adsabs/SciX_UAT_keywords huggingface dataset:
Capturing Statistical Isotropy Violation with Generalized Isotropic Angular Correlation Functions of Cosmic Microwave Background Anisotropy

The exquisitely measured maps of fluctuations in the cosmic microwave background (CMB) present the possibility of systematically testing the principle of statistical isotropy of the Universe. A systematic approach based on strong mathematical formulation allows any nonstatistical isotropic (nSI) feature to be traced to the nature of physical effects or observational artifacts. Bipolar spherical harmonics (BipoSH) representation has emerged as an overarching general formalism for quantifying the departures from statistical isotropy for a field on a 2D sphere. We adopt a little-known reduction of the BipoSH functions, dubbed minimal harmonics in the original paper by Manakov et al. We demonstrate that this reduction technique of BipoSH leads to a new generalized set of isotropic angular correlation functions referred to here as minimal BipoSH functions that are observable quantifications of nSI features in a sky map. This paper presents a novel observable quantification of deviation from statistical isotropy in terms of generalized angular correlation functions that are compact and complementary to the BipoSH spectra that generalize the angular power spectrum of CMB fluctuations.

Keywords: two-point correlation function; cosmic microwave background radiation
Variability of Draped Interplanetary Magnetic Field in the Subsolar Martian Ionosphere

In the absence of an intrinsic magnetic field, the solar wind interacts directly with the Martian atmosphere, and the interplanetary magnetic field (IMF) drapes around the ionosphere. With the aid of multi-instrument measurements from Mars Atmosphere and Volatile Evolution (MAVEN), we investigate the altitudinal profiles of the draped magnetic field in the subsolar Martian ionosphere. Our analysis of 141 profiles found that they have a median profile with a nearly constant field strength of about 30 nT above 160 km. However, these profiles also show large variability, for example, with a standard deviation of 16 nT at 250 km. Timescale analysis found that magnetic field transport with downward ion plasma motion dominates the draping of IMF at high altitudes. At low altitudes, magnetic diffusion takes over due to increasing collisions. At even lower altitudes, approaching the ionospheric peak, the draped field is quickly damped owing to high conductivity. We used a 1D model simulation to confirm the above processes involved and further indicate that undulating magnetic fields with oscillation periods longer than tens of minutes can penetrate deeply into the ionosphere. This causes the large variability of draped field observed down to below 200 km. The diverse profiles of draped field observed by MAVEN are thus likely due to varying IMF conditions.

Keywords: planetary ionospheres; magnetic fields
Spectral Energy Distributions of Southern Binary X-Ray Sources

The rapid variability of X-ray binaries (XRBs) produces a wide range of X-ray states that are linked to activity across the electromagnetic spectrum. It is particularly challenging to study a sample of sources large enough to include all types in their various states, and to cover the full range of frequencies that show flux density variations. Simultaneous observations with many telescopes are necessary. In this project, we monitor 48 XRBs with seven telescopes across the electromagnetic spectrum from 5 × 109 to 1019 Hz, including ground-based radio, IR, and optical observatories, and five instruments on two spacecraft over a 1 week period. We construct spectral energy distributions and matching X-ray color-intensity diagrams for 20 sources that have the most extensive detections. Our observations are consistent with several models of expected behavior proposed for the different classes: we detect no significant radio emission from pulsars or atoll sources, but we do detect radio emission from Z sources in the normal or horizontal branch, and from black holes in the high/soft, low/hard, and quiescent states. The survey data provide useful constraints for more detailed models predicting behavior from the different classes of sources.

Keywords: x-ray binary stars; high mass x-ray binary stars; low-mass x-ray binary stars
Revisiting the Distance, Environment, and Supernova Properties of SNR G57.2+0.8 that Hosts SGR 1935+2154

