adsabs/SciX_UAT_keywords huggingface dataset:
The JCMT BISTRO Survey: Alignment between Outflows and Magnetic Fields in Dense Cores/Clumps

We compare the directions of molecular outflows of 62 low-mass Class 0 and I protostars in nearby (<450 pc) star-forming regions with the mean orientations of the magnetic fields on 0.05-0.5 pc scales in the dense cores/clumps where they are embedded. The magnetic field orientations were measured using the JCMT POL-2 data taken by the BISTRO-1 survey and from the archive. The outflow directions were observed with interferometers in the literature. The observed distribution of the angles between the outflows and the magnetic fields peaks between 15° and 35°. After considering projection effects, our results could suggest that the outflows tend to be misaligned with the magnetic fields by 50° ± 15° in three-dimensional space and are less likely (but not ruled out) randomly oriented with respect to the magnetic fields. There is no correlation between the misalignment and the bolometric temperatures in our sample. In several sources, the small-scale (1000-3000 au) magnetic field is more misaligned with the outflow than the large-scale magnetic field, suggesting that the small-scale magnetic field has been twisted by the dynamics. In comparison with turbulent MHD simulations of core formation, our observational results are more consistent with models in which the energy densities in the magnetic field and the turbulence of the gas are comparable. Our results also suggest that the misalignment alone cannot sufficiently reduce the efficiency of magnetic braking to enable formation of the observed number of large Keplerian disks with sizes larger than 30-50 au.

Keywords: star formation; star forming regions; protostars; interstellar magnetic fields
Evolution of Dust and Water Ice in Cometary Comae by Radiative Torques

Comets provide unique information about the physical and chemical properties of the environment in which the solar system was formed. Understanding how cometary dust and ice evolve under the effect of sunlight is essential for constraining nuclear structure and triggering the mechanism of comet activity. In this paper, we first study the rotational disruption of dust grains lifted by outgassing from comet nuclei by radiative torques (RATs). We find that composite grains could be rapidly disrupted into small fragments by the RAT disruption mechanism. We then study rotational desorption of ice grains by RATs and find that icy grains could be desorbed from large heliocentric distances, beyond the sublimation radius of water at ${R}_{\mathrm{sub}}({{\rm{H}}}_{2}{\rm{O}})\sim 3\,\mathrm{au}$ . We also calculate the production rate of water vapor versus the heliocentric distance of comets due to rotational desorption. Our results could explain the variation of dust properties and the presence of small grains frequently observed from cometary comae. Finally, we suggest that the activity of distant comets could be triggered by rotational disruption of grains and desorption of water-ice grains at large heliocentric distances.

Keywords: comet nuclei; coma dust; comae; comet volatiles
Polarized Maser Emission with In-source Faraday Rotation

We discuss studies of polarization in astrophysical masers with particular emphasis on the case where the Zeeman splitting is small compared to the Doppler profile, resulting in a blend of the transitions between magnetic substates. A semiclassical theory of the molecular response is derived, and coupled to radiative transfer solutions for 1 and 2-beam linear masers, resulting in a set of nonlinear, algebraic equations for elements of the molecular density matrix. The new code, PRISM, implements numerical methods to compute these solutions. Using PRISM, we demonstrate a smooth transfer between this case and that of wider splitting. For a J = 1-0 system, with parameters based on the v = 1, J = 1-0 transition of SiO, we investigate the behavior of linear and circular polarization as a function of the angle between the propagation axis and the magnetic field, and with the optical depth, or saturation state, of the model. We demonstrate how solutions are modified by the presence of Faraday rotation, generated by various abundances of free electrons, and that strong Faraday rotation leads to additional angles where the Stokes Q changes sign. We compare our results to a number of previous models, from the analytical limits derived by Goldreich, Keeley, and Kwan in 1973, through computational results by W. Watson and coauthors, to the recent work by Lankhaar and Vlemmings in 2019. We find that our results are generally consistent with those of other authors given the differences in the approach and the approximations made.

