adsabs/SciX_UAT_keywords huggingface dataset:
GlobULeS. IV. UVIT/AstroSat Detection of Extremely Low Mass White Dwarf Companions to Blue Straggler Stars in NGC 362

We report the discovery of extremely low mass white dwarfs (ELM WDs) as a companion of blue straggler stars (BSSs) in the Galactic globular cluster NGC 362 using images from AstroSat's Ultra Violet Imaging Telescope (UVIT). Spectral energy distributions (SEDs) for 26 far-UV (FUV) bright member BSSs are created using data from the UVIT, the UltraViolet and Optical Telescope (UVOT), Gaia EDR3, and the 2.2 m ESO/MPI telescope. A single SED is fitted to 14 BSSs, whereas double-SED fits revealed ELM WDs as binary companions in 12 of the 26 BSSs studied. The effective temperature, radius, luminosity, and mass of the 12 ELM WDs are found to have a range of T eff = 9750-18,000 K, R = 0.1-0.4 R ⊙, L = 0.4-3.3 L ⊙, and M = 0.16-0.20 M ⊙. These suggest that 12 BSSs are post-mass-transfer systems formed through the case A/B mass transfer pathway. To the best of our knowledge, this is the first finding of ELM WDs as companions to BSSs in globular clusters. This cluster is known to have a binary BSS sequence, and the 12 binary and 14 single BSSs (as classified by the SEDs) follow the mass transfer and collisional sequence of BSSs in the color-magnitude diagram. The cooling ages of nine of the ELM WDs are found to be younger than 500 Myr. Though the binary BSSs may have formed during the core collapse (~200 Myr) or as part of the dynamical evolution of the cluster, they provide new insights on the dynamics of this cluster.

Keywords: ultraviolet astronomy
The Green Bank Northern Celestial Cap Pulsar Survey. VI. Discovery and Timing of PSR J1759+5036: A Double Neutron Star Binary Pulsar

The Green Bank North Celestial Cap survey is a 350 MHz all-sky survey for pulsars and fast radio transients using the Robert C. Byrd Green Bank Telescope. To date, the survey has discovered over 190 pulsars, including 33 millisecond pulsars and 24 rotating radio transients. Several exotic pulsars have been discovered in the survey, including PSR J1759+5036, a binary pulsar with a 176 ms spin period in an orbit with a period of 2.04 days, an eccentricity of 0.3, and a projected semi-major axis of 6.8 light seconds. Using seven years of timing data, we are able to measure one post-Keplerian parameter, advance of periastron, which has allowed us to constrain the total system mass to 2.62 ± 0.03 M⊙. This constraint, along with the spin period and orbital parameters, suggests that this is a double neutron star system, although we cannot entirely rule out a pulsar-white dwarf binary. This pulsar is only detectable in roughly 45% of observations, most likely due to scintillation. However, additional observations are required to determine whether there may be other contributing effects.

Keywords: binary pulsars; pulsars; radio pulsars; neutron stars
SKYSURF-5: Probing the Integrated Galaxy Light with a SDSS-SKYSURF Cross-matched Catalog

Project SKYSURF aims to account for the difference between observed integrated background light levels and those expected from galaxy-count measurements using archival Hubble Space Telescope (HST) images. Due to the scarcity of bright objects in a typical HST field of view, Poisson uncertainty and Cosmic Variance can significantly hinder calculations of the total integrated background light from galaxies. Since the existing SKYSURF analysis cannot constrain bright galaxy counts well, we catalog the bright object number density by cross-matching SKYSURF pointings with objects in the Sloan Digital Sky Survey. Here, we present the cross-matched catalogs and measure the distribution of integrated galaxy light from the SDSS objects. We find a median integrated light level in the r-band of 2.45 nW m‑2 sr‑1, consistent with previous findings given the level of incompleteness in SDSS and suggesting that SKYSURF pointings are in general not substantially biased toward object-rich fields on the sky.

Keywords: galaxy counts; cosmic background radiation; sky surveys
The Correlated Response of the Narrow FeKα Emission Line to the Primary Continuum Changes in the Seyfert Galaxy NGC 2992

The intensely varying Active Galactic nucleus (AGN) NGC 2992, on timescales of days to years, provides us with a unique testbed to study the response of the narrow FeKα emission line to the changes in the primary 2-10 keV AGN continuum. We find a strong correlation between the narrow FeKα line flux and the 2-10 keV flux with a Spearman correlation coefficient s = 0.70 and probability p < 0.001, over a period of ∼20 yr. There is no evidence of such a correlation in <1 yr, but the FeKα flux responds at ∼3 yr timescales, allowing us to put the reprocessor distance scale to 0.3 pc ≤ d ≤ 1 pc, consistent with that of torus reflection. The primary 2-10 keV continuum of NGC 2992 undergoes a high-low-high transition in ∼16 yr (2003-2019). Future long term monitoring will be crucial.

