adsabs/SciX_UAT_keywords huggingface dataset:
Heating at the Remote Footpoints as a Brake on Jet Flows along Loops in the Solar Atmosphere

We report on observations of a solar jet propagating along coronal loops taken by the Solar Dynamics Observatory, the Interface Region Imaging Spectrograph, and the 1 m New Vacuum Solar Telescope. The ejecta of the jet consist of multithermal components and propagate with a speed greater than 100 km s-1. Brightenings are found in the remote footpoints of the coronal loops having compact and round shape in the Hα images. The emission peak of the remote brightening in the Atmospheric Imaging Assembly (AIA) 94 Å passband lags 60 s behind that in the jet base. The brightenings in the remote footpoints are believed to be consequences of heating by nonthermal electrons, MHD waves, and/or a conduction front generated by the magnetic reconnection processes of the jet. The heating in the remote footpoints leads to extension of the brightening along the loops toward the jet base, which is believed to be the chromospheric evaporation. This apparently acts as a brake on the ejecta, leading to a deceleration in the range from 1.5 to 3 km s-2 with an error of ∼1.0 km s-2 when the chromospheric evaporation and the ejecta meet at locations near the loop apexes. The dynamics of this jet allows for a unique opportunity to diagnose the chromospheric evaporation from the remote footpoints, from which we deduce a velocity in the range of 330-880 km s-1.

Keywords: solar chromosphere; plasma jets; solar coronal loops; solar atmosphere; solar coronal transients; solar corona
TOI-1235 b: A Keystone Super-Earth for Testing Radius Valley Emergence Models around Early M Dwarfs

Small planets on close-in orbits tend to exhibit envelope mass fractions of either effectively zero or up to a few percent depending on their size and orbital period. Models of thermally driven atmospheric mass loss and of terrestrial planet formation in a gas-poor environment make distinct predictions regarding the location of this rocky/nonrocky transition in period-radius space. Here we present the confirmation of TOI-1235 b (P = 3.44 days, ${r}_{{\rm{p}}}={1.738}_{-0.076}^{+0.087}$ ${R}_{\oplus }$ ), a planet whose size and period are intermediate between the competing model predictions, thus making the system an important test case for emergence models of the rocky/nonrocky transition around early M dwarfs (Rs = 0.630 ± 0.015 ${R}_{\odot }$ , Ms = 0.640 ± 0.016 ${M}_{\odot }$ ). We confirm the TESS planet discovery using reconnaissance spectroscopy, ground-based photometry, high-resolution imaging, and a set of 38 precise radial velocities (RVs) from HARPS-N and HIRES. We measure a planet mass of ${6.91}_{-0.85}^{+0.75}$ ${M}_{\oplus }$ , which implies an iron core mass fraction of ${20}_{-12}^{+15}$ % in the absence of a gaseous envelope. The bulk composition of TOI-1235 b is therefore consistent with being Earth-like, and we constrain an H/He envelope mass fraction to be <0.5% at 90% confidence. Our results are consistent with model predictions from thermally driven atmospheric mass loss but not with gas-poor formation, suggesting that the former class of processes remains efficient at sculpting close-in planets around early M dwarfs. Our RV analysis also reveals a strong periodicity close to the first harmonic of the photometrically determined stellar rotation period that we treat as stellar activity, despite other lines of evidence favoring a planetary origin ( $P={21.8}_{-0.8}^{+0.9}$ days, ${m}_{{\rm{p}}}\sin i={13.0}_{-5.3}^{+3.8}$ ${M}_{\oplus }$ ) that cannot be firmly ruled out by our data.

Keywords: transit photometry; exoplanet structure; exoplanet formation; m dwarf stars; radial velocity
Building an Acceleration Ladder with Tidal Streams and Pulsar Timing

We analyse stellar streams in action-angle coordinates combined with recent local direct acceleration measurements to provide joint constraints on the potential of our galaxy. Our stream analysis uses the Kullback-Leibler divergence with a likelihood analysis based on the two-point correlation function. We provide joint constraints from pulsar accelerations and stellar streams for local and global parameters that describe the potential of the Milky Way (MW). Our goal is to build an "acceleration ladder," where direct acceleration measurements that are currently limited in dynamic range are combined with indirect techniques that can access a much larger volume of the MW. To constrain the MW potential with stellar streams, we consider the Palomar 5, Orphan, Nyx, Helmi, and GD1 streams. Of the potential models that we have considered here, the preferred potential for the streams is a two-component Staeckel potential. We also compare the vertical accelerations from stellar streams and pulsar timing, defining the function $f(z)={\alpha }_{1\mathrm{pulsar}}z-\tfrac{\partial {\rm{\Phi }}}{\partial z}$ , where Φ is the MW potential determined from stellar streams and α 1 pulsar z is the vertical acceleration determined from pulsar timing observations. Our analysis indicates that the Oort limit determined from streams is consistently (regardless of the choice of potential) lower than that determined from pulsar timing observations. The calibration we have derived here may be used to correct the estimate of the acceleration from stellar streams.

