adsabs/SciX_UAT_keywords huggingface dataset:
Magnetohydrodynamic Turbulent Evolution of a Magnetic Cloud in the Outer Heliosphere

This Letter exploits joint observations of the same interplanetary coronal mass ejection by widely separated spacecraft to study, for the first time, the turbulent evolution of the magnetohydrodynamic (MHD) properties of the embedded magnetic cloud, during its propagation throughout interplanetary space. Specifically, the event was observed by Wind at 1 au on 1998 March 4-6 and tracked to the location of Ulysses at 5.4 au 18 days later, when the two spacecraft were radially aligned with the Sun. The analysis of the MHD invariants within the magnetic cloud, along with its energy budget, provides compelling evidence of magnetic erosion of the structure thanks to its interaction with a trailing magnetic cloud. The helical configuration is thus largely deformed and degraded, and the initial dominance of magnetic over kinetic energy is observed to evolve toward a less imbalanced condition. This is consistent with the expected conversion of magnetic energy into kinetic energy due to magnetic reconnection processes. Local interaction of the magnetic cloud's (MC) outer layers with the solar wind acts to generate larger amplitude Alfvénic fluctuations in the downstream region, leading the MC to turbulently evolve toward a more complex cross-helicity configuration in the outer heliosphere. Finally, evidence of a flux rope locally generated by magnetic reconnection events at 1 au that likely decays by the time it reaches Ulysses is also reported.

Keywords: magnetohydrodynamics; interplanetary turbulence; solar coronal mass ejections; interplanetary magnetic fields; heliosphere; solar wind; solar magnetic reconnection
Far-infrared Luminosity Bursts Trace Mass Accretion onto Protostars

Evidence abounds that young stellar objects undergo luminous bursts of intense accretion that are short compared to the time it takes to form a star. It remains unclear how much these events contribute to the main-sequence masses of the stars. We demonstrate the power of time-series far-infrared (far-IR) photometry to answer this question compared to similar observations at shorter and longer wavelengths. We start with model spectral energy distributions that have been fit to 86 Class 0 protostars in the Orion molecular clouds. The protostars sample a broad range of envelope densities, cavity geometries, and viewing angles. We then increase the luminosity of each model by factors of 10, 50, and 100 and assess how these luminosity increases manifest in the form of flux increases over wavelength ranges of interest. We find that the fractional change in the far-IR luminosity during a burst more closely traces the change in the accretion rate than photometric diagnostics at mid-infrared and submillimeter wavelengths. We also show that observations at far-IR and longer wavelengths reliably track accretion changes without confusion from large, variable circumstellar and interstellar extinction that plague studies at shorter wavelengths. We close by discussing the ability of a proposed far-IR surveyor for the 2030s to enable improvements in our understanding of the role of accretion bursts in mass assembly.

Keywords: far infrared astronomy; protostars; stellar accretion; spectral energy distribution
Optimal Fitting and Debiasing for Detectors Read Out Up-the-Ramp

This paper derives the optimal fit to a pixel's count rate in the case of an ideal detector read out nondestructively in the presence of both read and photon noise. The approach is general for any readout scheme, provides closed-form expressions for all quantities, and has a computational cost that is linear in the number of resultants (groups of reads). I also derive the bias of the fit from estimating the covariance matrix and show how to remove it to first order. The ramp-fitting algorithm I describe provides the χ 2 value of the fit of a line to the accumulated counts, which can be interpreted as a goodness-of-fit metric. I provide and describe a pure Python implementation of these algorithms that can process a 10-resultant ramp on a 4096 × 4096 detector in ≈8 s with bias removal on a single core of a 2020 Macbook Air. This Python implementation, together with tests and a tutorial notebook, are available at https://github.com/t-brandt/fitramp. A companion paper describes a jump detection algorithm based on hypothesis testing of ramp fits and demonstrates all algorithms on data from JWST.

Keywords: astronomical detectors; astronomical instrumentation
The Parallax of VHS J1256-1257 from CFHT and Pan-STARRS-1

We present new parallax measurements from the CFHT Infrared Parallax Program and the Pan-STARRS 3$\pi$ Steradian Survey for the young ($\approx150-300$ Myr) triple system VHS J125601.92$-$125723.9. This system is composed of a nearly equal-flux binary ("AB") and a wide, possibly planetary-mass companion ("b"). The system's published parallactic distance ($12.7\pm1.0$ pc) implies absolute magnitudes unusually faint compared to known young objects and is in tension with the spectrophotometric distance for the central binary ($17.2\pm2.6$ pc). Our CFHT and Pan-STARRS parallaxes are consistent, and the more precise CFHT result places VHS J1256-1257 at $22.2^{+1.1}_{-1.2}$ pc. Our new distance results in higher values for the companion's mass ($19\pm5$ M$_{\rm Jup}$) and temperature ($1240\pm50$ K), and also brings the absolute magnitudes of all three components into better agreement with known young objects.

