adsabs/SciX_UAT_keywords huggingface dataset:
Resolving the Inner Parsec of the Blazar J1924-2914 with the Event Horizon Telescope

The blazar J1924-2914 is a primary Event Horizon Telescope (EHT) calibrator for the Galactic center's black hole Sagittarius A*. Here we present the first total and linearly polarized intensity images of this source obtained with the unprecedented 20 μas resolution of the EHT. J1924-2914 is a very compact flat-spectrum radio source with strong optical variability and polarization. In April 2017 the source was observed quasi-simultaneously with the EHT (April 5-11), the Global Millimeter VLBI Array (April 3), and the Very Long Baseline Array (April 28), giving a novel view of the source at four observing frequencies, 230, 86, 8.7, and 2.3 GHz. These observations probe jet properties from the subparsec to 100 pc scales. We combine the multifrequency images of J1924-2914 to study the source morphology. We find that the jet exhibits a characteristic bending, with a gradual clockwise rotation of the jet projected position angle of about 90° between 2.3 and 230 GHz. Linearly polarized intensity images of J1924-2914 with the extremely fine resolution of the EHT provide evidence for ordered toroidal magnetic fields in the blazar compact core.

Keywords: active galactic nuclei; active galaxies; blazars; jets; high energy astrophysics; very long baseline interferometry; radio interferometry
New Detections of Phosphorus Molecules toward Solar-type Protostars

Phosphorus is a necessary element for life on Earth, but at present, we have limited constraints on its chemistry in star- and planet-forming regions; to date, phosphorus carriers have only been detected toward a few low-mass protostars. Motivated by an apparent association between phosphorus molecule emission and outflow shocking, we used the IRAM 30 m telescope to target PN and PO lines toward seven solar-type protostars with well-characterized outflows and firmly detected phosphorus molecules in three new sources. This sample, combined with archival observations of three additional sources, enables the first exploration of the demographics of phosphorus chemistry in low-mass protostars. The sources with PN detections show evidence for strong outflow shocks based on their H2O 110-101 fluxes. On the other hand, no protostellar properties or bulk outflow mechanical properties are found to correlate with the detection of PN. This implies that gas-phase phosphorus is specifically linked to shocked gas within the outflows. Still, the PN and PO line kinematics suggest an emission origin in postshocked gas rather than directly shocked material. Despite sampling a wide range of protostellar properties and outflow characteristics, we find a fairly narrow range of source-averaged PO/PN ratios (0.6-2.2) and volatile P abundances as traced by (PN+PO)/CH3OH (~1%-3%). Spatially resolved observations are needed to further constrain the emission origins and environmental drivers of the phosphorus chemistry in these sources.

Keywords: astrochemistry; interstellar molecules; protostars
Comparative Analysis of TRGBs (CATs) from Unsupervised, Multi-halo-field Measurements: Contrast is Key

The tip of the red giant branch (TRGB) is an apparent discontinuity of the luminosity function (LF) due to the end of the red giant evolutionary phase and is used to measure distances in the local universe. In practice, tip localization via edge detection response (EDR) relies on several methods applied on a case-by-case basis. It is hard to evaluate how individual choices affect a distance estimation using only a single host field while also avoiding confirmation bias. To devise a standardized approach, we compare unsupervised, algorithmic analyses of the TRGB in multiple halo fields per galaxy. We first optimize methods for the lowest field-to-field dispersion, including spatial filtering, smoothing, and weighting of LF, color band selection, and tip selection based on the number of likely RGB stars and the ratio of stars below versus above the tip (R). We find R, which we call the tip contrast, to be the most important indicator of the quality of EDR measurements; higher R selection can decrease field-to-field dispersion. Further, since R is found to correlate with the age or metallicity of the stellar population based on theoretical modeling, it might result in a displacement of the detected tip magnitude. We find a tip-contrast relation with a slope of -0.023 ± 0.0046 mag/ratio, an ~5σ result that can be used to correct these variations in the detections. When using TRGB to establish a distance ladder, consistent TRGB standardization using tip-contrast relation across rungs is vital to make robust cosmological measurements.

