adsabs/SciX_UAT_keywords huggingface dataset:
Ancient Very Metal-poor Stars Associated with the Galactic Disk in the H3 Survey

Ancient, very metal-poor (VMP) stars offer a window into the earliest epochs of galaxy formation and assembly. We combine data from the H3 Spectroscopic Survey and Gaia to measure metallicities, abundances of α elements, stellar ages, and orbital properties of a sample of 482 VMP ([Fe/H] < -2) stars in order to constrain their origins. This sample is confined to 1 ≲ ∣Z∣ ≲ 3 kpc from the Galactic plane. We find that >70% of VMP stars near the disk are on prograde orbits and this fraction increases toward lower metallicities. This result is unexpected if metal-poor stars are predominantly accreted from many small systems with no preferred orientation, as such a scenario would imply a mostly isotropic distribution. Furthermore, we find there is some evidence for higher fractions of prograde orbits among stars with lower [α/Fe]. Isochrone-based ages for main-sequence turn-off stars reveal that these VMP stars are uniformly old (≈12 Gyr) irrespective of the α abundance and metallicity, suggesting that the metal-poor population was not born from the same well-mixed gas disk. We speculate that the VMP population has a heterogeneous origin, including both in situ formation in the ancient disk and accretion from a satellite with the same direction of rotation as the ancient disk at early times. Our precisely measured ages for these VMP stars on prograde orbits show that the Galaxy has had a relatively quiescent merging history over most of cosmic time, and implies the angular momentum alignment of the Galaxy has been in place for at least 12 Gyr.

Keywords: milky way disk; milky way formation; milky way evolution; metallicity; milky way galaxy; milky way dynamics
A 16 hr Transit of Kepler-167 e Observed by the Ground-based Unistellar Telescope Network

More than 5000 exoplanets have been confirmed and among them almost 4000 were discovered by the transit method. However, few transiting exoplanets have an orbital period greater than 100 days. Here we report a transit detection of Kepler-167 e, a "Jupiter analog" exoplanet orbiting a K4 star with a period of 1071 days, using the Unistellar ground-based telescope network. From 2021 November 18 to 20, citizen astronomers located in nine different countries gathered 43 observations, covering the 16 hr long transit. Using a nested sampling approach to combine and fit the observations, we detected the midtransit time to be UTC 2021 November 19 17:20:51 with a 1σ uncertainty of 9.8 minutes, making it the longest-period planet to ever have its transit detected from the ground. This is the fourth transit detection of Kepler-167 e, but the first made from the ground. This timing measurement refines the orbit and keeps the ephemeris up to date without requiring space telescopes. Observations like this demonstrate the capabilities of coordinated networks of small telescopes to identify and characterize planets with long orbital periods.

Keywords: exoplanets; transits; amateur astronomers; exoplanet detection methods; transit photometry; astronomy data analysis; observatories; light curves; optical telescopes; observational astronomy; astronomy education; astronomy data modeling
Formation of Polar Crown Filament Magnetic Fields by Supergranular Helicity Injection

To understand the magnetic fields of the polar crown filaments (PCFs) at high latitudes near polar regions of the Sun, we perform magnetofrictional numerical simulations on the long-term magnetic evolution of bipolar fields with roughly east–west polarity inversion lines (PILs) in a 3D spherical wedge domain near polar regions. The Coriolis-effect-induced vortical motions at the boundaries of several supergranular cells inject magnetic helicity from the photospheric boundary into the solar atmosphere. Supergranular-scale helicity injection, transfer, and condensation produce strongly sheared magnetic fields. Magnetic reconnections at footpoints of the sheared fields produce magnetic flux ropes (MFRs) with helicity signs consistent with the observed hemispheric helicity rule. The cross-sectional area of MFRs exhibits an uneven distribution, resembling a "foot-node-foot" periodic configuration. Experiments with different tilt directions of PILs indicate that the PCFs preferably form along PILs with the western end close to the polar region. The bending of PILs caused by supergranular flows, forming S-shape (Z-shape) PIL segments, promotes the formation of dextral (sinistral) MFRs. The realistic magnetic models we obtained can serve as starting points for the study of the plasma formation and eruption of PCFs.

