on has never been decisively clarified, yet the issue is critical for the comprehension and modeling of interstellar extinction observations. Cardelli, Clayton, & Mathis (CCM89) concluded that normalized extinction curves rely on only one parameter, but E. Fitzpatrick and others consider this finding at most a first-order approximation favored by uncertainties in measurement. However, the multiparameter fits successively introduced by Fitzpatrick & Massa were intended to give the best possible analytical representation of extinction curves, not to investigate their degrees of freedom. A deeper examination of these fits and of the CCM89 conclusion shows that they do not necessarily conflict. Fitzpatrick & Massa's parameterization of extinction curves and the large database (nearly 600 directions) published by Krelowski & Strobel are used in this paper to show that, within the precision allowed by the data, E(λ - V) correlates tightly with E(B - V) for all λ within the near-infrared to far-ultraviolet spectrum. This correlation confirms the relationships that led to the CCM89 fit and calls into question the reliability of today's interstellar dust models, which all need at least seven parameters (reddening included) to fit observed ultraviolet extinction curves.

Keywords: interstellar dust extinction
Spectroscopic Line Modeling of the Fastest Rotating O-type Stars

We present a spectroscopic analysis of the most rapidly rotating stars currently known, VFTS 102 ( ${v}_{e}\sin i=649\pm 52$ km s-1; O9: Vnnne+) and VFTS 285 ( ${v}_{e}\sin i=610\pm 41$ km s-1; O7.5: Vnnn), both members of the 30 Dor complex in the Large Magellanic Cloud. This study is based on high-resolution ultraviolet spectra from Hubble Space Telescope/Cosmic Origins Spectrograph and optical spectra from the Very Large Telescope (VLT) X-shooter plus archival VLT GIRAFFE spectra. We utilize numerical simulations of their photospheres, rotationally distorted shape, and gravity darkening to calculate model spectral line profiles and predicted monochromatic absolute fluxes. We use a guided grid search to investigate parameters that yield best fits for the observed features and fluxes. These fits produce estimates of the physical parameters for these stars (plus a Galactic counterpart, ζ Oph) including the equatorial rotational velocity, inclination, radius, mass, gravity, temperature, and reddening. We find that both stars appear to be radial-velocity constant. VFTS 102 is rotating at critical velocity, has a modest He enrichment, and appears to share the motion of the nearby OB-association LH 99. These properties suggest that the star was spun up through a close binary merger. VFTS 285 is rotating at 95% of critical velocity, has a strong He enrichment, and is moving away from the R136 cluster at the center of 30 Dor. It is mostly likely a runaway star ejected by a supernova explosion that released the components of the natal binary system.

Keywords: stellar rotation; massive stars; large magellanic cloud
An Evaluation of Electrostatic Lofting and Subsequent Particle Motion on Bennu

Electrostatic lofting is the detachment of particles from a surface that occurs if the electrostatic force on the particles is greater than the forces binding the particles to the surface. Electrostatic lofting has been hypothesized to occur on the Moon and observed in the laboratory environment. Because gravity is much weaker on asteroids than on the Moon, the hypothesis of electrostatic lofting has naturally been extended to these smaller airless bodies. We evaluate the feasibility of electrostatic lofting on Bennu using two formulations of the patched charge model. We find that submillimeter particles can be lofted from Bennu's dayside and, depending on their initial conditions, will reimpact or escape. The size and speed of the predicted electrostatically lofted particles are compared to those of the particle ejection events recently observed on Bennu. We find that dayside electrostatic lofting is not consistent with the size and speed of particles in the largest ejection events observed by the OSIRIS-REx mission. However, the escape of submillimeter particles has implications for the particle size distribution on Bennu's surface. Additionally, we model particle charging on Bennu's nightside due to secondary electron emission and find the resulting electrostatic force to be too weak to produce electrostatic lofting on the nightside.

