adsabs/SciX_UAT_keywords huggingface dataset:
Understanding the Structure of Rapid Intensity Fluctuations in the Chromosphere with IRIS

Several recent data sets have taken advantage of the unique capabilities of orbital and suborbital spacecraft to image the chromosphere and transition region at a very high cadence. We find that both the chromosphere and transition region exhibit spatially coherent transient features at frequencies above 80 mHz. We have analyzed narrowband imaging data from H I Lyα 1215 Å (provided by CLASP), Mg II k 2796 Å, and Si IV 1400 Å (provided by the Interface Region Imaging Spectrograph). We categorize the spatial structure of these rapid fluctuations in different magnetic environments. Intensity fluctuations above the noise level are observed in plages in all passbands. We have found jet-like features in 1215 and 1400 Å data that extend from the edges of plages as well as network magnetic concentrations. We have not found any recurrent features that are identified in both 1400 and 1215 Å data. Short loop-like features were only found in 1400 Å data. Temperature minimum grains generate non-propagating features in 1400 Å data. We compare our observations with previous research on dynamic chromospheric phenomena at lower frequencies. Candidate mechanisms, related to both jets and waves, predict chromospheric and transition region intensity fluctuations at high temporal frequencies, which can now be observationally probed.

Keywords: solar chromosphere; solar oscillations; solar transition region
Density Profiles of Collapsed Rotating Massive Stars Favor Long Gamma-Ray Bursts

Long-duration gamma-ray bursts (lGRBs) originate in relativistic collimated outflows-jets-that drill their way out of collapsing massive stars. Accurately modeling this process requires realistic stellar profiles for the jets to propagate through and break out of. Most previous studies have used simple power laws or pre-collapse models for massive stars. However, the relevant stellar profile for lGRB models is in fact that of a star after its core has collapsed to form a compact object. To self-consistently compute such a stellar profile, we use the open-source code GR1D to simulate the core-collapse process for a suite of low-metallicity rotating massive stellar progenitors that have undergone chemically homogeneous evolution. Our models span a range of zero-age main-sequence (ZAMS) masses: M ZAMS = 13, 18, 21, 25, 35, 40, and 45M ☉. All of these models, at the onset of core-collapse, feature steep density profiles, ρ ∝ r -α , with α ≈ 2.5, which would result in jets that are inconsistent with lGRB observables. We follow the collapses of four of the seven models until they form black holes (BHs) and the other three models until they form proto-neutron stars (PNSs). We find, across all models, that the density profile outside the newly formed BH or PNS is well represented by a flatter power law with α ≈ 1.35-1.55. Such flat density profiles are conducive to the successful formation and breakout of BH-powered jets and are, in fact, required to reproduce observable properties of lGRBs. Future models of lGRBs should be initialized with shallower post-collapse stellar profiles, like those presented here, instead of the much steeper pre-collapse profiles that are typically used.

Keywords: hydrodynamical simulations; general relativity; stellar mass black holes; gamma-ray bursts; core-collapse supernovae
The Hubble Tension Revisited: Additional Local Distance Ladder Uncertainties

In a recent paper, we investigated possible systematic uncertainties related to the Cepheid color-luminosity calibration method and their influence on the tension between the Hubble constant as inferred from distances to Type Ia supernovae and the cosmic microwave background as measured with the Planck satellite. Here, we study the impact of other sources of uncertainty in the supernova distance ladder, including Cepheid temperature and metallicity variations, supernova magnitudes, and GAIA parallax distances. Using Cepheid data in 19 Type Ia supernova host galaxies from Riess et al., anchor data from Riess et al., and a set of recalibrated Milky Way Cepheid distances, we obtain H 0 = 71.9 ± 2.2 km s-1 Mpc-1, 2.0σ from the Planck value. Excluding Cepheids with estimated color excesses \hat{E}(V-I)=0.15$ mag to mitigate the impact of the Cepheid color-luminosity calibration, the inferred Hubble constant is H 0 = 68.1 ± 2.6 km s-1 Mpc-1, removing the tension with the Planck value.