Keywords: solar prominences; quiescent solar prominence; supergranulation; solar magnetic fields; magnetohydrodynamical simulations
Nonlinear Interaction of Low-frequency Alfvén Waves and Ions

The interaction between Alfvén waves and particles is a critical phenomenon in space and laboratory plasmas, and it has been observed that low-frequency Alfvén waves can accelerate and heat ions through subharmonic resonant interactions. In this study, we use test particle simulations to verify the nonlinear heating of parallelly propagating low-frequency Alfvén waves on ions and analyze the underlying process in terms of the Poincaré section. Our results demonstrate that low-frequency Alfvén waves can periodically pick up ions, leading to oscillations of average parallel velocity and temperature of the plasma by phase mixing, ultimately resulting in the stabilization of acceleration. Furthermore, we have developed an analysis that can estimate the time required for heating and accelerating. In the case of multiple waves, our findings indicate that the presence of more chaotic modes does not necessarily result in better wave heating. We have also discussed the effect of random phases on the heating process. Overall, this research sheds light on the crucial role played by the interaction between Alfvén waves and particles in astrophysics and provides new insights into the mechanisms underlying the heating and acceleration of ions through subharmonic resonant interactions with low-frequency Alfvén waves. These findings may have significant implications for the understanding of plasma dynamics in a range of astrophysical environments.

Keywords: alfven waves; solar wind; interplanetary particle acceleration
Exploring the Gas-phase Metallicity Gradients of Star-forming Galaxies at Cosmic Noon

We explore the relationships between the [O/H] gas-phase metallicity radial gradients and multiple galaxy properties for 238 star-forming galaxies at 0.6 < z < 2.6 selected from the CANDELS Lyα Emission at Reionization survey with stellar mass $8.5\lt \mathrm{log}\,{M}_{* }/{M}_{\odot }\lt 10.5$ . The gradients cover the range from ‑0.11 to 0.22 dex kpc‑1, with the median value close to 0. We reconstruct the nonparametric star formation histories (SFHs) of the galaxies with spectral energy distribution modeling using Prospector with more than 40 photometric bands from the Hubble Space Telescope, Spitzer, and ground-based facilities. In general, we find weak or no correlations between the metallicity gradients and most galaxy properties, including the mass-weighted age, recent star formation rate, dust attenuation, and morphology as quantified by both parametric and nonparametric diagnostics. We find a significant but moderate correlation between the gradients and the "evolutionary time," a temporal metric that characterizes the evolutionary status of a galaxy, with flatter gradients observed in more evolved galaxies. Also, there is evidence that galaxies with multiple star formation episodes in their SFHs tend to develop more negative gas-phase metallicity gradients (higher [O/H] at the center). We conclude that gas kinematics, e.g., radial inflows and outflows, is likely an important process in setting the gas-phase metallicity gradients, in addition to the evolution of the SFH radial profile. Since the gradients are largely independent of the galaxies' physical properties and only weakly dependent on their SFH, it would appear that the timescale of the gas kinematics is significantly shorter than the evolution of star formation.

Keywords: galaxy evolution; galaxy abundances
Searching for Supernova Bursts in Super-Kamiokande IV

Super-Kamiokande has been searching for neutrino bursts characteristic of core-collapse supernovae continuously, in real time, since the start of operations in 1996. The present work focuses on detecting more distant supernovae whose event rate may be too small to trigger in real time, but may be identified using an offline approach. The analysis of data collected from 2008 to 2018 found no evidence of distant supernovae bursts. This establishes an upper limit of 0.29 yr-1 on the rate of core-collapse supernovae out to 100 kpc at 90% C.L. For supernovae that fail to explode and collapse directly to black holes the limit reaches to 300 kpc.