Keywords: plasma physics; asteroid surfaces
Initial Characterization of Active Transitioning Centaur, P/2019 LD2 (ATLAS), Using Hubble, Spitzer, ZTF, Keck, Apache Point Observatory, and GROWTH Visible and Infrared Imaging and Spectroscopy

We present visible and mid-infrared imagery and photometry of temporary Jovian co-orbital comet P/2019 LD2 taken with Hubble Space Telescope/Wide Field Camera 3 (HST/WFC3), Spitzer Space Telescope/Infrared Array Camera (Spitzer/IRAC), and the GROWTH telescope network, visible spectroscopy from Keck/Low-Resolution Imaging Spectrometer (LRIS), and archival Zwicky Transient Facility observations taken between 2019 April and 2020 August. Our observations indicate that the nucleus of LD2 has a radius between 0.2 and 1.8 km assuming a 0.08 albedo and a coma dominated by ∼100 μm-scale dust ejected at ∼1 m s-1 speeds with a ∼1' jet pointing in the southwest direction. LD2 experienced a total dust mass loss of ∼108 kg at a loss rate of ∼6 kg s-1 with Afρ/cross section varying between ∼85 cm/125 km2 and ∼200 cm/310 km2 from 2019 April 9 to 2019 November 8. If the increase in Afρ/cross section remained constant, it implies LD2's activity began ∼2018 November when within 4.8 au of the Sun, implying the onset of H2O sublimation. We measure CO/CO2 gas production of ≲1027 mol s-1/≲1026 mol s-1 from our 4.5 μm Spitzer observations; g-r = 0.59 ± 0.03, r-i = 0.18 ± 0.05, and i-z = 0.01 ± 0.07 from GROWTH observations; and H2O gas production of ≲80 kg s-1 scaling from our estimated C2 production of ${Q}_{{C}_{2}}\lesssim 7.5\times {10}^{24}$ mol s-1 from Keck/LRIS spectroscopy. We determine that the long-term orbit of LD2 is similar to Jupiter-family comets having close encounters with Jupiter within ∼0.5 Hill radius in the last ∼3 y and within 0.8 Hill radius in ∼9 y. Additionally, 78.8% of our orbital clones are ejected from the solar system within 1 × 106 yr, having a dynamical half-life of 3.4 × 105 yr.

Keywords: celestial mechanics; centaur group; short period comets
Constraining Scalar-tensor Theories Using Neutron Star-Black Hole Gravitational Wave Events

With the continuous upgrade of detectors, greater numbers of gravitational wave (GW) events have been captured by the LIGO Scientific Collaboration and Virgo Collaboration (LVC), which offer a new avenue to test general relativity and explore the nature of gravity. Although various model-independent tests have been performed by LVC in previous works, it is still interesting to ask what constraints can be placed on specific models by current GW observations. In this work, we focus on three models of scalar-tensor theories, the Brans-Dicke theory (BD), the theory with scalarization phenomena proposed by Damour and Esposito-Farèse (DEF), and screened modified gravity (SMG). Of the four possible neutron star-black hole events that have occurred so far, we use two of them to place constraints. The other two are excluded in this work because of possible unphysical deviations. We consider the inspiral range with the cutoff frequency at the innermost stable circular orbit and add a modification of dipole radiation into the waveform template. The scalar charges of neutron stars in the dipole term are derived by solving the Tolman-Oppenheimer-Volkoff equations for different equations of state. The constraints are obtained by performing the full Bayesian inference with the help of the open source software Bilby. The results show that the constraints given by GWs are comparable to those given by pulsar timing experiments for DEF theory, but are not competitive with the current solar system constraints for BD and SMG theories.