Keywords: brown dwarfs
Multiwavelength Vertical Structure in the AU Mic Debris Disk: Characterizing the Collisional Cascade

Debris disks are scaled-up analogs of the Kuiper Belt in which dust is generated by collisions between planetesimals. In the collisional cascade model of debris disks, the dust lost to radiation pressure and winds is constantly replenished by grinding collisions between planetesimals. The model assumes that collisions are destructive and involve large velocities; this assumption has not been tested beyond our solar system. We present 0.″25 (≈2.4 au) resolution observations of the λ = 450 μm dust continuum emission from the debris disk around the nearby M dwarf AU Microscopii with the Atacama Large Millimeter/submillimeter Array. We use parametric models to describe the disk structure, and a Monte Carlo Markov Chain (MCMC) algorithm to explore the posterior distributions of the model parameters; we fit the structure of the disk to both our data and archival λ = 1.3 mm data (Daley et al. 2019), from which we obtain two aspect ratio measurements at 1.3 mm (h 1300 = ${0.025}_{-0.002}^{+0.008}$ ) and at 450 μm (h 450 = ${0.019}_{-0.001}^{+0.006}$ ), as well as the grain-size distribution index q = 3.03 ± 0.02. Contextualizing our aspect ratio measurements within the modeling framework laid out in Pan & Schlichting (2012), we derive a power-law index of velocity dispersion as a function of grain size p = 0.28 ± 0.06 for the AU Mic debris disk. This result implies that smaller bodies are more easily disrupted than larger bodies by collisions, which is inconsistent with the strength regime usually assumed for such small bodies. Possible explanations for this discrepancy are discussed.

Keywords: debris disks; circumstellar disks; m dwarf stars
Catalog and Statistical Examinations of Lyα Solar Flares from GOES/EUVS-E Measurements

The Lyman-alpha (Lyα) line of neutral hydrogen at 121.6 nm is by far the brightest emission line in the vacuum ultraviolet spectral range of the Sun. The emission at this line could be a major energy input to the upper layers of the Earth's atmosphere, strongly impacting the geospace environment. The Geostationary Operational Environmental Satellite (GOES) series, starting with GOES-13, began to carry a multichannel Extreme UltraViolet Sensor (EUVS) with one channel (E-channel) targeting the Lyα line. In the present work, we produce a Lyα flare catalog from the GOES-15/EUVS-E data between 2010 April 8 and 2016 June 6 with an automatic flare detection algorithm. This algorithm is designed to search events at various scales and find their real start and end times. Based on the obtained flare list, statistics on the temporal behavior such as the duration, rise, and decay times, and the event asymmetries of Lyα flares is presented. On average (defined by the median of the distributions), the duration, rise and decay times of the flares were estimated to be 20.8 minutes, 5.6 minutes, and 14.2 minutes, respectively. We also discuss the frequency distributions of the peak flux and the fluence of Lyα flares, both of which reveal power-law behaviors with power-law indices of 2.71 ± 0.06 and 2.42 ± 0.06, respectively, implying that more flares are accumulated at small scales and these small-scale events play an important role in explaining the violent solar energy release.

Keywords: astrostatistics distributions; solar flares; solar ultraviolet emission; algorithms
Relationship of Transport Coefficients with Statistical Quantities of Charged Particles

In previous studies, a general spatial transport equation was derived from the Fokker-Planck equation. The latter equation contains an infinite number of spatial derivative terms T n = κ nz ∂ n F/∂z n with n = 1, 2, 3, ⋯ . Due to the complexity of the general equation, some simplified equations with finitely many spatial derivative terms have been used by astrophysical researches, e.g., the diffusion equation, the hyperdiffusion equation, subdiffusion transport equation, etc. In this paper, the simplified transport equations with the spatial derivative terms up to the first, second, third, fourth, and fifth order are listed, and their transport coefficient formulas are derived, respectively. We find that most of the transport coefficients are determined by the corresponding statistical quantities. In addition, we find that the well-known statistical quantities, the skewness ${ \mathcal S }$ and the kurtosis ${ \mathcal K }$ , are determined by some transport coefficients. The results can help one to use various transport coefficients determined by the statistical quantities, including many that are relatively newfound in this paper, to study charged particle parallel transport processes.

