adsabs/SciX_UAT_keywords huggingface dataset:
Two-year Cosmology Large Angular Scale Surveyor (CLASS) Observations: 40 GHz Telescope Pointing, Beam Profile, Window Function, and Polarization Performance

The Cosmology Large Angular Scale Surveyor (CLASS) is a telescope array that observes the cosmic microwave background (CMB) over 75% of the sky from the Atacama Desert, Chile, at frequency bands centered near 40, 90, 150, and 220 GHz. CLASS measures the large angular scale (1° ≲ θ ≤ 90°) CMB polarization to constrain the tensor-to-scalar ratio at the r ∼ 0.01 level and the optical depth to last scattering to the sample variance limit. This paper presents the optical characterization of the 40 GHz telescope during its first observation era, from 2016 September to 2018 February. High signal-to-noise observations of the Moon establish the pointing and beam calibration. The telescope boresight pointing variation is <0°023 (<1.6% of the beam's full width at half maximum (FWHM)). We estimate beam parameters per detector and in aggregate, as in the CMB survey maps. The aggregate beam has an FWHM of 1°579 ± 0°001 and a solid angle of 838 ± 6 μsr, consistent with physical optics simulations. The corresponding beam window function has a sub-percent error per multipole at ℓ < 200. An extended 90° beam map reveals no significant far sidelobes. The observed Moon polarization shows that the instrument polarization angles are consistent with the optical model and that the temperature-to-polarization leakage fraction is <10-4 (95% C.L.). We find that the Moon-based results are consistent with measurements of M42, RCW 38, and Tau A from CLASS's CMB survey data. In particular, Tau A measurements establish degree-level precision for instrument polarization angles.

Keywords: astronomical instrumentation; cosmic microwave background radiation; early universe; observational cosmology; polarimeters; the moon
Quantifying Poynting Flux in the Quiet Sun Photosphere

Poynting flux is the flux of magnetic energy, which is responsible for chromospheric and coronal heating in the solar atmosphere. It is defined as a cross product of the electric and magnetic fields, and in ideal MHD conditions it can be expressed in terms of the magnetic field and plasma velocity. Poynting flux has been computed for active regions and plages, but estimating it in the quiet Sun (QS) remains challenging due to resolution effects and polarimetric noise. However, with the upcoming DKIST capabilities, such estimations will become more feasible than ever before. Here, we study QS Poynting flux in SUNRISE/IMaX observations and MURaM simulations. We explore two methods for inferring transverse velocities from observations-FLCT and a neural network-based method DeepVel-and show DeepVel to be the more suitable method in the context of small-scale QS flows. We investigate the effect of azimuthal ambiguity on Poynting flux estimates, and we describe a new method for azimuth disambiguation. Finally, we use two methods for obtaining the electric field. The first method relies on an idealized Ohm's law, whereas the second is a state-of-the-art inductive electric field inversion method PDFI_SS. We compare the resulting Poynting flux values with theoretical estimates for chromospheric and coronal energy losses and find that some of the Poynting flux estimates are sufficient to match the losses. Using MURaM simulations, we show that photospheric Poynting fluxes vary significantly with optical depth, and that there is an observational bias that results in underestimated Poynting fluxes due to an unaccounted shear term contribution.

Keywords: the sun; solar physics; solar atmosphere; solar photosphere; solar chromospheric heating
The AO327 Drift Survey Catalog and Data Release of Pulsar Detections

The AO327 drift survey for radio pulsars and transients used the Arecibo telescope from 2010 until its collapse in 2020. AO327 collected ∼3100 hr of data at 327 MHz with a time resolution of 82 μs and a frequency resolution of 24 kHz. While the main motivation for such surveys is the discovery of new pulsars and new, even unforeseen, types of radio transients, they also serendipitously collect a wealth of data on known pulsars. We present an electronic catalog of data and data products of 206 pulsars whose periodic emission was detected by AO327 and are listed in the Australia Telescope National Facility catalog of all published pulsars. The AO327 data products include dedispersed time series at full time resolution, average ("folded") pulse profiles, Gaussian pulse profile templates, and an absolute phase reference that allows phase aligning the AO327 pulse profiles in a physically meaningful manner with profiles from data taken with other instruments. We also provide machine-readable tables with uncalibrated flux measurements at 327 MHz and pulse widths at 50% and 10% of the pulse peak determined from the fitted Gaussian profile templates. The AO327 catalog data set can be used in applications like population analysis of radio pulsars, pulse profile evolution studies in time and frequency, cone and core emission of the pulsar beam, scintillation, pulse intensity distributions, and others. It also constitutes a ready-made resource for teaching signal-processing and pulsar astronomy techniques.