We have performed a multiwavelength study of supernova remnant (SNR) G57.2+0.8 and its environment. The SNR hosts the magnetar SGR 1935+2154, which emitted an extremely bright millisecond-duration radio burst on 2020 April 28. We used the 12CO and 13CO J = 1-0 data from the Milky Way Image Scroll Painting CO line survey to search for molecular gas associated with G57.2+0.8, in order to constrain the physical parameters (e.g., the distance) of the SNR and its magnetar. We report that SNR G57.2+0.8 is likely impacting the molecular clouds (MCs) at the local standard of rest (LSR) velocity ${V}_{\mathrm{LSR}}\sim 30\,\mathrm{km}\,{{\rm{s}}}^{-1}$ and excites a weak 1720 MHz OH maser with a peak flux density of 47 mJy beam-1. The chance coincidence of a random OH spot falling in the SNR is ≤12%, and the OH-CO correspondence chance is 7% at the maser spot. This combines to give <1% false probability of the OH maser, suggesting a real maser detection. The LSR velocity of the MCs places the SNR and magnetar at a kinematic distance of 6.6 ± 0.7 kpc. The nondetection of thermal X-ray emission from the SNR and the relatively dense environment suggests G57.2+0.8 be an evolved SNR with an age $t\gtrsim 1.6\times {10}^{4}(d/6.6\,\,\mathrm{kpc})\,\,\mathrm{yr}$ . The explosion energy of G57.2+0.8 is lower than $2\times {10}^{51}{({n}_{0}/10{\mathrm{cm}}^{-3})}^{1.16}{(d/6.6\mathrm{kpc})}^{3.16}\,\mathrm{erg}$ , which is not very energetic even assuming a high ambient density ${n}_{0}=10\,\,{\mathrm{cm}}^{-3}$ . This reinforces the opinion that magnetars do not necessarily result from very energetic supernova explosions.

Keywords: molecular clouds; supernova remnants; radio transient sources; magnetars; x-ray bursts; soft gamma-ray repeaters
Sparse Logistic Regression for RR Lyrae versus Binaries Classification

RR Lyrae (RRL) stars are old, low-mass, radially pulsating variable stars in their core helium burning phase. They are popular stellar tracers and primary distance indicators since they obey well-defined period-luminosity relations in the near-infrared regime. Their photometric identification is not trivial; indeed, RRL star samples can be contaminated by eclipsing binaries, especially in large data sets produced by fully automatic pipelines. Interpretable machine-learning approaches for separating eclipsing binaries from RRL stars are thus needed. Ideally, they should be able to achieve high precision in identifying RRL stars while generalizing new data from different instruments. In this paper, we train a simple logistic regression classifier on Catalina Sky Survey (CSS) light curves. It achieves a precision of 87% at 78% recall for the RRL star class on unseen CSS light curves. It generalizes on out-of-sample data (ASAS/ASAS-SN light curves) with a precision of 85% at 96% recall. We also considered a L1-regularized version of our classifier, which reaches 90% sparsity in the light-curve features with a limited trade-off in accuracy on our CSS validation set and-remarkably-also on the ASAS/ASAS-SN light-curve test set. Logistic regression is natively interpretable, and regularization allows us to point out the parts of the light curves that matter the most in classification. We thus achieved both good generalization and full interpretability.

Keywords: astrostatistics; stellar classification; eclipsing binary stars; intrinsic variable stars; periodic variable stars; rrc variable stars; gaussian processes regression; rr lyrae variable stars; pulsating variable stars; short period variable stars
Protostellar Collapse: Regulation of the Angular Momentum and Onset of an Ionic Precursor

Through the magnetic braking and the launching of protostellar outflows, magnetic fields play a major role in the regulation of angular momentum in star formation, which directly impacts the formation and evolution of protoplanetary disks and binary systems. The aim of this paper is to quantify those phenomena in the presence of nonideal magnetohydrodynamics effects, namely, the ohmic and ambipolar diffusion. We perform three-dimensional simulations of protostellar collapses varying the mass of the prestellar dense core, the thermal support (the α ratio), and the dust grain size distribution. The mass mostly influences the magnetic braking in the pseudo-disk, while the thermal support impacts the accretion rate and hence the properties of the disk. Removing the grains smaller than 0.1 μm in the Mathis-Rumpl-Nordsieck distribution enhances the ambipolar diffusion coefficient. Similar to previous studies, we find that this change in the distribution reduces the magnetic braking with an impact on the disk. The outflow is also significantly weakened. In either case, the magnetic braking largely dominates the outflow as a process to remove the angular momentum from the disk. Finally, we report a large ionic precursor to the outflow with velocities of several km s-1, which may be observable.

Keywords: star formation; interstellar dust; magnetic fields; magnetohydrodynamics; protoplanetary disks; gravitational collapse
Probing the Origin of Changing-look Quasar Transitions with Chandra

Extremely variable quasars can also show strong changes in broad-line emission strength and are known as changing-look quasars (CLQs). To study the CLQ transition mechanism, we present a pilot sample of CLQs with X-ray observations in both the bright and faint states. From a sample of quasars with bright-state archival SDSS spectra and (Chandra or XMM-Newton) X-ray data, we identified five new CLQs via optical spectroscopic follow-up and then obtained new target-of-opportunity X-ray observations with Chandra. No strong absorption is detected in either the bright- or the faint-state X-ray spectra. The intrinsic X-ray flux generally changes along with the optical variability, and the X-ray power-law slope becomes harder in the faint state. Large-amplitude mid-infrared variability is detected in all five CLQs, and it echoes the variability in the optical with a time lag expected from the light-crossing time of the dusty torus for CLQs with robust lag measurements. The changing-obscuration model is not consistent with the observed X-ray spectra and spectral energy distribution changes seen in these CLQs. It is highly likely that the observed changes are due to the changing accretion rate of the supermassive black hole, so the multiwavelength emission varies accordingly, with promising analogies to the accretion states of X-ray binaries.

