adsabs/SciX_UAT_keywords huggingface dataset:
Local Molecular Gas toward the Aquila Rift Region

We present the results of a ∼250 square degrees CO mapping (+26° ≲ l ≲ +50° and -5° ≲ b ≲ +5°) toward the Aquila Rift region at a spatial resolution of ∼50″ and a grid spacing of 30″. The high dynamic range CO maps with a spectral resolution of ∼0.2 km s-1 display highly structured molecular cloud (MC) morphologies with valuable velocity information, revealing complex spatial and dynamical features of the local molecular gas. In combination with the MWISP CO data and the Gaia DR2, distances of the main MC structures in the local ISM are well determined toward the Aquila Rift region. We find that the total MC mass within 1 kpc is about ≳4.1 × 105 ${M}_{\odot }$ in the whole region. In fact, the mass of the molecular gas is dominated by the W40 giant molecular cloud (GMC) at ∼474 pc (∼1.4 × 105 ${M}_{\odot }$ ) and the GMC complex G036.0+01.0 at ∼560-670 pc (∼2.0 × 105 ${M}_{\odot }$ ), while the MCs at ∼220-260 pc have gas masses of ∼102-103 ${M}_{\odot }$ . Interestingly, an ∼80 pc long filamentary MC G044.0-02.5 at a distance of ∼404 pc shows a systematic velocity gradient along and perpendicular to the major axis of the filament. The H I gas with enhanced emission has similar spatial morphologies and velocity features compared to the corresponding CO structure, indicating that large-scale converging H I flows are probably responsible for the formation of the MC. Meanwhile, the long filamentary MC consists of many sub-filaments with lengths ranging from ∼0.5 pc to several pc, as well as prevalent networks of filaments in other large-scale local MCs.

Keywords: interstellar medium; molecular clouds; star formation; surveys; interstellar dynamics; interstellar molecules; stellar-interstellar interactions
A Study of Ten Early-type Contact Binary Stars in the Small Magellanic Cloud

To study early-type binary systems in different evolutionary stages or environments, the Small Magellanic Cloud (SMC) is an ideal laboratory due to its low metallicity compared to that of the Milky Way. We conduct a study on the period changes of the close binary systems with B-type spectral classifications in the SMC using OGLE collections. Ten B-type binaries that show no significant periodic variations based on the current observational data were analyzed. Through O - C analysis, four of the ten early-type binaries show a long-term period decrease, one shows a long-term period increase, and the other five systems are ambiguous due to the limitations of the observational data. Among the period-decreasing systems, two may be mainly caused by mass transfer, while the rest may be caused by angular momentum loss. The Wilson-Devinney code (W-D method) is used to analyze their I-band photometric light curves. According to the W-D results, five early-type binaries are in the deep contact state, three are in the shallow contact state, while two are in the medium contact state, and the temperature ratios of these early-type binaries are all close to unity. The five deep contact binaries are highly unstable systems and therefore serve as important objects for the study of binary mergers. Finally, a discussion on the evolution of early-type binary stars is conducted by combining the analyses of the light curves and the periodic changes of ten early-type binaries, that implies that the majority of early-type binaries in the SMC may form contact binaries from a phase of rapid mass transfer.

Keywords: small magellanic cloud; contact binary stars; eclipsing binary stars; early stellar evolution
Simulating Atomic Dark Matter in Milky Way Analogs

Dark sector theories naturally lead to multicomponent scenarios for dark matter where a subcomponent can dissipate energy through self-interactions, allowing it to efficiently cool inside galaxies. We present the first cosmological hydrodynamical simulations of Milky Way analogs where the majority of dark matter is collisionless cold dark matter (CDM) but a subcomponent (6%) is strongly dissipative minimal atomic dark matter (ADM). The simulations, implemented in GIZMO and utilizing FIRE-2 galaxy formation physics to model the standard baryonic sector, demonstrate that the addition of even a small fraction of dissipative dark matter can significantly impact galactic evolution despite being consistent with current cosmological constraints. We show that ADM gas with roughly standard model-like masses and couplings can cool to form a rotating "dark disk" with angular momentum closely aligned with the visible stellar disk. The morphology of the disk depends sensitively on the parameters of the ADM model, which affect the cooling rates in the dark sector. The majority of the ADM gas gravitationally collapses into dark "clumps" (regions of black hole or mirror star formation), which form a prominent bulge and a rotating thick disk in the central galaxy. These clumps form early and quickly sink to the inner ~kiloparsec of the galaxy, affecting the galaxy's star formation history and present-day baryonic and CDM distributions.