Keywords: interplanetary turbulence; interplanetary physics; interplanetary magnetic fields
SOLES I: The Spin-Orbit Alignment of K2-140 b

Obliquity measurements for stars hosting relatively long-period giant planets with weak star-planet tidal interactions may play a key role in distinguishing between formation theories for shorter-period hot Jupiters. Few such obliquity measurements have been made to date due to the relatively small sample of known wide-orbiting, transiting Jovian-mass planets and the challenging nature of these targets, which tend to have long transit durations and orbit faint stars. We report a measurement of the Rossiter-McLaughlin effect across the transit of K2-140 b, a Jupiter-mass planet with period P = 6.57 days orbiting a V = 12.6 star. We find that K2-140 is an aligned system with projected spin-orbit angle λ = 0.5° ± 9.7°, suggesting a dynamically cool formation history. This observation builds toward a population of tidally detached giant planet spin-orbit angles that will enable a direct comparison with the distribution of close-orbiting hot-Jupiter orbital configurations, elucidating the prevalent formation mechanisms of each group.

Keywords: planetary alignment; exoplanet dynamics; star-planet interactions; exoplanets; planetary theory; exoplanet astronomy; exoplanet formation; exoplanet systems; exoplanet detection methods; exoplanet evolution; extrasolar gaseous giant planets; planetary system formation
Starbursting Nuclei in Old Dwarf Galaxies

Nuclei of early-type dwarf galaxies (dEs) are usually younger than the galaxy main body, and this discrepancy in age has been a puzzle. To explore the origin of young nuclei in dEs, we study a sample of dEs having compact star-forming blobs that are visually similar to dEs' nuclei but by far bluer. We find that (1) the compact star-forming blobs have a typical stellar mass of one percent of the host galaxy stellar mass; (2) some of the blobs are positioned slightly off from the center of the galaxies; (3) the Hα equivalent width measured from the publicly available Sloan Digital Sky Survey fiber spectroscopy shows their formation ages being an order of few megayear; (4) their emission line metallicities, 12 + log(O/H), are as high as the solar value, while the underlying galaxies have the typical stellar populations of dEs, i.e., log(Z/Z ${}_{\odot }$ ) ∼ -0.8. Based on the results, we argue that the central star-forming blobs can provide a caught-in-the-act view of nuclei formation in dEs, and discuss possible formation mechanisms of young nuclei in old dEs. We particularly propose that these off-centered compact star-forming regions may act as seeds of nuclei as proposed in the "wet migration" scenario of Guillard et al.

Keywords: dwarf galaxies; nucleated dwarf galaxies; star formation; early-type galaxies
Luminous Fast Blue Optical Transients and Type Ibn/Icn SNe from Wolf-Rayet/Black Hole Mergers

Progenitor models for the "luminous" subclass of Fast Blue Optical Transients (LFBOTs; prototype: AT2018cow) are challenged to simultaneously explain all of their observed properties: fast optical rise times of days or less; peak luminosities ≳1044 erg s-1; low yields ≲0.1M ⊙ of 56Ni; aspherical ejecta with a wide velocity range (≲3000 km s-1 to ≳0.1-0.5c with increasing polar latitude); presence of hydrogen-depleted-but-not-free dense circumstellar material (CSM) on radial scales from ~1014 cm to ~3 × 1016 cm; embedded variable source of non-thermal X-ray/γ-rays, suggestive of a compact object. We show that all of these properties are consistent with the tidal disruption and hyper-accretion of a Wolf-Rayet (WR) star by a black hole or neutron star binary companion. In contrast with related previous models, the merger occurs with a long delay (≳100 yr) following the common envelope (CE) event responsible for birthing the binary, as a result of gradual angular momentum loss to a relic circumbinary disk. Disk-wind outflows from the merger-generated accretion flow generate the 56Ni-poor aspherical ejecta with the requisite velocity range. The optical light curve is powered primarily by reprocessing X-rays from the inner accretion flow/jet, though CSM shock interaction also contributes. Primary CSM sources include WR mass loss from the earliest stages of the merger (≲1014 cm) and the relic CE disk and its photoevaporation-driven wind (≳1016 cm). Longer delayed mergers may instead give rise to supernovae Type Ibn/Icn (depending on the WR evolutionary state), connecting these transient classes with LFBOTs.