Keywords: astrophysical masers; silicon monoxide masers; circumstellar masers; radiative transfer; circumstellar envelopes; magnetic fields
Early-time Light Curves of Type Ia Supernovae Observed with TESS

We present the early-time light curves of Type Ia supernovae (SNe Ia) observed in the first six sectors of Transiting Exoplanet Survey Satellite (TESS) data. Ten of these SNe were discovered by ASAS-SN, seven by ATLAS, six by ZTF, and one by Gaia. For nine of these objects with sufficient dynamic range (>3.0 mag from detection to peak), we fit power-law models and searched for signatures of companion stars. We found a diversity of early-time light-curve shapes, although most of our sources are consistent with fireball models where the flux increases as ∝t2. Three SNe displayed a flatter rise with flux ∝t. We did not find any obvious evidence for additional structures, such as multiple power-law components, in the early rising light curves. For assumptions about the SN properties and the observer viewing angle (ejecta mass of 1.4 M⊙, expansion velocity of 104 km s-1, opacity of 0.2 cm2 g-1, and viewing angle of 45°) and a further assumption that any companion stars would be in Roche lobe overflow, it is possible to place upper limits on the radii of any companion stars. Six of the nine SNe had complete coverage of the early-time light curves, and we placed upper limits on the radii of companion stars of ≲32 R⊙ for these SNe, ≲20 R⊙ for five of the six, and ≲4 R⊙ for two of the six. The small sample size did not allow us to put limits on the occurrence rate of companion stars in the progenitors of SNe Ia. However, we expect that TESS observed enough SNe in its two-year primary mission (26 sectors) to either detect the signature of a large companion (R > 20 R⊙) or constrain the occurrence rate of such systems, at least for the fiducial SN properties adopted here. We also show that TESS is capable of detecting emission from a 1 R⊙ companion for an SN Ia within 50 Mpc and has a reasonable chance of doing so after about six years.

Keywords: type ia supernovae; supernovae
A Larger Sample Confirms Small Planets around Hot Stars Are Misaligned

The distribution of stellar obliquities provides critical insight into the formation and evolution pathways of exoplanets. In the past decade, it was found that hot stars hosting hot Jupiters are more likely to have high obliquities than cool stars, but it is not clear whether this trend exists only for hot Jupiters or holds for other types of planets. In this work, we extend the study of the obliquities of hot (6250–7000 K) stars with transiting super-Earth-sized and sub-Neptune-sized planets. We constrain the obliquity distribution based on measurements of the stars' projected rotation velocities. Our sample consists of 170 TESS and Kepler planet-hosting stars and 180 control stars chosen to have indistinguishable spectroscopic characteristics. In our analysis, we find evidence suggesting that the planet hosts have a systematically higher compared to the control sample. This result implies that the planet hosts tend to have lower obliquities. However, the observed difference in is not significant enough to confirm spin–orbit alignment as it is 3.8σ away from perfect alignment. We also find evidence that within the planet-hosting stars there is a trend of higher obliquity (lower ) for the hotter stars (T eff > 6250 K) than for the cooler stars in the sample. This suggests that hot stars hosting smaller planets exhibit a broader obliquity distribution ( ) than cooler planet-hosting stars, indicating that high obliquities are not exclusive to hot Jupiters and instead are more broadly tied to hot stars. ∗ The data presented herein were obtained at the W. M. Keck Observatory, operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation.

Keywords: exoplanets; exoplanet dynamics
The Panchromatic Hubble Andromeda Treasury: Triangulum Extended Region (PHATTER). I. Ultraviolet to Infrared Photometry of 22 Million Stars in M33