Keywords: distance indicators; stellar distance; standard candles
Revisiting the Integrated Star Formation Law. II. Starbursts and the Combined Global Schmidt Law

We compile observations of molecular gas contents and infrared-based star formation rates (SFRs) for 112 circumnuclear star-forming regions, in order to reinvestigate the form of the disk-averaged Schmidt surface density star-formation law in starbursts. We then combine these results with total gas and SFR surface densities for 153 nearby nonstarbursting disk galaxies from de los Reyes & Kennicutt (2019), to investigate the properties of the combined star formation law, following Kennicutt (1998). We confirm that the combined Schmidt law can be fitted with a single power law with slope n = 1.5 ± 0.05 (including fitting method uncertainties), somewhat steeper than the value n = 1.4 ± 0.15 found by Kennicutt. Fitting separate power laws to the nonstarbursting and starburst galaxies, however, produces very different slopes (n = 1.34 ± 0.07 and 0.98 ± 0.07, respectively), with a pronounced offset in the zero-point (∼0.6 dex) of the starburst relation to higher SFR surface densities. This offset is seen even when a common conversion factor between CO intensity and molecular hydrogen surface density is applied, and it is confirmed when disk surface densities of interstellar dust are used as proxies for gas measurements. Tests for possible systematic biases in the starburst data fail to uncover any spurious sources for such a large offset. We tentatively conclude that the global Schmidt law in galaxies, at least as it is conventionally measured, is bimodal or possibly multimodal. Possible causes may include changes in the small-scale structure of the molecular interstellar medium or the stellar initial mass function. A single n ∼ 1.5 power law still remains as a credible approximation or "recipe" for analytical or numerical models of galaxy formation and evolution.

Keywords: disk galaxies; galaxy evolution; spiral galaxies; interacting galaxies; luminous infrared galaxies; starburst galaxies; blue compact dwarf galaxies; star formation; interstellar dust
The Energy Sources of Double-peaked Superluminous Supernova PS1-12cil and Luminous Supernova SN 2012aa

In this paper, we present the study of the energy reservoir powering the light curves (LCs) of PS1-12cil and SN 2012aa, which are superluminous and luminous supernovae (SNe), respectively. The multiband and bolometric LCs of these two SNe show unusual secondary bumps after the main peaks. The two-peaked LCs cannot be explained by any simple energy-source models (e.g., the 56Ni cascade decay model, the magnetar spindown model, or the ejecta-circumstellar medium interaction model). Therefore, we employ the 56Ni plus ejecta-circumstellar medium (CSM) interaction (CSI) model, the magnetar plus CSI model, and the double CSI model to fit their bolometric LCs, and find that both these two SNe can be explained by the double CSI model and the magnetar plus CSI model. Based on the modeling, we calculate the the time when the shells were expelled by the progenitors: provided that they were powered by double ejecta-shell CSI, the inner and outer shells might be expelled ∼0.2-3.6 and ∼2-25 yr before the explosions of the SNe, respectively; the shells were expelled ∼2-20 yr before the explosions of the SNe if they were powered by magnetars plus CSI.

Keywords: supernovae; magnetars; circumstellar matter; stellar mass loss
SOLES. VII. The Spin-Orbit Alignment of WASP-106 b, a Warm Jupiter along the Kraft Break

