adsabs/SciX_UAT_keywords huggingface dataset:
Cold Deuterium Fractionation in the Nearest Planet-forming Disk

Deuterium fractionation provides a window into the thermal history of volatiles in the solar system and protoplanetary disks. While evidence of active molecular deuteration has been observed toward a handful of disks, it remains unclear whether this chemistry affects the composition of forming planetesimals due to limited observational constraints on the radial and vertical distribution of deuterated molecules. To shed light on this question, we introduce new Atacama Large Millimeter/submillimeter Array observations of DCO+ and DCN J = 2-1 at an angular resolution of 0.″5 (30 au) and combine them with archival data of higher energy transitions toward the protoplanetary disk around TW Hya. We carry out a radial excitation analysis assuming both LTE and non-LTE to localize the physical conditions traced by DCO+ and DCN emission in the disk, thus assessing deuterium fractionation efficiencies and pathways at different disk locations. We find similar disk-averaged column densities of 1.9 × 1012 and 9.8 × 1011 cm-2 for DCO+ and DCN, with typical kinetic temperatures for both molecules of 20-30 K, indicating a common origin near the comet- and planet-forming midplane. The observed DCO+/DCN abundance ratio, combined with recent modeling results, provide tentative evidence of a gas-phase C/O enhancement within <40 au. Observations of DCO+ and DCN in other disks, as well as HCN and HCO+, will be necessary to place the trends exhibited by TW Hya in context, and fully constrain the main deuteration mechanisms in disks.

Keywords: protoplanetary disks; planet formation; isotopic abundances; astrochemistry
The Curious Case of the Chromospherically (and Isochronally) Candescent K Stars

A significant fraction of apparently isochronally young, chromospherically active (UV-luminous) K and early-M stars appear to have anomalous kinematics and display weak X-ray emission. We demonstrate that the combination of UV excesses, X-ray fluxes, and newly available rotation rates from the TESS mission can potentially serve to assess the youth (or lack thereof) of these candidate pre-main sequence field stars. This approach holds promise for purposes of distinguishing between "bona fide" young, low-mass stars and "imposters"—overluminous, UV-bright ZAMS or evolved main sequence stars—and could shed light on why the latter might masquerade as the former.

Keywords: stellar evolution
The NANOGrav 15 yr Data Set: Detector Characterization and Noise Budget

Pulsar timing arrays (PTAs) are galactic-scale gravitational wave (GW) detectors. Each individual arm, composed of a millisecond pulsar, a radio telescope, and a kiloparsecs-long path, differs in its properties but, in aggregate, can be used to extract low-frequency GW signals. We present a noise and sensitivity analysis to accompany the NANOGrav 15 yr data release and associated papers, along with an in-depth introduction to PTA noise models. As a first step in our analysis, we characterize each individual pulsar data set with three types of white-noise parameters and two red-noise parameters. These parameters, along with the timing model and, particularly, a piecewise-constant model for the time-variable dispersion measure, determine the sensitivity curve over the low-frequency GW band we are searching. We tabulate information for all of the pulsars in this data release and present some representative sensitivity curves. We then combine the individual pulsar sensitivities using a signal-to-noise ratio statistic to calculate the global sensitivity of the PTA to a stochastic background of GWs, obtaining a minimum noise characteristic strain of 7 × 10-15 at 5 nHz. A power-law-integrated analysis shows rough agreement with the amplitudes recovered in NANOGrav's 15 yr GW background analysis. While our phenomenological noise model does not model all known physical effects explicitly, it provides an accurate characterization of the noise in the data while preserving sensitivity to multiple classes of GW signals.

Keywords: millisecond pulsars; pulsar timing method; gravitational wave astronomy; gravitational wave detectors; radio astronomy
Extragalactic Magnetism with SOFIA (SALSA Legacy Program): The Magnetic Fields in the Multiphase Interstellar Medium of the Antennae Galaxies

