adsabs/SciX_UAT_keywords huggingface dataset:
Detailed Description of the Collision Frequency in the Solar Atmosphere

This work aims to provide an accurate description and calculations of collision frequencies in conditions relevant to the solar atmosphere. To do so, we focus on the detailed description of the collision frequency in the solar atmosphere based on a classical formalism with Chapman-Cowling collision integrals, as described by Zhdanov. These collision integrals allow linking the macroscopic transport fluxes of multifluid models to the kinetic scales involved in the Boltzmann equations. In this context, the collision frequencies are computed accurately while being consistent at the kinetic level. We calculate the collision frequencies based on this formalism and compare them with approaches commonly used in the literature for conditions typical of the solar atmosphere. To calculate the collision frequencies, we focus on the collision integral data provided by Bruno et al., which is based on a multicomponent hydrogen-helium mixture used for conditions typical for the atmosphere of Jupiter. We perform a comparison with the classical formalism of Vranjes & Krstic and Leake & Linton. We highlight the differences obtained in the distribution of the cross sections as functions of the temperature. Then, we quantify the disparities obtained in numerical simulations of a 2.5D solar atmosphere by calculating collision frequencies and ambipolar diffusion. This strategy allows us to validate and assess the accuracy of these collision frequencies for conditions typical of the solar atmosphere.

Keywords: solar chromosphere; collision physics
Calibration of the Tip of the Red Giant Branch

The tip of the red giant branch (TRGB) method provides one of the most accurate and precise means of measuring the distances to nearby galaxies. Here we present a multi-wavelength, VIJHK absolute calibration of the TRGB based on observations of TRGB stars in the Large Magellanic Cloud (LMC), grounded on a geometric distance, determined by detached eclipsing binaries (DEBs). This paper presents a more detailed description of the method first presented by Freedman et al. for measuring corrections for the total line-of-sight extinction and reddening to the LMC. In this method, we use a differential comparison of the red giant population in the LMC, first with red giants in the Local Group galaxy IC 1613, and then with those in the Small Magellanic Cloud (SMC). As a consistency check, we derive an independent calibration of the TRGB sequence using the SMC alone, invoking its geometric distance also calibrated by DEBs. An additional consistency check comes from near-infrared observations of Galactic globular clusters covering a wide range of metallicities. In all cases we find excellent agreement in the zero-point calibration. We then examine the recent claims by Yuan et al., demonstrating that, in the case of the SMC, they corrected for extinction alone while neglecting the essential correction for reddening. In the case of IC 1613, we show that their analysis contains an incorrect treatment of (over-correction for) metallicity. Using our revised (and direct) measurement of the LMC TRGB extinction, we find a value of H0 = 69.6 ± 0.8 (±1.1% stat) ± 1.7 (±2.4% sys) km s-1 Mpc-1.

Keywords: observational cosmology; galaxy distances; interstellar extinction; hubble constant
Compton-thick AGN in the NuSTAR Era. VIII. A joint NuSTAR-XMM-Newton Monitoring of the Changing-look Compton-thick AGN NGC 1358

We present the multi-epoch monitoring with NuSTAR and XMM-Newton of NGC 1358, a nearby Seyfert 2 galaxy whose properties made it a promising candidate X-ray changing-look active galactic nucleus (AGN), i.e., a source whose column density could transition from its 2017 Compton-thick (having LOS hydrogen column density N H,LOS > 1024 cm-2) state to a Compton-thin (N H,LOS < 1024 cm-2) one. The multi-epoch X-ray monitoring confirmed the presence of significant N H,LOS variability over timescales of weeks to years, and allowed us to confirm the changing-look nature of NGC 1358, which has most recently been observed in a Compton-thin status. Multi-epoch monitoring with NuSTAR and XMM-Newton is demonstrated to be highly effective in simultaneously constraining three otherwise highly degenerate parameters: the torus average column density and covering factor, and the inclination angle between the torus axis and the observer. We find a tentative anticorrelation between column density and luminosity, which can be understood under the framework of chaotic cold accretion clouds driving recursive AGN feedback. The monitoring campaign of NGC 1358 has proven the efficiency of our newly developed method to select candidate N H,LOS-variable, heavily obscured AGN, which we plan to soon extend to a larger sample to better characterize the properties of the obscuring material surrounding accreting supermassive black holes, as well as to constrain AGN feeding models.