We present panchromatic resolved stellar photometry for 22 million stars in the Local Group dwarf spiral Triangulum (M33), derived from Hubble Space Telescope observations with the Advanced Camera for Surveys in the optical (F475W, F814W), and the Wide Field Camera 3 in the near-ultraviolet (F275W, F336W) and near-infrared (F110W, F160W) bands. The large, contiguous survey area covers ∼14 square kpc and extends to 3.5 kpc (14', or 1.5-2 scale lengths) from the center of M33. The PHATTER observing strategy and photometry technique closely mimics that of Panchromatic Hubble Andromeda Treasury, but with updated photometry techniques that take full advantage of all overlapping pointings (aligned to within <5-10 milliarcseconds) and improved treatment of spatially varying point-spread functions. The photometry reaches a completeness-limited depth of F475W∼28.5 in the lowest surface density regions observed in M33 and F475W∼26.5 in the most crowded regions found near the center of M33. We find the young populations trace several relatively tight arms, while the old populations show a clear, looser two-armed structure. We present extensive analysis of the data quality, including artificial star tests to quantify completeness, photometric uncertainties, and flux biases. This stellar catalog is the largest ever produced for M33, and is publicly available for download by the community.

Keywords: triangulum galaxy; stellar populations; local group; multi-color photometry; celestial objects catalogs
Detection and Classification of Astronomical Targets with Deep Neural Networks in Wide-field Small Aperture Telescopes

Wide-field small aperture telescopes are widely used for optical transient observations. Detection and classification of astronomical targets in observed images are the most important and basic step. In this paper, we propose an astronomical target detection and classification framework based on deep neural networks. Our framework adopts the concept of the Faster R-CNN and uses a modified Resnet-50 as a backbone network and a feature pyramid network to extract features from images of different astronomical targets. To increase the generalization ability of our framework, we use both simulated and real observation images to train the neural network. After training, the neural network could detect and classify astronomical targets automatically. We test the performance of our framework with simulated data and find that our framework has almost the same detection ability as that of the traditional method for bright and isolated sources and our framework has two times better detection ability for dim targets, albeit all celestial objects detected by the traditional method can be classified correctly. We also use our framework to process real observation data and find that our framework can improve 25% detection ability than that of the traditional method when the threshold of our framework is 0.6. Rapid discovery of transient targets is quite important and we further propose to install our framework in embedded devices such as the Nvidia Jetson Xavier to achieve real-time astronomical targets detection and classification abilities.

Keywords: classification; convolutional neural networks; transient detection; astrostatistics techniques
Detection of Quasiperiodic Oscillations in the Blazar S4 0954+658 with TESS

We report the detection of several quasiperiodicities around 0.6-2.5 days in the optical emission of the blazar S4 0954+658. The source was observed by the Transiting Exoplanet Survey Satellite in six sectors and it showed these features in all but one of them, with a quasiperiodic oscillation of 1.52 days apparently present in portions of four of them. We used the generalized Lomb-Scargle periodogram method to search for significant signals and we confirmed them using a weighted wavelet transform for time-frequency domain analyses. We discuss several possible explanations for these rapid quasiperiodic variations and suggest that an origin in the innermost part of the accretion disk is most likely. Within this framework, we provide estimates for the mass of the black hole at the core of this blazar.

Keywords: blazars; active galactic nuclei; optical astronomy; black hole physics
A Galaxy Morphology Classification Model Based on Momentum Contrastive Learning

The taxonomy of galaxy morphology plays an important role in astrophysics and provides great help for the study of galaxy evolution. To integrate the advantages of unsupervised learning without labels and supervised learning with high classification accuracy, this paper proposes a galaxy morphology classification model based on a momentum contrastive learning algorithm named Momentum Contrastive Learning Galaxy (MCL-Galaxy), which mainly includes two parts (i) pre-training of the model, where the ResNet_50 backbone network acts as an encoder to learn the galaxy morphology image features, which are stored in the queue and their consistency is ensured by using the momentum contrastive learning algorithm; and (ii) transfer learning, where Mahalanobis distance can assist in improving classification accuracy in downstream tasks where both encoder and queue are transferred. To evaluate the performance of MCL-Galaxy, we use the data set of the Galaxy Zoo challenge project on Kaggle for comparative testing. The experimental results show that the classification accuracy of MCL-Galaxy can reach 90.12%, which is 8.12% higher than the unsupervised state-of-the-art results. Although it is 3.1% lower than the advanced supervised method, it has the advantage of no label and can achieve a higher accuracy rate at the first epoch of classification iteration. This suggests that the gap between unsupervised and supervised representation learning in the field of Galaxy Morphologies classification tasks is well bridged.