Keywords: milky way mass; milky way dynamics; milky way dark matter halo
Neutral Atmospheric Density Measurement Using Insight-HXMT Data by the Earth Occultation Technique

The Earth occultation technique has broad applications in both astronomy and atmospheric density measurements. We construct the background model during the occultation of the Crab Nebula observed by the Insight-Hard X-ray Modulation Telescope (Insight-HXMT) at energies between 6 and 100 keV. We propose a Bayesian atmospheric density retrieval method based on the Earth occultation technique, combining Poisson and Gaussian statistics. By modeling the atmospheric attenuation of X-ray photons during the occultation, we simultaneously retrieved the neutral densities of the atmosphere at different altitude ranges. Our method considers the correlation of densities between neighboring atmospheric layers and reduces the potential systematic bias to which previous work may be subject. Previous analyses based on light-curve fitting or spectral fitting also lost some spectral or temporal information of the data. In contrast to previous work, the occultation data observed by the three telescopes on board Insight-HXMT is fully used in our analysis, further reducing the statistical error in density retrieval. We apply our method to cross-check the (semi)empirical atmospheric models, using 115 sets of occultation data of the Crab Nebula observed by Insight-HXMT. We find that the retrieved neutral density is ~10%, ~20%, and ~25% less than the values of the widely used atmospheric model NRLMSISE-00, in the altitude range of 55-80 km, 80-90 km, and 90-100 km, respectively. We also show that the newly released atmospheric model NRLMSIS 2.0 is generally consistent with our density measurements.

Keywords: earth atmosphere; occultation; atmospheric composition; pulsar wind nebulae
Criss-cross Nebula: A Case Study of Shock Regions with Resolved Microstructures at Scales of ∼1000 au

Using integral field spectroscopy (IFS) from MaNGA, we study the resolved microstructures in a shocked region in the Criss-cross Nebula (CCN), with an unprecedentedly high resolution of ≲1000 au. We measure surface brightness maps for 34 emission lines, which can be broadly divided into three categories: (1) the [O III] λ5007-like group including seven high-ionization lines and two [O II] auroral lines that uniformly present a remarkable lane structure, (2) the Hα λ6563-like group, including 23 low-ionization or recombination lines that present a clump-like structure, and (3) [O II] λ3726 and [O II] λ3729 showing high densities at both the [O III] λ5007 lane and the Hα clump. We use these measurements to constrain resolved shock models implemented in MAPPINGS V. We find our data can be reasonably well fitted by a model that includes a plane-parallel shock with a velocity of 133 ± 5 km s ‑1, plus an isotropic two-dimensional Gaussian component, which is likely another clump of gas ionized by photons from the shocked region, and a constant background. We compare the electron density and temperature profiles as predicted by our model with those calculated using observed emission-line ratios. We find different line ratios to provide inconsistent temperature maps, and the discrepancies can be attributed to observational effects caused by limited spatial resolution and projection of the shock geometry, as well as contamination of the additional Gaussian component. Implications on shock properties and perspectives on future IFS-based studies of the CCN are discussed.

Keywords: shocks; nebulae; interstellar medium
Importance of Cosmic-Ray Propagation on Sub-GeV Dark Matter Constraints

We study sub-GeV dark matter (DM) particles that may annihilate or decay into Standard Model particles producing an exotic injection component in the Milky Way that leaves an imprint in both photon and cosmic-ray (CR) fluxes. Specifically, the DM particles may annihilate or decay into e + e ‑, μ + μ ‑, or π + π ‑ and may radiate photons through their e ± products. The resulting e ± products can be directly observed in probes such as Voyager 1. Alternatively, the e ± products may produce bremsstrahlung radiation and upscatter the low-energy Galactic photon fields via the inverse Compton process, generating a broad emission from X-ray to γ-ray energies observable in experiments such as XMM-Newton. We find that we get a significant improvement in the DM annihilation and decay constraints from XMM-Newton (excluding thermally averaged cross sections of 10‑31 cm3 s‑1 ≲ <σ v> ≲ 10‑26 cm3 s‑1 and decay lifetimes of 1026 s ≲ τ ≲ 1028 s, respectively) by including best-fit CR propagation and diffusion parameters. This yields the strongest astrophysical constraints for this mass range of DM of 1 MeV to a few GeV and even surpasses cosmological bounds across a wide range of masses as well.

