adsabs/SciX_UAT_keywords huggingface dataset:
Dynamic Time Warping as a Means of Assessing Solar Wind Time Series

Over the last decades, international attempts have been made to develop realistic space weather prediction tools aiming to forecast the conditions on the Sun and in the interplanetary environment. These efforts have led to the development of appropriate metrics to assess the performance of those tools. Metrics are necessary to validate models, to compare different models, and to monitor the improvements to a certain model over time. In this work, we introduce dynamic time warping (DTW) as an alternative way of evaluating the performance of models and, in particular, of quantifying the differences between observed and modeled solar wind time series. We present the advantages and drawbacks of this method, as well as its application to Wind observations and EUHFORIA predictions at Earth. We show that DTW can warp sequences in time, aiming to align them with the minimum cost by using dynamic programming. It can be applied for the evaluation of modeled solar wind time series in two ways. The first calculates the sequence similarity factor, a number that provides a quantification of how good the forecast is compared to an ideal and a nonideal prediction scenario. The second way quantifies the time and amplitude differences between the points that are best matched between the two sequences. As a result, DTW can serve as a hybrid metric between continuous measurements (e.g., the correlation coefficient) and point-by-point comparisons. It is a promising technique for the assessment of solar wind profiles, providing at once the most complete evaluation portrait of a model.

Keywords: magnetohydrodynamics; time series analysis; solar wind; space weather
Secondary School Students observe Venus with NASA Infrared Telescope Facility (IRTF)

Astronomy and astrophysics are regarded as highly motivating topics for students in primary and secondary schools, and they have been a recurrent and effective resource to inspire passion about science. In fact, during the last years we have witnessed a boost of facilities providing small robotic telescopes for teachers and students to remotely undertake their own observing projects. A step forward is presented here, where we describe the experience of secondary school students attending professional observations of Venus at NASA's Infrared Telescope Facility and, in a second observing run, conducting the observations by themselves. In addition to quickly mastering the basic operation of the control software for the SpeX instrument, the students successfully performed different types of data acquisition, including drift scan imaging.

Keywords: astronomy education; observational astronomy; infrared observatories; astronomical techniques; direct imaging; drift scan imaging; venus; planetary atmospheres; atmospheric clouds
1RXH J082623.6-505741: A New Long-period Cataclysmic Variable with an Evolved Donor and a Low Mass-transfer Rate

We report the discovery of 1RXH J082623.6-505741, a 10.4 hr orbital period compact binary. Modeling extensive optical photometry and spectroscopy reveals a ~0.4 M ⊙ K-type secondary transferring mass through a low-state accretion disk to a nonmagnetic ~0.8 M ⊙ white dwarf. The secondary is overluminous for its mass and dominates the optical spectra at all epochs and must be evolved to fill its Roche Lobe at this orbital period. The X-ray luminosity L X ~ 1-2 × 1032 erg s-1 derived from both new XMM-Newton and archival observations, although high compared to most CVs, still only requires a modest accretion rate onto the white dwarf of $\dot{M}$ ~ 3 × 10-11 to 3 × 10-10 M ⊙ yr-1, lower than expected for a cataclysmic variable with an evolved secondary. No dwarf nova outbursts have yet been observed from the system, consistent with the low derived mass-transfer rate. Several other cataclysmic variables with similar orbital periods also show unexpectedly low mass-transfer rates, even though selection effects disfavor the discovery of binaries with these properties. This suggests the abundance and evolutionary state of long-period, low mass-transfer rate cataclysmic variables are worthy of additional attention.

Keywords: cataclysmic variable stars; x-ray binary stars; spectroscopic binary stars
Rotational Disruption of Nonspherical Cometary Dust Particles by Radiative Torques

Rigorous statistical numerical analysis of the response of a nonspherical dust particle ensemble composed of aggregates of astronomical silicate is presented. It is found that the rotational disruption mechanism is not only likely to occur but to be a key element in explaining many separate observations of cometary dust. Namely, radiative torques are shown to spin-up and align cometary dust within the timescales of cometary activity. Additionally, the radiative torque alignment and disruption mechanisms within certain conditions are shown to be consistent with observations of rapid polarization of dust and spectral bluing of dust. The results indicate that radiative torques should be taken into account nearly universally when considering the evolution of cometary dust.