Keywords: active galactic nuclei; x-ray active galactic nuclei
AstroSat Observations of GRO J2058+42 during the 2019 Outburst

We present results from AstroSat observations of the recent outburst of GRO J2058+42, an X-ray pulsar in a Be-binary system. The source was observed by the LAXPC and SXT instruments on AstroSat on 2019 April 10 during the declining phase of its latest giant outburst. Light curves showed a strong pulsation of the pulsar with a period of 194.2201 ± 0.0016 s and a spin-up rate of (1.65 ± 0.06) × 10-11 Hz s-1. Intermittent flaring was detected in light curves between the 3 and 80 keV energy bands, with an increase in intensity of up to 1.8 times its average intensity. Pulse profiles obtained between the 3 and 80 keV energy bands of the pulsar showed strong dependence on energy. During AstroSat observations, a broad peak was consistently observed in the power density spectrum of the source with a peak oscillation frequency of 0.090 Hz along with its higher harmonics, which may be due to quasi-periodic oscillations, a commonly observed phenomenon in transient X-ray pulsars during their outburst. AstroSat observations also detected cyclotron absorption features in its spectrum corresponding to (9.7-14.4) keV, (19.3-23.8) keV, and (37.8-43.1) keV. The pulse-phase-resolved spectroscopy of the source showed a phase-dependent variation in its energy and the relative strength of these features. The spectrum was well fitted with an absorbed blackbody, Fermi-Dirac cutoff model and alternatively with an absorbed CompTT model. Both of these models were combined with an Fe line and three Gaussian absorption lines to account for the observed cyclotron resonance scattering features in the spectrum.

Keywords: x-ray sources; high mass x-ray binary stars; neutron stars; be stars; binary pulsars
Irradiated Ocean Planets Bridge Super-Earth and Sub-Neptune Populations

Small planets (∼1-3.9 ${R}_{\oplus }$ ) constitute more than half of the inventory of the 4000-plus exoplanets discovered so far. Smaller planets are sufficiently dense to be rocky, but those with radii larger than ∼1.6 ${R}_{\oplus }$ are thought to display in many cases hydrogen/helium gaseous envelopes up to ∼30% of the planetary mass. These low-mass planets are highly irradiated and the question of their origin, evolution, and possible links remains open. Here we show that close-in ocean planets affected by the greenhouse effect display hydrospheres in supercritical state, which generate inflated atmospheres without invoking the presence of large hydrogen/helium gaseous envelopes. We present a new set of mass-radius relationships for ocean planets with different compositions and different equilibrium temperatures, which are found to be well adapted to low-density sub-Neptune planets. Our model suggests that super-Earths and water-rich sub-Neptunes could belong to the same family of planets, I.e., hydrogen/helium-free planets, with differences between their interiors simply resulting from the variation in the water content.

Keywords: exoplanets; hydrosphere; planetary interior; planetary theory; exoplanet astronomy; exoplanet structure
Solar Radio Spectro-polarimeter (50-500 MHz). I. Design, Development, and Characterization of a Cross-polarized, Log-periodic Dipole Antenna

The Zeeman effect has been routinely used to image and quantify the solar photospheric magnetic field (B). Such a direct measuring technique is not yet available for the corona (Lin et al. 2004). Since almost all transient nonthermal radio emissions from the corona are either partially or fully circularly polarized, observing their polarization signatures over broad frequency ranges would be of help to estimate B as a function of heliocentric height. This article aims to describe the design and development of a Cross-polarized Log-Periodic Dipole Antenna (CLPDA), an integral part of a radio spectro-polarimeter, which works in the 50-500 MHz frequency-range and to explain the tests that were carried out to characterize it. The above frequency range corresponds to a heliocentric height range ≈1.03 < r < 2.5 R ⊙ (R ⊙ = photospheric radius), wherein the numerous coronal nonthermal transients associated with space-weather effects are observed to originate. The CLPDA is used to determine the strength and sense of polarization of the received radio signal. The uncertainty involved in the determination depends on the polarization-isolation (PI) between the two orthogonal components of a CLPDA. Some of the recent advancements made in the antenna design concepts at high frequencies (~GHz) were adopted to reduce the PI at low frequencies (~MHz). Throughout the above frequency range, the CLPDA has a gain, return loss, and PI of ≈6.6 dBi, ≲-10 dB, and ≲-27 dB, respectively. The average PI of the CLPDA varies from -30 to -24 dB over an azimuthal angle range 0° to ±45° within which the observations are performed regularly.