Keywords: core-collapse supernovae; supernova neutrinos; particle astrophysics
Nature Versus Nurture: A Bayesian Framework for Assessing Apparent Correlations between Planetary Orbital Properties and Stellar Ages

Many exoplanets have orbital characteristics quite different from those seen in our own solar system, including planets locked in orbital resonances and planets on orbits that are elliptical or highly inclined from their host star's spin axis. It is debated whether the wide variety in system architecture is primarily due to differences in formation conditions (nature) or due to evolution over time (nurture). Identifying trends between planetary and stellar properties, including stellar age, can help distinguish between these competing theories and offer insights as to how planets form and evolve. However, it can be challenging to determine whether observed trends between planetary properties and stellar age are driven by the age of the system—pointing to evolution over time being an important factor—or other parameters to which the age may be related, such as stellar mass or stellar temperature. The situation is complicated further by the possibilities of selection biases, small number statistics, uncertainties in stellar age, and orbital evolution timescales that are typically much shorter than the range of observed ages. Here, we develop a Bayesian statistical framework to assess the robustness of such observed correlations and to determine whether they are indeed due to evolutionary processes, are more likely to reflect different formation scenarios, or are merely coincidental. We apply this framework to reported trends between stellar age and 2:1 orbital resonances, spin-orbit misalignments, and hot Jupiters' orbital eccentricities. We find strong support for the nurture hypothesis only in the final case.

Keywords: exoplanet evolution; bayesian statistics; exoplanet systems; stellar ages; exoplanet dynamics
Background Short-period Eclipsing Binaries in the Original Kepler Field

During the primary Kepler mission, between 2009 and 2013, about 150,000 preselected targets were observed with a 29.42 minute long cadence. However, a survey of background stars that fall within the field of view (FOV) of the downloaded apertures of the primary targets has revealed a number of interesting objects. In this paper, we present the results of this search, focusing on short-period eclipsing binary (SPEB) stars in the background pixels of primary Kepler targets. We used Lomb-Scargle and Phase Dispersion Minimization methods to reveal pixels that show significant periodicities, resulting in the identification of 547 previously unknown faint SPEBs, mostly W UMa-type stars, and almost doubling the number of SPEBs in the original Kepler FOV. We prepared the light curves for scientific analysis and cross-matched the pixel coordinates with Gaia and other catalogs to identify the possible sources. We have found that the mean of the brightness distribution of the new background SPEBs is ~4-5 mag fainter than other, primary target eclipsing binaries in the Kepler Eclipsing Binary catalog. The period distribution nonetheless follows the same trend, but the spatial distribution appears to be different from that described by Kirk et al. for the catalog eclipsing binaries.

Keywords: space telescopes; contact binary stars; eclipsing binary stars; w ursae majoris variable stars
The Diverse Morphology, Stellar Population, and Black Hole Scaling Relations of the Host Galaxies of Nearby Quasars

We present rest-frame B and I imaging of 35 low-redshift ( $z\lt 0.5$ ) Palomar-Green quasars using the Hubble Space Telescope Wide Field Camera 3. We perform multicomponent two-dimensional image decomposition to separate the host galaxy from its bright active nucleus, characterize its morphology, and measure its photometric properties. Special care is devoted to quantifying the structural parameters of the galaxy bulge, determining its B - I color, and estimating its stellar mass. Roughly half of the sample, comprising the less luminous ( ${L}_{5100}\lesssim {10}^{45}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$ ) but most high Eddington ratio quasars, reside in disk galaxies that are often barred and possess pseudo bulges. The large stellar masses, large effective radii, and faint surface brightnesses suggest that the host galaxies of the most luminous quasars are mostly ellipticals. Major mergers constitute only a small percentage (≲20%) of our sample. Our quasar sample roughly obeys the scaling relations between black hole mass and host galaxy (bulge, core, total) stellar mass. Hosts with black holes more massive than $\sim {10}^{8}\,{M}_{\odot }$ behave similarly to classical bulges and early-type galaxies, while those with less massive black holes, particularly the narrow-line Seyfert 1s, are consistent with pseudo bulges in late-type galaxies. The host galaxy bulges, irrespective of whether they are classical or pseudo, follow a relatively tight inverse relation between the effective radius and the mean effective surface brightness of inactive classical bulges and ellipticals. We argue that pseudo bulges experience recent or ongoing nuclear star formation.