Mergers are thought to be a fundamental channel for galaxy growth, perturbing the gas dynamics and the magnetic fields (B-fields) in the interstellar medium (ISM). However, the mechanisms that amplify and dissipate B-fields during a merger remain unclear. We characterize the morphology of the ordered B-fields in the multiphase ISM of the closest merger of two spiral galaxies, the Antennae galaxies. We compare the inferred B-fields using 154 μm thermal dust and 11 cm radio synchrotron emission polarimetric observations. We find that the 154 μm B-fields are more ordered across the Antennae galaxies than the 11 cm B-fields. The turbulent-to-ordered 154 μm B-field increases at the galaxy cores and star-forming regions. The relic spiral arm has an ordered spiral 154 μm B-field, while the 11 cm B-field is radial. The 154 μm B-field may be dominated by turbulent dynamos with high 12CO(1-0) velocity dispersion driven by star-forming regions, while the 11 cm B-field is cospatial with high H I velocity dispersion driven by galaxy interaction. This result shows the dissociation between the warm gas mainly disturbed by the merger, and the dense gas still following the dynamics of the relic spiral arm. We find a ~8.9 kpc scale ordered B-field connecting the two galaxies. The base of the tidal tail is cospatial with the H I and 12CO(1-0) emission and has compressed and/or sheared 154 μm and 11 cm B-fields driven by the merger. We suggest that amplified B-fields, with respect to the rest of the system and other spiral galaxies, may be supporting the gas flow between both galaxies and the tidal tail. * SALSA provides a software repository at https://github.com/galmagfields/hawc, and publicly available data at http://galmagfields.com/.

Keywords: galaxy mergers; astrophysical magnetism; extragalactic magnetic fields; star formation; polarimetry; dust continuum emission; radio continuum emission; galaxy evolution
Oxygen-enhanced Extremely Metal-poor Damped Lyα Systems: A Signpost of the First Stars?

We present precise abundance determinations of two near-pristine damped Lyα systems (DLAs) to assess the nature of the [O/Fe] ratio at [Fe/H] < -3.0 (i.e., <1/1000 of the solar metallicity). Prior observations indicate that the [O/Fe] ratio is consistent with a constant value, [O/Fe] ≃ +0.4, when -3 < [Fe/H] < -2, but this ratio may increase when [Fe/H] ≲ -3. In this paper, we test this picture by reporting new, high-precision [O/Fe] abundances in two of the most metal-poor DLAs currently known. We derive values of [O/Fe] = +0.50 ± 0.10 and [O/Fe] = +0.62 ± 0.05 for these two z ≃ 3 near-pristine gas clouds. These results strengthen the idea that the [O/Fe] abundances of the most metal-poor DLAs are elevated compared to DLAs with [Fe/H] ≳ -3. We compare the observed abundance pattern of the latter system to the nucleosynthetic yields of Population III supernovae (SNe), and find that the enrichment can be described by a (19-25) M⊙ Population III SN that underwent a (0.9-2.4) × 1051 erg explosion. These high-precision measurements showcase the behavior of [O/Fe] in the most metal-poor environments. Future high-precision measurements in new systems will contribute to a firm detection of the relationship between [O/Fe] and [Fe/H]. These data will reveal whether we are witnessing a chemical signature of enrichment from Population III stars and allow us to rule out contamination from Population II stars.

Keywords: damped lyman-alpha systems; intergalactic medium; population iii stars; population ii stars; chemical abundances
Quantifying Uncertainties on the Tip of the Red Giant Branch Method

We present an extensive grid of numerical simulations quantifying the uncertainties in measurements of the tip of the red giant branch (TRGB). These simulations incorporate a luminosity function composed of 2 mag of red giant branch (RGB) stars leading up to the tip, with asymptotic giant branch (AGB) stars contributing exclusively to the luminosity function for at least a magnitude above the RGB tip. We quantify the sensitivity of the TRGB detection and measurement to three important error sources: (1) the sample size of stars near the tip, (2) the photometric measurement uncertainties at the tip, and (3) the degree of self-crowding of the RGB population. The self-crowding creates a population of supra-TRGB stars due to the blending of one or more RGB stars just below the tip. This last population is ultimately difficult, although still possible, to disentangle from true AGB stars. In the analysis given here, the precepts and general methodology as used in the Chicago-Carnegie Hubble Program (CCHP) have been followed. However, in the appendix, we introduce and test a set of new tip detection kernels, which internally incorporate self-consistent smoothing. These are generalizations of the two-step model used by the CCHP (smoothing followed by Sobel-filter tip detection), where the new kernels are based on successive binomial-coefficient approximations to the derivative-of-a-Gaussian edge-detector, as is commonly used in modern digital image processing.

