adsabs/SciX_UAT_keywords huggingface dataset:
Twin Stars and the Stiffness of the Nuclear Equation of State: Ruling Out Strong Phase Transitions below 1.7 n0 with the New NICER Radius Measurements

We explore the connection between the stiffness of a hadronic equation of state (EoS) with a sharp phase transition to quark matter to its tidal deformability. For this we employ a hadronic relativistic mean field model with a parameterized effective nucleon mass to vary the stiffness in conjunction with a constant speed of sound EoS for quark matter. We compute multiple scenarios with phase transitions according to the four possible cases of a hybrid star EoS with a stable second branch. We demonstrate how the effective nucleon mass can be constrained by using gravitational-wave data. We find that certain values of the effective nucleon mass are incompatible with GW170817 and a phase transition simultaneously. By using the recent NICER measurements of J0030+0451 we constrain our results further and find that strong phase transitions with a visible jump in the mass-radius relation are ruled out at 1σ at densities below 1.7 times saturation density.

Keywords: neutron stars; compact objects
Formation of CO2 Driven by Photochemistry of Water Ice Mixed with Carbon Grains

We present results on photochemistry of carbon-grains/water-ice mixtures at temperatures from 10 to 150 K. Such a temperature range corresponds to the physical conditions found in molecular clouds, hot cores and corinos, protostellar envelopes, and planet-forming and debris disks. We demonstrate that UV irradiation of carbon-grains/water-ice mixtures leads to the formation of CO2, which, beyond the desorption temperature of CO2 partly escapes into the gas phase, and partly remains trapped on the surface of grains. Thus, we present the first direct evidence of the efficient formation of CO2 on carbon surfaces covered by water ice at high temperatures (up to 150 K) leading to a conclusion that the known low-temperature formation route of CO2 remains valid at high temperatures as long as H2O is present on carbon grains. Moreover, we demonstrate an improved capability of the dust-surface/crystalline-water-ice interface (as compared to amorphous water ice) to trap CO2 in the solid state well above the CO2 desorption temperature. The high-temperature chemical pathway to CO2 may lead to the chemical erosion of carbonaceous grains in planet-forming disks, providing an alternative explanation of the loss of solid carbon in the innermost disk regions that resulted in the formation of carbon-poor Earth and other terrestrial planets in the solar system.

Keywords: astrochemistry; laboratory astrophysics; interstellar dust
Light Curves of Trans-Neptunian Objects from the K2 Mission of the Kepler Space Telescope

The K2 mission of the Kepler Space Telescope allowed the observations of light curves of small solar system bodies throughout the whole solar system. In this paper, we present the results of a collection of K2 trans-Neptunian object observations between campaigns C03 (2014 November-2015 February) and C19 (2018 August-September), which includes 66 targets. Due to the faintness of our targets, the detectability rate of a light-curve period is ~56%, notably lower than in the case of other small-body populations, like Hildas or Jovian Trojans. We managed to obtain light-curve periods with an acceptable confidence for 37 targets; the majority of these cases are new identifications. We were able to give light-curve amplitude upper limits for the other 29 targets. Several of the newly detected light-curve periods are longer than ~24 hr, in many cases close to ~80 hr; i.e., these targets are slow rotators. This relative abundance of slowly rotating objects is similar to that observed among Hildas, Jovian Trojans, and Centaurs in the K2 mission, as well as among main belt asteroids measured with the TESS space telescope. Trans-Neptunian objects show notably higher light-curve amplitudes at large (D ≳ 300 km) sizes than found among large main belt asteroids, in contrast to the general expectation that due to their lower compressive strength, they reach hydrostatic equilibrium at smaller sizes than their inner solar system counterparts.

