adsabs/SciX_UAT_keywords huggingface dataset:
A Channel to Form Fast-spinning Black Hole–Neutron Star Binary Mergers as Multimessenger Sources. II. Accretion-induced Spin-up

In this work, we investigate an alternative channel for the formation of fast-spinning black hole–neutron star (BHNS) binaries, in which super-Eddington accretion is expected to occur in accreting BHs during the stable mass transfer phase within BH-stripped helium (BH–He-rich) star binary systems. We evolve intensive MESA grids of close-orbit BH–He-rich star systems to systematically explore the projected aligned spins of BHs in BHNS binaries, as well as the impact of different accretion limits on the tidal disruption probability and electromagnetic (EM) signature of BHNS mergers. Most of the BHs in BHNS mergers cannot be effectively spun up through accretion if the accretion rate is limited to $\lesssim 10\,{\dot{M}}_{\mathrm{Edd}}$ , where ${\dot{M}}_{\mathrm{Edd}}$ is the standard Eddington accretion limit. In order to reach high spins (e.g., χ BH ≳ 0.5), the BHs are required to be born less massive (e.g., ≲3.0 M ⊙) in binary systems with initial periods of ≲0.2–0.3 days and accrete material at $\sim 100\,{\dot{M}}_{\mathrm{Edd}}$ . However, even under this high accretion limit, ≳6 M ⊙ BHs are typically challenging to significantly spin up and generate detectable associated EM signals. Our population simulations suggest that different accretion limits have a slight impact on the ratio of tidal disruption events. However, as the accretion limit increases, the EM counterparts from the cosmological BHNS population can become bright overall.

Keywords: gravitational waves; close binary stars; black holes; neutron stars
The XMM-Newton Line Emission Analysis Program (X-LEAP). I. Emission-line Survey of O VII, O VIII, and Fe L-shell Transitions

The XMM-Newton Line Emission Analysis Program (X-LEAP) is designed to study diffuse X-ray emissions from the Milky Way (MW) hot gas, as well as emissions from the foreground solar wind charge exchange (SWCX). This paper presents an all-sky survey of spectral feature intensities corresponding to the O VII, O VIII, and iron L-shell (Fe-L) emissions. These intensities are derived from 5418 selected XMM-Newton observations with long exposure times and minimal contamination from point or extended sources. For 90% of the measured intensities, the values are within ≈2–18 photons cm‑2 s‑1 sr‑1 (line unit (LU)), ≈0–8 LU, and ≈0–9 LU, respectively. We report long-term variations in O VII and O VIII intensities over 22 yr, closely correlating with the solar cycle and attributed to SWCX emissions. These variations contribute ∼30% and ∼20% to the observed intensities on average and peak at ≈4 and ≈1 LU during solar maxima. We also find evidence of short-term and spatial variations in SWCX, indicating the need for a more refined SWCX model in future studies. In addition, we present SWCX- and absorption-corrected all-sky maps for a better view of the MW hot gas emission. These maps show a gradual decrease in oxygen intensity moving away from the Galactic center and a concentration of Fe-L intensity in the Galactic bubbles and disk.

Keywords: diffuse x-ray background; circumgalactic medium; solar wind
Hidden Gems on a Ring: Infant Massive Clusters and Their Formation Timeline Unveiled by ALMA, HST, and JWST in NGC 3351

We use 0.1″ observations from the Atacama Large Millimeter Array (ALMA), Hubble Space Telescope (HST), and JWST to study young massive clusters (YMCs) in their embedded "infant" phase across the central starburst ring in NGC 3351. Our new ALMA data reveal 18 bright and compact (sub-)millimeter continuum sources, of which 8 have counterparts in JWST images and only 6 have counterparts in HST images. Based on the ALMA continuum and molecular line data, as well as ancillary measurements for the HST and JWST counterparts, we identify 14 sources as infant star clusters with high stellar and/or gas masses (∼105 M ⊙), small radii (≲ 5 pc), large escape velocities (6–10 km s‑1), and short freefall times (0.5–1 Myr). Their multiwavelength properties motivate us to divide them into four categories, likely corresponding to four evolutionary stages from starless clumps to exposed H II region–cluster complexes. Leveraging age estimates for HST-identified clusters in the same region, we infer an evolutionary timeline, ranging from ∼1–2 Myr before cluster formation as starless clumps, to ∼4–6 Myr after as exposed H II region–cluster complexes. Finally, we show that the YMCs make up a substantial fraction of recent star formation across the ring, exhibit a nonuniform azimuthal distribution without a very coherent evolutionary trend along the ring, and are capable of driving large-scale gas outflows.

