adsabs/SciX_UAT_keywords huggingface dataset:
Exoplanets in the Antarctic Sky. IV. Dual-band Photometry of Variables Found by the CSTAR-II Commissioning Survey at the North Sky

From the experiences learned in three decades of exoplanet search, wide-field transit surveys have proven to be one of the most effective ways to detect exoplanets. Wide field of view, however, suffers from high false-positive rates caused by blended eclipsing binaries. The chromaticity in eclipse depth is an effective feature to distinguish low-depth eclipsing binaries from transiting exoplanets, making multiple-band photometry follow-up advantageous before a target is passed onto more expensive spectroscopic follow-up. Moreover, a multiple-band photometric survey is itself a powerful method to find and vet planetary candidates and narrow down the candidate list of high-priority targets. In this work, we report the first results of a dual-band (Sloan-g and -i) wide-field photometry survey -- the Chinese Small Telescope ARray II (CSTAR-II), an updated version of the original CSTAR. As a key component of the Chinese Exoplanet Searching Program from Antarctica, CSTAR-II has been tested thoroughly at a remote arctic site near Mohe during the winter of 2014. In total, 13,531 light curves with the best overall photometric precision of ∼3 mmag were extracted from 7721 stars in the Sloan-g and -i bands. Using a robust method, we have detected 63 variables, of which 48 are newly discovered. The dual-band photometric results as well as the stellar properties of the detected sources are provided in this work.

Keywords: eclipsing binary stars; pulsating variable stars; surveys; multi-color photometry
Spectroscopic Confirmation of Two X-Ray Diffuse and Massive Galaxy Clusters at Low Redshift

We present MMT spectroscopic observations of two massive galaxy cluster candidates at redshift z ~ 0.07 that show extended and diffuse X-ray emission in the ROSAT All-Sky Survey (RASS) images. The targets were selected from a previous catalog of 303 newly identified cluster candidates with the similar properties using the intracluster medium emission. Using the new MMT Hectospec data and Sloan Digital Sky Survey archival spectra, we identify a number of member galaxies for the two targets and confirm that they are galaxy clusters at z = 0.079 and 0.067, respectively. The size of the two clusters, calculated from the distribution of the member galaxies, is roughly 2 Mpc in radius. We estimate cluster masses using three methods based on their galaxy number overdensities, galaxy velocity dispersions, and X-ray emission. The overdensity-based masses are (6 ~ 8) × 1014 M ⊙, comparable to the masses of large clusters at low redshift. The masses derived from velocity dispersions are significantly lower, likely due to their diffuse and low concentration features. Our result suggests the existence of a population of large clusters with very diffuse X-ray emission that has been missed by most previous searches using the RASS images. If most of the 303 candidates in the previous catalog are confirmed to be real clusters, this may help to reduce the discrepancy of cosmological results between the cosmic microwave background and galaxy cluster measurements.

Keywords: galaxy clusters; observational cosmology; galaxy spectroscopy; emission line galaxies
Comprehensive Study of the Chemical Composition and Spatial Outgassing Behavior of Hyperactive Comet 46P/Wirtanen Using Near-IR Spectroscopy during its Historic 2018 Apparition

We present a comprehensive analysis of the chemical composition of the Jupiter-family comet and potential spacecraft target 46P/Wirtanen, in the near-IR wavelength range. We used iSHELL at the NASA Infrared Telescope Facility to observe the comet on 11 pre-, near-, and postperihelion dates in 2018 December and 2019 January and February during its historic apparition. We report rotational temperatures, production rates, and mixing ratios with respect to H2O and C2H6 or 3σ upper limits of the primary volatiles H2O, HCN, CH4, C2H6, CH3OH, H2CO, NH3, CO, C2H2, and HC3N. We also discuss the spatial outgassing of the primary volatiles, to understand their sources and the spatial associations between them. The spatial profiles of H2O in 46P/Wirtanen suggest the presence of extended H2O outgassing sources in the coma, similar to the EPOXI target comet 103P/Hartley 2. 46P/Wirtanen is among the few known hyperactive comets, and we note that its composition and outgassing behavior are similar to those of other hyperactive comets in many ways. We note that the analyzed parent volatiles showed different variations (relative mixing ratios) during the apparition. We compared the chemical composition of 46P/Wirtanen with the mean abundances in Jupiter-family comets and the comet population as measured with ground-based near-IR facilities to date. The molecular abundances in 46P/Wirtanen suggest that although they were changing, the variations were small compared to the range in the comet population, with CH3OH showing notably more variation as compared to the other molecules.