Keywords: red giant stars; distance indicators
X-Ray Spectral Analysis of the Jet Termination Shock in Pictor A on Subarcsecond Scales with Chandra

Hot spots observed at the edges of extended radio lobes in high-power radio galaxies and quasars mark the position of mildly relativistic termination shock, where the jet bulk kinetic energy is converted to the internal energy of the jet particles. These are the only astrophysical systems where mildly relativistic shocks can be directly resolved at various wavelengths of the electromagnetic spectrum. The western hot spot in the radio galaxy Pictor A is an exceptionally good target in this respect, due to the combination of its angular size and high surface brightness. In our previous work, after a careful Chandra image deconvolution, we resolved this hot spot into a disk-like feature perpendicular to the jet axis, and identified it as the front of the jet termination shock. We argued for a synchrotron origin of the observed X-ray photons, which implied electron energies reaching at least 10-100 TeV at the shock front. Here, we present a follow-up on that analysis, proposing, in particular, a novel method for constraining the shape of the X-ray continuum emission with subarcsecond resolution. The method is based on a Chandra hardness map analysis, using separately deconvolved maps in the soft and hard X-ray bands. In this way, we have found there is a systematic, yet statistically significant gradient in the hardness ratio across the shock, such that the implied electron energy index ranges from s ≤ 2.2 at the shock front to s > 2.7 in the near downstream. We discuss the implications of the obtained results for a general understanding of particle acceleration at mildly relativistic shocks.

Keywords: non-thermal radiation sources; active galaxies; radio galaxies; relativistic jets; x-ray sources; x-ray photometry; x-ray quasars; shocks
Continuum Enhancements, Line Profiles, and Magnetic Field Evolution during Consecutive Flares

During solar flares, magnetic energy can be converted into electromagnetic radiation from radio waves to γ-rays. Enhancements in the continuum at visible wavelengths, as well as continuum enhancements in the FUV and NUV passbands, give rise to white-light flares. In addition, the strong energy release in these events can lead to the rearrangement of the magnetic field at the photospheric level, causing morphological changes in large and stable magnetic structures like sunspots. In this context, we describe observations acquired by satellite instruments (Interface Region Imaging Spectrograph (IRIS), Solar Dynamics Observatory/Helioseismic and Magnetic Imager, Hinode/Solar Optical Telescope) and ground-based telescopes (Rapid Oscillations in the Solar Atmosphere (ROSA)/Dunn Solar Telescope) during two consecutive C7.0 and X1.6 flares that occurred in active region NOAA 12205 on 2014 November 7. The flare was accompanied by an eruption. The results of the analysis show the presence of continuum enhancements during the evolution of the events, observed both in ROSA images and in IRIS spectra. In the latter, a prominent blueshifted component is observed at the onset of the eruption. We investigate the role played by the evolution of the δ sunspots of the active region in the flare triggering, and finally we discuss the changes in the penumbrae surrounding these sunspots as a further consequence of these flares.

Keywords: solar flares; solar white-light flares; solar magnetic reconnection; active solar chromosphere; solar chromosphere; solar photosphere; solar transition region; solar ultraviolet emission; solar magnetic fields; high resolution spectroscopy
The MAVERIC Survey: New Compact Binaries Revealed by Deep Radio Continuum Observations of the Galactic Globular Cluster Terzan 5

Owing to its massive, dense core, Terzan 5 has the richest population of millisecond pulsars (MSPs) known among Galactic globular clusters. Here we report new deep 2-8 GHz radio continuum observations of Terzan 5 obtained with the Karl G. Jansky Very Large Array. We have identified a total of 24 sources within the cluster half-light radius, including 17 within the core radius. Nineteen are associated with previously studied MSPs and X-ray binaries. Three of the new radio sources have steep radio spectra and are located within the cluster core, as expected for MSPs. These three sources have hard X-ray photon indices (Γ = 1.3-1.5) and highly variable X-ray emission, suggesting they are binary MSPs belonging to the spider class. For the most X-ray luminous of these sources, the redback spider classification is confirmed by its X-ray light curve, which shows an orbital period of 12.32 hr and double-peaked structure around X-ray maximum. The likely discovery of bright binary MSPs in a well-studied cluster like Terzan 5 highlights how deep radio continuum imaging can complement pulsar search and timing observations in finding probable eclipsing systems. The other new radio source in the core has a flat radio spectrum and is X-ray faint ( ${L}_{X}\approx 2\times {10}^{31}$ erg s-1) with a photon index Γ = 2.1 ± 0.5, consistent with the properties expected for a quiescent stellar-mass black hole X-ray binary.