Keywords: astrophysical black holes; active galactic nuclei; x-ray active galactic nuclei; accretion
Evidence of Runaway Gas Cooling in the Absence of Supermassive Black Hole Feedback at the Epoch of Cluster Formation

Cosmological simulations, as well as mounting evidence from observations, have shown that supermassive black holes play a fundamental role in regulating the formation of stars throughout cosmic time. This has been clearly demonstrated in the case of galaxy clusters in which powerful feedback from the central black hole is preventing the hot intracluster gas from cooling catastrophically, thus reducing the expected star formation rates by orders of magnitude. These conclusions, however, have been almost entirely based on nearby clusters. Based on new Chandra X-ray observations, we present the first observational evidence for massive, runaway cooling occurring in the absence of supermassive black hole feedback in the high-redshift galaxy cluster SpARCS104922.6 + 564032.5 (z = 1.709). The hot intracluster gas appears to be fueling a massive burst of star formation (≈900 M⊙ yr-1) that is offset by dozens of kpc from the central galaxy. The burst is co-spatial with the coolest intracluster gas but not associated with any galaxy in the cluster. In less than 100 million years, such runaway cooling can form the same amount of stars as in the Milky Way. Therefore, intracluster stars are not only produced by tidal stripping and the disruption of cluster galaxies, but can also be produced by runaway cooling of hot intracluster gas at early times. Overall, these observations show the dramatic impact when supermassive black hole feedback fails to operate in clusters. They indicate that in the highest overdensities, such as clusters and protoclusters, runaway cooling may be a new and important mechanism for fueling massive bursts of star formation in the early universe.

Keywords: high-redshift galaxy clusters; supermassive black holes; cooling flows; intracluster medium; x-ray observatories
Habitability and Water Loss Limits on Eccentric Planets Orbiting Main-sequence Stars

A planet's climate can be strongly affected by its orbital eccentricity and obliquity. Here we use a one-dimensional energy balance model modified to include a simple runaway greenhouse (RGH) parameterization to explore the effects of these two parameters on the climate of Earth-like aqua planets—completely ocean-covered planets—orbiting F-, G-, K-, and M-dwarf stars. We find that the range of instellations for which planets exhibit habitable surface conditions throughout an orbit decreases with increasing eccentricity. However, the appearance of temporarily habitable conditions during an orbit creates an eccentric habitable zone (EHZ) that is sensitive to orbital eccentricity and obliquity, planetary latitude, and the spectral type of the host star. We find that the fraction of a planet's orbit over which it exhibits habitable surface conditions is larger on eccentric planets orbiting M-dwarf stars, due to the lower broadband planetary albedos of these planets. Planets with larger obliquities have smaller EHZs, but exhibit warmer climates if they do not enter a snowball state during their orbits. We also find no transient RGH state on planets at all eccentricities. Rather, planets spend their entire orbits either in an RGH or not. For G-dwarf planets receiving 100% of the modern solar constant and with eccentricities above 0.55, an entire Earth ocean inventory can be lost in 3.6 Gyr. M-dwarf planets, due to their larger incident X-ray and extreme ultraviolet flux, can become desiccated in only 690 Myr with eccentricities above 0.38. This work has important implications for eccentric planets that may exhibit surface habitability despite technically departing from the traditional habitable zone as they orbit their host stars.

Keywords: astrobiology; eccentricity; exoplanets; habitable zone; elliptical orbits; low mass stars; solar-terrestrial interactions; planetary atmospheres
OGLE-ing the Magellanic System: Cepheids in the Bridge

We present a detailed analysis of the Magellanic Bridge Cepheid sample constructed using the Optical Gravitational Lensing Experiment Collection of Variable Stars. Our updated Bridge sample contains 10 classical and 13 anomalous Cepheids. We calculate their individual distances using optical period-Wesenheit relations and construct three-dimensional maps. Classical Cepheid (CC) on-sky locations match very well neutral hydrogen and young stars distributions; thus, they add to the overall young Bridge population. In three dimensions, 8 out of 10 CCs form a bridge-like connection between the Magellanic Clouds. The other two are located slightly farther away and may constitute the Counter Bridge. We estimate ages of our Cepheids to be less than 300 Myr for from 5 up to 8 out of 10, depending on whether the rotation is included. This is in agreement with a scenario where these stars were formed in situ after the last encounter of the Magellanic Clouds. Cepheids' proper motions reveal that they are moving away from both Large and Small Magellanic Clouds. Anomalous Cepheids are more spread than CCs in both two and three dimensions, even though they form a rather smooth connection between the Magellanic Clouds. However, this connection does not seem to be bridge-like, as there are many outliers around both Magellanic Clouds.