Keywords: hubble constant; type ia supernovae; cepheid distance; interstellar extinction
An Extremely Temporary Co-orbital: The Dynamical State of Active Centaur 2019 LD2

We investigate the recent and future orbital evolution of the solar system small body 2019 LD2 (hereafter "LD2"), which was recently found to show cometary activity. While LD2's orbit initially looks similar to that of a Jupiter Trojan, numerical integrations show that it is only co-orbital with Jupiter for approximately a single orbit around the Sun. This would classify LD2 as an active Centaur, but we stress this object remains unique; within the next ∼40-50 years LD2 is likely to become a Jupiter Family Comet, offering an opportunity to observe this critical transition.

Keywords: centaur group; orbits; jupiter trojans
An ALMA Survey of H2CO in Protoplanetary Disks

H2CO is one of the most abundant organic molecules in protoplanetary disks and can serve as a precursor to more complex organic chemistry. We present an Atacama Large Millimeter/submillimeter Array survey of H2CO toward 15 disks covering a range of stellar spectral types, stellar ages, and dust continuum morphologies. H2CO is detected toward 13 disks and tentatively detected toward a fourteenth. We find both centrally peaked and centrally depressed emission morphologies, and half of the disks show ring-like structures at or beyond expected CO snowline locations. Together these morphologies suggest that H2CO in disks is commonly produced through both gas-phase and CO-ice-regulated grain-surface chemistry. We extract disk-averaged and azimuthally-averaged H2CO excitation temperatures and column densities for four disks with multiple H2CO line detections. The temperatures are between 20-50 K, with the exception of colder temperatures in the DM Tau disk. These temperatures suggest that H2CO emission in disks generally emerges from the warm molecular layer, with some contributions from the colder midplane. Applying the same H2CO excitation temperatures to all disks in the survey, we find that H2CO column densities span almost three orders of magnitude (∼5 × 1011-5 × 1014 cm-2). The column densities appear uncorrelated with disk size and stellar age, but Herbig Ae disks may have less H2CO compared to T Tauri disks, possibly because of less CO freeze-out. More H2CO observations toward Herbig Ae disks are needed to confirm this tentative trend, and to better constrain under which disk conditions H2CO and other oxygen-bearing organics efficiently form during planet formation.

Keywords: astrochemistry; protoplanetary disks; radio interferometry; interstellar molecules
A New Window into the Nature of X-Ray Binaries in M101 from Their Optical Emission

The high-energy emission from nearby, star-forming galaxies is dominated by X-ray binaries, where a neutron star or black hole is accreting mass from either a low-mass (≲3 M⊙) or high-mass (≳8 M⊙) star. Donor stars with intermediate masses ≈3-7 M⊙ are also possible, but rarer in our Galaxy. Since it is not possible to separate low-, intermediate-, and high-mass X-ray binaries (LMXBs, IMXBs, and HMXBs) from their X-ray properties alone, we use optical images of M101 taken with the Hubble Space Telescope to directly constrain the masses of donor stars in X-ray binaries down to ≈3 M⊙. For X-ray binaries that still live within their parent star cluster, the age of the cluster provides strong constraints on the mass of the donor and hence type of binary. We present the classification, on a source-by-source basis, of 140 X-ray point sources in the nearby spiral galaxy M101 (D = 6.4 ± 0.2 Mpc). We find that, overall, HMXBs appear to follow the spiral arms, while LMXBs dominate the bulge region as expected, but also appear to form an inter-arm disk population. The X-ray luminosity functions for HMXBs and LMXBs are well fit by a power-law distribution, dN/dLX ∝ Lα, with α = -1.71 ± 0.06 (HMXBs) and α = -1.96 ± 0.08 (LMXBs), and the brightest sources are consistent with the expectations from sampling statistics without requiring a physical cutoff. Overall, our results for HMXB and LMXB populations agree well with the specific star formation rate map presented for M101 recently by Lehmer and collaborators.

Keywords: spiral galaxies; high mass x-ray binary stars; low-mass x-ray binary stars; x-ray binary stars
Differences in Periodic Magnetic Helicity Injection Behavior between Flaring and Non-flaring Active Regions: Case Study

The evolution of magnetic helicity has a close relationship with solar eruptions and is of interest as a predictive diagnostic. In this case study, we analyze the evolution of the normalized emergence, shearing, and total magnetic helicity components in the case of three flaring and three non-flaring active regions (ARs) using Spaceweather Helioseismic Magnetic Imager Active Region Patches vector magnetic field data. The evolution of the three magnetic helicity components is analyzed with wavelet transforms, revealing significant common periodicities of the normalized emergence, shearing, and total helicity fluxes before flares in the flaring ARs. The three non-flaring ARs do not show such common periodic behavior. This case study suggests that the presence of significant periodicities in the power spectrum of magnetic helicity components could serve as a valuable precursor for flares.