Keywords: coma dust; astrophysical dust processes; circumstellar dust
JWST/MIRI Simulated Imaging: Insights into Obscured Star Formation and AGNs for Distant Galaxies in Deep Surveys

The James Webb Space Telescope MIRI instrument will revolutionize extragalactic astronomy with unprecedented sensitivity and angular resolution in mid-IR. Here we assess the potential of MIRI photometry to constrain galaxy properties in the Cosmic Evolution Early Release Science (CEERS) survey. We derive estimated MIRI fluxes from the spectral energy distributions (SEDs) of real sources that fall in a planned MIRI pointing. We also obtain MIRI fluxes for hypothetical active galactic nucleus (AGN)-galaxy mixed models varying the AGN fractional contribution to the total IR luminosity (fracAGN). Based on these model fluxes, we simulate CEERS imaging (3.6 hr exposure) in six bands from F770W to F2100W using MIRISIM and reduce these data using JWST PIPELINE. We perform point-spread-function-matched photometry with TPHOT and fit the source SEDs with X-CIGALE, simultaneously modeling photometric redshift and other physical properties. Adding the MIRI data, the accuracy of both redshift and fracAGN is generally improved by factors of ≳2 for all sources at z ≲ 3. Notably, for pure-galaxy inputs (fracAGN = 0), the accuracy of fracAGN is improved by ∼100 times thanks to MIRI. The simulated CEERS MIRI data are slightly more sensitive to AGN detections than the deepest X-ray survey, based on the empirical LX-L6 μm relation. Like X-ray observations, MIRI can also be used to constrain the AGN accretion power (accuracy ≈0.3 dex). Our work demonstrates that MIRI will be able to place strong constraints on the mid-IR luminosities from star formation and AGNs and thereby facilitate studies of the galaxy/AGN coevolution.

Keywords: infrared astronomy; active galactic nuclei; polycyclic aromatic hydrocarbons; infrared photometry; infrared galaxies; astronomical simulations; spectral energy distribution; supermassive black holes; infrared telescopes
VapoRock: Thermodynamics of Vaporized Silicate Melts for Modeling Volcanic Outgassing and Magma Ocean Atmospheres

Silicate vapors play a key role in planetary evolution, especially dominating early stages of rocky planet formation through outgassed magma ocean atmospheres. Our open-source thermodynamic modeling software "VapoRock" combines the MELTS liquid model with gas-species properties from multiple thermochemistry tables. VapoRock calculates the partial pressures of 34 gaseous species in equilibrium with magmatic liquid in the system Si-Mg-Fe-Al-Ca-Na-K-Ti-Cr-O at desired temperatures and oxygen fugacities (fO2, or partial pressure of O2). Comparison with experiments shows that pressures and melt-oxide activities (which vary over many orders of magnitude) are reproduced to within a factor of ~3, consistent with measurement uncertainties. We also benchmark the model against a wide selection of igneous rock compositions including bulk silicate Earth, predicting elemental vapor abundances that are comparable to (Na, Ca, and Al) or more realistic than (K, Si, Mg, Fe, and Ti) those of the closed-source MAGMA code (with maximum deviations by factors of 10-300 for K and Si). Vapor abundances depend critically on the activities of liquid components. The MELTS model underpinning VapoRock was calibrated and extensively tested on natural igneous liquids. In contrast, MAGMA's liquid model assumes ideal mixtures of a limited set of chemically simplified pseudospecies, which only roughly approximates the nonideal compositional interactions typical of many-component natural silicate melts. Finally, we explore how relative abundances of SiO and SiO2 provide a spectroscopically measurable proxy for oxygen fugacity in devolatilized exoplanetary atmospheres, potentially constraining fO2 in outgassed exoplanetary mantles.