Keywords: dark matter; galactic cosmic rays
Spectral-line Survey of the Region of Massive Star Formation W51e1/e2 in the 4 mm Wavelength Range

We present the results of a spectral-line survey of the W51e1/e2 star-forming region at 68-88 GHz. 79 molecules and their isotopologues were detected, from simple diatomic or triatomic molecules, such as SO, SiO, and CCH, to complex organic compounds, such as CH3OCH3 or CH3COCH3. A number of lines that are absent from the Lovas list of molecular lines observed in space were detected, and most of these were identified. A significant number of the detected molecules are typical for hot cores. These include the neutral molecules HCOOCH3, CH3CH2OH, and CH3COCH3, which are currently believed to exist in the gas phase only in hot cores and shock-heated gas. In addition, vibrationally excited C4H and HC3N lines with upper-level energies of several hundred Kelvins were found. Such lines can arise only in hot gas with temperatures on the order of 100 K or higher. Apart from neutral molecules, various molecular ions were also detected. Some of these (HC18O+, H13CO+, and HCS+) usually exist in molecular clouds with high visual extinctions. Potential formation pathways of complex organic molecules and hydrocarbons, along with nitriles, are considered. These formation routes are first discussed in the context of laboratory experiments elucidating the synthesis of organic molecules in interstellar ices in cold molecular clouds, followed by sublimation into the gas phase in the hot core stage. Thereafter, we discuss the predominant formation of hydrocarbons and their nitriles in the gas phase through bimolecular neutral-neutral reactions.

Keywords: interstellar medium; pre-biotic astrochemistry; star forming regions
Formation of Smaller Anions from CnN- (n = 1-3, 5-7) in the Circumstellar Medium

We probe a new pathway for the formation of smaller anions from the temporary negative ion states (anion resonances) of CnN- (n = 1-3, 5-7) in the circumstellar envelope of IRC+10216. CnN- (n = 1-3, 5-7) anions were collisionally excited to their resonance states and were observed to decay into a variety of smaller anions. The measured kinetic-energy-release distributions for the anionic fragments arising from each of the parent anions indicate a concerted manner of occurrence of these fragments, implying rich dissociation dynamics. ${{\rm{C}}}_{2}^{-}$ and C2N- were found to be dominant fragments of these anions, suggesting their presence in the external layers of IRC+10216 where UV photons penetrate. CnN- (n = 1-3) were also observed to undergo dissociative and nondissociative double-electron detachments, with the former being dominant. The significance of this new pathway in determining the stability and abundance of anions in IRC+10216 is discussed.

Keywords: astrochemistry; astrophysical processes; interstellar dynamics; interstellar abundances; interstellar molecules
Uncovering Hidden Massive Black Hole Companions with Tidal Disruption Events

Dynamical perturbations from supermassive black hole (SMBH) binaries can increase the rates of tidal disruption events (TDEs). However, most previous work focuses on TDEs from the heavier black hole in the SMBH binary (SMBHB) system. In this work, we focus on the lighter black holes in SMBHB systems and show that they can experience a similarly dramatic increase in their TDE rate due to perturbations from a more massive companion. While the increase in TDEs around the more massive black hole is mostly due to chaotic orbital perturbations, we find that, around the smaller black hole, the eccentric Kozai-Lidov mechanism is dominant and capable of producing a comparably large number of TDEs. In this scenario, the mass derived from the light curve and spectra of TDEs caused by the lighter SMBH companion is expected to be significantly smaller than the SMBH mass estimated from galaxy scaling relations, which are dominated by the more massive companion. This apparent inconsistency can help find SMBHB candidates that are not currently accreting as active galactic nuclei and that are at separations too small for them to be resolved as two distinct sources. In the most extreme cases, these TDEs provide us with the exciting opportunity to study SMBHBs in galaxies where the primary SMBH is too massive to disrupt Sun-like stars.