Keywords: dark matter; dark matter distribution; milky way dark matter halo; baryon density; galaxy rotation curves; hydrodynamical simulations; n-body simulations
Metrics for Optimizing Searches for Tidally Decaying Exoplanets

Tidal interactions between short-period exoplanets and their host stars drive orbital decay and have likely led to engulfment of planets by their stars. Precise transit timing surveys, with baselines now spanning decades for some planets, are directly detecting orbital decay for a handful of planets, with corroboration for planetary engulfment coming from independent lines of evidence. More than that, recent observations have perhaps even caught the moment of engulfment for one unfortunate planet. These portentous signs bolster prospects for ongoing surveys, but optimizing such a survey requires considering the astrophysical parameters that give rise to robust timing constraints and large tidal decay rates, as well as how best to schedule observations conducted over many years. The large number of possible targets means it is not feasible to continually observe all planets that might exhibit detectable tidal decay. In this study, we explore astrophysical and observational properties for a short-period exoplanet system that can maximize the likelihood for observing tidally driven transit timing variations. We consider several fiducial observational strategies and real exoplanet systems reported to exhibit decay. We show that moderately frequent (a few transits per year) observations may suffice to detect tidal decay within just a few years. Tidally driven timing variations take time to grow to detectable levels, so we estimate how long that growth takes as a function of timing uncertainties and tidal decay rate and provide thresholds for deciding that tidal decay has been detected.

Keywords: exoplanet dynamics; star-planet interactions; transit timing variation method
On the Energy-specific Photodissociation Pathways of 14N2 and 14N15N Isotopomers to N Atoms of Different Reactivity: A Quantum Dynamical Perspective

Photodissociation of the nitrogen molecule in the vacuum ultraviolet (VUV) is a major source of reactive nitrogen atoms in the upper atmosphere of Earth and throughout the solar system. Recent experimental studies have revealed strong energy dependence of the VUV photodissociation branching ratios to the N(4S3/2)+N(2D J ) and N(4S3/2)+N(2P J ) product channels, the primary dissociation pathways in the 108,000-116,000 cm-1 energy region. This produces N(2D J ) and N(2P J ) excited atoms that differ significantly in their chemical reactivity. The branching ratios oscillate with increase in the VUV excitation energy. We use high-level ab initio quantum chemistry to compute the potential curves of 17 electronic excited states and their nonadiabatic and spin-orbit couplings. The dynamics follow the sequential evolution from the optically excited but bound ${}^{1}{{\rm{\Sigma }}}_{u}^{+}$ singlets. Spin-orbit coupling enables transfer to the dissociative triplet and quintet states. We compute the photodissociation yields through the dense manifold of electronic states leading to both exit channels. The dynamical simulations accurately capture the branching oscillations and enable a detailed look into the photodissociation mechanism. The major contribution to the dissociation is through the two lowest 3Π u states. However, for both isotopomers, at about 110,000 cm-1 there is an abnormally low dissociation rate into the N(4S3/2)+N(2P J ) channel that enables comparable participation of triplet ${}^{3}{{\rm{\Sigma }}}_{u}^{-}$ and quintet 5Π u electronic states. This leads to the first peak in the branching ratio. At higher energies, trapping of the population in the 33Π u bound triplet state occurs. This favors dissociation to the lower-energy N(4S3/2)+N(2D J ) channel and results in the observed second switch in branching ratios.