Keywords: planet formation; chemical thermodynamics; astrochemistry; exoplanet atmospheres; exoplanet atmospheric composition
On the Occurrence of Clathrate Hydrates in Extreme Conditions: Dissociation Pressures and Occupancies at Cryogenic Temperatures with Application to Planetary Systems

We investigate the thermodynamic stability of clathrate hydrates at cryogenic temperatures from the 0 K limit to 200 K in a wide range of pressures, covering the thermodynamic conditions of interstellar space and the surface of the hydrosphere in satellites. Our evaluation of the phase behaviors is performed by setting up quantum partition functions with variable pressures on the basis of a rigorous statistical mechanics theory that requires only the intermolecular interactions as input. Noble gases, hydrocarbons, nitrogen, and oxygen are chosen as the guest species, which are key components of the volatiles in such satellites. We explore the hydrate/water two-phase boundary of those clathrate hydrates in water-rich conditions and the hydrate/guest two-phase boundary in guest-rich conditions, either of which occurs on the surface or subsurface of icy satellites. The obtained phase diagrams indicate that clathrate hydrates can be in equilibrium with either water or the guest species over a wide range far distant from the three-phase coexistence condition and that the stable pressure zone of each clathrate hydrate expands significantly on intense cooling. The implication of our findings for the stable form of water in Titan is that water on the surface exists only as clathrate hydrate with the atmosphere down to a shallow region of the crust, but clathrate hydrate in the remaining part of the crust can coexist with water ice. This is in sharp contrast to the surfaces of Europa and Ganymede, where the thin oxygen air coexists exclusively with pure ice.

Keywords: solid matter physics
Split Peas in a Pod: Intra-system Uniformity of Super-Earths and Sub-Neptunes

The planets within compact multiplanet systems tend to have similar sizes, masses, and orbital period ratios, like "peas in a pod." This pattern was detected when considering planets with radii between 1 and 4 R⊕. However, these same planets show a bimodal radius distribution, with few planets between 1.5 and 2 R⊕. The smaller "super-Earths" are consistent with being stripped rocky cores, while the larger "sub-Neptunes" likely have gaseous H/He envelopes. Given these distinct structures, it is worthwhile to test for intra-system uniformity separately within each category of planets. Here, we find that the tendency for intra-system uniformity is twice as strong when considering planets within the same size category than it is when combining all planets together. The sub-Neptunes tend to be ${1.7}_{-0.3}^{+0.6}$ times larger than the super-Earths in the same system, corresponding to an envelope mass fraction of about 2.6% for a 5 M⊕ planet. For the sub-Neptunes, the low-metallicity stars are found to have planets with more equal sizes, with modest statistical significance (p ~ 0.005). There is also a modest (~2σ) tendency for wider-orbiting planets to be larger, even within the same size category.

Keywords: exoplanets; super earths; mini neptunes; exoplanet systems
Speckle Interferometry of Nearby Multiple Stars. II. 2007-2020 Positional Measurements and Orbits of Sixteen Objects

Long-term monitoring at the 6 m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences made it possible to improve the orbits of 15 objects (HIP 689, HIP 3951, HIP 10438, HIP 43948, HIP 69962, HIP 95995, HIP 102029, HIP 102357, HIP 104383, HIP 105947, HIP 106255, HIP 108917, HIP 111546, HIP 113726, HIP 114922) and construct an orbital solution for HIP 65327 for the first time. Observations have been carried out since 2007; that is, the accumulated data correspond to an interval of 13 yr. As a result, most of the orbits were classified as "accurate" using the qualitative criteria by Worley & Heintz. A comparison of the mass sums and masses of the components calculated by two independent methods was made for objects with orbital solutions. The Gaia EDR3 parallax was used to obtain the fundamental parameters, as well as the Hipparcos and Gaia DR2 parallaxes.