Keywords: black holes; high energy astrophysics; time domain astronomy; transient sources; supermassive black holes; galaxy mergers; active galaxies; tidal disruption
Avoiding the Geometric Boundary Effect in Shear Measurement

In image processing, source detections are inevitably affected by the presence of the geometric boundaries in the images, including the physical boundaries of the CCD, and the boundaries of masked regions due to column defects, bright diffraction spikes, etc. These boundary conditions make the source detection process not statistically isotropic and can lead to additive shear bias near the boundaries. We build a phenomenological model to understand the bias, and propose a simple method to effectively eliminate the influence of geometric boundaries on shear measurement. We demonstrate the accuracy and efficiency of this method using both simulations and the z-band imaging data from the third data release of the DECam Legacy Survey.

Keywords: gravitational lensing
GRB 211211A-like Events and How Gravitational Waves May Tell Their Origins

GRB 211211A is a rare burst with a genuinely long duration, yet its prominent kilonova association provides compelling evidence that this peculiar burst was the result of a compact binary merger. However, the exact nature of the merging objects, whether they were neutron star pairs, neutron star-black hole systems, or neutron star-white dwarf systems, remains unsettled. This Letter delves into the rarity of this event and the possibility of using current and next-generation gravitational wave detectors to distinguish between the various types of binary systems. Our research reveals an event rate density of $\gtrsim {5.67}_{-4.69}^{+13.04}\times {10}^{-3}\,{\mathrm{Gpc}}^{-3}\ {\mathrm{yr}}^{-1}$ for GRB 211211A-like gamma-ray bursts (GRBs), which, assuming GRB 211211A is the only example of such a burst, is significantly smaller than that of typical long- and short-GRB populations. We further calculated that if the origin of GRB 211211A is a result of a neutron star-black hole merger, it would be detectable with a significant signal-to-noise ratio (S/N), given the LIGO-Virgo-KAGRA designed sensitivity. On the other hand, a neutron star-white dwarf binary would also produce a considerable S/N during the inspiral phase at decihertz and is detectable by next-generation spaceborne detectors DECIGO and the Big Bang Observer. However, to detect this type of system with millihertz spaceborne detectors like LISA, Taiji, and TianQin, the event must be very close, approximately 3 Mpc in distance or smaller.

Keywords: gamma-ray bursts; gravitational wave detectors; gravitational wave sources
Gaia Astrometry Challenges the High Central Oxygen Abundance Claimed for the Pulsating Helium-Atmosphere White Dwarf KIC 08626021

The asteroseismic radius determination previously reported for the pulsating helium-atmosphere white dwarf star KIC 08626021 is 6σ discrepant with constraints from Gaia astrometry. This calls into question the other results of the asteroseismic analysis, especially the high (central) oxygen abundance that stellar evolutionary models have been unable to reproduce.

Keywords: asteroseismology; astrometry; astronomical methods; stellar cores; white dwarf stars
The Gaia-ESO Survey: Carbon Abundance in the Galactic Thin and Thick Disks

This paper focuses on carbon, which is one of the most abundant elements in the universe and is of high importance in the field of nucleosynthesis and galactic and stellar evolution. The origin of carbon and the relative importance of massive and low- to intermediate-mass stars in producing it is still a matter of debate. We aim at better understanding the origin of carbon by studying the trends of [C/H], [C/Fe], and [C/Mg] versus [Fe/H] and [Mg/H] for 2133 FGK dwarf stars from the fifth Gaia-ESO Survey internal data release (GES iDR5). The availability of accurate parallaxes and proper motions from Gaia DR2 and radial velocities from GES iDR5 allows us to compute Galactic velocities, orbits, absolute magnitudes, and, for 1751 stars, Bayesian-derived ages. Three different selection methodologies have been adopted to discriminate between thin- and thick-disk stars. In all the cases, the two stellar groups show different [C/H], [C/Fe], and [C/Mg] and span different age intervals, with the thick-disk stars being, on average, older than the thin-disk ones. The behaviors of [C/H], [C/Fe], and [C/Mg] versus [Fe/H], [Mg/H], and age all suggest that C is primarily produced in massive stars. The increase of [C/Mg] for young thin-disk stars indicates a contribution from low-mass stars or the increased C production from massive stars at high metallicities due to the enhanced mass loss. The analysis of the orbital parameters R med and | {Z}\max | supports an “inside-out” and “upside-down” formation scenario for the disks of the Milky Way.