Keywords: galaxy classification systems; astronomy data analysis; neural networks
Study of Eclipses for Redback Pulsar J1227-4853

We present a multifrequency study of eclipse properties of a transitional redback millisecond pulsar J1227-4853 discovered in 2014 with the GMRT. Emission from this pulsar is eclipsed at 607 MHz for about 37% of its orbit around the superior conjunction. We observe eclipse ingress and egress transitions that last for 12% and 15% of its orbit, respectively, resulting in only 36% of the orbit being unaffected by eclipsing material. We report an excess dispersion measure (DM) at eclipse boundaries of 0.079(3) pc cm-3, and the corresponding electron column density (Ne) is 24.4(8) × 1016 cm-2. Simultaneous timing and imaging studies suggest that the eclipses in J1227-4853 are not caused by temporal smearing due to excess dispersion and scattering but could be caused by removal of pulsar flux due to cyclotron absorption of the pulsed signal by intra-binary material constraining the companion's magnetic field. Additionally, near the inferior conjunction at orbital phases 0.71 and 0.82 the pulsed emission is significantly delayed, which is associated with a fading of the pulsed and continuum flux densities. At orbital phase ∼0.82, we measure a change in DM of 0.035(3) pc cm-3 and Ne of 10.8(8) × 1016 cm-2 associated with a dimming of up to ∼30% of the peak flux density. Such flux fading around a fixed orbital phase is not reported for other eclipsing binaries. Moreover, this event around the inferior conjunction could be caused by absorption of the pulsed signal by fragmented blobs of plasma generated from mass loss through the L2 Lagrangian point.

Keywords: accretion; binary pulsars; eclipses; millisecond pulsars
Atmospheric Effects on Neutron Star Parameter Constraints with NICER

We present an analysis of the effects of uncertainties in the atmosphere models on the radius, mass, and other neutron star parameter constraints for the NICER observations of rotation-powered millisecond pulsars. To date, NICER has applied the X-ray pulse profile modeling technique to two millisecond-period pulsars: PSR J0030+0451 and the high-mass pulsar PSR J0740+6620. These studies have commonly assumed a deep-heated, fully ionized hydrogen atmosphere model, although they have explored the effects of partial ionization and helium composition in some cases. Here, we extend that exploration and also include new models with partially ionized carbon composition, externally heated hydrogen, and an empirical atmospheric beaming parameterization to explore deviations in the expected anisotropy of the emitted radiation. None of the studied atmosphere cases have any significant influence on the inferred radius of PSR J0740+6620, possibly due to its X-ray faintness, tighter external constraints, and/or viewing geometry. In the case of PSR J0030+0451, both the composition and ionization state could significantly alter the inferred radius. However, based on the evidence (prior predictive probability of the data), partially ionized hydrogen and carbon atmospheres are disfavored. The difference in the evidence for ionized hydrogen and helium atmospheres is too small to be decisive for most cases, but the inferred radius for helium models trends to larger sizes around or above 14-15 km. External heating or deviations in the beaming that are less than 5% at emission angles smaller than 60°, on the other hand, have no significant effect on the inferred radius.

Keywords: neutron stars; x-ray astronomy
Particle-in-cell Simulations of Decaying Plasma Turbulence: Linear Instabilities versus Nonlinear Processes in 3D and 2.5D Approximations