Keywords: solar active region magnetic fields; sunspots; solar flares; solar activity; space weather; solar active regions
Coplanar Circumbinary Planets Can Be Unstable to Large Tilt Oscillations in the Presence of an Inner Polar Planet

Mutually misaligned circumbinary planets may form in a warped or broken gas disk or from later planet-planet interactions. With numerical simulations and analytic estimates we explore the dynamics of two circumbinary planets with a large mutual inclination. A coplanar inner planet causes prograde apsidal precession of the binary and the stationary inclination for the outer planet is higher for larger outer planet orbital radius. In this case a coplanar outer planet always remains coplanar. On the other hand, a polar inner planet causes retrograde apsidal precession of the binary orbit and the stationary inclination is smaller for larger outer planet orbital radius. For a range of outer planet semimajor axes, an initially coplanar orbit is librating meaning that the outer planet undergoes large tilt oscillations. Circumbinary planets that are highly inclined to the binary are difficult to detect-it is unlikely for a planet to have an inclination below the transit detection limit in the presence of a polar inner planet. These results suggest that there could be a population of circumbinary planets that are undergoing large tilt oscillations.

Keywords: binary stars; exoplanets; exoplanet dynamics; exoplanet astronomy
The Distribution of Semidetached Binaries. I. An Efficient Pipeline

Semidetached binaries are in the stage of mass transfer and play a crucial role in studying the physics of mass transfer between interacting binaries. Large-scale time-domain surveys provide many light curves of binary systems, while Gaia offers high-precision astrometric data. In this paper, we develop, validate, and apply a pipeline that combines the Markov Chain Monte Carlo method with a forward model and DBSCAN clustering to search for semidetached binaries and estimate the inclination, relative radius, mass ratio, and temperature ratio of each using light curves. We train our model on the mock light curves from Physics of Eclipsing Binaries (PHOEBE), which provides broad coverage of light-curve simulations for semidetached binaries. Applying our pipeline to Transiting Exoplanet Survey Satellite sectors 1-26, we have identified 77 semidetached binary candidates. Utilizing the distance from Gaia, we determine their masses and radii with median fractional uncertainties of ~26% and ~7%, respectively. With the added 77 candidates, the catalog of semidetached binaries with orbital parameters has been expanded by approximately 20%. The comparison and statistical results show that our semidetached binary candidates align well with the compiled samples and the PARSEC model in T eff-L and M-R relations. Combined with the literature samples, comparative analysis with stability criteria for conserved mass transfer indicates that ~97.4% of samples are undergoing nuclear-timescale mass transfer, and two samples (GO Cyg and TIC 454222105) are located within the limits of stability criteria for dynamical- and thermal-timescale mass transfer, and are currently undergoing thermal-timescale mass transfer. Additionally, one system (IR Lyn) is very close to the upper limit of delayed dynamical-timescale mass transfer.

Keywords: semi-detached binary stars; eclipsing binary stars; light curves; fundamental parameters of stars; astronomy data analysis; catalogs
Threat from Within: Excitation of Venus's Co-orbital Asteroids to Earth-crossing Orbits

All five currently known asteroids in the 1:1 mean-motion resonance (co-orbital) with Venus cross Earth's orbit. We explore a scenario in which these near-Earth asteroids originate in a reservoir of asteroids co-orbiting with Venus on low-eccentricity orbits. Such an asteroid reservoir was proposed as the only viable source of Venus's co-orbital dust ring. So far, efforts to discover low-eccentricity Venus co-orbital (LEVCO) asteroids have been unsuccessful; however, their existence has not been ruled out. We show that LEVCO asteroids, stable for millions to billions of years, eventually evolve into Earth-crossing configurations, where they may pose a threat to Earth. We find that the orbits of these asteroids cross Earth's orbit for 22.5 million yr, on average, an order of magnitude longer than the corresponding Earth-crossing time of most asteroids escaping from the main belt. Using the results of the latest survey of LEVCO asteroids, we conclude that, given their absolute magnitudes, H, most of the observed Venus co-orbitals likely do not originate from the hypothetical population of LEVCO asteroids. However, we infer that there are up to ~500 asteroids originating from the LEVCO region with H < 26.3 (10-40 m in diameter) that currently cross the orbit of Earth. Up to ~20 of those have H < 24.1 (30-100 m in diameter), easily detectable by various near-Earth asteroid surveys. We estimate the current mass of the LEVCO reservoir as M ≈ 1013-1016 kg, 3-6 orders of magnitude lower than the current mass of the main belt, depending on their size-frequency distribution.