Based on observations collected with the FLAMES instrument at VLT/UT2 (Paranal Observatory, ESO, Chile), for the Gaia-ESO Large Public Spectroscopic Survey (188.B-3002, 193.B-0936).

Keywords: late-type stars; stellar abundances; stellar ages; galaxy stellar content
The Launching of Cold Clouds by Galaxy Outflows. IV. Cosmic-Ray-driven Acceleration

We carry out a suite of simulations of the evolution of cosmic-ray (CR) driven, radiatively cooled cold clouds embedded in hot material, as found in galactic outflows. In such interactions, CRs stream toward the cloud at the Alfvén speed, which decreases dramatically at the cloud boundary, leading to a bottleneck in which pressure builds up in front of the cloud. At the same time, CRs stream along the sides of the cloud, forming a boundary layer where large filaments develop. Shear in this boundary layer is the primary mode of cloud destruction, which is relatively slow in all cases, but slowest in the cases with the lowest Alfvén speeds. Thus, the CR pressure in the bottleneck region has sufficient time to accelerate the cold clouds efficiently. Furthermore, radiative cooling has relatively little impact on these interactions. Our simulations are two-dimensional and limited by a simplified treatment of CR dynamics, the neglect of CR heating, and an idealized magnetic field geometry. Nevertheless, our results suggest that CRs, when acting as the primary source of momentum input, are capable of accelerating clouds to velocities comparable to those observed in galaxy outflows.

Keywords: magnetohydrodynamical simulations
Magnetic Fields of the Starless Core L 1512

We present JCMT POL-2 850 μm dust polarization observations and Mimir H-band stellar polarization observations toward the starless core L 1512. We detect the highly ordered core-scale magnetic field traced by the POL-2 data, of which the field orientation is consistent with the parsec-scale magnetic fields traced by Planck data, suggesting the large-scale fields thread from the low-density region to the dense core region in this cloud. The surrounding magnetic field traced by the Mimir data shows a wider variation in the field orientation, suggesting there could be a transition of magnetic field morphology at the envelope-scale. L 1512 was suggested to be presumably older than 1.4 Myr in a previous study via time-dependent chemical analysis, hinting that the magnetic field could be strong enough to slow the collapse of L 1512. In this study, we use the Davis-Chandrasekhar-Fermi method to derive a plane-of-sky magnetic field strength (B pos) of 18 ± 7 μG and an observed mass-to-flux ratio (λ obs) of 3.5 ± 2.4, suggesting that L 1512 is magnetically supercritical. However, the absence of significant infall motion and the presence of an oscillating envelope are inconsistent with the magnetically supercritical condition. Using a virial analysis, we suggest the presence of a hitherto hidden line-of-sight magnetic field strength of ~27 μG with a mass-to-flux ratio (λ tot) of ~1.6, in which case both magnetic and kinetic pressures are important in supporting the L 1512 core. On the other hand, L 1512 may have just reached supercriticality and will collapse at any time.

Keywords: interstellar magnetic fields; interstellar medium; molecular clouds; polarimetry; submillimeter astronomy; star forming regions; star formation; starlight polarization
Thermal Wave Instability as an Origin of Gap and Ring Structures in Protoplanetary Disks

Recent millimeter and infrared observations have shown that gap- and ring-like structures are common in both dust thermal emission and scattered light of protoplanetary disks. We investigate the impact of the so-called thermal wave instability (TWI) on the millimeter and infrared scattered light images of disks. We perform 11D simulations of the TWI and confirm that the TWI operates when the disk is optically thick enough for stellar light, i.e., small-grain-to-gas mass ratio of 0.0001. The midplane temperature varies as the waves propagate, and hence gap and ring structures can be seen in both millimeter and infrared emission. The millimeter substructures can be observed even if the disk is fully optically thick since it is induced by the temperature variation, while density-induced substructures would disappear in the optically thick regime. The fractional separation between TWI-induced ring and gap is r/r 0.20.4 at 1050 au, which is comparable to those found by the Atacama Large Millimeter/submillimeter Array. Due to the temperature variation, snow lines of volatile species move radially and multiple snow lines are observed even for a single species. The wave propagation velocity is as fast as 0.6 au yr1, which can be potentially detected with a multiepoch observation with a time separation of a few years.

Keywords: protoplanetary disks; planet formation