Keywords: x-ray transient sources; common envelope evolution; supernovae
How Metals Are Transported Into and Out of a Galactic Disk: Dependence on Hydrodynamic Schemes in Numerical Simulations

Metallicity is a fundamental probe for understanding the baryon physics in a galaxy. Since metals are intricately associated with radiative cooling, star formation, and stellar feedback, reproducing the observed metal distribution through numerical experiments will provide a prominent way to examine our understanding of galactic baryon physics. In this study, we analyze the dependence of the galactic metal distribution on numerical schemes and quantify the differences in metal mixing among modern galaxy simulation codes (the mesh-based code ENZO and the particle-based codes GADGET-2 and GIZMO-PSPH). In particular, we examine different stellar feedback strengths and an explicit metal diffusion scheme in particle-based codes, as a way to alleviate the well-known discrepancy in metal transport between mesh-based and particle-based simulations. We demonstrate that a sufficient number of gas particles are needed in the gas halo to properly investigate the metal distribution therein. Including an explicit metal diffusion scheme does not significantly affect the metal distribution in the galactic disk but does change the amount of low-metallicity gas in a hot diffuse halo. We also find that the spatial distribution of metals depends strongly on how the stellar feedback is modeled. We demonstrate that the previously reported discrepancy in metals between mesh-based and particle-based simulations can be mitigated with our proposed prescription, enabling these simulations to be reliably utilized in the study of metals in galactic halos and the circumgalactic medium.

Keywords: galaxy dynamics; hydrodynamical simulations; galaxy chemical evolution; interstellar medium; stellar winds; cosmology; galaxy evolution
Spectroscopic Monitoring of the Candidate Tidal Disruption Event in F01004-2237

We present results of spectroscopic monitoring observations of the ultraluminous infrared galaxy F01004-2237. This galaxy was observed to undergo changes in its optical spectrum, detected by comparing a spectrum from 2015 with one from 2000. These changes were coincident with photometric brightening. The main changes detected in the optical spectrum are enhanced He II λ4686 emission and the appearance of He I λ3898,λ5876 emission lines. The favored interpretation of these changes was that of a tidal disruption event (TDE) happening in 2010. However, subsequent work suggested that these changes are caused by another hitherto unknown effect related to variations in the accretion rate in the active galactic nucleus (AGN). Our optical spectroscopic monitoring observations show that the evolution of the He lines is in line with the evolution seen in TDEs and opposite of what is observed from reverberation-mapping studies of AGNs, renewing the discussion of the interpretation of the flare as a TDE.

Keywords: tidal disruption; active galactic nuclei; ultraluminous infrared galaxies; transient sources; high energy astrophysics
New Infrared Spectral Indices of Luminous Cold Stars: From Early K to M Types

We present infrared spectral indices (1.0-2.3 μm) of Galactic late-type giants and red supergiants (RSGs). We used existing and new spectra obtained at resolution power R = 2000 with SpeX on the IRTF telescope. While a large CO equivalent width (EW), at 2.29 μm ([CO, 2.29] ≳ 45 Å) is a typical signature of RSGs later than spectral type M0, $[\mathrm{CO}]$ of K-type RSGs and giants are similar. In the [CO, 2.29] versus [Mg I, 1.71] diagram, RSGs of all spectral types can be distinguished from red giants because the Mg I line weakens with increasing temperature and decreasing gravity. We find several lines that vary with luminosity, but not temperature: Si I (1.59 μm), Sr (1.033 μm), Fe+Cr+Si+CN (1.16 μm), Fe+Ti (1.185 μm), Fe+Ti (1.196 μm), Ti+Ca (1.28 μm), and Mn (1.29 μm). Good markers of CN enhancement are the Fe+Si+CN line at 1.087 μm and CN line at 1.093 μm. Using these lines, at the resolution of SpeX, it is possible to separate RSGs and giants. Contaminant O-rich Mira and S-type AGBs are recognized by strong molecular features due to water vapor features, TiO band heads, and/or ZrO absorption. Among the 42 candidate RSGs that we observed, all but one were found to be late types. Twenty-one have EWs consistent with those of RSGs, 16 with those of O-rich Mira AGBs, and one with an S-type AGB. These infrared results open new, unexplored, potential for searches at low resolution of RSGs in the highly obscured innermost regions of the Milky Way.