Keywords: star clusters; interstellar medium; star formation; barred spiral galaxies; ring galaxies; galaxy nuclei; molecular gas
Experimental Determination of the Dissociative Recombination Rate Coefficient for Rotationally Cold CH+ and Its Implications for Diffuse Cloud Chemistry

Observations of CH+ are used to trace the physical properties of diffuse clouds, but this requires an accurate understanding of the underlying CH+ chemistry. Until this work, the most uncertain reaction in that chemistry was dissociative recombination (DR) of CH+. Using an electron-ion merged-beams experiment at the Cryogenic Storage Ring, we have determined the DR rate coefficient of the CH+ electronic, vibrational, and rotational ground state applicable for different diffuse cloud conditions. Our results reduce the previously unrecognized order-of-magnitude uncertainty in the CH+ DR rate coefficient to ~20% and are applicable at all temperatures relevant to diffuse clouds, ranging from quiescent gas to gas locally heated by processes such as shocks and turbulence. Based on a simple chemical network, we find that DR can be an important destruction mechanism at temperatures relevant to quiescent gas. As the temperature increases locally, DR can continue to be important up to temperatures of ~600 K, if there is also a corresponding increase in the electron fraction of the gas. Our new CH+ DR rate-coefficient data will increase the reliability of future studies of diffuse cloud physical properties via CH+ abundance observations.

Keywords: diffuse molecular clouds; laboratory astrophysics; electron recombination reactions; reaction rates
How Switchbacks Can Maintain a Longer Time in the Interplanetary Space

Parker Solar Probe, the closest spacecraft to the Sun, has renewed our understanding of the solar corona and the interplanetary space. One of its important findings is the prevalence of switchbacks, which display localized magnetic reversals along the otherwise Parker spirals. While some switchbacks might disappear quickly, others can maintain for a long period of time, and there are indications that many switchbacks strengthen from the solar corona to the interplanetary space despite their magnetic tension force, which tends to straighten the magnetic field lines. Therefore, how these switchbacks could be maintained for a long period of time remains a mystery. In this paper, we employed a 3D data-driven global full magnetohydrodynamics numerical model to explore the evolution of switchbacks formed in the dynamic corona. Our simulations indicate that two factors can affect the lifetime of a switchback. One factor is the combination of angle and leg length ensures that the switchback with greater curvature after reconnection can last longer, and the greater the angle, the more magnetic field lines that can be reconnected, and thus the longer the duration. We call this influencing factor flux tube shape factor. The other factor is the velocity shear, i.e., when the solar wind at the convex-outward turning of a switchback is faster than that at the concave-outward turning, the switchback becomes enhanced during propagation, and it weakens when the velocity difference is opposite.

Keywords: magnetohydrodynamical simulations; solar wind
Target Selection and Validation of DESI Emission Line Galaxies

The Dark Energy Spectroscopic Instrument (DESI) will precisely constrain cosmic expansion and the growth of structure by collecting ~40 million extragalactic redshifts across ~80% of cosmic history and one-third of the sky. The Emission Line galaxy (ELG) sample, which will comprise about one-third of all DESI tracers, will be used to probe the universe over the 0.6 < z < 1.6 range, including the 1.1 < z < 1.6 range, which is expected to provide the tightest constraints. We present the target selection for the DESI Survey Validation (SV) and Main Survey ELG samples, which relies on the imaging of the Legacy Surveys. The Main ELG selection consists of a g-band magnitude cut and a (g - r) versus (r - z) color box, while the SV selection explores extensions of the Main selection boundaries. The Main ELG sample is composed of two disjoint subsamples, which have target densities of about 1940 deg-2 and 460 deg-2, respectively. We first characterize their photometric properties and density variations across the footprint. We then analyze the DESI spectroscopic data that have been obtained from 2020 December to 2021 December in the SV and Main Survey. We establish a preliminary criterion for selecting reliable redshifts, based on the [O II] flux measurement, and assess its performance. Using this criterion, we are able to present the spectroscopic efficiency of the Main ELG selection, along with its redshift distribution. We thus demonstrate that the Main selection 1940 deg-2 subsample alone should provide 400 deg-2 and 460 deg-2 reliable redshifts in the 0.6 < z < 1.1 and the 1.1 < z < 1.6 ranges, respectively.