Although close-orbiting, massive exoplanets-known as hot and warm Jupiters-are among the most observationally accessible known planets, their formation pathways are still not universally agreed upon. One method to constrain the possible dynamical histories of such planets is to measure the systems' sky-projected spin-orbit angles using the Rossiter-McLaughlin effect. By demonstrating whether planets orbit around the stellar equator or on offset orbits, Rossiter-McLaughlin observations offer clues as to whether the planet had a quiescent or violent formation history. Such measurements are, however, only a reliable window into the history of the system if the planet in question orbits sufficiently far from its host star; otherwise, tidal interactions with the host star can erase evidence of past dynamical upheavals. We present a WIYN/NEID Rossiter-McLaughlin measurement of the tidally detached ( ${\boldsymbol{a}}/{R}_{* }={13.18}_{-0.37}^{+0.35}$ ) warm Jupiter WASP-106 b, which orbits a star along the Kraft break (T eff = 6002 ± 164 K). We find that WASP-106 b is consistent with a low spin-orbit angle ( $\lambda ={6}_{-16}^{+17}\,^\circ $ and $\psi ={26}_{-17}^{+12}\,^\circ $ ), suggesting a relatively quiescent formation history for the system. We conclude by comparing the stellar obliquities of hot and warm Jupiter systems, with the WASP-106 system included, to gain insight into the possible formation routes of these populations of exoplanets.

Keywords: planetary alignment; exoplanet dynamics; star-planet interactions; exoplanets; planetary theory; exoplanet systems
High-fidelity Reaction Kinetic Modeling of Hot-Jupiter Atmospheres Incorporating Thermal and UV Photochemistry Enhanced by Metastable CO(a3Π)

A detailed modeling of simultaneous UV-photochemical and thermochemical processes in exoplanet atmosphere-like conditions is essential for the analysis and interpretation of a vast amount of current and future spectral data from exoplanets. However, a detailed reaction kinetic model that incorporates both UV photochemistry and thermal chemistry is challenging due to the massive size of the chemical system as well as the lack of understanding of photochemistry compared to thermal-only chemistry. Here, we utilize an automatic chemical reaction mechanism generator to build a high-fidelity thermochemical reaction kinetic model later then incorporated with UV photochemistry enhanced by metastable triplet-state carbon monoxide (a3Π). Our model results show that two different photochemical reactions driven by Lyα photons (i.e., H2 + CO(a3Π) → H + HCO and CO(X1Σ+) + CO(a3Π) → C(3P) + CO2) can enhance thermal chemistry resulting in significant increases in the formation of CH4, H2O, and CO2 in H2-dominated systems with trace amounts of CO, which qualitatively matches the observations from previous experimental studies. Our model also suggests that at temperatures above 2000 K, thermal chemistry becomes the dominant process. Finally, the chemistry simulated up to 2500 K does not produce any larger species such as C3 species, benzene, or larger (i.e., PAHs). This might indicate that the photochemistry of C2 species such as C2H2 might play a key role in the formation of organic aerosols observed in a previous experimental study.

Keywords: exoplanet atmospheres; exoplanet atmospheric composition; theoretical models; hot jupiters; planetary atmospheres; astrochemistry
Solar Tachocline Confinement by the Nonaxisymmetric Modes of a Dynamo Magnetic Field

We recently presented the first 3D numerical simulation of the solar interior for which tachocline confinement was achieved by a dynamo-generated magnetic field. In this follow-up study, we analyze the degree of confinement as the magnetic field strength changes (controlled by varying the magnetic Prandtl number) in a coupled radiative zone (RZ) and convection zone (CZ) system. We broadly find three solution regimes, corresponding to weak, medium, and strong dynamo magnetic field strengths. In the weak-field regime, the large-scale magnetic field is mostly axisymmetric with regular, periodic polarity reversals (reminiscent of the observed solar cycle) but fails to create a confined tachocline. In the strong-field regime, the large-scale field is mostly nonaxisymmetric with irregular, quasi-periodic polarity reversals and creates a confined tachocline. In the medium-field regime, the large-scale field resembles a strong-field dynamo for extended intervals but intermittently weakens to allow temporary epochs of strong differential rotation. In all regimes, the amplitude of poloidal field strength in the RZ is very well explained by skin-depth arguments, wherein the oscillating field that gives rise to the skin depth (in the medium- and strong-field cases) is a nonaxisymmetric field structure at the base of the CZ that rotates with respect to the RZ. These simulations suggest a new picture of solar tachocline confinement by the dynamo, in which nonaxisymmetric, very long-lived (effectively permanent) field structures rotating with respect to the RZ play the primary role, instead of the regularly reversing axisymmetric field associated with the 22 yr cycle.