Keywords: late-type supergiant stars; infrared astronomy; massive stars; stellar evolution
ECoPANN: A Framework for Estimating Cosmological Parameters Using Artificial Neural Networks

In this work, we present a new method to estimate cosmological parameters accurately based on the artificial neural network (ANN), and a code called ECoPANN (Estimating Cosmological Parameters with ANN) is developed to achieve parameter inference. We test the ANN method by estimating the basic parameters of the concordance cosmological model using the simulated temperature power spectrum of the cosmic microwave background (CMB). The results show that the ANN performs excellently on best-fit values and errors of parameters, as well as correlations between parameters when compared with that of the Markov Chain Monte Carlo (MCMC) method. Besides, for a well-trained ANN model, it is capable of estimating parameters for multiple experiments that have different precisions, which can greatly reduce the consumption of time and computing resources for parameter inference. Furthermore, we extend the ANN to a multibranch network to achieve a joint constraint on parameters. We test the multibranch network using the simulated temperature and polarization power spectra of the CMB, Type Ia supernovae, and baryon acoustic oscillations and almost obtain the same results as the MCMC method. Therefore, we propose that the ANN can provide an alternative way to accurately and quickly estimate cosmological parameters, and ECoPANN can be applied to the research of cosmology and even other broader scientific fields.

Keywords: cosmological parameters; observational cosmology; computational methods; astronomy data analysis; neural networks
The Physical Properties of Star-forming Galaxies with Strong [O III] Lines at z = 3.25

We present an analysis of physical properties of 34 [O III] emission-line galaxies (ELGs) at z = 3.254 ± 0.029 in the Extended Chandra Deep Field South (ECDFS). These ELGs are selected from deep narrow H2S(1) and broad K s imaging of 383 arcmin2 obtained with CFHT/WIRCam. We construct spectral energy distributions (SEDs) from U to K s to derive the physical properties of ELGs. These [O III] ELGs are identified as starburst galaxies with strong [O III] lines of L OIII ~ 1042.6-1044.2 erg s-1 and have stellar masses of M * ~ 109.0-1010.6 M ⊙ and star formation rates of ~10-210 M ⊙ yr-1. Our results show that 24% of our sample galaxies are dusty with A V > 1 mag and EW([O III])rest ~ 70-500 Å, which are often missed in optically selected [O III] ELG samples. Their rest-frame UV and optical morphologies from HST/ACS and HST/WFC3 deep imaging reveal that these [O III] ELGs are mostly multiple-component systems (likely mergers) or compact. And 20% of them are nearly invisible in the rest-frame UV owing to heavy dust attenuation. Interestingly, we find that our sample ELGs reside in an overdensity consisting of two components: one southeast (SE) with an overdensity factor of δ gal ~ 41 over a volume of 133 cMpc3, and the other northwest (NW) with δ gal ~ 38 over a volume of 103 cMpc3. The two overdense substructures are expected to be virialized at z = 0 with a total mass of ~ 1.1 × 1015 M ⊙ and ~ 4.8 × 1014 M ⊙ and probably merge into a Coma-like galaxy cluster.

Keywords: galaxy formation; galaxy evolution; high-redshift galaxies
Supernovae in Orion: The Missing Link in the Star-forming History of the Region

The Orion Complex is a notable star-forming region fragmented into several different populations with substantial differences in their phase space. I propose a model that attempts to explain the how the Complex has evolved into this current configuration. In the model presented here, the large-scale expansion can be attributable to a supernova that exploded 6 Myr ago. The remnants of this explosion can be seen as Barnard's loop, as the center of the expansion is consistent with the geometrical center of the H II bubble. This is similar to the H II bubble and the ballistic expansion that is associated with λ Ori, a region that was also the site of an ancient supernova. Assuming that the Orion Complex originally formed as one long filament spanning from the bottom of Orion A to ψ2 Ori (or potentially as far as λ Ori), Barnard's loop supernova could have split the cloud, which led to the formation of Orion C & D. Furthermore, the shockwave that propagated into the filament could have swept along the gas through several parsecs, which led to the formation of the singularly most massive cluster in the solar neighborhood, the Orion Nebula Cluster. I also discuss other related nearby events, such as the formation of the Monogem ring and various runaways that have been ejected from the Orion Complex.

Keywords: supernova remnants; stellar feedback; young star clusters; runaway stars; h ii regions; star formation; stellar populations