Keywords: accretion; quasars; active galactic nuclei; variable radiation sources; catalogs
The Dielectric Function of "Astrodust" and Predictions for Polarization in the 3.4 and 10 μm Features

The dielectric function of interstellar dust material is modeled using observations of extinction and polarization in the infrared, together with estimates for the mass of interstellar dust. The "astrodust" material is assumed to be a mix of amorphous silicates and other materials, including hydrocarbons producing an absorption feature at 3.4 μm. The detailed shape of the 10 μm polarization profile depends on the assumed porosity and grain shape, but the 10 μm spectropolarimetric data are not yet good enough to clearly favor one shape over another, nor to constrain the porosity. The expected 3.4 μm feature polarization is consistent with existing upper limits, provided the 3.4 μm absorption is preferentially located in grain surface layers; a separate population of non-aligned carbonaceous grains is not required. We predict the 3.4 μm polarization feature to be (Δp)3.4 μm/p(10 μm) ≈ 0.016, just below current upper limits. Polarization by the same grains at submillimeter wavelengths is also calculated.

Keywords: interstellar dust; interstellar dust extinction; interstellar dust processes; solid matter physics; silicate grains; carbonaceous grains; polycyclic aromatic hydrocarbons; very small grains
Lyα Emitting Galaxies (LAEs) at Cosmic Dawn: Implications and Predictions

The detection of Lyα emitting galaxies (LAEs) puts severe constraints on the reionization history. In this paper, we derive the properties of very high-z LAEs predicted in the only two reionization scenarios shown in a previous paper to be consistent with the current data on 15 independent evolving global (or averaged) cosmic properties regarding luminous objects and the intergalactic medium and the optical depth to electron scattering of ionized hydrogen to cosmic microwave background photons: one with a monotonic behavior, which is completed by z = 6, as commonly considered, and another one with a nonmonotonic behavior with two full ionization events at z = 6 and z = 10. We find that the Lyα luminosity functions of very high-z LAEs are very distinct in those two scenarios. Thus, comparing these predictions to the observations that will soon be available thanks to new instruments such as the James Webb Space Telescope, it should be possible to unveil the right reionization scenario. In the meantime, we can compare the predicted redshift distribution and UV (or Lyα) luminosities of very high-z LAEs to those of the few objects already observed at z > 7.5. By doing that, we find that such data are in tension with the single reionization scenario, while they are fully compatible with the double reionization scenario.

Keywords: reionization; intergalactic medium; galaxy evolution; galaxy abundances; lyman-alpha galaxies
A γ-Ray-emitting Collisional Ring Galaxy System in Our Galactic Neighborhood

The astrophysical γ-ray photons carry the signatures of the violent phenomena happening on various astronomical scales in our Universe. This includes supernova remnants, pulsars, and pulsar wind nebulae in the Galactic environment and extragalactic relativistic jets associated with active galactic nuclei (AGN). However, ∼30% of the γ-ray sources detected with the Fermi Large Area Telescope lack multiwavelength counterpart association, precluding us from characterizing their origin. Here we report, for the first time, the association of a collisional ring galaxy system in our Galactic neighborhood (distance ∼10 Mpc), formed as a consequence of a smaller "bullet" galaxy piercing through a larger galaxy, as the multifrequency counterpart of an unassociated γ-ray source 4FGL J1647.5‑5724. The system, also known as "Kathryn's Wheel," contains two dwarf irregular galaxies and an edge-on, late-type, spiral galaxy surrounded by a ring of star-forming knots. We utilized observations taken from the Neil Gehrels Swift observatory, Rapid ASKAP Continuum Survey, SuperCOSMOS Hα Survey, Dark Energy Survey, and VIsible MultiObject Spectrograph at Very Large Telescope to ascertain the association with 4FGL J1647.5‑5724 and to explore the connection between the star-forming activities and the observed γ-ray emission. We found that star formation alone cannot explain the observed γ-ray emission, and additional contribution likely from the pulsars/supernova remnants or buried AGN is required. We conclude that arcsecond/subarcsecond-scale observations of this extraordinary γ-ray-emitting galaxy collision will be needed to resolve the environment and explore the origin of cosmic rays.