Keywords: millisecond pulsars; globular star clusters; radio continuum emission; surveys; catalogs
How Long-lived Grains Dominate the Shape of the Zodiacal Cloud

Grain–grain collisions shape the three-dimensional size and velocity distribution of the inner Zodiacal Cloud and the impact rates of dust on inner planets, yet they remain the least understood sink of zodiacal dust grains. For the first time, we combine the collisional grooming method combined with a dynamical meteoroid model of Jupiter-family comets (JFCs) that covers 4 orders of magnitude in particle diameter to investigate the consequences of grain–grain collisions in the inner Zodiacal Cloud. We compare this model to a suite of observational constraints from meteor radars, the Infrared Astronomical Satellite, mass fluxes at Earth, and inner solar probes, and use it to derive the population and collisional strength parameters for the JFC dust cloud. We derive a critical specific energy of ${Q}_{D}^{* }=5\times {10}^{5}\pm 4\times {10}^{5}\,{R}_{\mathrm{met}}^{-0.24}$ J kg‑1 for particles from JFC particles, making them 2–3 orders of magnitude more resistant to collisions than previously assumed. We find that the differential power-law size index ‑4.2 ± 0.1 for particles generated by JFCs provides a good match to observed data. Our model provides a good match to the mass-production rates derived from the Parker Solar Probe observations and their scaling with the heliocentric distance. The higher resistance to collisions of dust particles might have strong implications to models of collisions in solar and exosolar dust clouds. The migration via Poynting–Robertson drag might be more important for denser clouds, the mass-production rates of astrophysical debris disks might be overestimated, and the mass of the source populations might be underestimated. Our models and code are freely available online.

Keywords: meteoroids; micrometeoroids; zodiacal cloud; exozodiacal dust; short period comets; comets; interplanetary dust; meteoroid dust clouds; dynamical evolution; impact phenomena
Simulation of Head-on Collisions between Filamentary Molecular Clouds Threaded by a Lateral Magnetic Field and Subsequent Evolution

Filamentary molecular clouds are regarded as the place where newborn stars form. In particular, a hub region, a place where it appears as if several filaments are colliding, often indicates active star formation. To understand the star formation in filament structures, we investigate the collisions between two filaments using two-dimensional magnetohydrodynamical simulations. As a model of filaments, we assume that the filaments are in magnetohydrostatic equilibrium under a global magnetic field perpendicular to the filament axis. We set two identical filaments with an infinite length and make them collide with a zero-impact parameter (head-on). When the two filaments collide while sharing the same magnetic flux, we found two types of evolution after a merged filament is formed: runaway radial collapse and stable oscillation with a finite amplitude. The condition for the radial collapse is independent of the collision velocity and is given by the total line mass of the two filaments exceeding the magnetically critical line mass for which no magnetohydrostatic solution exists. The radial collapse proceeds in a self-similar manner, resulting in a unique distribution irrespective of the various initial line masses of the filament, as the collapse progresses. When the total line mass is less massive than the magnetically critical line mass, the merged filament oscillates, and the density distribution is well-fitted by a magnetohydrostatic equilibrium solution. The condition necessary for the radial collapse is also applicable to the collision whose direction is perpendicular to the global magnetic field.

Keywords: molecular clouds; interstellar filaments; magnetic fields; magnetohydrodynamical simulations; star formation
Betatron Acceleration of Suprathermal Electrons Upstream of the Martian Bow Shock

Betatron acceleration, a plasma process obtaining particle energy in the perpendicular direction but reserving energy in the field-aligned direction, is the consequence of magnetic strength enhancement when the first adiabatic invariant is conserved. Such process has been widely reported in the terrestrial magnetosphere but is barely reported in other planetary environments. Here, based on the in situ measurements from the Mars Atmosphere and Volatile Evolution mission, we report two events of betatron acceleration upstream of the Martian bow shock. In both events, betatron accelerations increase the fluxes of suprathermal electrons. The acceleration processes in these events are quantitatively reproduced with an analytical model. Gratifyingly, we find the acceleration factors derived from the analytical model are well consistent with the observations of magnetic strength enhancement. These results for the first time show that the betatron acceleration is an active upstream of the Martian bow shock and is very useful to help us understand the generation of energetic electrons in the Martian environment.