Keywords: kuiper belt; trans-neptunian objects; light curves
The Missing Metal Problem in Galaxy Clusters: Characterizing the Early Enrichment Population

Rich and poor galaxy clusters have the same measured halo metallicity, 0.35-0.4 Z ⊙, even though they are an order of magnitude apart in stellar fraction, M */M gas. The measured intracluster medium (ICM) metallicity in high-mass clusters cannot be explained by the visible stellar population as stars typically make up 3%-20% of the total baryon mass. The independence of metallicity of M */M gas suggests an external and universal source of metals such as an early enrichment population (EEP). Galaxy cluster RX J1416.4+2315, classified as a fossil system, has a stellar fraction of M */M gas = 0.054 ± 0.018, and here we improve the halo metallicity determination using archival Chandra and XMM-Newton observations. We determine the ICM metallicity of RXJ1416 to be 0.303 ± 0.053 Z ⊙ within 0.3 < R/R 500 < 1, excluding the central galaxy. We combine this measurement with other clusters with a wider range of M */M gas, resulting in the fit of Z tot = (0.36 ± 0.01) + (0.10 ± 0.17)(M */M gas). This fit is largely independent of M */M gas and shows that for a low M */M gas system, the observed stellar population can make only 10%-20% of the total metals. We quantify the Fe contribution of the EEP further by adopting a standard Fe yield for visible stellar populations, and find that Z EEP = (0.36 ± 0.01) - - (0.96 ± 0.17)(M */M gas). To account for the observed Fe mass, a supernova (SN) rate of 10 ± 5 SNe yr-1 (Type Ia) and 40 ± 19 SNe yr-1 (core collapse) is required over the redshift range 3 < z < 10 for a single galaxy cluster with mass ~3 × 1014 M ⊙ at z = 0. These SNe might be visible in observations of high-redshift clusters and protoclusters with the James Webb Space Telescope.

Keywords: galaxy clusters; intracluster medium; population ii stars; x-ray astronomy
Energy Conversion through a Fluctuation-Dissipation Relation at Kinetic Scales in the Earth's Magnetosheath

Low-frequency fluctuations in the interplanetary medium represent a turbulent environment where universal scaling behavior, generated by an energy cascade, has been investigated. On the contrary, in some regions, for example, the magnetosheath, universality of statistics of fluctuations is lost. However, at kinetic scales where energy must be dissipated, the energy conversion seems to be realized through a mechanism similar to the free solar wind. Here we propose a Langevin model for magnetic fluctuations at kinetic scales, showing that the resulting fluctuation-dissipation relation is capable of describing the gross features of the spectral observations at kinetic scales in the magnetosheath. The fluctuation-dissipation relation regulates the energy conversion by imposing a relationship between fluctuations and dissipation, which at high frequencies are active at the same time in the same range of scales and represent two ingredients of the same physical process.

Keywords: interplanetary medium; heliosphere; space plasmas; interplanetary turbulence
The Pre-He White Dwarf in the Post-mass Transfer Binary EL CVn

EL CVn is the prototype of a class of eclipsing binaries that consist of an A- or F-type main-sequence star and a hot, low-mass, pre-He white dwarf (pre-He WD), the stripped down remains of the former mass donor. Here we present the first direct detection and characterization of the spectrum of the pre-He WD in EL CVn that was made possible through far-UV spectroscopy with the Hubble Space Telescope Cosmic Origins Spectrograph. These spectra straddle the wavelength range where flux dominance shifts from the pre-He WD to the A star. Radial velocities of both components were measured from the far-UV spectra and new optical spectra from the Apache Point Observatory Astrophysical Research Consortium Echelle Spectrograph. We also obtained fast cadence photometry of the eclipses with the pt5m telescope at the Roque de los Muchachos Observatory. A combined analysis of the velocities and light curve yields the component masses and radii. We applied a Doppler tomography algorithm to reconstruct the individual spectra, and we compared these to models to estimate the effective temperatures. The pre-He WD has low mass (0.176 ± 0.004 M ⊙), is small (0.284 ± 0.003 R ⊙), and is relatively hot (11,800 ± 400 K), and these parameters are approximately consistent with predictions for a star stripped through stable mass transfer. The spectral lines of the pre-He WD show that its atmosphere is H-rich, He-depleted, and metal-poor, probably as the result of elemental diffusion that has occurred since mass transfer ceased.