Keywords: pulsars; neutron stars; catalogs; surveys
Dust-scattering Halo and Giant Hard X-Ray Flare from the Supergiant Fast X-Ray Transient IGR J16479-4514 Investigated with XMM-Newton and INTEGRAL

We report results from the analysis of XMM-Newton and INTEGRAL data of IGR J16479-4514. The unpublished XMM-Newton observation, performed in 2012, occurred during the source eclipse. No pointlike X-ray emission was detected from the source; conversely, extended X-ray emission was clearly detected up to a size distance compatible with a dust-scattering halo produced by the source X-ray emission before being eclipsed by its companion donor star. The diffuse emission of the dust-scattering halo could be observed without any contamination from the central point X-ray source, compared to a previous XMM-Newton observation published in 2008. Our comprehensive analysis of the 2012 unpublished spectrum of the diffuse emission, as well as the 2008 reanalyzed spectra extracted from three adjacent time intervals and different extraction regions (optimized for pointlike and extended emission), allowed us to clearly disentangle the scattering halo spectrum from the residual pointlike emission during the 2008 eclipse. Moreover, the pointlike emission detected in 2008 could be separated into two components attributed to the direct emission from the source and scattering in the stellar wind, respectively. From archival unpublished INTEGRAL data, we identified a very strong (∼3 × 10-8 erg cm-2 s-1) and fast (∼25 minute duration) flare that was classified as a giant hard X-ray flare, since the measured peak luminosity is ∼7 × 1037 erg s-1. Giant X-ray flares from supergiant fast X-ray transients are very rare; to date, only one has been reported from a different source. We propose a physical scenario to explain the origin in the case of IGR J16479-4514.

Keywords: accretion; high mass x-ray binary stars; x-ray transient sources
Evidence that Interaction with the Spacecraft Plasma Wake Generates Plasma Waves Close to the Electron Cyclotron Frequency in the Near-Sun Solar Wind

Prior observations of the near-Sun solar wind (sunward of 0.25 au) identified frequent, intense plasma waves near the local electron cyclotron frequency (f ce), and its harmonics. In this Letter, it is shown that near-f ce wave properties are consistent with generation via interaction between the observing spacecraft's ion wake and the ambient plasma and magnetic fields. This result implies that many observed near-f ce waves are not intrinsic to the unobstructed solar wind flow, and therefore are unlikely to play a significant role in the dynamic evolution of particle distributions in the solar wind.

Keywords: solar wind; space vehicles; space plasmas
Cluster Formation in GGD 12-15: Infall Motion with Rotation of the Natal Clump

We report results of observations of the GGD 12-15 region, where cluster formation is actively taking place, using various molecular emission lines. The C18O (J = 1-0) emission line reveals a massive clump in the region with a mass of ~2800 M ⊙ distributed over ~2 pc. The distribution of the C18O (J = 3-2) emission is similar to that of a star cluster forming therein, with an elliptical shape of ~1 pc in size. A bipolar molecular outflow driven by IRS 9Mc, a constituent star of the cluster, is blowing in the direction perpendicular to the elongated C18O (J = 3-2) distribution, covering the entire clump. There is a massive core with a radius of 0.3 pc and a mass of 530 M ⊙ in the center of the clump. There are two velocity components around the core, which are prominent in a position-velocity (PV) diagram along the major axis of the clump. In addition, a PV diagram along the minor axis of the clump, which is parallel to the outflow, shows a velocity gradient opposite to that of the outflow. The velocity structure strongly indicates the infalling motion of the clump. Comparison of the observational data with a simple model of infalling oblate clumps indicates that the clump is undergoing gravitational contraction with rotation.