Keywords: multiple stars; binary stars; low mass stars; speckle interferometry; orbits; orbital elements; stellar masses
A Comparative Analysis of Scale-invariant Phenomena in Repeating Fast Radio Bursts and Glitching Pulsars

The recent discoveries of a remarkable glitch/antiglitch accompanied by fast radio burst (FRB)-like bursts from the Galactic magnetar SGR J1935+2154 have revealed the physical connection between the two. In this work, we study the statistical properties of radio bursts from the hyperactive repeating source FRB 20201124A and of glitches from the pulsar PSR B1737–30. For FRB 20201124A, we confirm that the probability density functions of fluctuations of energy, peak flux, duration, and waiting time well follow the Tsallis q-Gaussian distribution. The derived q values from q-Gaussian distribution keep approximately steady for different temporal interval scales, which indicates that there is a common scale-invariant structure in repeating FRBs. Similar scale-invariant properties can be found in PSR B1737–30's glitches, implying an underlying association between the origins of repeating FRBs and pulsar glitches. These statistical features can be well understood within the same physical framework of self-organized criticality systems.

Keywords: radio transient sources; radio bursts; pulsars
Galaxy Cluster Mass Estimates in the Presence of Substructure

We develop and implement a model to analyze the internal kinematics of galaxy clusters that may contain subpopulations of galaxies that do not independently trace the cluster potential. The model allows for substructures within the cluster environment and disentangles cluster members from contaminating foreground and background galaxies. We estimate the cluster velocity dispersion and/or mass while marginalizing over uncertainties in all of the above complexities. Using mock observations from the MultiDark simulation, we compare the true substructures from the simulation with the substructures identified by our model, showing that 50% of the identified substructures have at least 79% of its members are also members of the same true substructure, which is on par with other substructure identification algorithms. Furthermore, we show a ∼35% decrease in scatter in the inferred velocity dispersion versus true cluster mass relationship when comparing a model that allows three substructures to a model that assumes no substructure. In a first application to our published data for A267, we identify up to four distinct galaxy subpopulations. We use these results to explore the sensitivity of inferred cluster properties to the treatment of substructure. Compared to a model that assumes no substructure, our substructure model reduces the dynamical mass of A267 by ∼22% and shifts the cluster mean velocity by ∼100 km s-1, approximately doubling the offset with respect to the velocity of A267's brightest cluster galaxy. Embedding the spherical Jeans equation within this framework, we infer for A267 a halo mass M200 = (7.0 ± 1.3) × 1014 M⊙ h-1 and concentration ${\mathrm{log}}_{10}{c}_{200}=0.71\pm 0.38$ , consistent with the mass-concentration relation found in cosmological simulations.

Keywords: galaxy clusters; abell clusters; galaxy distances; redshift surveys; jeans mass; astronomy data modeling; astronomy data analysis
Investigating Loop Quantum Gravity with Event Horizon Telescope Observations of the Effects of Rotating Black Holes

A mathematically consistent rotating black hole model in loop quantum gravity (LQG) is yet lacking. The scarcity of rotating black hole solutions in LQG substantially hampers the development of testing LQG from observations, e.g., from the Event Horizon Telescope (EHT) observations. The EHT observation revealed event horizon-scale images of the supermassive black holes Sgr A* and M87*. The EHT results are consistent with the shadow of a Kerr black hole of general relativity. We present LQG-motivated rotating black hole (LMRBH) spacetimes, which are regular everywhere and asymptotically encompass the Kerr black hole as a particular case. The LMRBH metric describes a multi-horizon black hole in the sense that it can admit up to three horizons, such that an extremal LMRBH, unlike the Kerr black hole, refers to a black hole with angular momentum a > M. The metric, depending on the parameters, describes (1) black holes with only one horizon (BH-I), (2) black holes with an event horizon and a Cauchy horizon (BH-II), (3) black holes with three horizons (BH-III), or (4) no-horizon spacetime, which we show is almost ruled out by EHT observations. We constrain the LQG parameter with the aid of the EHT shadow observational results of M87* and Sgr A*, respectively, for inclination angles of 17° and 50°. In particular, the VLTI bound for Sgr A*, δ ∈ (-0.17, 0.01), constrains the parameters (a, l) such that for 0 < l ≤ 0.347851M (l ≤ 2 × 106 km), the allowed range of a is (0, 1.0307M). Together with the EHT bounds of Sgr A* and M87* observables, our analysis concludes that a substantial part of BH-I and BH-II parameter space agrees with the EHT results of M87* and Sgr A*. While the EHT M87* results totally rule out BH-III, but not that by Sgr A*.