Keywords: gravitational waves; non-standard theories of gravity
NeutralUniverseMachine: An Empirical Model for the Evolution of H I and H2 Gas in the Universe

Accurately modeling the cold gas content in the universe is challenging for current theoretical models. We propose a new empirical model NeutralUniverseMachine for the evolution of H I and H2 gas along with dark matter halos based on the UniverseMachine catalog. It is able to accurately describe the observed H I and H2 mass functions, molecular-to-atomic ratio, H I-halo mass relation, H I/H2-stellar mass relations at z ~ 0, as well as the evolution of cosmic gas densities ρ H I and ${\rho }_{{{\rm{H}}}_{2}}$ at 0 < z < 6. The predictions from our model include the following: (i) There is weak evolution of H I mass function at 0 < z < 3, but the evolution of H2 mass function is much stronger at the massive end. (ii) The average H I and H2 masses at a given stellar mass decrease by around 1 dex since z = 3 for the star-forming galaxies, but the evolution for the quenched galaxies is much weaker. (iii) Star-forming galaxies have a varying H I depletion time τ H I from 0.1-10 Gyr, and the dependence of τ H I on stellar mass and redshift is much stronger than those of the H2 depletion time. The quenched galaxies have a much longer gas depletion time and weaker redshift evolution. (iv) The cosmic baryon density associated with galaxies is dominated by stars at z < 1.2 and mainly contributed by H I gas at higher redshifts. (v) The H I bias gradually increases with the redshift from 0.69 to 2.33 at 0 < z < 3 and is consistent with recent H I intensity mapping experiments.

Keywords: baryon density; h i line emission; galaxy dark matter halos; star formation; circumgalactic medium; molecular gas; cold neutral medium; theoretical models; galaxy evolution
Eccentricity Driven Climate Effects in the Kepler-1649 System

The discovery of terrestrial exoplanets is uncovering increasingly diverse architectures. Of particular interest are those systems that contain exoplanets at a variety of star-planet separations, allowing direct comparison of exoplanet evolution (comparative planetology). The Kepler-1649 system contains two terrestrial planets similar both in size and insolation flux to Venus and Earth, although their eccentricities remain largely unconstrained. Here we present results of dynamical studies of the system and the potential effects on climate. The eccentricities of the Kepler-1649 system are poorly constrained, and we show that there are dynamically viable regions for further terrestrial planets in between the two known planets for a limited range of eccentricities. We investigate the effect of eccentricity of the outer planet on the dynamics of both planets and show that this results in high-frequency (1000-3000 years) eccentricity oscillations in long-term stable configurations. We calculate the resulting effect of these eccentricity variations on insolation flux and present the results of 3D climate simulations for the habitable zone planet. Our simulations demonstrate that, despite large eccentricity variations, the planet can maintain stable climates with relatively small temperature variations on the substellar hemisphere for a variety of initial climate configurations. Such systems thus provide key opportunities to explore alternative Venus/Earth climate evolution scenarios.

Keywords: exoplanets; exoplanet dynamics; exoplanet atmospheres; habitable planets
Discovery and Rapid Follow-up Observations of the Unusual Type II SN 2018ivc in NGC 1068

We present the discovery and high-cadence follow-up observations of SN 2018ivc, an unusual SNe II that exploded in NGC 1068 (D = 10.1 Mpc). The light curve of SN 2018ivc declines piecewise-linearly, changing slope frequently, with four clear slope changes in the first 30 days of evolution. This rapidly changing light curve indicates that interaction between the circumstellar material and ejecta plays a significant role in the evolution. Circumstellar interaction is further supported by a strong X-ray detection. The spectra are rapidly evolving and dominated by hydrogen, helium, and calcium emission lines. We identify a rare high-velocity emission-line feature blueshifted at ∼7800 $\mathrm{km}\,{{\rm{s}}}^{-1}$ (in Hα, Hβ, Pβ, Pγ, He I, and Ca II), which is visible from day 18 until at least day 78 and could be evidence of an asymmetric progenitor or explosion. From the overall similarity between SN 2018ivc and SN 1996al, the Hα equivalent width of its parent H II region, and constraints from pre-explosion archival Hubble Space Telescope images, we find that the progenitor of SN 2018ivc could be as massive as 52 ${M}_{\odot }$ but is more likely <12 ${M}_{\odot }$ . SN 2018ivc demonstrates the importance of the early discovery and rapid follow-up observations of nearby supernovae to study the physics and progenitors of these cosmic explosions.

Keywords: circumstellar gas; core-collapse supernovae; type ii supernovae