Keywords: molecular gas; young star clusters; interstellar dynamics; interstellar molecules; stellar winds; h ii regions; molecular clouds; radio astronomy; star forming regions
Lyα Scattering Models Trace Accretion and Outflow Kinematics in T Tauri Systems

T Tauri stars produce broad Lyα emission lines that contribute ~88% of the total UV flux incident on the inner circumstellar disks. Lyα photons are generated at the accretion shocks and in the protostellar chromospheres and must travel through accretion flows, winds, and jets, the protoplanetary disks, and the interstellar medium before reaching the observer. This trajectory produces asymmetric, double-peaked features that carry kinematic and opacity signatures of the disk environments. To understand the link between the evolution of Lyα emission lines and the disks themselves, we model HST-COS spectra from targets included in Data Release 3 of the Hubble UV Legacy Library of Young Stars as Essential Standards program. We find that resonant scattering in a simple spherical expanding shell is able to reproduce the high-velocity emission line wings, providing estimates of the average velocities within the bulk intervening H I. The model velocities are significantly correlated with the K-band veiling, indicating a turnover from Lyα profiles absorbed by outflowing winds to emission lines suppressed by accretion flows as the hot inner disk is depleted. Just 30% of targets in our sample have profiles with redshifted absorption from accretion flows, many of which have resolved dust gaps. At this stage, Lyα photons may no longer intersect with disk winds along the path to the observer. Our results point to a significant evolution of Lyα irradiation within the gas disks over time, which may lead to chemical differences that are observable with ALMA and JWST. * Based on observations collected at the European Southern Observatory under ESO program 106.20Z8.

Keywords: classical t tauri stars; protoplanetary disks; hubble space telescope; stellar accretion; stellar winds
Magnetic Flux Transport in Radiatively Inefficient Accretion Flows and the Pathway toward a Magnetically Arrested Disk

Large-scale magnetic fields play a vital role in determining the angular momentum transport and generating jets/outflows in accreting systems, yet their origins remain poorly understood. We focus on radiatively inefficient accretion flows (RIAFs) around black holes (BHs), and conduct 3D general-relativistic magnetohydrodynamic simulations using the Athena++ code. We first reconfirm that the magnetorotational instability driven dynamo in the RIAF alone does not spontaneously form a magnetically arrested disk (MAD), conducive for strong-jet formation. We next investigate the other possibility, where the large-scale magnetic fields are advected inward from external sources (e.g., the companion star in X-ray binaries and the magnetized ambient medium in active galactic nuclei). Although the actual configurations of the external fields could be complex and uncertain, they are likely to be closed. As a first study, we treat them as closed field loops of different sizes, shapes, and field strengths. Unlike earlier studies of flux transport, where the magnetic flux is injected into the initial laminar flow, we inject the magnetic field loops into the quasi-stationary turbulent RIAF in inflow equilibrium, then follow their evolution. We find that a substantial fraction (~15%-40%) of the flux injected at large radii reaches the BH, with a weak dependence on the loop parameters, except when the loops are injected at high latitudes, away from the midplane. The relatively high efficiency of the flux transport observed in our study hints that a MAD might easily be formed relatively close to the BH, provided that a source of the large-scale field exists at larger radii.

Keywords: accretion; magnetic fields; relativistic fluid dynamics; relativistic disks; black holes
The Stars Kepler Missed: Investigating the Kepler Target Selection Function Using Gaia DR2