Keywords: solar radio emission; solar radio telescopes; radio spectroscopy; spectropolarimetry; solar-terrestrial interactions; solar magnetic fields; solar corona; active solar corona
The Complex X-Ray Obscuration Environment in the Radio-loud Type 2 Quasar 3C 223

3C 223 is a radio-loud, Type 2 quasar at z = 0.1365 with an intriguing X-ray Multi-mirror Mission (XMM)-Newton spectrum that implicated it as a rare, Compton-thick (N H ≳ 1.25 × 1024 cm-2) active galactic nucleus (AGN). We obtained contemporaneous XMM-Newton and Nuclear Spectroscopic Telescope Array (NuSTAR) spectra to fit the broadband X-ray spectrum with the physically motivated MYTORUS and BORUS02 models. We confirm earlier results that the obscuring gas is patchy with both high (though not Compton-thick) levels of obscuration (N H > 1023 cm-2) and gas clouds with column densities up to an order of magnitude lower. The spectral fitting results indicate additional physical processes beyond those modeled in the spectral grids of MYTORUS and BORUS02 impact the emergent spectrum: the Compton-scattering region may be extended beyond the putative torus; a ring of heavy Compton-thick material blocks most X-ray emission along the line of sight; or the radio jet is beamed, boosting the production of Fe Kα line photons in the global medium compared with what is observed along the line of sight. We revisit a recent claim that no radio-loud Compton-thick AGN have yet been conclusively shown to exist, finding three reported cases of radio-loud AGN with global average (but not line-of-sight) column densities that are Compton thick. Now that it is possible to separately determine line-of-sight and global column densities, inhomogeneity in the obscuring medium has consequences for how we interpet the spectrum and classify an AGN as "Compton thick."

Keywords: active galactic nuclei; high energy astrophysics; x-ray active galactic nuclei; quasars; radio loud quasars; x-ray quasars; radio active galactic nuclei; fanaroff-riley radio galaxies
Analytic Planetary Transit Light Curves and Derivatives for Stars with Polynomial Limb Darkening

We derive analytic, closed-form solutions for the light curve of a planet transiting a star with a limb-darkening profile that is a polynomial function of the stellar elevation, up to an arbitrary integer order. We provide improved analytic expressions for the uniform, linear, and quadratic limb-darkened cases, as well as novel expressions for higher-order integer powers of limb darkening. The formulae are crafted to be numerically stable over the expected range of usage. We additionally present analytic formulae for the partial derivatives of instantaneous flux with respect to the radius ratio, impact parameter, and limb-darkening coefficients. These expressions are rapid to evaluate and compare quite favorably in speed and accuracy to existing transit light-curve codes. We also use these expressions to numerically compute the first partial derivatives of exposure-time-averaged transit light curves with respect to all model parameters. An additional application is modeling eclipsing binary or eclipsing multiple star systems in cases where the stars may be treated as spherically symmetric. We provide code which implements these formulae in C++, Python, IDL, and Julia, with tests and examples of usage (https://github.com/rodluger/Limbdark.jl).

Keywords: exoplanet astronomy; exoplanet detection methods; transit photometry; computational astronomy; astronomy software; analytical mathematics; transits; light curves; eclipses; limb darkening
The Thermal Sunyaev-Zel'dovich Effect from Massive, Quiescent 0.5 ≤ z ≤ 1.5 Galaxies