Keywords: cosmochemistry; small molecules; ultraviolet spectroscopy; isotopic abundances; reaction rates; theoretical models; photodissociation reactions
Simultaneous Magnetic Polar Cap Heating during a Flaring Episode from the Magnetar 1RXS J170849.0-400910

During a pointed 2018 NuSTAR observation, we detected a flare with a 2.2 hr duration from the magnetar 1RXS J170849.0-400910. The flare, which rose in ∼25 s to a maximum flux 6 times larger than the persistent emission, is highly pulsed with an rms pulsed fraction of 53%. The pulse profile shape consists of two peaks separated by half a rotational cycle, with a peak flux ratio of ∼2. The flare spectrum is thermal with an average temperature of 2.1 keV. Phase-resolved spectroscopy shows that the two peaks possess the same temperature, but differ in size. These observational results, along with simple light curve modeling, indicate that two identical antipodal spots, likely the magnetic poles, are heated simultaneously at the onset of the flare and for its full duration. Hence, the origin of the flare has to be connected to the global dipolar structure of the magnetar. This might best be achieved externally, via twists to closed magnetospheric dipolar field lines seeding bombardment of polar footpoint locales with energetic pairs. Approximately 1.86 hr following the onset of the flare, a short burst with its own 3 minutes thermal tail occurred. The burst tail is also pulsating at the spin period of the source and phase-aligned with the flare profile, implying an intimate connection between the two phenomena. The burst may have been caused by a magnetic reconnection event in the same twisted dipolar field lines anchored to the surface hot spots, with subsequent return currents supplying extra heat to these polar caps.

Keywords: neutron stars; magnetars; x-ray bursts
Toward Optimal Signal Extraction for Imaging X-Ray Polarimetry

We describe an optimal signal extraction process for imaging X-ray polarimetry using an ensemble of deep neural networks. The initial photoelectron angle, used to recover the polarization, has errors following a von Mises distribution. This is complicated by events converting outside of the fiducial gas volume, whose tracks have little polarization sensitivity. We train a deep ensemble of convolutional neural networks to select against these events and to measure event angles and errors for the desired gas-conversion tracks. We show how the expected modulation amplitude from each event gives an optimal weighting to maximize signal-to-noise ratio of the recovered polarization. Applying this weighted maximum likelihood event analysis yields sensitivity (MDP99) improvements of ~10% over earlier heuristic weighting schemes and mitigates the need to adjust said weighting for the source spectrum. We apply our new technique to a selection of astrophysical spectra, including complex extreme examples, and compare the polarization recovery to the current state of the art.

Keywords: polarimetry; convolutional neural networks; astrostatistics; x-ray telescopes; x-ray astronomy
Magnetic Fields in the Massive Star-forming Region GL 437

In this note, I report a R-band polarimetric study on a massive star-forming region GL 437 (a.k.a. AFGL 437) to infer the magnetic field (B-field) geometry of this region. The mean B-field in the diffused region, is found to be parallel to the extended cloud structure and the Galactic plane. I compared present optical polarization results with archival submm results adapted from Curran & Chrysostomou. A flipped field geometry is seen in denser parts of GL 437 which is an interesting finding. An infrared source WK 34 embedded in the cloud is associated with a poorly collimated outflow. These outflows are parallel to the inner field orientation but misaligned with outer B-fields. An investigation of gas kinematics of this region will be carried out to understand if the gas motion have some role in changing the field geometry.

Keywords: interstellar magnetic fields; starlight polarization
Erosion-driven Size Redistribution of Protoplanetary Disk Solids and the Onset of Streaming Instability and Pebble Accretion

The formation of the first planetesimals and the final growth of planetary cores relies on the abundance of small pebbles. The efficiencies of both the streaming instability (SI) process, suggested to catalyze the early growth of planetesimals, and the pebble-accretion process, suggested to accelerate the growth of planetary cores, depend on the sizes of solids residing in the disk. In particular, these processes were found to be sensitive to size distribution of solids, and efficient planetesimal formation and growth through these channels require a limited pebble size distribution. Here we show that aeolian erosion, a process that efficiently grinds down boulders into a mono-sized distribution of pebbles, provides a natural upper limit for the maximal pebble sizes (in terms of their Stokes number). We find the dependence of this upper limit on the radial separation, disk age, turbulence strength, and the grain-size composition of the boulders in the disk. SI is favorable in areas with a Stokes number less than 0.1, which is found in the inner sub-astronomical-unit regions of the disk. This upper limit shapes the size distribution of small pebbles and thereby catalyzes the early onset of planetesimal formation due to SI, and the later core accretion growth through pebble accretion.