Keywords: stellar evolution; eclipsing binary stars; white dwarf stars
OGLE-2018-BLG-0532Lb: Cold Neptune with Possible Jovian Sibling

We report the discovery of the planet OGLE-2018-BLG-0532Lb, with very obvious signatures in the light curve that lead to an estimate of the planet-host mass ratio $q={M}_{\mathrm{planet}}/{M}_{\mathrm{host}}\simeq 1\times {10}^{-4}$ . Although there are no obvious systematic residuals to this double-lens/single-source (2L1S) fit, we find that χ2 can be significantly improved by adding either a third lens (3L1S, Δχ2 = 81) or second source (2L2S, Δχ2 = 77) to the lens-source geometry. After thorough investigation, we conclude that we cannot decisively distinguish between these two scenarios and therefore focus on the robustly detected planet. However, given the possible presence of a second planet, we investigate to what degree and with what probability such additional planets may affect seemingly single-planet light curves. Our best estimates for the properties of the lens star and the secure planet are a host mass M ∼ 0.25 M⊙, system distance DL ∼ 1 kpc, and planet mass ${m}_{p,1}=8\,{M}_{\oplus }$ with projected separation ${a}_{1,\perp }=1.4\,\mathrm{au}$ . However, there is a relatively bright I = 18.6 (and also relatively blue) star projected within $\lt 50\,\mathrm{mas}$ of the lens, and if future high-resolution images show that this is coincident with the lens, then it is possible that it is the lens, in which case, the lens would be both more massive and more distant than the best-estimated values above.

Keywords: gravitational microlensing
Late-time Radio and Millimeter Observations of Superluminous Supernovae and Long Gamma-Ray Bursts: Implications for Central Engines, Fast Radio Bursts, and Obscured Star Formation

We present the largest and deepest late-time radio and millimeter survey to date of superluminous supernovae (SLSNe) and long-duration gamma-ray bursts (LGRBs) to search for associated nonthermal synchrotron emission. Using the Karl G. Jansky Very Large Array (VLA) and the Atacama Large Millimeter/submillimeter Array (ALMA), we observed 43 sources at 6 and 100 GHz on a timescale of ∼ 1-19 yr post-explosion. We do not detect radio/millimeter emission from any of the sources, with the exception of a 6 GHz detection of PTF10hgi, as well as the detection of 6 GHz emission near the location of the SLSN PTF12dam, which we associate with its host galaxy. We use our data to place constraints on central engine emission due to magnetar wind nebulae and off-axis relativistic jets. We also explore nonrelativistic emission from the SN ejecta, and place constraints on obscured star formation in the host galaxies. In addition, we conduct a search for fast radio bursts (FRBs) from some of the sources using VLA phased-array observations; no FRBs are detected to a limit of 16 mJy (7σ; 10 ms duration) in about 40 minutes on source per event. A comparison to theoretical models suggests that continued radio monitoring may lead to detections of persistent radio emission on timescales of ≳ a decade.

Keywords: radio transient sources; extragalactic radio sources; radio astrometry; core-collapse supernovae; supernova remnants; relativistic jets; magnetars; star formation; stellar physics
Planet Hunters TESS. V. A Planetary System Around a Binary Star, Including a Mini-Neptune in the Habitable Zone

We report on the discovery and validation of a transiting long-period mini-Neptune orbiting a bright (V = 9.0 mag) G dwarf (TOI 4633; R = 1.05 R ⊙, M = 1.10 M ⊙). The planet was identified in data from the Transiting Exoplanet Survey Satellite by citizen scientists taking part in the Planet Hunters TESS project. Modelling of the transit events yields an orbital period of 271.9445 ± 0.0040 days and radius of 3.2 ± 0.20 R ⊕. The Earth-like orbital period and an incident flux of ${1.56}_{-0.16}^{+0.20}$ F ⊕ places it in the optimistic habitable zone around the star. Doppler spectroscopy of the system allowed us to place an upper mass limit on the transiting planet and revealed a non-transiting planet candidate in the system with a period of 34.15 ± 0.15 days. Furthermore, the combination of archival data dating back to 1905 with new high angular resolution imaging revealed a stellar companion orbiting the primary star with an orbital period of around 230 yr and an eccentricity of about 0.9. The long period of the transiting planet, combined with the high eccentricity and close approach of the companion star makes this a valuable system for testing the formation and stability of planets in binary systems.