Particle-in-cell (PIC) simulations are used to examine the decay of strongly intermittent Alfvénic turbulence in a collisionless, homogeneous, and magnetized plasma. Results from three computational models are compared in simulations with similar plasma parameters and dimensions of approximately 100 di, where di is the ion inertial length. Each model utilizes three-dimensional velocities, but spatial variations differ: the 2.5D perpendicular PIC model uses two-dimensional spatial variations with the background magnetic field Bo perpendicular to the simulation plane, the 2.5D parallel PIC model uses two-dimensional spatial variations with Bo in the simulation plane, and the 3D model includes spatial variations in full three-dimensional space. Results from the three models are compared using plots of the joint probability distribution functions (PDFs) of maximum local linear instability growth rates versus the maximum local nonlinear frequencies. All results agree with previous demonstrations that linear growth rates are generally slower than the nonlinear frequencies of the turbulence at kdi = 1.0. However, it is the 3D PIC joint PDFs that most closely resemble joint PDFs recently observed in space plasmas because the 3D PDFs capture both the linear and nonlinear plasma processes, whereas the 2.5D parallel PIC runs do not represent the nonlinear turbulence processes and the 2.5D perpendicular PIC computations do not well represent the consequences of microinstabilities. These results suggest that 3D simulations are needed to properly capture important features of both microinstabilities and nonlinear turbulence.

Keywords: interplanetary turbulence; solar wind
Balmer Break Galaxy Candidates at z ∼ 6: A Potential View on the Star Formation Activity at z ≳ 14

We search for galaxies with a strong Balmer break (Balmer break galaxies; BBGs) at z ∼ 6 over a 0.41 deg2 effective area in the COSMOS field. Based on rich imaging data, including data obtained with the Atacama Large Millimeter/submillimeter Array (ALMA), three candidates are identified by their extremely red K-[3.6] colors, as well as by nondetection in the X-ray, optical, far-infrared, and radio bands. The nondetection in the deep ALMA observations suggests that they are not dusty galaxies but BBGs at z ∼ 6, although contamination from active galactic nuclei at z ∼ 0 cannot be completely ruled out for the moment. Our spectral energy distribution analyses reveal that the BBG candidates at z ∼ 6 have stellar masses of ≈5 × 1010 M⊙ dominated by old stellar populations with ages of ≳ 700 Myr. Assuming that all three candidates are real BBGs at z ∼ 6, we estimate the stellar mass density to be ${2.4}_{-1.3}^{+2.3}\times {10}^{4}\,{M}_{\odot }$ Mpc-3. This is consistent with an extrapolation from the lower-redshift measurements. The onset of star formation in the three BBG candidates is expected to be several hundred million yr before the observed epoch of z ∼ 6. We estimate the star formation rate density (SFRD) contributed by progenitors of the BBGs to be 2.4-12 × 10-5 M⊙ yr-1 Mpc-3 at z > 14 (99.7% confidence range). Our result suggests a smooth evolution of the SFRD beyond z = 8.

Keywords: galaxy formation; early universe; star formation; high-redshift galaxies
Investigating the Stability and Distribution of Surface Ice in Mercury's Northernmost Craters

Observations made by Earth-based radar telescopes and the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft provided compelling evidence for water ice in Mercury's polar craters. In our investigation, we constructed higher-resolution (125 m pixel-1) digital elevation models (DEMs) for four of the largest northernmost craters, Kandinsky, Tolkien, Chesterton, and Tryggvadóttir. The DEMs were leveraged to model solar illumination and the thermal environment, products that were used to identify permanently shadowed regions and simulate surface temperatures. From these models, we predicted the regions of surface stability for ice and volatile organic compounds. These predictions were then compared against the Arecibo radar, Mercury Laser Altimeter (MLA), and Mercury Dual Imaging System (MDIS) data. Our radar analysis shows that areas of high radar backscatter are correlated with areas predicted to host surface ice. Additionally, we identify radar backscatter heterogeneities within the deposits that could be associated with variations in ice purity, mantling of the ice, or ice abundances. The MDIS analysis did not reveal conclusive evidence for ice or volatiles at the surface, while MLA results support the presence of water ice at the surface in these craters. However, evidence for boundaries between the surface ice and low-reflectance volatile organic compounds, as suggested could be present by our models, was inconclusive owing to the limited MESSENGER data in these regions. BepiColombo's upcoming orbital mission at Mercury has the opportunity to obtain new measurements of these high-latitude craters and test our predictions for the distribution of surface volatiles in these environments.

Keywords: mercury (planet); planetary surfaces; surface ices; planetary polar regions