Keywords: mars; planetary magnetospheres; magnetic fields; space plasmas; interplanetary particle acceleration
Measurement of Galactic 26Al with the Compton Spectrometer and Imager

The Compton Spectrometer and Imager (COSI) is a balloon-borne compact Compton telescope designed to survey the 0.2-5 MeV sky. COSI's energy resolution of ~0.2% at 1.8 MeV, single-photon reconstruction, and wide field of view make it capable of studying astrophysical nuclear lines, particularly the 1809 keV γ-ray line from decaying Galactic 26Al. Most 26Al originates in massive stars and core-collapse supernova nucleosynthesis, but the path from stellar evolution models to Galaxy-wide emission remains unconstrained. In 2016, COSI had a successful 46 day flight on a NASA superpressure balloon. Here, we detail the first search for the 1809 keV 26Al line in the COSI 2016 balloon flight using a maximum-likelihood analysis. We find a Galactic 26Al flux of (8.6 ± 2.5) × 10-4 ph cm-2 s-1 within the Inner Galaxy (∣ℓ∣ ≤ 30°, ∣b∣ ≤ 10°) with 3.7σ significance above background. Within uncertainties, this flux is consistent with expectations from previous measurements by SPectrometer on INTEGRAL (SPI) and the Compton Telescope on the Compton Gamma-Ray Observatory (COMPTEL). This analysis demonstrates COSI's powerful capabilities for studies of γ-ray lines and underscores the scientific potential of future compact Compton telescopes. In particular, the next iteration of COSI as a NASA Small Explorer satellite has recently been approved for launch in 2025.

Keywords: gamma-ray lines; gamma-ray telescopes; stellar nucleosynthesis; high altitude balloons; astronomy data modeling
Experimental and Theoretical Radiative Parameters of Highly Excited Odd-parity Levels in Ir II

Using the time-resolved laser-induced fluorescence technique, the radiative lifetimes for 15 odd-parity levels from 47,003 to 61,475 cm-1 in Ir II were measured. To the best of our knowledge, 11 lifetime results among these levels are reported for the first time, and hence they should be a good complement to the measured lifetime data of 10 levels previously published in the literature. The pseudorelativistic Hartree-Fock including core-polarization corrections method was used to calculate the lifetimes and branching fractions (BFs) of the investigated energy levels. Combining the experimental lifetime with the theoretical BFs, the transition probabilities and oscillator strengths for 124 transitions were determined.

Keywords: atomic spectroscopy; atomic physics; transition probabilities; radiative processes
Revealing Multiple Nested Molecular Outflows with Rotating Signatures in HH270mms1-A with ALMA

We present molecular line observations of the protostellar outflow associated with HH270mms1 in the Orion B molecular cloud with ALMA. The 12CO (J = 3‑2) emissions show that the outflow velocity structure consists of four distinct components of low (≲10 km s‑1), intermediate (∼10–25 km s‑1) and high (≳40 km s‑1) velocities in addition to the entrained gas velocity (∼25–40 km s‑1). The high- and intermediate-velocity flows have well-collimated structures surrounded by the low-velocity flow. The chain of knots is embedded in the high-velocity flow or jet, which is the evidence of episodic mass ejections induced by time-variable mass accretion. We could detect the velocity gradients perpendicular to the outflow axis in both the low- and intermediate-velocity flows. We confirmed the rotation of the envelope and disk in the 13CO and C17O emission and found that their velocity gradients are the same as those of the outflow. Thus, we concluded that the velocity gradients in the low- and intermediate-velocity flows are due to the outflow rotation. Using observational outflow properties, we estimated the outflow launching radii to be 67.1–77.1 au for the low-velocity flow and 13.3–20.8 au for the intermediate-velocity flow. Although we could not detect the rotation in the jets due to the limited spatial resolution, we estimated the jet launching radii to be (2.36–3.14) × 10‑2 au using the observed velocity of each knot. Thus, the jet is driven from the inner disk region. We could identify the launching radii of distinct velocity components within a single outflow with all the prototypical characteristics expected from recent theoretical works.

Keywords: protostars; star formation