We use combined South Pole Telescope (SPT)+Planck temperature maps to analyze the circumgalactic medium (CGM) encompassing 138,235 massive, quiescent 0.5 ≤ z ≤ 1.5 galaxies selected from data from the Dark Energy Survey (DES) and Wide-Field Infrared Survey Explorer (WISE). Images centered on these galaxies were cut from the 1.85 arcmin resolution maps with frequency bands at 95, 150, and 220 GHz. The images were stacked, filtered, and fit with a graybody dust model to isolate the thermal Sunyaev-Zel'dovich (tSZ) signal, which is proportional to the total energy contained in the CGM of the galaxies. We separated these M⋆ = 1010.9M⊙-1012M⊙ galaxies into 0.1 dex stellar mass bins, detecting tSZ per bin up to 5.6σ and a total signal-to-noise ratio of 10.1σ. We also detect dust with an overall signal-to-noise ratio of 9.8σ, which overwhelms the tSZ at 150 GHz more than in other lower-redshift studies. We corrected for the 0.16 dex uncertainty in the stellar mass measurements by parameter fitting for an unconvolved power-law energy-mass relation, ${E}_{\mathrm{therm}}={E}_{\mathrm{therm},\mathrm{peak}}{\left({M}_{\star }/{M}_{\star ,\mathrm{peak}}\right)}^{\alpha }$ , with the peak stellar mass distribution of our selected galaxies defined as M⋆,peak = 2.3 × 1011M⊙. This yields an ${E}_{\mathrm{therm},\mathrm{peak}}={5.98}_{-1.00}^{+1.02}\,\times {10}^{60}$ erg and $\alpha ={3.77}_{-0.74}^{+0.60}$ . These are consistent with z ≈ 0 observations and within the limits of moderate models of active galactic nucleus feedback. We also computed the radial profile of our full sample, which is similar to that recently measured at lower-redshift by Schaan et al.

Keywords: cosmic background radiation; galaxy evolution; intergalactic medium; large-scale structure of the universe; sunyaev-zeldovich effect; quasars
Morphological-based Analyses for Parameterizing Symmetry in Radio Galaxies

The morphology of radio galaxies can provide significant clues to describe the formation and evolution of galaxies in the Universe. Here, we aim to extract the morphological parameters of radio galaxies and define symmetry criteria as some of the essential factors of their shape explanations. We employed 67 radio galaxies, which include Fanaroff-Riley type 1 and type 2 galaxies, and their radio images from the FIRST and LoTSS surveys. We developed an automatic segmentation process to extract morphological properties such as the size of objects, eccentricity, and orientation of segmented regions from data sets. Using a maximum likelihood estimator, we show that the distributions of sizes follow a power-law function with exponents of -0.39 ± 0.06 and -0.55 ± 0.05 for the FIRST and LoTSS data, respectively. We found that type 2 radio galaxies have slightly lower eccentricities than type 1. We studied the relationships between size, eccentricity, and redshift in scatter plots. The size of galaxies (kpc2) demonstrates gently growing trends with increasing eccentricity in their scatter plots. We discussed the possible effect of the redshifts of the galaxies on this result. Depending on the number of segmented regions, we defined symmetry criteria based on proximity to the center of a galaxy in the optical band, eccentricity, orientation, and the quarter (q) of appearance in the image. We found that the mean symmetry obtained for two segmented regions that mainly emerged in two quarters via the condition of $| {q}^{{\prime} }-q^{\prime\prime} | =2$ has a higher value than those obtained for other cases.

Keywords: radio galaxies; catalogs; astronomy data analysis
Sensitivity Reach of Gamma-Ray Measurements for Strong Cosmological Magnetic Fields

A primordial magnetic field with strength in the 1-10 pG range can resolve the tension between different measurements of the Hubble constant and provide an explanation for the excess opacity in the 21 cm line at redshift 15 < z < 20 if it is present during the recombination and reionization epochs. This field can also survive in the voids of the large-scale structure in the present day universe. We study the sensitivity reach of the gamma-ray technique for measurement of such a relatively strong cosmological magnetic field using deep exposure(s) of the nearest hard spectrum blazar(s) with CTA telescopes. We show that the gamma-ray measurement method can sense the primordial magnetic field with a strength of up to 10-11 G. Combination of the cosmic microwave background and gamma-ray constraints can thus sense the full range of possible cosmological magnetic fields to confirm or rule out their relevance to the problem of the origin of cosmic magnetic fields, as well as their influence on recombination and reionization epochs.