Keywords: magellanic clouds; cepheid variable stars
Physical Nature of the Eclipsing δ Scuti Star AO Serpentis

We present the absolute properties of the eclipsing binary AO Ser with a pulsating component from our BV photometric and high-resolution spectroscopic observations, which were performed between 2017 April and May. The radial velocities (RVs) for both components were measured, and the effective temperature and projected rotational velocity of the primary star were determined to be Teff,1 = 8,820 ± 62 K and ${v}_{1}\sin {i}_{1}$ = 90 ± 18 km s-1, respectively, by comparing the observed spectrum with the Kurucz models. The accurate fundamental parameters of AO Ser were determined by a simultaneous analysis of the light and RV curves. The masses and radii of the primary and secondary components are M1 = 2.55 ± 0.09 M⊙ and R1 = 1.64 ± 0.02 R⊙ and M2 = 0.49 ± 0.02 M⊙ and R2 = 1.38 ± 0.02 R⊙, respectively. Multiple frequency analyses for the eclipse-subtracted light residuals were conducted. As a result, we detected two frequencies of f1 = 21.852 days-1 and f2 = 23.484 days-1. The evolutionary position on the HR diagram and the pulsational characteristics indicate that the primary star is a δ Sct pulsator with a radial fundamental mode. On the other hand, the relatively evolved secondary is oversized for its own mass.

Keywords: eclipsing binary stars; fundamental parameters of stars; stellar oscillations; photometry; spectroscopy; multi-periodic pulsation; asteroseismology
Planetary Transits at Radio Wavelengths: Secondary Eclipses of Hot Jupiter Extended Atmospheres

When a planet transits in front of its host star, a fraction of its light is blocked, decreasing the observed flux from the star. The same is expected to occur when observing the stellar radio flux. However, at radio wavelengths, the planet also radiates, depending on its temperature, and thus modifies the transit depths. We explore this scenario simulating the radio lightcurves of transits of hot Jupiters, Kepler-17b, and WASP-12b, around solar-like stars. We calculated the bremsstrahlung radio emission at 17, 100, and 400 GHz originating from the star, considering a solar atmospheric model. The planetary radio emission was calculated modeling the planets in two scenarios: as a blackbody or with a dense and hot extended atmosphere. In both cases the planet radiates and contributes to the total radio flux. For a blackbody planet, the transit depth is in the order of 2%-4% and it is independent of the radio frequency. Hot Jupiters planets with atmospheres appear bigger and brighter in radio, thus having a larger contribution to the total flux of the system. Therefore, the transit depths are larger than in the case of blackbody planets, reaching up to 8% at 17 GHz. Also the transit depth is frequency-dependent. Moreover, the transit caused by the planet passing behind the star is deeper than when the planet transits in front of the star, being as large as 18% at 400 GHz. In all cases, the contribution of the planetary radio emission to the observed flux is evident when the planet transits behind the star.

Keywords: eclipses; hot jupiters; exoplanet atmospheres; radio continuum emission
Constraints on the Faint End of the Galaxy Stellar Mass Function at z ≃ 4–8 from Deep JWST Data

We analyze a sample of 3300 galaxies between redshifts z ≃ 3.5 and z ≃ 8.5 selected from James Webb Space Telescope (JWST) images in the Hubble Ultra Deep Field and UKIDSS Ultra Deep Survey field, including objects with stellar masses as low as ≃108 M ⊙ up to z ≃ 8. The depth and wavelength coverage of the JWST data allows us, for the first time, to derive robust stellar masses for such high-z, low stellar mass galaxies on an individual basis. We compute the galaxy stellar mass function, after complementing our sample with ancillary data from CANDELS to constrain the GMSF at high stellar masses ( ${ \mathcal M }\gt {M}^{* }$ ). Our results show a steepening of the low stellar mass end slope (α) with redshift, with α = ‑1.61 ± 0.05 at z ≃ 4 and α = ‑1.98 ± 0.14 at z ≃ 7. We also observe an evolution of the normalization ϕ * from z ≃ 7 to z ≃ 4, with ${\phi }_{z\simeq 4}^{* }/{\phi }_{z\simeq 7}^{* }={130}_{-50}^{+210}$ . Our study incorporates a novel method for the estimation of the Eddington bias, which takes into account its possible dependence both on stellar mass and redshift, while allowing for skewness in the error distribution. We finally compute the resulting cosmic stellar mass density and find a flatter evolution with redshift than previous studies.