Keywords: black hole physics; event horizons; photon sphere
What if the Universe Expands Linearly? A Local General Relativity to Solve the "Zero Active Mass" Problem

Modern cosmology presents important challenges such as the Hubble Tension, El Gordo's collision, or the impossible galaxies (z > 10). Slight modifications to the standard model propose new parameters (e.g., the early and dynamical dark energy). On the other hand, alternatives such as the coasting universes (e.g., the hyperconical model and the spatially flat R h = ct universe) are statistically compatible with most of the observational tests, but still present theoretical problems in matching the observed matter contents since they predict a "zero active gravitational mass." To solve these open issues, we suggest that general relativity might be not valid at cosmic scales, but it would be valid at local scales. This proposal is addressed from two main features of the embedding hyperconical model: (1) the background metric would be independent of the matter content, and (2) the observed cosmic acceleration would be fictitious and because of a distorted stereographic projection of coordinates that produce an apparent radial inhomogeneity from homogeneous manifolds. Finally, to support the discussion, standard observational tests were updated here, showing that the hyperconical model is adequately fitted to Type Ia supernovae, quasars, galaxy clusters, baryon acoustic oscillations, and cosmic chronometer data sets.

Keywords: general relativity; spacetime metric; hubble time; cosmological parameters
Fabrication and Performance of Lobster Eye X-Ray Micro Pore Optics with the Ultra-high Aspect Ratio

Since the idea of bionic Lobster eye micropore optics was put forward, the possibility of focusing hard X-rays by this new lightweight X-ray optics has been proposed. Limited by the technological conditions of the aspect ratio (≥500), low surface roughness (≤1 nm) and the difficulty of applying metal coatings inside such narrow square channels, the high quality of these new optics have not been realized. This work demonstrates the test results for an Ultra-high aspect ratio (500:1) of iridium-coated with microchannel plate technology and atomic layer deposition technology. The sidewalls of the square channel are smoothed with a special acid-base treatment and the Root-Mean-Square of the inner wall was 0.52 ± 0.1 nm in 3 μm × 3 μm scale roughness, such that they work well as X-ray mirrors. The thickness of the metal iridium film layer was 19 nm. At the working voltage of 2 kV, the current was 0.1 mA and the angular resolution of the slumped chip in horizontal and vertical directions was 3.'9 and 4.'2, respectively. The simulation results were in good agreement with the X-ray test results.

Keywords: x-ray transient sources; x-ray telescopes; x-ray astronomy; x-ray surveys; x-ray identification
Measuring Black Hole Masses from Tidal Disruption Events and Testing the MBH-σ* Relation

Liu and collaborators recently proposed an elliptical accretion disk model for tidal disruption events (TDEs). They showed that the accretion disks of optical/UV TDEs are large and highly eccentric and suggested that the broad optical emission lines with complex and diverse profiles originate in a cool eccentric accretion disk of random inclination and orientation. In this paper, we calculate the radiation efficiency of the elliptical accretion disk and investigate the implications for observations of TDEs. We compile observational data for the peak bolometric luminosity and total radiation energy after peak brightness of 18 TDE sources and compare these data to the predictions from the elliptical accretion disk model. Our results show that the observations are consistent with the theoretical predictions and that the majority of the orbital energy of the stellar debris is advected into the black hole (BH) without being converted into radiation. Furthermore, we derive the masses of the disrupted stars and the masses of the BHs of the TDEs. The BH masses obtained in this paper are also consistent with those calculated with the MBH-σ* relation. Our results provide an effective method for measuring the masses of BHs in large numbers of TDEs to be discovered in ongoing and next-generation sky surveys, regardless of whether the BHs are located at the centers of galactic nuclei or wander in disks and halos.

Keywords: supermassive black holes; accretion; m-sigma relation; tidal disruption