Keywords: emission line galaxies; surveys; large-scale structure of the universe
Comparing Globular Cluster System Properties with Host Galaxy Environment

We present Hubble Space Telescope photometry in the optical (F475X) and near-infrared (F110W) bands of the globular cluster (GC) systems of the inner halos of a sample of 15 massive elliptical galaxies. The targets are selected from the volume-limited MASSIVE survey, and chosen to sample a range of environments from sparsely populated groups to the brightest cluster galaxies in dense clusters. We also present a quantitative model of the relation between (F475X - F110W) color and cluster metallicity [M/H], using simulated GCs. Because much of the GC population in such galaxies is built up through accretion, the metallicity distribution of the GC systems might be expected to vary with galaxy environment. The photometry is used to create a completeness-corrected metallicity distribution for each galaxy in the sample, and to fit a double Gaussian curve to each histogram in order to model the two standard red and blue subpopulations. Finally, the properties of the GC metallicity distribution are correlated against galaxy environment. We find that almost no GCS properties and host galaxy environmental properties are correlated, with the exception of a weak but consistent correlation between blue fraction and nth-nearest-neighbor surface density. The results suggest that the systemic properties of the GC systems, at least in the inner to midhalo regions, are influenced more strongly by the local environment at early times, rather than by the environmental properties we see today. * 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 NAS5-26555. These observations are associated with programs 14219 and 15265.

Keywords: elliptical galaxies; galaxy formation; galaxy stellar halos; globular star clusters
Constraining the CME Core Heating and Energy Budget with SOHO/UVCS

We describe the energy budget of a coronal mass ejection (CME) observed on 1999 May 17 with the Ultraviolet Coronagraph Spectrometer (UVCS). We constrain the physical properties of the CME's core material as a function of height along the corona by using the spectra taken by the single-slit coronagraph spectrometer at heliocentric distances of 2.6 and 3.1 solar radii. We use plasma diagnostics from intensity ratios, such as the O VI doublet lines, to determine the velocity, density, temperature, and nonequilibrium ionization states. We find that the CME core's velocity is approximately 250 km s-1, and its cumulative heating energy is comparable to its kinetic energy for all of the plasma heating parameterizations that we investigated. Therefore, the CME's unknown heating mechanisms have the energy to significantly affect the CME's eruption and evolution. To understand which parameters might influence the unknown heating mechanism, we constrain our model heating rates with the observed data and compare them to the rate of heating generated within a similar CME that was constructed by the MAS code's 3D MHD simulation. The rate of heating from the simulated CME agrees with our observationally constrained heating rates when we assume a quadratic power law to describe a self-similar CME expansion. Furthermore, the heating rates agree when we apply a heating parameterization that accounts for the CME flux rope's magnetic energy being converted directly into thermal energy. This UVCS analysis serves as a case study for the importance of multislit coronagraph spectrometers for CME studies.

Keywords: spectroscopy; solar coronal mass ejections; solar ultraviolet emission; plasma astrophysics; spectrometers
Spectral Structures of Type II Solar Radio Bursts and Solar Energetic Particles

We investigated the relationship between the spectral structures of type II solar radio bursts in the hectometric and kilometric wavelength ranges and solar energetic particles (SEPs). To examine the statistical relationship between type II bursts and SEPs, we selected 26 coronal mass ejection (CME) events with similar characteristics (e.g., initial speed, angular width, and location) observed by the Large Angle and Spectrometric Coronagraph, regardless of the characteristics of the corresponding type II bursts and the SEP flux. Then, we compared associated type II bursts observed by the Radio and Plasma Wave Experiment on board the Wind spacecraft and the SEP flux observed by the Geostationary Operational Environmental Satellite orbiting around the Earth. We found that the bandwidth of the hectometric type II bursts and the peak flux of the SEPs has a positive correlation (with a correlation coefficient of 0.64). This result supports the idea that the nonthermal electrons of type II bursts and the nonthermal ions of SEPs are generated by the same shock and suggests that more SEPs may be generated for a wider or stronger CME shock with a longer duration. Our result also suggests that considering the spectral structures of type II bursts can improve the forecasting accuracy for the peak flux of gradual SEPs.