The Kepler Mission revolutionized exoplanet science and stellar astrophysics by obtaining highly precise photometry of over 200,000 stars over 4 yr. A critical piece of information to exploit Kepler data is its selection function, since all targets had to be selected from a sample of half a million stars on the Kepler CCDs using limited information. Here we use Gaia DR2 to reconstruct the Kepler selection function and explore possible biases with respect to evolutionary state, stellar multiplicity, and kinematics. We find that the Kepler target selection is nearly complete for stars brighter than Kp < 14 mag and was effective at selecting main-sequence stars, with the fraction of observed stars decreasing from 95% to 60% between 14 < Kp < 16 mag. We find that the observed fraction for subgiant stars is only 10% lower, confirming that a significant number of subgiants selected for observation were believed to be main-sequence stars. Conversely we find a strong selection bias against low-luminosity red giant stars (R ≈ 3-5R⊙, Teff ≈ 5500 K), dropping from 90% at Kp = 14 mag to below 30% at Kp = 16 mag, confirming that the target selection was efficient at distinguishing dwarfs from giants. We compare the Gaia Re-normalized Unit Weight Error (RUWE) values of the observed and nonobserved main-sequence stars and find a difference in elevated (>1.2) RUWE values at ∼σ significance, suggesting that the Kepler target selection shows some bias against either close or wide binaries. We furthermore use the Gaia proper motions to show that the Kepler selection function was unbiased with respect to kinematics.

Keywords: astronomy databases; astronomy data analysis; multiple stars; exoplanet astronomy
Saturation of the Filamentation Instability and Dispersion Measure of Fast Radio Bursts

Nonlinear effects are crucial for the propagation of fast radio bursts (FRBs) near the source. We study the filamentation of FRBs in the relativistic winds of magnetars, which are commonly invoked as the most natural FRB progenitors. As a result of filamentation, the particle number density and radiation intensity develop strong gradients along the direction of the wind magnetic field. A steady state is reached when the plasma pressure balances the ponderomotive force. In such a steady state, particles are confined in periodically spaced thin sheets, and electromagnetic waves propagate between them as in a waveguide. We show the following. (i) The dispersion relation resembles that in the initial homogeneous plasma, but the effective plasma frequency is determined by the separation of the sheets, not directly by the mean particle density. (ii) The contribution of relativistic magnetar winds to the dispersion measure of FRBs could be several orders of magnitude larger than previously thought. The dispersion measure of the wind depends on the properties of individual bursts (e.g., the luminosity) and therefore can change significantly among different bursts from repeating FRBs. (iii) Induced Compton scattering is suppressed because most of the radiation propagates in near-vacuum regions.

Keywords: radio transient sources; plasma astrophysics
A Common Proper-motion Companion to the Herbig Be Star HD 259431

We report on new measurements with the SPHERE instrument on the VLT of a companion 3"117 N (PA = 345°3) of the Herbig Be star HD 259431 (MWC 147). Comparison with previous literature measurements shows the companion to have a common proper motion with HD 259431. It is likely a 1.2 M⊙ young star surrounded by a disk.

Keywords: protoplanetary disks; star formation; pre-main sequence stars; herbig ae/be stars; emission line stars; infrared excess; astrometry; coronagraphic imaging
Quasar Luminosity Function at z = 7

We present the quasar luminosity function (LF) at z = 7, measured with 35 spectroscopically confirmed quasars at 6.55 < z < 7.15. The sample of 22 quasars from the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) project, combined with 13 brighter quasars in the literature, covers an unprecedentedly wide range of rest-frame ultraviolet magnitudes over -28 < M 1450 < -23. We found that the binned LF flattens significantly toward the faint end populated by the SHELLQs quasars. A maximum likelihood fit to a double power-law model has a break magnitude ${M}_{1450}^{* }=-{25.60}_{-0.30}^{+0.40}$ , a characteristic density ${{\rm{\Phi }}}^{* }={1.35}_{-0.30}^{+0.47}$ Gpc-3 mag-1, and a bright-end slope $\beta =-{3.34}_{-0.57}^{+0.49}$ , when the faint-end slope is fixed to α = -1.2 as observed at z ≤ 6. The overall LF shape remains remarkably similar from z = 4 to 7, while the amplitude decreases substantially toward higher redshifts, with a clear indication of an accelerating decline at z ≥ 6. The estimated ionizing photon density, 1048.2±0.1 s-1 Mpc-3, is less than 1% of the critical rate to keep the intergalactic medium ionized at z = 7, and thus indicates that quasars are not a major contributor to cosmic reionization.