Keywords: planet formation; protoplanetary disks; planetesimals
Molecules with ALMA at Planet-forming Scales (MAPS). I. Program Overview and Highlights

Planets form and obtain their compositions in dust- and gas-rich disks around young stars, and the outcome of this process is intimately linked to the disk chemical properties. The distributions of molecules across disks regulate the elemental compositions of planets, including C/N/O/S ratios and metallicity (O/H and C/H), as well as access to water and prebiotically relevant organics. Emission from molecules also encodes information on disk ionization levels, temperature structures, kinematics, and gas surface densities, which are all key ingredients of disk evolution and planet formation models. The Molecules with ALMA at Planet-forming Scales (MAPS) ALMA Large Program was designed to expand our understanding of the chemistry of planet formation by exploring disk chemical structures down to 10 au scales. The MAPS program focuses on five disks-around IM Lup, GM Aur, AS 209, HD 163296, and MWC 480-in which dust substructures are detected and planet formation appears to be ongoing. We observed these disks in four spectral setups, which together cover ~50 lines from over 20 different species. This paper introduces the Astrophysical Journal Supplement's MAPS Special Issue by presenting an overview of the program motivation, disk sample, observational details, and calibration strategy. We also highlight key results, including discoveries of links between dust, gas, and chemical substructures, large reservoirs of nitriles and other organics in the inner disk regions, and elevated C/O ratios across most disks. We discuss how this collection of results is reshaping our view of the chemistry of planet formation.

Keywords: astrochemistry; protoplanetary disks; planet formation; astrobiology; millimeter astronomy; submillimeter astronomy
On the Origin of the Sudden Heliospheric Open Magnetic Flux Enhancement During the 2014 Pole Reversal

Coronal holes are recognized as the primary sources of heliospheric open magnetic flux (OMF). However, a noticeable gap exists between in situ measured OMF and that derived from remote-sensing observations of the Sun. In this study, we investigate the OMF evolution and its connection to solar structures throughout 2014, with special emphasis on the period from September to October, where a sudden and significant OMF increase was reported. By deriving the OMF evolution at 1 au, modeling it at the source surface, and analyzing solar photospheric data, we provide a comprehensive analysis of the observed phenomenon. First, we establish a strong correlation between the OMF increase and the solar magnetic field derived from a potential-field source-surface model (cc Pearson = 0.94). Moreover, we find a good correlation between the OMF and the open flux derived from solar coronal holes (cc Pearson = 0.88), although the coronal holes only contain 14%–32% of the Sun's total open flux. However, we note that while the OMF evolution correlates with coronal hole open flux, there is no correlation with the coronal hole area evolution (cc Pearson = 0.0). The temporal increase in OMF correlates with the vanishing remnant magnetic field at the southern pole, caused by poleward flux circulations from the decay of numerous active regions months earlier. Additionally, our analysis suggests a potential link between the OMF enhancement and the concurrent emergence of the largest active region in solar cycle 24. In conclusion, our study provides insights into the strong increase in OMF observed during 2014 September–October.

Keywords: solar magnetic fields; solar physics; heliosphere
Double Shells of the Planetary Nebula NGC 7009 Minor Axis

We analyzed the minor-axis spectra of the elliptical planetary nebula (PN) NGC 7009 observed with Keck HIRES with a 0.″862 × 10″ slit placed at about 7.″5 and 10″ away from the center and a 0.″862 × 14″ slit at the center. The mean densities derived from the integrated [S II] 6716/6731 Å fluxes along the Keck HIRES slit length indicate a density range of 103.7-104.1 cm-3, while the local densities derived from the slit spectral images show a large local density variation of about 102.8-104.6 cm-3: local densities vary more substantially than values integrated over the line of sight. The expansion rates of the main and outer shells obtained by [S II] are about 21.7 and 30.0 km s-1, respectively. The kinematic results of the [S II] spectral lines correspond to the outermost regions of the two shells and are not representative of the whole PN but are closely related to the other emission lines observed in the shell gas. We conclude that the density contrast leads to the formation of the inner shell, while the change in ionization state leads to the formation of the outer shell. We suggest that the inner main and outer shells result from two successive major ejections. The physical conditions of the central star must have been different when these shells first formed.