Keywords: short period comets; comets; comet volatiles; near infrared astronomy; comae; molecular spectroscopy
XMM-Newton and NICER Measurement of the Rms Spectrum of the Millihertz Quasiperiodic Oscillations in the Neutron-star Low-mass X-Ray Binary 4U 1636-53

We used two XMM-Newton and six Neutron Star Interior Composition Explorer observations to investigate the fractional rms amplitude of the millihertz quasiperiodic oscillations (mHz QPOs) in the neutron-star low-mass X-ray binary 4U 1636-53. We studied, for the first time, the fractional rms amplitude of the mHz QPOs versus energy in 4U 1636-53 down to 0.2 keV. We find that, as the energy increases from ∼0.2 to ∼3 keV, the rms amplitude of the mHz QPOs increases, different from the decreasing trend that has been previously observed above 3 keV. This finding has not yet been predicted by any current theoretical model; however, it provides an important observational feature to speculate whether a newly discovered mHz oscillation originates from the marginally stable nuclear burning process on the neutron-star surface.

Keywords: low-mass x-ray binary stars; neutron stars; astrophysical explosive burning
On the Robustness of the Velocity Anisotropy Parameter in Probing the Stellar Kinematics in Milky Way-Like Galaxies: Takeaway from TNG50 Simulation

We analyze the velocity anisotropy of stars in real and energy space for a sample of Milky Way-like galaxies in the TNG50 simulation. We employ different selection criteria, including spatial, kinematic, and metallicity cuts, and make three halo classes ( ${ \mathcal A }$ - ${ \mathcal C }$ ) that show mild-to-strong sensitivity to different selections. The above classes cover 48%, 16%, and 36% of the halos, respectively. We analyze the β radial profiles and divide them into either monotonically increasing radial profiles or ones with peaks and troughs. We demonstrate that halos with monotonically increasing β profiles are mostly from class ${ \mathcal A }$ , while those with peaks/troughs are part of classes ${ \mathcal B }$ and ${ \mathcal C }$ . This means that care must be taken, as the observationally reported peaks/troughs might be a consequence of different selection criteria. We infer the anisotropy parameter β energy space and compare that against the β radial profile. It is seen than 65% of halos with very mild sensitivity to different selections in real space are those for which the β radial and energy profiles are closely related. Consequently, we propose that comparing the β radial and energy profiles might be a novel way to examine the sensitivity to different selection criteria and thus examining the robustness of the anisotropy parameter in tracing stellar kinematics. We compare simulated β radial profiles against various observations and demonstrate that, in most cases, the model diversity is comparable with the error bars from different observations, meaning that the TNG50 models are in good overall agreement with observations.

Keywords: galaxy stellar halos; milky way galaxy; hydrodynamical simulations
Reflectivity of Venus's Dayside Disk During the 2020 Observation Campaign: Outcomes and Future Perspectives

We performed a unique Venus observation campaign to measure the disk brightness of Venus over a broad range of wavelengths in 2020 August and September. The primary goal of the campaign was to investigate the absorption properties of the unknown absorber in the clouds. The secondary goal was to extract a disk mean SO2 gas abundance, whose absorption spectral feature is entangled with that of the unknown absorber at ultraviolet wavelengths. A total of three spacecraft and six ground-based telescopes participated in this campaign, covering the 52-1700 nm wavelength range. After careful evaluation of the observational data, we focused on the data sets acquired by four facilities. We accomplished our primary goal by analyzing the reflectivity spectrum of the Venus disk over the 283-800 nm wavelengths. Considerable absorption is present in the 350-450 nm range, for which we retrieved the corresponding optical depth of the unknown absorber. The result shows the consistent wavelength dependence of the relative optical depth with that at low latitudes, during the Venus flyby by MESSENGER in 2007, which was expected because the overall disk reflectivity is dominated by low latitudes. Last, we summarize the experience that we obtained during this first campaign, which should enable us to accomplish our second goal in future campaigns.