Keywords: exoplanet systems; exoplanet dynamics; transit photometry; binary stars; habitable zone; mini neptunes; radial velocity
Constraining Stellar Rotation at the Zero-age Main Sequence with TESS

The zero-age main sequence (ZAMS) is a critical phase for stellar angular momentum evolution, as stars transition from contraction-dominated spin-up to magnetic wind-dominated spin-down. We present the first robust observational constraints on rotation for FGK stars at ≈40 Myr. We have analyzed TESS light curves for 1410 members of five young open clusters with ages between 25 and 55 Myr: IC 2391, IC 2602, NGC 2451A, NGC 2547, and Collinder 135. In total, we measure 868 rotation periods, including 96 new, high-quality periods for stars around 1 M ⊙. This is an increase of ten times the existing literature sample at the ZAMS. We then use the τ 2 method to compare our data to models for stellar angular momentum evolution. Although the ages derived from these rotation models do not match isochronal ages, we show that these observations can clearly discriminate between different models for stellar wind torques. Finally, τ 2 fits indicate that magnetic braking and/or internal angular momentum transport significantly impact rotational evolution even on the pre-main sequence.

Keywords: stellar rotation; stellar evolution; late-type stars; open star clusters
Photometric Observations of the Binary Near-Earth Asteroid (65803) Didymos in 2015-2021 Prior to DART Impact

We performed photometric observations of the binary near-Earth asteroid (65803) Didymos in support of the Double Asteroid Redirection Test (DART) mission that will test the Kinetic Impactor technology for diverting dangerous asteroids. It will hit the Didymos secondary, called Dimorphos, on 2022 September 26. We observed Didymos with 11 telescopes with diameters from 3.5 to 10.4 m during four apparitions in 2015-2021, obtaining data with rms residuals from 0.006 to 0.030 mag. We analyzed the light-curve data and decomposed them into the primary rotational and secondary orbital light curves. We detected 37 mutual eclipse/occultation events between the binary system components. The data presented here, in combination with 18 mutual events detected in 2003, provide the basis for modeling the Dimorphos orbit around the Didymos primary. The orbit modeling is discussed in detail by Scheirich & Pravec and Naidu et al. The primary light curves were complex, showing multiple extrema on some epochs. They suggest a presence of complex topography on the primary's surface that is apparent in specific viewing/illumination geometries; the primary shape model by Naidu et al. (Icarus 348, 113777, 2020) needs to be refined. The secondary rotational light-curve data were limited and did not provide a clear solution for the rotation period and equatorial elongation of Dimorphos. We define the requirements for observations of the secondary light curve to provide the needed information on Dimorphos's rotation and elongation when Didymos is bright in 2022 July-September before the DART impact.

Keywords: asteroid satellites; ccd photometry; near-earth objects
The Prevalence and Influence of Circumstellar Material around Hydrogen-rich Supernova Progenitors

Narrow transient emission lines (flash-ionization features) in early supernova (SN) spectra trace the presence of circumstellar material (CSM) around the massive progenitor stars of core-collapse SNe. The lines disappear within days after the SN explosion, suggesting that this material is spatially confined, and originates from enhanced mass loss shortly (months to a few years) prior to the explosion. We performed a systematic survey of H-rich (Type II) SNe discovered within less than 2 days from the explosion during the first phase of the Zwicky Transient Facility survey (2018-2020), finding 30 events for which a first spectrum was obtained within <2 days from the explosion. The measured fraction of events showing flash-ionization features (>36% at the 95% confidence level) confirms that elevated mass loss in massive stars prior to SN explosion is common. We find that SNe II showing flash-ionization features are not significantly brighter, nor bluer, nor more slowly rising than those without. This implies that CSM interaction does not contribute significantly to their early continuum emission, and that the CSM is likely optically thin. We measured the persistence duration of flash-ionization emission and find that most SNe show flash features for ≈5 days. Rarer events, with persistence timescales >10 days, are brighter and rise longer, suggesting these may be intermediate between regular SNe II and strongly interacting SNe IIn.