Keywords: high-redshift galaxies; galaxy evolution; stellar mass functions; james webb space telescope
Meet the Parents: The Progenitor Binary for the Supermassive Black Hole Candidate in E1821+643

The remnants of binary black hole mergers can be given recoil kick velocities up to 5000 km s-1 due to anisotropic emission of gravitational waves. E1821+643 is a recoiling supermassive black hole candidate with spectroscopically offset, broad emission lines, consistent with motion of the black hole at ~2100 km s-1 along the line of sight relative to its host galaxy. This suggests a recoil kick of ~2200 km s-1. Such a kick is powerful enough to eject E1821+643 from its M gal ~ 2 × 1012 M ⊙ host galaxy. In this work, we address the question: assuming that E1821+643 is a recoiling black hole, what are the likely properties of the progenitor binary that formed E1821+643? Using astrophysically motivated priors, we infer that E1821+643 was likely formed from a binary black hole system with masses of ${m}_{1}\sim {1.9}_{-0.4}^{+0.5}\times {10}^{9}{M}_{\odot }$ , ${m}_{2}\sim {8.1}_{-3.2}^{+3.9}\times {10}^{8}{M}_{\odot }$ (90% credible intervals). Given our model, the black holes in this binary were likely to be spinning rapidly with dimensionless spin magnitudes of ${\chi }_{1}={0.87}_{-0.26}^{+0.11}$ , ${\chi }_{2}={0.77}_{-0.37}^{+0.19}$ . Such a high recoil velocity is impossible for spins aligned to the orbital angular momentum axis. This suggests that the progenitor for E1821+643 merged in hot gas, which is thought to provide an environment where spin alignment from accretion proceeds slowly relative to the merger timescale. We infer that E1821+643, if it is a recoiling black hole, is likely to be a rapidly rotating black hole with a dimensionless spin of χ = 0.92 ± 0.04. A 2.6 × 109 M ⊙ black hole, recoiling from a gas-rich environment at v ~ 2200 km s-1, is likely to persist as an active galactic nucleus for ~107 yr, in which time it traverses ~25 kpc.

Keywords: quasars; supermassive black holes
Bridging the Gap between Cosmic Dawn and Reionization Favors Models Dominated by Faint Galaxies

It has been claimed that traditional models struggle to explain the tentative detection of the 21 cm absorption trough centered at z ~ 17 measured by the EDGES collaboration. On the other hand, it has been shown that the EDGES results are consistent with an extrapolation of a declining UV luminosity density, following a simple power law of deep Hubble Space Telescope observations of 4 < z < 9 galaxies. We here explore the conditions by which the EDGES detection is consistent with current reionization and post-reionization observations, including the neutral hydrogen fraction at z ~ 6-8, Thomson-scattering optical depth, and ionizing emissivity at z ~ 5. By coupling a physically motivated source model derived from radiative transfer hydrodynamic simulations of reionization to a Markov Chain Monte Carlo sampler, we find that it is entirely possible to reconcile existing high-redshift (cosmic dawn) and low-redshift (reionization) constraints. In particular, we find that high contributions from low-mass halos along with high photon escape fractions are required to simultaneously reproduce cosmic dawn and reionization constraints. Our analysis further confirms that low-mass galaxies produce a flatter emissivity evolution, which leads to an earlier onset of reionization with a gradual and longer duration, resulting in a higher optical depth. While the models dominated by faint galaxies successfully reproduce the measured globally averaged quantities over the first one billion years, they underestimate the late redshift-instantaneous measurements in efficiently star-forming and massive systems. We show that our (simple) physically motivated semianalytical prescription produces results that are consistent with the (sophisticated) state-of-the-art THESAN radiation-magnetohydrodynamic simulation of the reionization.