Keywords: solar dynamo; solar differential rotation; solar radiative zone; solar convective zone; solar interior
The Late-Epoch, Matter-Bounded Spectrum of the Nova V1405 Cassiopeiae

Optical and near-infrared spectra of the classical nova V1405 Cassiopeiae (V1405 Cas) from more than two years after outburst show a still bright nova of intermediate excitation with coronal lines, some high-ionization but non-coronal forbidden lines, and very strong emission features of He II. However, the common nebular lines of [N II], [O II], and [O III] are absent and the lines of He I are very weak. Analysis with the photoionization code CLOUDY indicates a emission line region that is sharply matter-bounded, truncating before the gas excitation drops sufficiently to support the parent ions of lower excitation lines.

Keywords: classical novae
A Generalized Phase Diversity Technique Using Multiple Defocused Images

Phase diversity techniques commonly employ a pair of focused-defocused images to retrieve the incident wave front and to restore the observed scene. However, the combination of more images, each one affected by a different amount of defocus, has been barely explored in solar astronomy. In this work we reformulate the "classic" two-images phase diversity approach to accommodate an arbitrary number of phase differences and we investigate its performance in synthetic magnetohydrodynamical simulations of the solar scene corrupted by noise and degraded by a certain set of aberrations. We employ different combinations of images defocused from ±0.5 λ up to ±2 λ (peak to peak) and compare both the retrieved wave front with the incident one and the restored images with the unaberrated noiseless scene. We investigate the effect of using a series of images defocused both symmetrically and asymmetrically with respect to the focused one. In these two cases the performance of the method is improved with the use of more than two images, although it benefits more from the use of symmetric defocuses. We find also that there is a qualitative best choice of the number of phase diversity images in terms of the goodness of the wave front retrieval and of the restored object. The presented method has a potential use either in instruments equipped with a refocusing mechanism or during the laboratory calibrations of the instrument provided that an optical target can be defocused manually by different amounts.

Keywords: astronomical techniques; astronomical instrumentation; solar instruments
A Dust Trap in the Young Multiple System HD 34700

Millimeter observations of disks around young stars reveal substructures indicative of gas pressure traps that may aid grain growth and planet formation. We present Submillimeter Array observations of HD 34700: two Herbig Ae stars in a close binary system (Aa/Ab, ∼0.25 au), surrounded by a disk presenting a large cavity and spiral arms seen in scattered light, and two distant, lower-mass companions. These observations include 1.3 mm continuum emission and the 12CO 2-1 line at ∼0"5 (178 au) resolution. They resolve a prominent azimuthal asymmetry in the continuum and Keplerian rotation of a circumbinary disk in the 12CO line. The asymmetry is located at a radius of 155+11-7 au, consistent with the edge of the scattered-light cavity, being resolved in both radius (72 +14-15 au) and azimuth (FWHM = 64°+8-7). The strong asymmetry in millimeter continuum emission could be evidence for a dust trap, together with the more symmetric morphology of 12CO emission and small grains. We hypothesize an unseen circumbinary companion responsible for the cavity in scattered light and creating a vortex at the cavity edge that manifests in dust trapping. The disk mass has limitations imposed by the detection of 12CO and nondetection of 13CO. We discuss its consequences for the potential past gravitational instability of this system, likely accounting for the rapid formation of a circumbinary companion. We also report the discovery of resolved continuum emission associated with HD 34700B (projected separation ∼1850 au), which we explain through a circumstellar disk.