Keywords: interplanetary physics; solar radio emission; solar flares; solar coronal radio emission; interplanetary shocks; the sun; heliosphere; radio astrometry; solar coronal mass ejections; solar energetic particles; interplanetary particle acceleration
The Statistical Properties of Spiral Arms in Nearby Disk Galaxies

We analyze 4378 nearby bright disk (S0 and spiral) galaxies selected from the Sloan Digital Sky Survey to characterize their spiral structure and systematically investigate the relationships between spiral arm properties (strength, pitch angle, and number) and the global properties of the host galaxies. This is to date the largest sample of galaxies with comprehensive measurements of spiral properties based on Fourier decomposition. We find that spiral pitch angle decreases (arms become more tightly wound) toward galaxies of earlier Hubble type, higher stellar mass, redder color, and greater degree of central concentration. The dependence of pitch angle on stellar mass is mainly driven by color, and for a given concentration, spiral arms are more tightly wound in redder galaxies. Spiral pitch angles show a bimodal distribution, peaking at φ = 12° ± 3°4 and 23° ± 4°3. Spiral arms weaken in galaxies of earlier type, redder color, and higher concentration, but for a given concentration, spiral arms become more prominent in more massive and bluer galaxies. We confirm that spiral arm strength loosely correlates with pitch angle, although the scatter in this relation is considerable and depends systematically on mass and color; for a given pitch angle, more massive or bluer galaxies have stronger arms. Galaxies of earlier Hubble type, higher mass concentration, or redder color have fewer spiral arms. Lastly, galaxies with stronger bars have fewer but stronger arms. We discuss the possible origins of these various relationships, which provide useful empirical guidance to theories of spiral structure. Depending on the galaxy, both the density wave and swing amplification mechanisms operate.

Keywords: galaxy evolution; galaxy formation; spiral galaxies; hubble classification scheme; spiral pitch angle; galaxy structure
New Ammonia Masers in the High-mass Star-forming Region Sgr B2(N)

We report a systemic search for nonmetastable NH3 masers toward a high-mass star-forming region Sgr B2(N) using the Shanghai 65 m Tianma radio telescope with its Ku-band (12-18 GHz) and K-band (18-26.5 GHz) receivers. A total of 18 maser emission transitions were detected, and eight of these are newly identified NH3 maser transitions in interstellar space. Most (five) of the new maser transitions were found from the Ku-band observations which were absent from previous searches. Rotation diagram analysis for the 18 quasi-thermal transitions derived a high gas kinematic temperature (∼400 K) and an extremely high H2 column density (∼5 × 1025 cm-2). Such conditions suggest that the NH3 masers are likely pumped by vibrational excitation. Compared with quiet maser activity observed more than 20 yr ago, NH3 masers may be bursting in our observation time when the gas kinematic temperature might increase from ∼150 to ∼400 K. As extreme conditions (either high gas kinematic temperature and/or high gas column density) are required to excite nonmetastable NH3 masers, it can be argued that the detected NH3 maser outburst may be linked to a more intensive accretion-burst event from an high-mass young stellar object in the Sgr B2(N) region.