Keywords: supermassive black holes; quasars; reionization
The Transmission Spectrum of WASP-17 b From the Optical to the Near-infrared Wavelengths: Combining STIS, WFC3, and IRAC Data Sets

We present the transmission spectrum of the inflated hot Jupiter WASP-17 b, observed with the STIS and WFC3 instruments aboard the Hubble Space Telescope, allowing for a continuous wavelength coverage from ~0.4 to ~1.7 μm. Observations taken with IRAC channels 1 and 2 on the Spitzer Space Telescope are also included, adding photometric measurements at 3.6 and 4.5 μm. HST spectral data were analyzed with Iraclis, a pipeline specialized in the reduction of STIS and WFC3 transit and eclipse observations. Spitzer photometric observations were reduced with the TLCD-LSTM method, utilizing recurrent neural networks. The outcome of our reduction produces incompatible results between STIS visit 1 and visit 2, which leads us to consider two scenarios for G430L. Additionally, by modeling the WFC3 data alone, we can extract atmospheric information without having to deal with the contrasting STIS data sets. We run separate retrievals on the three spectral scenarios with the aid of TauREx 3, a fully Bayesian retrieval framework. We find that, independently of the data considered, the exoplanet atmosphere displays strong water signatures and, potentially, the presence of aluminum oxide and titanium hydride. A retrieval that includes an extreme photospheric activity of the host star is the preferred model, but we recognize that such a scenario is unlikely for an F6-type star. Due to the incompleteness of all STIS spectral light curves, only further observations with this instrument would allow us to properly constrain the atmospheric limb of WASP-17 b, before the James Webb Space Telescope or Ariel will come online.

Keywords: exoplanet atmospheres; hubble space telescope; astronomy data reduction; bayesian statistics
Runaway and Hypervelocity Stars from Compact Object Encounters in Globular Clusters

The dense environments in the cores of globular clusters (GCs) facilitate many strong dynamical encounters among stellar objects. These encounters have been shown to be capable of ejecting stars from the host GC, whereupon they become runaway stars, or hypervelocity stars (HVSs) if unbound to the galactic potential. We study high-speed stellar ejecta originating from GCs by using Monte Carlo N-body models, in particular focusing on binary–single encounters involving compact objects. We pair our model-discriminated populations with observational catalogs of Milky Way GCs (MWGCs) to compose a present-day Galactic population of stellar ejecta. We find that these kinds of encounters can accelerate stars to velocities in excess of 2000 km s‑1, to speeds beyond the previously predicted limits for ejecta from star-only encounters and in the same regime of Galactic center ejections. However, the same ejections can only account for 1.5%–20% of the total population of stellar runaways, and only 0.0001%–1% of HVS, with similar relative rates found for runaway white dwarfs. We also provide credible regions for ejecta from 149 MWGCs, which we hope will be useful as supplementary evidence when pairing runaway stars with origin GCs.

Keywords: globular star clusters; runaway stars; hypervelocity stars; stellar dynamics
The Unistellar Exoplanet Campaign: Citizen Science Results and Inherent Education Opportunities

This paper presents early results from and prospects for exoplanet science using a citizen science private/public partnership observer network managed by the SETI Institute in collaboration with Unistellar. The network launched in 2020 January and includes 163 citizen scientist observers across 21 countries. These observers can access a citizen science mentoring service developed by the SETI Institute and are also equipped with Unistellar Enhanced Vision Telescopes. Unistellar technology and the campaign's associated photometric reduction pipeline enable each telescope to readily obtain and communicate light curves to observers with signal-to-noise ratio suitable for publication in research journals. Citizen astronomers of the Unistellar Exoplanet (UE) Campaign routinely measure transit depths of ≳1% and contribute their results to the exoplanet research community. The match of the detection system, targets, and scientific and educational goals is robust. Results to date include 281 transit detections out of 651 processed observations. In addition to this campaign's capability to contribute to the professional field of exoplanet research, UE endeavors to drive improved science, technology, engineering, and mathematics education outcomes by engaging students and teachers as participants in science investigations, that is, learning science by doing science.

Keywords: astronomy education; amateur astronomers; exoplanets; transit photometry