Keywords: near-earth objects; orbital evolution; orbital resonances; venus; asteroids; asteroid dynamics; atira group; aten group; dynamical evolution
MAGIC Observations of the Nearby Short Gamma-Ray Burst GRB 160821B

The coincident detection of GW170817 in gravitational waves and electromagnetic radiation spanning the radio to MeV gamma-ray bands provided the first direct evidence that short gamma-ray bursts (GRBs) can originate from binary neutron star (BNS) mergers. On the other hand, the properties of short GRBs in high-energy gamma-rays are still poorly constrained, with only ∼20 events detected in the GeV band, and none in the TeV band. GRB 160821B is one of the nearest short GRBs known at z = 0.162. Recent analyses of the multiwavelength observational data of its afterglow emission revealed an optical-infrared kilonova component, characteristic of heavy-element nucleosynthesis in a BNS merger. Aiming to better clarify the nature of short GRBs, this burst was automatically followed up with the MAGIC telescopes, starting from 24 s after the burst trigger. Evidence of a gamma-ray signal is found above ∼0.5 TeV at a significance of ∼ 3σ during observations that lasted until 4 hr after the burst. Assuming that the observed excess events correspond to gamma-ray emission from GRB 160821B, in conjunction with data at other wavelengths, we investigate its origin in the framework of GRB afterglow models. The simplest interpretation with one-zone models of synchrotron-self-Compton emission from the external forward shock has difficulty accounting for the putative TeV flux. Alternative scenarios are discussed where the TeV emission can be relatively enhanced. The role of future GeV-TeV observations of short GRBs in advancing our understanding of BNS mergers and related topics is briefly addressed. * Contact MAGIC Collaboration (contact.magic@mpp.mpg.de) for queries. Corresponding authors are K. Noda, L. Nava, and S. Inoue.

Keywords: gamma-ray bursts
The Neutron Star Population in M28: A Joint Chandra/GBT Look at Pulsar Paradise

We present the results of a deep study of the neutron star (NS) population in the globular cluster M28 (NGC 6626), using the full 330 ks 2002-2015 ACIS data set from the Chandra X-ray Observatory and coordinated radio observations taken with the Green Bank Telescope (GBT) in 2015. We investigate the X-ray luminosity (L X ), spectrum, and orbital modulation of the seven known compact binary millisecond pulsars in the cluster. We report two simultaneous detections of the redback PSR J1824-2452I (M28I) and its X-ray counterpart at L X = [8.3 ± 0.9] × 1031 erg s-1. We discover a double-peaked X-ray orbital flux modulation in M28I during its pulsar state, centered around pulsar inferior conjunction. We analyze the spectrum of the quiescent NS low-mass X-ray binary to constrain its mass and radius. Using both hydrogen and helium NS atmosphere models, we find an NS radius of R = 9.2-11.5 km and R = 13.0-17.5 km, respectively, for an NS mass of 1.4 M ⊙ (68% confidence ranges). We also search for long-term variability in the 46 brightest X-ray sources and report the discovery of six new variable low-luminosity X-ray sources in M28.

Keywords: neutron stars; millisecond pulsars; low-mass x-ray binary stars
The X-Ray Pulsar XTE J1858+034 Observed with NuSTAR and Fermi/GBM: Spectral and Timing Characterization plus a Cyclotron Line

Accreting X-ray pulsars (XRPs) undergo luminous X-ray outbursts during which the spectral and timing behavior of the neutron star can be studied in detail. We analyze a NuSTAR observation of the XRP XTE J1858+034 during its outburst in 2019. The spectrum is fit with a phenomenological, a semiempirical, and a physical spectral model. A candidate cyclotron line is found at 48 keV, implying a magnetic field of 5.4 × 1012 G at the site of emission. This is also supported by the physical best-fit model. We propose an orbital period of about 81 days based on the visual inspection of the X-ray outburst recurrence time. Based on Fermi/GBM data, the standard disk accretion-torque theory allowed us to infer a distance of 10.9 ± 1.0 kpc. Pulse profiles are single-peaked and show a pulsed fraction that is strongly energy-dependent at least up to 40 keV.