Keywords: interstellar medium; planetary nebulae; high resolution spectroscopy
Superparticle Method for Simulating Collisions

For problems in astrophysics, planetary science, and beyond, numerical simulations are often limited to simulating fewer particles than in the real system. To model collisions, the simulated particles (a.k.a. superparticles) need to be inflated to represent a collectively large collisional cross section of real particles. Here we develop a superparticle-based method that replicates the kinetic energy loss during real-world collisions, implement it in an N-body code, and test it. The tests provide interesting insights into dynamics of self-gravitating collisional systems. They show how particle systems evolve over several freefall timescales to form central concentrations and equilibrated outer shells. The superparticle method can be extended to account for the accretional growth of objects during inelastic mergers.

Keywords: n-body simulations; planetesimals; gravitational collapse; planet formation; protoplanetary disks
Hubble Space Telescope and Hyper-Suprime-Cam Weak-lensing Study of the Equal-mass Dissociative Merger CIZA J0107.7+5408

A dissociative merger is formed by the interplay of ram pressure and gravitational forces, which can lead to a spatial displacement of the dark matter and baryonic components of the recently collided subclusters. CIZA J0107.7+5408 is a nearby (z = 0.105) dissociative merger that hosts two X-ray brightness peaks and a bimodal galaxy distribution. Analyzing MMT/Hectospec observations, we investigate the line-of-sight and spatial distribution of cluster galaxies. Utilizing deep, high-resolution Hubble Space Telescope Advanced Camera for Surveys imaging and large field-of-view Subaru Hyper-Suprime-Cam observations, we perform a weak-lensing analysis of CIZA J0107.7+5408. Our weak-lensing analysis detects a bimodal mass distribution that is spatially consistent with the cluster galaxies but significantly offset from the X-ray brightness peaks. Fitting two Navarro-Frenk-White halos to the lensing signal, we find an equal-mass merger with subcluster masses of ${M}_{200,\mathrm{NE}}={2.8}_{-1.1}^{+1.1}\times {10}^{14}$ M ⊙ and ${M}_{200,{SW}}={3.1}_{-1.2}^{+1.2}\times {10}^{14}$ M ⊙. Moreover, the mass-to-light ratios of the subclusters, ${(M/L)}_{\mathrm{NE}}={571}_{-91}^{+89}\ {M}_{\odot }/{L}_{\odot ,B}$ and ${(M/L)}_{\mathrm{SW}}={564}_{-89}^{+87}\ {M}_{\odot }/{L}_{\odot ,B}$ , are found to be consistent with each other and within the range of mass-to-light ratios found for galaxy clusters.

Keywords: weak gravitational lensing; galaxy clusters; dark matter; hubble space telescope
JWST-MIRI Synthetic Photometry Composition using 460 Spitzer-IRS Spectra of Nearby Galaxies

We use extragalactic Spitzer-InfraRed Spectrograph (IRS) spectroscopy to determine the polycyclic aromatic hydrocarbon band, emission line, and stellar and dust continuum contributions to the James Webb Space Telescope (JWST)-Mid-InfraRed Instrument (MIRI) photometric filters, F560W through F1280W, appropriate for z ~ 0 star-forming galaxies. Our data set consists of 460 IRS-SL spectra from 5.25 to 14.8 μm. Of these, 340 are from large radial strips that sample a wide range of environments across three nearby galaxies. We also include 120 spectra from the Spitzer Infrared Nearby Galaxy Survey that are centered on the brightest star-forming regions in 46 nearby galaxies. This large compilation of extragalactic mid-infrared spectra facilitates the interpretation of future work with JWST-MIRI photometry of galaxies.

Keywords: polycyclic aromatic hydrocarbons; dust continuum emission; infrared spectroscopy; infrared photometry