Keywords: quasars; active galactic nuclei; galaxy structure; galaxy bulges
The Visualization and Measurements of Mass Functions with LEGO

We promote the concept of mass functions for interdisciplinary science education and communication. A mass function characterizes the frequency distribution of the masses of objects in the universe. We present an experiment to demonstrate this concept to a diverse audience of science students, using popular LEGO toys. We discovered that the LEGO mass function is surprisingly similar compared to mass functions of astronomical objects such as stars and galaxies.

Keywords: astronomy data visualization; stellar mass functions; initial mass function; interdisciplinary astronomy; pareto distribution; mass ratio
Inhomogeneous Enrichment of Radioactive Nuclei in the Galaxy: Deposition of Live 53Mn, 60Fe, 182Hf, and 244Pu into Deep-sea Archives. Surfing the Wave?

While modeling the galactic chemical evolution (GCE) of stable elements provides insights to the formation history of the Galaxy and the relative contributions of nucleosynthesis sites, modeling the evolution of short-lived radioisotopes (SLRs) can provide supplementary timing information on recent nucleosynthesis. To study the evolution of SLRs, we need to understand their spatial distribution. Using a three-dimensional GCE model, we investigated the evolution of four SLRs: 53Mn, 60Fe, 182Hf, and 244Pu with the aim of explaining detections of recent (within the last ≈1-20 Myr) deposition of live 53Mn, 60Fe, and 244Pu of extrasolar origin into deep-sea reservoirs. We find that core-collapse supernovae are the dominant propagation mechanism of SLRs in the Galaxy. This results in the simultaneous arrival of these four SLRs on Earth, although they could have been produced in different astrophysical sites, which can explain why live extrasolar 53Mn, 60Fe, and 244Pu are found within the same, or similar, layers of deep-sea sediments. We predict that 182Hf should also be found in such sediments at similar depths.

Keywords: interstellar medium; galactic abundances; astrochemistry
Isotopic Enrichment of Planetary Systems from Asymptotic Giant Branch Stars

Short-lived radioisotopes, in particular 26Al and 60Fe, are thought to contribute to the internal heating of the Earth, but are significantly more abundant in the solar system compared to the interstellar medium. The presence of their decay products in the oldest solar system objects argues for their inclusion in the Sun's protoplanetary disk almost immediately after the star formation event that formed the Sun. Various scenarios have been proposed for their delivery to the solar system, usually involving one or more core-collapse supernovae of massive stars. An alternative scenario involves the young Sun encountering an evolved asymptotic giant branch (AGB) star. AGBs were previously discounted as a viable enrichment scenario for the solar system due to the presumed low probability of an encounter between an old, evolved star and a young pre-main-sequence star. We report the discovery in Gaia data of an interloping AGB star in the star-forming region NGC2264, demonstrating that old, evolved stars can encounter young forming planetary systems. We use simulations to calculate the yields of 26Al and 60Fe from AGBs and their contribution to the long-term geophysical heating of a planet, and find that these are comfortably within the range previously calculated for the solar system.

Keywords: solar system formation; asymptotic giant branch stars; star forming regions
Evidence for Evolved Stellar Binary Mergers in Observed B-type Blue Supergiants

Blue supergiants are the brightest stars in their host galaxies, and yet their evolutionary status has been a long-standing problem in stellar astrophysics. In this pioneering work, we present a large sample of 59 early B-type supergiants in the Large Magellanic Cloud with newly derived stellar parameters and identify the signatures of stars born from binary mergers among them. We simulate novel 1D merger models of binaries consisting of post main-sequence giants with helium-rich cores (primaries) and main-sequence companions (secondaries), and consider the effects of interaction of the secondary with the core of the primary along with the mixing induced by the merger in the envelope. Thereafter, the evolution of the newborn 17–43 $\,{{\rm{M}}}_{\odot }$ stars is followed until core-carbon depletion, close to their final pre-explosion stage. Unlike stars born alone with comparable masses, stars born from mergers of evolved binaries are blue throughout their core helium-burning phase and replicate the surface gravities and Hertzsprung–Russell diagram positions of most of our sample, thus indicating that B-type supergiants structurally resemble stars born from such mergers. Moreover, the large nitrogen-to-carbon and nitrogen-to-oxygen number ratios, coupled with helium enhancements exhibited by at least half our data sample, is uniquely reproduced by our merger models. Collectively, these findings provide compelling evidence toward the important role of binary mergers in producing the currently observed population of blue supergiants in our Universe.