Keywords: venus; atmospheric clouds; planetary science; solar system astronomy; planetary atmospheres; observational astronomy
Deep Symbolic Regression for Physics Guided by Units Constraints: Toward the Automated Discovery of Physical Laws

Symbolic regression (SR) is the study of algorithms that automate the search for analytic expressions that fit data. While recent advances in deep learning have generated renewed interest in such approaches, the development of SR methods has not been focused on physics, where we have important additional constraints due to the units associated with our data. Here we present Φ-SO, a physical symbolic optimization framework for recovering analytical symbolic expressions from physics data using deep reinforcement learning techniques by learning units constraints. Our system is built, from the ground up, to propose solutions where the physical units are consistent by construction. This is useful not only in eliminating physically impossible solutions but also because the grammatical rules of dimensional analysis enormously restrict the freedom of the equation generator, thus vastly improving performance. The algorithm can be used to fit noiseless data, which can be useful, for instance, when attempting to derive an analytical property of a physical model, and it can also be used to obtain analytical approximations of noisy data. We test our machinery on a standard benchmark of equations from the Feynman Lectures on Physics and other physics textbooks, achieving state-of-the-art performance in the presence of noise (exceeding 0.1%) and show that it is robust even in the presence of substantial (10%) noise. We showcase its abilities on a panel of examples from astrophysics.

Keywords: neural networks; regression; astronomy data modeling; algorithms
Simultaneous NICER and NuSTAR Observations of the Ultracompact X-Ray Binary 4U 0614+091

We present the first joint NuSTAR and NICER observations of the ultracompact X-ray binary 4U 0614+091. This source shows quasiperiodic flux variations on the timescale of ~days. We use reflection modeling techniques to study various components of the accretion system as the flux varies. We find that the flux of the reflected emission and the thermal components representing the disk and the compact object trend closely with the overall flux. However, the flux of the power-law component representing the illuminating X-ray corona scales in the opposite direction, increasing as the total flux decreases. During the lowest flux observation, we see evidence of accretion disk truncation from roughly 6 gravitational radii to 11.5 gravitational radii. This is potentially analogous to the truncation seen in black hole low-mass X-ray binaries, which tends to occur during the low/hard state at sufficiently low Eddington ratios.

Keywords: accretion; stellar accretion disks; neutron stars; x-ray binary stars; low-mass x-ray binary stars
The Panchromatic Hubble Andromeda Treasury. XX. The Disk of M31 is Thick

We present a new approach to measuring the thickness of a partially face-on stellar disk, using dust geometry. In a moderately-inclined disk galaxy, the fraction of reddened stars is expected to be 50% everywhere, assuming that dust lies in a thin midplane. In a thickened disk, however, a wide range of radii project onto the line of sight. Assuming stellar density declines with radius, this geometrical projection leads to differences in the numbers of stars on the near and far sides of the thin dust layer. The fraction of reddened stars will thus differ from the 50% prediction, with a deviation that becomes larger for puffier disks. We map the fraction of reddened red giant branch (RGB) stars across M31, which shows prominent dust lanes on only one side of the major axis. The fraction of reddened stars varies systematically from 20% to 80%, which requires that these stars have an exponential scale height h z that is 0.14 ± 0.015 times the exponential scale length (h r ≈ 5.5 kpc). M31's RGB stars must therefore have h z = 770 ± 80 pc, which is far thicker than the Milky Way's thin disk, but comparable to its thick disk. The lack of a significant thin disk in M31 is unexpected, but consistent with its interaction history and high disk velocity dispersion. We suggest that asymmetric reddening be used as a generic criterion for identifying "thick disk"-dominated systems, and discuss prospects for future 3D tomographic mapping of the gas and stars in M31.