Keywords: protoplanetary disks; circumstellar disks; planetary system formation; circumstellar dust; interferometry; submillimeter astronomy
Stabilization of Dayside Surface Liquid Water via Tropopause Cold Trapping on Arid Slowly Rotating Tidally Locked Planets

Terrestrial-type exoplanets orbiting nearby red dwarf stars (M dwarfs) are among the best targets for atmospheric characterization and biosignature searches in the near future. Recent evolutionary studies have suggested that terrestrial planets in the habitable zone of M dwarfs are probably tidally locked and have limited surface water inventories as a result of their host stars' high early luminosities. Several previous climate simulations of such planets have indicated that their remaining water would be transported to the planet's permanent nightside and become trapped as surface ice, leaving the dayside devoid of water. Here we use a three-dimensional general circulation model with a water cycle and accurate radiative transfer scheme to investigate the surface water evolution on slowly rotating tidally locked terrestrial planets with limited surface water inventories. We show that there is a competition for water trapping between the nightside surface and the substellar tropopause in this type of climate system. Although under some conditions the surface water remains trapped on the nightside as an ice sheet, in other cases liquid water stabilizes in a circular area in the substellar region as a wetland. Planets with 1 bar N2 and atmospheric CO2 levels greater than 0.1 bar retain stable dayside liquid water, even with very small surface water inventories. Our results reveal the diversity of possible climate states on terrestrial-type exoplanets and highlight the importance of surface liquid water detection techniques for future characterization efforts.

Keywords: astrobiology; computational methods; atmospheric circulation; extrasolar rocky planets; water vapor; exoplanet atmospheres
Searching for TeV Gamma-Ray Emission from SGR 1935+2154 during Its 2020 X-Ray and Radio Bursting Phase

Magnetar hyperflares are the most plausible explanation for fast radio bursts (FRBs)-enigmatic powerful radio pulses with durations of several milliseconds and high brightness temperatures. The first observational evidence for this scenario was obtained in 2020 April when an FRB was detected from the direction of the Galactic magnetar and soft gamma-ray repeater SGR 1935+2154. The FRB was preceded by two gamma-ray outburst alerts by the BAT instrument aboard the Swift satellite, which triggered follow-up observations by the High Energy Stereoscopic System (H.E.S.S.). H.E.S.S. observed SGR 1935+2154 for 2 hr on 2020 April 28. The observations are coincident with X-ray bursts from the magnetar detected by INTEGRAL and Fermi-GBM, thus providing the first very high energy gamma-ray observations of a magnetar in a flaring state. High-quality data acquired during these follow-up observations allow us to perform a search for short-time transients. No significant signal at energies E > 0.6 TeV is found, and upper limits on the persistent and transient emission are derived. We here present the analysis of these observations and discuss the obtained results and prospects of the H.E.S.S. follow-up program for soft gamma-ray repeaters.

Keywords: soft gamma-ray repeaters; radio transient sources; gamma-rays; high energy astrophysics; magnetars; gamma-ray sources; burst astrophysics; gamma-ray transient sources; gamma-ray telescopes; gamma-ray astronomy
Firmamento: A Multimessenger Astronomy Tool for Citizen and Professional Scientists

Firmamento (https://firmamento.hosting.nyu.edu) is a new-concept, web-based, and mobile-friendly data analysis tool dedicated to multifrequency/multimessenger emitters, as exemplified by blazars. Although initially intended to support a citizen researcher project at New York University–Abu Dhabi, Firmamento has evolved to be a valuable tool for professional researchers due to its broad accessibility to classical and contemporary multifrequency open data sets. From this perspective Firmamento facilitates the identification of new blazars and other multifrequency emitters in the localization uncertainty regions of sources detected by current and planned observatories such as Fermi-LAT, Swift, eROSITA, CTA, ASTRI Mini-Array, LHAASO, IceCube, KM3Net, SWGO, etc. The multiepoch and multiwavelength data that Firmamento retrieves from over 90 remote and local catalogs and databases can be used to characterize the spectral energy distribution and the variability properties of cosmic sources as well as to constrain physical models. Firmamento distinguishes itself from other online platforms due to its high specialization, the use of machine learning and other methodologies to characterize the data, and for its commitment to inclusivity. From this particular perspective, its objective is to assist both researchers and citizens interested in science, strengthening a trend that is bound to gain momentum in the coming years as data retrieval facilities improve in power and machine-learning/artificial-intelligence tools become more widely available.

Keywords: astronomy software; astronomy data analysis; astronomy databases