Keywords: massive stars; binary stars; b supergiant stars; stellar evolutionary models; spectroscopy; type ii supernovae; stellar mergers; stellar abundances; magellanic clouds; large magellanic cloud
Obscuring Fraction of Active Galactic Nuclei Implied by Supernova and Radiative Feedbacks

We study the obscuring structure of circumnuclear disks (CNDs) by considering supernova (SN) feedbacks from nuclear starburst and the effect of anisotropic radiative pressure from active galactic nuclei (AGNs). We suppose that the mass accretion onto a central supermassive black hole (SMBH) is triggered by SN-driven turbulence within CNDs, and we explore how the structures of CNDs depend on the BH mass (MBH) and AGN luminosity (LAGN). We find that the obscuring fraction (fobs) peaks at ∼10% of the Eddington luminosity (LEdd), and its maximal value is fobs ∼ 0.6 for less massive SMBHs (e.g., MBH < 108 M⊙). This is because the scale height of CNDs is determined by the SN-driven accretion for a smaller LAGN, while the dusty molecular gas in CNDs is blown away by the radiation pressure from AGNs beyond the critical luminosity. On the other hand, for massive SMBHs (e.g., MBH > 108 M⊙), fobs is always smaller than 0.2, and it is almost independent of LAGN because the scale height of CNDs is mainly controlled by the maximal star formation efficiency ( ${C}_{* ,\max }$ ) in CNDs. In comparison with the obscuring fractions suggested from the mid-infrared observations of nearby AGNs, the SN plus radiative feedback model with ${C}_{* ,\max }={10}^{-7}\,{\mathrm{yr}}^{-1}$ reproduces the observations for MBH = 108 M⊙ well. We also find that the intense starburst or the existence of dust-free absorbers inside CNDs are necessary for explaining X-ray observations.

Keywords: active galaxies; active galactic nuclei; galaxy nuclei
CLASSY. VIII. Exploring the Source of Ionization with UV Interstellar Medium Diagnostics in Local High-z Analogs

In the current JWST era, rest-frame UV spectra play a crucial role in enhancing our understanding of the interstellar medium (ISM) and stellar properties of the first galaxies in the epoch of reionization (z > 6). Here, we compare well-known and reliable optical diagrams sensitive to the main ionization source (i.e., star formation, SF; active galactic nuclei, AGN; and shocks) to UV counterparts proposed in the literature—the so-called "UV–BPT diagrams"—using the HST COS Legacy Archive Spectroscopic SurveY (CLASSY), which is the largest high-quality, high-resolution, and broad-wavelength range atlas of far-UV spectra for 45 local star-forming galaxies. In particular, we explore where CLASSY UV line ratios are located in the different UV diagnostic plots, taking into account state-of-the-art photoionization and shock models, and, for the first time, the measured ISM and stellar properties (e.g., gas-phase metallicity, ionization parameter, carbon abundance, and stellar age). We find that the combination of C III] λ λ1907,9 He II λ1640 and O III] λ1666 can be a powerful tool to separate between SF, shocks, and AGN at subsolar metallicities. We also confirm that alternative diagrams without O III] λ1666 still allow us to define an SF-locus, with some caveats. Diagrams including C IV λ λ1548,51 should be taken with caution given the complexity of this doublet profile. Finally, we present a discussion detailing the ISM conditions required to detect UV emission lines, visible only in low gas-phase metallicity (12 + log(O/H) ≲ 8.3) and high ionization parameter (log(U) ≳ ‑2.5) environments. Overall, CLASSY and our UV toolkit will be crucial in interpreting the spectra of the earliest galaxies that JWST is currently revealing. *Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

Keywords: dwarf galaxies; ultraviolet astronomy; galaxy chemical evolution; galaxy spectroscopy; high-redshift galaxies; emission line galaxies