Keywords: x-ray binary stars; neutron stars; pulsars; accretion; stellar accretion disks; magnetic fields
Discovery, Timing, and Multiwavelength Observations of the Black Widow Millisecond Pulsar PSR J1555-2908

We report the discovery of PSR J1555-2908, a 1.79 ms radio and gamma-ray pulsar in a 5.6 hr binary system with a minimum companion mass of 0.052 M ⊙. This fast and energetic ( $\dot{E}=3\times {10}^{35}$ erg s-1) millisecond pulsar was first detected as a gamma-ray point source in Fermi Large Area Telescope (LAT) sky survey observations. Guided by a steep-spectrum radio point source in the Fermi error region, we performed a search at 820 MHz with the Green Bank Telescope that first discovered the pulsations. The initial radio pulse timing observations provided enough information to seed a search for gamma-ray pulsations in the LAT data, from which we derive a timing solution valid for the full Fermi mission. In addition to the discovery and timing of radio and gamma-ray pulsations, we searched for X-ray pulsations using NICER but no significant pulsations were detected. We also obtained time-series r-band photometry that indicates strong heating of the companion star by the pulsar wind. Material blown off the heated companion eclipses the 820 MHz radio pulse during inferior conjunction of the companion for ≈10% of the orbit, which is twice the angle subtended by its Roche lobe in an edge-on system.

Keywords: millisecond pulsars; gamma-ray sources; binary pulsars; pulsars; compact binary stars; radio pulsars
TESS Hunt for Young and Maturing Exoplanets (THYME). XI. An Earth-sized Planet Orbiting a Nearby, Solar-like Host in the 400 Myr Ursa Major Moving Group

Young terrestrial worlds are critical test beds to constrain prevailing theories of planetary formation and evolution. We present the discovery of HD 63433 d—a nearby (22 pc), Earth-sized planet transiting a young Sun-like star (TOI-1726, HD 63433). HD 63433 d is the third planet detected in this multiplanet system. The kinematic, rotational, and abundance properties of the host star indicate that it belongs to the young (414 ± 23 Myr) Ursa Major moving group, whose membership we update using new data from the third data release of the Gaia mission and TESS. Our transit analysis of the TESS light curves indicates that HD 63433 d has a radius of 1.1 R ⊕ and closely orbits its host star with a period of 4.2 days. To date, HD 63433 d is the smallest confirmed exoplanet with an age less than 500 Myr, and the nearest young Earth-sized planet. Furthermore, the apparent brightness of the stellar host (V ≃ 6.9 mag) makes this transiting multiplanet system favorable to further investigations, including spectroscopic follow-up to probe the atmospheric loss in a young Earth-sized world.

Keywords: exoplanet systems
Spatial and Temporal Analysis of Quiescent Coronal Rain over an Active Region

The solar corona produces coronal rain, hundreds of times colder and denser material than the surroundings. Coronal rain is known to be deeply linked to coronal heating, but its origin, dynamics, and morphology are still not well understood. The leading theory for its origin is thermal instability (TI) occurring in coronal loops in a state of thermal nonequilibrium (TNE), the TNE-TI scenario. Under steady heating conditions, TNE-TI repeats in cycles, leading to long-period EUV intensity pulsations and periodic coronal rain. In this study, we investigate coronal rain on the large spatial scales of an active region (AR) and over the long temporal scales of EUV intensity pulsations to elucidate its distribution at such scales. We conduct a statistical study of coronal rain observed over an AR off limb with Interface Region Imaging Spectrograph and Solar Dynamics Observatory imaging data, spanning chromospheric to transition region (TR) temperatures. The rain is widespread across the AR, irrespective of the loop inclination, and with minimal variation over the 5.45 hr duration of the observation. Most rain has a downward (87.5%) trajectory; however, upward motions (12.5%) are also ubiquitous. The rain dynamics are similar over the observed temperature range, suggesting that the TR emission and chromospheric emission are colocated on average. The average clump widths and lengths are similar in the SJI channels and wider in the AIA 304 Å channel. We find ubiquitous long-period EUV intensity pulsations in the AR. Short-term periodicity is found (16 minutes) linked to the rain appearance, which constitutes a challenge to explain under the TNE-TI scenario.

Keywords: solar prominences; solar coronal heating; solar chromosphere; solar transition region; active solar corona