Keywords: interstellar masers; interstellar line emission; molecular clouds; molecular gas; molecular spectroscopy; star formation; galactic center
Bright-mode Emission from PSR B0823+26 Using the Five-hundred-meter Aperture Spherical Radio Telescope

Using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), we have recorded over 1.2 × 104 single pulses from PSR B0823+26 (J0826+2637) at 1.25 GHz with 500 MHz bandwidth. These high-sensitivity observations detected with FAST are unprecedented. We investigated potentially interesting emission features by analyzing the polarimetric individual pulses during the bright state. The average pulse profile has a weak postcursor component and a wide interpulse along with a narrow main pulse. The pulse energy distribution of the main pulse shows the presence of triple emission modes. When the emission ceases in the main pulse component, low-level emission in the interpulse component is detected, whereas the absence of any emission in the postcursor component is shown. In the postcursor emission region, bright pulses are detected in 422 rotations with the relative pulse energy described by a power-law distribution with index of -2.52 ± 0.09, while the peak flux density ratio appears to follow a logarithmic normal distribution. The intervals between bright pulses can be described with a Poisson process with the occurrence rate estimated to be one bright pulse every 14 s. The fluctuation spectral analysis reveals the existence of a form of periodic amplitude modulation unrelated to subpulse drifting in both the main pulse and interpulse components. Furthermore, the modulation patterns in the main pulse and interpulse are found to be locked in pulse longitude, signifying some information transfer between the two magnetic polar regions.

Keywords: radio pulsars
Tracking X-Ray Source Movement in a Retracting Flux Tube

Solar flares produce sources of localized, enhanced X-ray emission, thought to be due to the acceleration of nonthermal electrons and the transport of energy away from the reconnection site. The 2002 November 28 C1.6 limb flare showed clear X-ray source motion in the Reuven Ramaty High Energy Solar Spectroscopic Imager observations at 3-10 keV propagating from the apex of the flaring arcade, down toward the footpoints, and then rising back into the corona. Previous work attempted to model this motion using simulations driven by heating with an electron beam or thermal conduction front, finding reasonable agreement only if there were large initial densities. This work extends the previous model by considering a flux tube that retracts through a current sheet away from a magnetic reconnection site. The retraction model includes drag to slow motion in the current sheet, which allows us to vary the energy released by the retraction. This retraction causes a dense and superhot plug of material to form at the loop apex, naturally causing a thermal X-ray source to form in the corona. We find that the observed X-ray source motion, however, is most likely thermal and a signature of the evaporation fronts after initially filling the flux tube.

Keywords: magnetohydrodynamical simulations; solar x-ray flares; solar flare spectra
Duffing Oscillator Model of Solar Cycles

We propose that the solar cycle variability could be described in the framework of an external quasi-sinusoidal influence on an oscillator with cubic nonlinearity and linear damping (Duffing oscillator). To demonstrate this, we compare the empirical amplitude-frequency dependence with the theoretical one obtained by the Krylov-Bogolyubov averaging method. The empirical data are a composite time series of 2.0 version of sunspot number series, which starts in 1700, and the sunspot group number series by Svalgaard & Schatten, scaled to sunspot number, for 1610-1699 interval. We find that while this interpretation of solar cycle is a mathematical approximation, it explains several properties of solar cycle variability.

Keywords: solar cycle; maunder minimum; analytical mathematics
The X-Ray Outburst of the Galactic Center Magnetar over Six Years of Chandra Observations

The magnetar SGR J1745-2900, discovered at a distance of parsecs from the Milky Way central black hole, Sagittarius A⋆, represents the closest pulsar to a supermassive black hole ever detected. Furthermore, its intriguing radio emission has been used to study the environment of the black hole, as well as to derive a precise position and proper motion for this object. The discovery of SGR J1745-2900 has led to interesting debates about the number, age, and nature of pulsars expected in the Galactic center region. In this work, we present extensive X-ray monitoring of the outburst of SGR J1745-2900 using the Chandra X-ray Observatory, the only instrument with the spatial resolution to distinguish the magnetar from the supermassive black hole (2"4 angular distance). It was monitored from its outburst onset in 2013 April until 2019 August, collecting more than 50 Chandra observations for a total of more than 2.3 Ms of data. Soon after the outburst onset, the magnetar emission settled onto a purely thermal emission state that cooled from a temperature of about 0.9-0.6 keV over 6 yr. The pulsar timing properties showed at least two changes in the period derivative, increasing by a factor of about 4 during the outburst decay. We find that the long-term properties of this outburst challenge current models for the magnetar outbursts.

Keywords: neutron stars; magnetars; pulsars