Keywords: core-collapse supernovae; type ii supernovae; supernovae; massive stars; circumstellar matter
A New Method to Constrain Neutron Star Structure from Quasi-periodic Oscillations

We develop a new method to measure neutron star (NS) parameters and derive constraints on the equation of state (EoS) of dense matter by fitting the frequencies of simultaneous quasi-periodic oscillation (QPO) modes observed in the X-ray flux of accreting NSs in low-mass X-ray binaries. To this aim, we calculate the fundamental frequencies of geodesic motion around rotating NSs based on an accurate general-relativistic approximation for their external spacetime. Once the fundamental frequencies are related to the observed frequencies through a QPO model, they can be fit to the data to obtain estimates of the three parameters describing the spacetime, namely the NS mass, angular momentum and quadrupole moment. From these parameters we derive information on the NS structure and EoS. We present a proof of principle of our method applied to pairs of kHz QPO frequencies observed from three systems (4U1608-52, 4U0614+09, and 4U1728-34). We identify the kHz QPOs with the azimuthal and the periastron precession frequencies of matter orbiting the NS, and via our Bayesian inference technique we derive constraints on the neutrons stars' masses and radii. This method is applicable to other geodesic-frequency-based QPO models.

Keywords: neutron stars; low-mass x-ray binary stars; gravitation
The CaFe Project: Optical Fe II and Near-infrared Ca II Triplet Emission in Active Galaxies. I. Photoionization Modeling

Optical Fe II emission is a strong feature in quasar spectra originating in the broad-line region (BLR). The difficulty in understanding the complex Fe II pseudo-continuum has led us to search for other reliable, simpler ionic species such as Ca II. In this first part of the series, we confirm the strong correlation between the strengths of two emission features, the optical Fe II and the NIR Ca II, both from observations and photoionization modeling. With the inclusion of an up-to-date compilation of observations with both optical Fe II and NIR Ca II measurements, we span a wider and more extended parameter space and confirm the common origin of these two spectral features with our photoionization models using CLOUDY. Taking into account the effect of dust into our modeling, we constrain the BLR parameter space (primarily in terms of the ionization parameter and local cloud density) as a function of the strengths of Fe II and Ca II emission.

Keywords: active galaxies; quasars; active galactic nuclei; supermassive black holes; accretion; radiative transfer; scaling relations
Substructure Formation in a Protostellar Disk of L1527 IRS

We analyze multifrequency, high-resolution continuum data obtained by the Atacama Large Millimeter/submillimeter Array and the Jansky Very Lary Array to study the detailed structure of the dust distribution in the infant disk of a Class 0/I source, L1527 IRS. We find three clumps aligning in the north-south direction in the 7 mm radio continuum image. The three clumps remain even after subtracting free-free contamination, which is estimated from the 1.3 cm continuum observations. The northern and southern clumps are located at a distance of ∼15 au from the central clump and are likely optically thick at 7 mm wavelength. The clumps have similar integrated intensities. The symmetric physical properties could be realized when a dust ring, or spiral arms, around the central protostar is projected to the plane of the sky. We demonstrate for the first time that such substructure may form even in the disk-forming stage, where the surrounding materials actively accrete toward a disk-protostar system.

Keywords: interstellar medium; protostars; young stellar objects; circumstellar dust; dust continuum emission; star formation; planetary system formation
Influence of Heliolatitudinal Anisotropy of Solar FUV/EUV Emissions on Lyα Helioglow: SOHO/SWAN Observations and WawHelioGlow Modeling

Observations of the Sun's surface suggest a nonuniform radiated flux as related to the presence of bright active regions and darker coronal holes. The variations of the FUV/EUV source radiation can be expected to affect the Lyα backscatter glow measured by spaceborne instruments. In particular, inferring the heliolatitudinal structure of the solar wind from helioglow variations in the sky can be quite challenging if the heliolatitudinal structure of the solar FUV/EUV radiation is not properly included in the modeling of the heliospheric glow. We present results of analysis of the heliolatitudinal structure of the solar Lyα radiation as inferred from comparison of SOHO/SWAN satellite observations of the helioglow intensity with modeling results obtained from the recently developed WawHelioGlow model. We find that in addition to time-dependent heliolatitudinal anisotropy of the solar wind, time-dependent heliolatitudinal variations of the intensity of the solar Lyα and photoionizing emissions also must be taken into account to reproduce the observed helioglow modulation in the sky. We present a particular latitudinal and temporal dependence of the solar Lyα flux obtained as a result of our analysis. We also analyze differences between polar-equatorial anisotropies close to the solar surface and seen by an observer located far from the Sun. We discuss the implications of these findings for the interpretation of heliospheric-glow observations.

Keywords: solar ultraviolet emission; heliosphere; diffuse radiation