Keywords: gamma-rays; star forming regions; dwarf irregular galaxies; interacting galaxies; galaxy collisions
The Hot Main Kuiper Belt Size Distribution from OSSOS

Using the absolute detection calibration and abundant detections of the Outer Solar System Origins Survey project, we provide population measurements for the main Kuiper Belt. For absolute magnitude H r < 8.3, there are 30,000 nonresonant main-belt objects, with twice as many hot-component objects than cold, and with total mass of 0.014 M ⊕, only one-seventh of which is in the cold belt (assuming a cold-object albedo about half that of hot-component objects). We show that trans-Neptunian objects with 5.5 < H r < 8.3 (rough diameters 400-100 km) have indistinguishable absolute magnitude (size) distributions, regardless of being in the cold classical Kuiper Belt (thought to be primordial) or the "hot" population (believed to be implanted after having been formed elsewhere). We discuss how this result was not apparent in previous examinations of the size distribution due to the complications of fitting assumed power-law functional forms to the detections at differing depths. This shared size distribution is surprising in light of the common paradigm that the hot-population planetesimals formed in a higher density environment much closer to the Sun, in an environment that also (probably later) formed larger (dwarf planet and bigger) objects. If this paradigm is correct, our result implies that planetesimal formation was relatively insensitive to the local disk conditions and that the subsequent planet-building process in the hot population did not modify the shape of the planetesimal size distribution in this 50-300 km range.

Keywords: classical kuiper belt objects; luminosity function; sky surveys
MARS: A New Maximum-entropy-regularized Strong Lensing Mass Reconstruction Method

Free-form strong-lensing (SL) mass reconstructions typically suffer from overfitting, which manifests itself as false-positive small-scale fluctuations. We present a new free-form MAximum-entropy ReconStruction (MARS) method without the assumption that light traces mass (LTM). The MARS algorithm enables us to achieve excellent convergence in source positions (~0.″001), minimize spurious small-scale fluctuations, and provide a quasi-unique solution independently of initial conditions. Our method is tested with the publicly available synthetic SL data FF-SIMS. The comparison with the truth shows that the mass reconstruction quality is on par with those of the best-performing LTM methods published in the literature, which have been demonstrated to outperform existing free-form methods. In terms of the radial mass profile reconstruction, we achieve <1% agreement with the truth for the regions constrained by multiple images. Finally, we apply MARS to A1689 and find that the cluster mass in the SL regime is dominated by the primary halo centered on the brightest cluster galaxy and the weaker secondary halo is also coincident with the bright cluster member ~160 kpc northeast. Within the SL field, the A1689 radial profile is well described by a Navarro-Frenk-White profile with c 200 = 5.53 ± 0.77 and ${r}_{s}={538}_{-100}^{+90}$ kpc, and we find no evidence that A1689 is overconcentrated.

Keywords: dark matter distribution; strong gravitational lensing; galaxy clusters
The Short-period S-stars S4711, S62, S4714 and the Lense-Thirring Effect due to the Spin of Sgr A*