Keywords: extragalactic magnetic fields; blazars
Ion Nongyrotropy in Solar Wind Discontinuities

Magnetic field fluctuations in the solar wind are essentially Alfvénic with a good correlation between plasma and magnetic field variations. One of the most investigated types of such fluctuations is (rotational) discontinuities, rapid rotations of the solar wind magnetic field, usually accompanied by velocity jumps, ΔVl, comparable to Alfvén speed jumps, ΔVA. Although models of stationary discontinuities predict $| {\rm{\Delta }}{V}_{l}| =| {\rm{\Delta }}{V}_{{\rm{A}}}| $ , observations often show $| {\rm{\Delta }}{V}_{{\rm{A}}}| /| {\rm{\Delta }}{V}_{l}| \gt 1$ . This difference has previously been interpreted as: (1) a possible contribution of anisotropy that decreases ΔVA, or (2) a discontinuity non-stationarity due to residual magnetic energy. We propose an alternate interpretation: an ion nonadiabatic interaction with intense (thin) discontinuities that shapes the nongyrotropic ion distribution to include a nondiagonal term of the pressure tensor, with a cross-discontinuity gradient decreasing ΔVA. Using several examples of ARTEMIS observations of intense solar wind discontinuities, we demonstrate the existence of an ion population that contributes to such a nondiagonal pressure component with spatial profile and amplitude sufficient to significantly decrease ΔVA. The observed pressure nongyrotropy (a finite nondiagonal pressure component) balances the discontinuity configuration and can explain the $| {\rm{\Delta }}{V}_{{\rm{A}}}| /| {\rm{\Delta }}{V}_{l}| \gt 1$ paradox for intense discontinuities.

Keywords: solar wind; interplanetary discontinuities; interplanetary turbulence
Occultation Mapping of Io's Surface in the Near-infrared. I. Inferring Static Maps

With hundreds of active volcanoes varying in intensity on different timescales, Jupiter's moon Io is the most volcanically active body in the solar system. Io has been observed from Earth using high-cadence near-infrared photometry during occultations by Jupiter and other Galilean moons since the 1980s. These observations encode a wealth of information about the volcanic features on its surface. We built a generative model for the observed occultation light curves using the code starry, which enables fast, analytic, and differentiable computation of occultation light curves in emitted and reflected light. Using this model, we are able to recover surface thermal emission maps of Io containing known volcanic hot spots without having to make assumptions about the locations, shapes, or number of hot spots. Our model is also directly applicable to the problem of mapping the surfaces of stars and exoplanets.

Keywords: io; volcanoes; volcanism; occultation; bayesian statistics; exoplanets
Formation of GW190521 via Gas Accretion onto Population III Stellar Black Hole Remnants Born in High-redshift Minihalos

The recent gravitational-wave merger event, GW190521, has challenged our understanding of stellar-mass black hole (BH) formation. The primary and secondary BHs are both inferred to fall inside the pair-instability (PI) mass gap. Here we propose that the formation of such binaries is possible through gas accretion onto the BH remnants of Population III stars born in high-redshift (z > 10) minihalos. Once the parent halo has grown to the atomic-cooling limit, even brief episodes of gas accretion in the dense central regions of the halo can increase the masses of Population III remnant BHs above the PI limit. Starting with a binary black hole (BBH) with an initial mass of O(100) M⊙ we find that it would only need to spend about 100 Myr in the inner few parsecs of an atomic-cooling halo to accrete about 50 M⊙ of material and resemble a system similar to GW190521. The dynamical friction timescale for the binary to sink to the dense inner region of its parent halo is comparable or shorter than the accretion timescale required to increase their mass above the PI limit. Once in the core of the halo, the binary can enter a phase of hyper-Eddington accretion, where it would only take a few thousand years to exceed the PI limit through accretion. Even more massive BBHs could form through this channel, and be detectable by detectors with improved low-frequency sensitivity. Single Population III BH remnants would also grow through accretion and could later form binaries dynamically. As little as a few percent of Population III BH remnants may be sufficient to match the rate of massive BBH mergers inferred from GW190521 of ${0.13}_{-0.11}^{+0.3}\,{\mathrm{Gpc}}^{-3}\,{\mathrm{yr}}^{-1}$ .

Keywords: gravitational waves; black holes; ligo; bondi accretion; population iii stars
The Behavior of HgMn Stars in the Far-UV-Paper 24: HD 159975 (μ Oph)

The analysis of two high resolution spectra of the Hg Mn star HD 159975 recorded by the SWP camera on board the International Ultraviolet Explorer does not reveal variations of the far-ultraviolet flux over a 18 yr time interval. From its effective temperature and surface gravity, HD 155975 appears to have evolved away from the Main Sequence in a theoretical Hertzsprung Russell diagram. It is one of the rare subgiant HgMn stars. Several Si II resonance or low excitation lines are strong absorbers in the mean high resolution SWP spectrum of HD 159975. The Al II resonance line at 1670.79 Å is a strong absorber too. There is no evidence of real variations of the low excitation Si II lines.

Keywords: chemically peculiar stars; mercury-manganese stars