Keywords: reionization; galaxies
Nuclear X-Ray Activity in Low-surface-brightness Galaxies: Prospects for Constraining the Local Black Hole Occupation Fraction with a Chandra Successor Mission

About half of nearby galaxies have a central surface brightness ≥1 mag below that of the sky. The overall properties of these low-surface-brightness galaxies (LSBGs) remain understudied, and in particular we know very little about their massive black hole population. This gap must be closed to determine the frequency of massive black holes at z = 0 as well as to understand their role in regulating galaxy evolution. Here we investigate the incidence and intensity of nuclear, accretion-powered X-ray emission in a sample of 32 nearby LSBGs with the Chandra X-ray Observatory. A nuclear X-ray source is detected in four galaxies (12.5%). Based on an X-ray binary contamination assessment technique developed for normal galaxies, we conclude that the detected X-ray nuclei indicate low-level accretion from massive black holes. The active fraction is consistent with that expected from the stellar mass distribution of the LSBGs, but not their total baryonic mass, when using a scaling relation from an unbiased X-ray survey of normal galaxies. This suggests that their black holes co-evolved with their stellar population. In addition, the apparent agreement nearly doubles the number of galaxies available within ∼100 Mpc for which a measurement of nuclear activity can efficiently constrain the frequency of black holes as a function of stellar mass. We conclude by discussing the feasibility of measuring this occupation fraction to a few percent precision below ≲1010M⊙ with high-resolution, wide-field X-ray missions currently under consideration.

Keywords: x-ray active galactic nuclei; active galactic nuclei; low surface brightness galaxies
Exploring the Impact of the Ejecta Velocity Profile on the Evolution of Kilonova: Diversity of the Kilonova Lightcurves

A kilonova is a short-lived explosive event in the Universe, resulting from the merger of two compact objects. Despite its importance as a primary source of heavy elements through r-process nucleosynthesis, its nature is not well understood due to its rarity. In this work, we introduce a model that determines the density of a radially stratified relativistic ejecta. We apply the model to kilonova ejecta and explore several hypothesized velocity profiles as a function of the merger's ejection time. These velocity profiles result in diverse density profiles of the ejecta, for which we conduct radiative transfer simulations using TARDIS with the solar r-process composition. Consequently, we investigate the impact of the ejecta velocity profile on the resulting evolution of the lightcurve and spectra through the line transitions of heavy elements. The change in the rate at which these elements accumulate in the line-forming region leaves its imprint on the kilonova lightcurve at specific wavelengths, causing the lightcurves to decay at different rates. Furthermore, in several profiles, plateau-like behaviors (slow and/or flat decline) are also observed. In conclusion, this work proposes potential scenarios of the evolution of kilonova due to the ejecta velocity profile.

Keywords: supernovae; neutron stars; radiative transfer
Photospheric Radius Expansion and a Double-peaked Type-I X-Ray Burst from GRS 1741.9-2853

We present an analysis of two type-I X-ray bursts observed by NuSTAR originating from the very faint transient neutron star (NS) low-mass X-ray binary GRS 1741.9-2853 during a period of outburst in 2020 May. We show that the persistent emission can be modeled as an absorbed, Comptonized blackbody in addition to Fe Kα emission, which can be attributed to relativistic disk reflection. We measure a persistent bolometric, unabsorbed luminosity of ${L}_{\mathrm{bol}}={7.03}_{-0.05}^{+0.04}\times {10}^{36}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$ , assuming a distance of 7 kpc, corresponding to an Eddington ratio of 4.5%. This persistent luminosity combined with light-curve analysis leads us to infer that the bursts were the result of pure He burning rather than mixed H/He burning. Time-resolved spectroscopy reveals that the bolometric flux of the first burst exhibits a double-peaked structure, placing the source within a small population of accreting NSs that exhibit multiple-peaked type-I X-ray bursts. We find that the second, brighter burst shows evidence for photospheric radius expansion (PRE) and that at its peak, this PRE event had an unabsorbed bolometric flux of ${F}_{\mathrm{peak}}={2.94}_{-0.26}^{+0.28}\times {10}^{-8}\,\mathrm{erg}\,{\mathrm{cm}}^{-2}\,{{\rm{s}}}^{-1}$ . This yields a new distance estimate of d = 9.0 ± 0.5 kpc, assuming that this corresponds to the Eddington limit for pure He burning on the surface of a canonical NS. Additionally, we performed a detailed timing analysis that failed to find evidence for quasi-periodic oscillations or burst oscillations, and we place an upper limit of 16% on the rms variability around 589 Hz, the frequency at which oscillations have previously been reported.

Keywords: neutron stars; low-mass x-ray binary stars; x-ray bursts; x-ray sources