Recently, some S-stars (S4711, S62, S4714) orbiting the supermassive black hole (SMBH) in Sgr A* with short orbital periods (7.6 yr ≤ Pb ≤ 12 yr) were discovered. It was suggested that they may be used to measure the general relativistic Lense-Thirring (LT) precessions of their longitudes of ascending node Ω induced by the SMBH's angular momentum J•. In fact, the proposed numerical estimates hold only in the particular case of a perfect alignment of J• with the line of sight, which does not seem to be the case. Moreover, the inclination I and the argument of perinigricon ω also undergo LT precessions for an arbitrary orientation of J• in space. We explicitly show the analytical expressions of ${\dot{I}}^{\mathrm{LT}},{\dot{{\rm{\Omega }}}}^{\mathrm{LT}},{\omega }^{\mathrm{LT}}$ in terms of the SMBH's spin polar angles i•, ɛ•. It turns out that the LT precessions, in arcseconds per year $\left(^{\prime\prime} \,{\mathrm{yr}}^{-1}\right)$ , range within $\left|{\dot{I}}^{\mathrm{LT}}\right|\lesssim {7}^{{\prime\prime} }\,{\mathrm{yr}}^{-1}$ , $\left|{\dot{{\rm{\Omega }}}}^{\mathrm{LT}}\right|\lesssim {9}^{{\prime\prime} }\,{\mathrm{yr}}^{-1}$ , and $-{13}^{{\prime\prime} }\,{\mathrm{yr}}^{-1}\lesssim {\dot{\omega }}^{\mathrm{LT}}\lesssim {14}^{{\prime\prime} }\,{\mathrm{yr}}^{-1}$ for S4714, $\left|{\dot{I}}^{\mathrm{LT}}\right|\lesssim {5}^{{\prime\prime} }\,{\mathrm{yr}}^{-1}$ , $\left|{\dot{{\rm{\Omega }}}}^{\mathrm{LT}}\right|\lesssim {5}^{{\prime\prime} }\,{\mathrm{yr}}^{-1}$ , and $\left|{\dot{\omega }}^{\mathrm{LT}}\right|\lesssim {10}^{{\prime\prime} }\,{\mathrm{yr}}^{-1}$ for S62, and $\left|{\dot{I}}^{\mathrm{LT}}\right|\lesssim {0.3}^{{\prime\prime} }\,{\mathrm{yr}}^{-1}$ , $\left|{\dot{{\rm{\Omega }}}}^{\mathrm{LT}}\right|\lesssim {0.3}^{{\prime\prime} }\,{\mathrm{yr}}^{-1}$ , and $\left|{\dot{\omega }}^{\mathrm{LT}}\right|\lesssim {0.7}^{{\prime\prime} }\,{\mathrm{yr}}^{-1}$ for S4711. For each star, the corresponding values of ${i}_{\max }^{\bullet },{\varepsilon }_{\max }^{\bullet }$ , and ${i}_{\min }^{\bullet },{\varepsilon }_{\min }^{\bullet }$ are determined as well, along with those ${i}_{0}^{\bullet },{\varepsilon }_{0}^{\bullet }$ that cancel the LT precessions. The LT perinigricon precessions ${\dot{\omega }}^{\mathrm{LT}}$ are overwhelmed by the systematic uncertainties in the Schwarzschild ones due to the current errors in the stars' orbital parameters and the mass of Sgr A* itself.

Keywords: kerr black holes; orbital elements; general relativity
An Extremely Massive White Dwarf Escaped from the Hyades Star Cluster

We searched the Gaia DR3 database for ultramassive white dwarfs with kinematics consistent with having escaped the nearby Hyades open cluster, identifying three such candidates. Two of these candidates have masses estimated from Gaia photometry of approximately 1.1 solar masses; their status as products of single-stellar evolution that have escaped the cluster was deemed too questionable for immediate follow-up analysis. The remaining candidate has an expected mass >1.3 solar masses, significantly reducing the probability of it being an interloper. Analysis of follow-up Gemini GMOS spectroscopy for this source reveals a nonmagnetized hydrogen atmosphere white dwarf with a mass and age consistent with having formed from a single star. Assuming a single-stellar-evolution formation channel, we estimate a 97.8% chance that the candidate is a true escapee from the Hyades. With a determined mass of 1.317 solar masses, this is potentially the most massive known single-evolution white dwarf and is by far the most massive with a strong association with an open cluster.

Keywords: white dwarf stars; stellar evolution; star clusters
The Magellanic Stream at 20 kpc: A New Orbital History for the Magellanic Clouds

We present new simulations of the formation of the Magellanic Stream based on an updated first-passage interaction history for the Magellanic Clouds, including both the Galactic and Magellanic Coronae and a live dark matter halo for the Milky Way. This new interaction history is needed because previously successful orbits need updating to account for the Magellanic Corona and the loosely bound nature of the Magellanic Group. These orbits involve two tidal interactions over the last 3.5 Gyr and reproduce the Stream's position and appearance on the sky, mass distribution, and velocity profile. Most importantly, our simulated Stream is only ~20 kpc away from the Sun at its closest point, whereas previous first-infall models predicted a distance of 100-200 kpc. This dramatic paradigm shift in the Stream's 3D position would have several important implications. First, estimates of the observed neutral and ionized masses would be reduced by a factor of ~5. Second, the stellar component of the Stream is also predicted to be <20 kpc away. Third, the enhanced interactions with the MW's hot corona at this small distance would substantially shorten the Stream's lifetime. Finally, the MW's UV radiation field would be much stronger, potentially explaining the Hα emission observed along most of the Stream. Our prediction of a 20 kpc Stream could be tested by searching for UV absorption lines toward distant MW halo stars projected onto the Stream.

Keywords: galaxy physics; galaxy dynamics; magellanic clouds; magellanic stream