Keywords: interstellar dust extinction; andromeda galaxy; interstellar reddening; interstellar medium; galaxy structure; galaxy stellar disks; galaxy disks; multi-color photometry; interstellar dust
Probing the Jet-Torus Interaction in the Radio Galaxy NGC 1052 by Sulfur-bearing Molecules

The radio galaxy NGC 1052 casts absorption features of sulfur-bearing molecules, H2S, SO, SO2, and CS toward the radio continuum emission from the core and jets. Using the Atacama Large Millimeter/submillimeter Array, we have measured the equivalent widths of SO absorption features in multiple transitions and determined the temperatures of 344 ± 43 K and 26 ± 4 K in submillimeter and millimeter wavelengths, respectively. Since submillimeter and millimeter continuum represents the core and jets, the high and low temperatures of the absorbers imply a warm environment in the molecular torus and cooler downstream flows. The high temperature in the torus is consistent with the presence of 22 GHz H2O maser emission, vibrationally excited HCN and HCO+ absorption lines, and sulfur-bearing molecules in the gas phase released from dust. The origin of the sulfur-bearing gas is ascribed to the evaporation of the icy dust component through a jet-torus interaction. Shock heating is the sole plausible mechanism to maintain such a high temperature of gas and dust in the torus. The implication of the jet-torus interaction also supports the collimation of the sub-relativistic jets by the gas pressure of the torus.

Keywords: active galactic nuclei; molecular spectroscopy; radio galaxies; radio jets
Properties Underlying the Variation of the Magnetic Field Spectral Index in the Inner Solar Wind

Using data from orbits 1-11 of the Parker Solar Probe mission, the magnetic field spectral index was measured across a range of heliocentric distances. The previously observed transition between a value of -5/3 far from the Sun and a value of -3/2 close to the Sun was recovered, with the transition occurring at around 50 R ⊙ and the index saturating at -3/2 as the Sun is approached. A statistical analysis was performed to separate the variation of the index on distance from its dependence on other parameters of the solar wind that are plausibly responsible for the transition, including the cross helicity, residual energy, turbulence age, and magnitude of magnetic fluctuations. Of all parameters considered, the cross helicity was found to be by far the strongest candidate for the underlying variable responsible. The velocity spectral index was also measured and found to be consistent with -3/2 over the range of values of cross helicity measured. Possible explanations for the behavior of the indices are discussed, including the theorized different behavior of imbalanced, compared to balanced, turbulence.

Keywords: solar wind; magnetohydrodynamics; space plasmas; heliosphere
AGN-driven Cold Gas Outflow of NGC 1068 Characterized by Dissociation-sensitive Molecules

Recent developments in (sub)millimeter facilities have drastically changed the amount of information obtained from extragalactic spectral scans. In this paper, we present a feature extraction technique using principal component analysis (PCA) applied to arcsecond-resolution (1.″0-2.″0 = 72-144 pc) spectral scan data sets for the nearby type-2 Seyfert galaxy NGC 1068, using Band 3 of the Atacama Large Millimeter/submillimeter Array. We apply PCA to 16 well-detected molecular line intensity maps convolved to a common 150 pc resolution. In addition, we include the [S III]/[S II] line ratio and [C I] 3 P 1-3 P 0 maps in the literature, both of whose distributions show a remarkable resemblance to that of a kiloparsec-scale biconical outflow from the central active galactic nucleus. We identify two prominent features: (1) central concentration at the circumnuclear disk (CND) and (2) two peaks across the center that coincide with the biconical outflow peaks. The concentrated molecular lines in the CND are mostly high-dipole molecules (e.g., H13CN, HC3N, and HCN). Line emissions from molecules known to be enhanced in an irradiated interstellar medium, CN, C2H, and HNC, show similar concentrations and extended components along the bicone, suggesting that molecule dissociation is a dominant chemical effect of the cold molecular outflow of this galaxy. Although further investigation should be made, this scenario is consistent with the faintness or absence of emission lines from CO isotopologues, CH3OH, and N2H+ in the outflow, which are easily destroyed by dissociating photons and electrons.

Keywords: active galactic nuclei; galaxy nuclei; galaxy winds; interstellar phases; molecular gas; seyfert galaxies; multivariate analysis
Forecasting [C II] Line-intensity Mapping Measurements between the End of Reionization and the Epoch of Galaxy Assembly

We combine recent simulation work on the SFR-[C II] correlation at high redshift with empirical modeling of the galaxy-halo connection (via UniverseMachine) to forecast [C II] auto power spectra from z ∼ 4 to z ∼ 8. We compare these to sensitivities realistically expected from various instruments expected to come online in the next decade. If the predictions of our model are correct, [C II] should be detectable up to z ∼ 6 in this generation of surveys, but detecting [C II] past the end of reionization will require a generational leap in line-intensity survey capabilities.

Keywords: theoretical models; high-redshift galaxies; radio astronomy
Supernova X-Ray Database (SNaX) Updated to Ensure Long-term Stability

The Supernova X-Ray Database was established a few years ago to make X-ray data on supernovae (SNe) publicly available via an elegant searchable web interface. The database has recently been updated to PhP7, had security updates done, and moved to a new server, ensuring its long-term stability. We urge astronomers to continue to download the data as needed for their work. Those with X-ray data on SNe are requested to upload it to the database via the easily fillable spreadsheet, making it accessible to everyone.

Keywords: astronomy databases; catalogs; x-ray transient sources; supernovae; core-collapse supernovae
Characteristics of the Heliospheric Current Sheets at the Sector Boundaries: Wind Observations from 1995-2020

We report results of a statistical study of 1197 heliospheric current sheet (HCS) events associated with the sector boundaries observed by the Wind spacecraft between 1995 and 2020. The average property of the HCS events can be characterized as follows: (1) The width of the current sheets ranges between ~600 km and 1.1 × 106 km, with an average width of 1.06 ± 2.37 × 105 km; (2) The longitude (in Geocentric Solar-Ecliptic coordinate) of the HCS normal shows a large peak at ~210° (0° sunward pointing) and a longer tail at smaller angles; (3) The latitudinal angle (inclination) of the HCS normal shows a near symmetric distribution (peak and average ~0°); (4) The yearly occurrence rate is relatively constant (~46 or 3.4 events per solar rotation), without showing a clear solar cycle dependence; (5) There are solar cycle variations in the properties of the plasma and field within the current sheets and these variations follow closely with the background solar wind plasma and field; (6) A mild (~10%) proton temperature increase within the HCS, suggesting that heating of the solar wind proton can occur within the current sheet; and (7) A sudden decrease in the proton temperature anisotropy (T∥/T⊥) toward unity within ~3 hr of the HCS was identified. These results suggest that on the large scale the HCS at 1 au is a relatively stable and persistent solar wind structure throughout the solar cycle. On the small scale the HCS property is probably controlled by the dynamics of the current system, which is still poorly known.

Keywords: heliosphere
A Modified Spheromak Model Suitable for Coronal Mass Ejection Simulations

Coronal mass ejections (CMEs) are some of the primary drivers of extreme space weather. They are large eruptions of mass and magnetic field from the solar corona and can travel the distance between Sun and Earth in half a day to a few days. Predictions of CMEs at 1 au, in terms of both its arrival time and magnetic field configuration, are very important for predicting space weather. Magnetohydrodynamic modeling of CMEs, using flux rope-based models, is a promising tool for achieving this goal. In this study, we present one such model for CME simulations, based on spheromak magnetic field configuration. We have modified the spheromak solution to allow for independent input of poloidal and toroidal fluxes. The motivation for this is the possibility of estimating these fluxes from solar magnetograms and extreme ultraviolet data from a number of different approaches. We estimate the poloidal flux of CME using post-eruption arcades and toroidal flux from the coronal dimming. In this modified spheromak, we also have the option to control the helicity sign of flux ropes, which can be derived from the solar disk magnetograms using the magnetic tongue approach. We demonstrate the applicability of this model by simulating the 2012 July 12 CME in the solar corona.

Keywords: magnetohydrodynamical simulations; solar coronal mass ejections; solar wind