adsabs/SciX_UAT_keywords huggingface dataset:
Optimal Photometry of Point Sources: Joint Source Flux and Background Determination on Array Detectors-from Theory to Practical Implementation

In this paper we study the joint determination of source and background flux for point sources as observed by digital array detectors. We explicitly compute the two-dimensional Cramér-Rao absolute lower bound (CRLB) as well as the performance bounds for high-dimensional implicit estimators from a generalized Taylor expansion. This later approach allows us to obtain computable prescriptions for the bias and variance of the joint estimators. We compare these prescriptions with empirical results from numerical simulations in the case of the weighted least squares estimator (introducing an improved version, denoted stochastic weighted least-squares) as well as with the maximum likelihood estimator, finding excellent agreement. We demonstrate that these estimators provide quasi-unbiased joint estimations of the flux and background, with a variance that approaches the CRLB very tightly and are, hence, optimal, unlike the case of sequential estimation used commonly in astronomical photometry which is sub-optimal. We compare our predictions with numerical simulations of realistic observations, as well as with observations of a bona fide non-variable stellar source observed with TESS, and compare it to the results from the sequential estimation of background and flux, confirming our theoretical expectations. Our practical estimators can be used as benchmarks for general photometric pipelines, or for applications that require maximum precision and accuracy in absolute photometry.

Keywords: photometry; ccd photometry; maximum likelihood estimation; minimum chi-squared; bayesian statistics
A Catalog of 71 Coronal Line Galaxies in MaNGA: [Ne V] Is an Effective AGN Tracer

Despite the importance of active galactic nuclei (AGNs) in galaxy evolution, accurate AGN identification is often challenging, as common AGN diagnostics can be confused by contributions from star formation and other effects (e.g., Baldwin-Phillips-Terlevich diagrams). However, one promising avenue for identifying AGNs is "coronal emission lines" ("CLs"), which are highly ionized species of gas with ionization potentials ≥100 eV. These CLs may serve as excellent signatures for the strong ionizing continuum of AGNs. To determine if CLs are in fact strong AGN tracers, we assemble and analyze the largest catalog of optical CL galaxies using the Sloan Digital Sky Survey's Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) catalog. We detect CL emission in 71 MaNGA galaxies, out of the 10,010 unique galaxies from the final MaNGA catalog, with ≥5σ confidence. In our sample, we measure [Ne V]λ3347, λ3427, [Fe VII]λ3586, λ3760, λ6086, and [Fe X]λ6374 emission and crossmatch the CL galaxies with a catalog of AGNs that were confirmed with broad-line, X-ray, IR, and radio observations. We find that [Ne V] emission, compared to [Fe VII] and [Fe X] emission, is best at identifying high-luminosity AGNs. Moreover, we find that the CL galaxies with the least dust extinction yield the most iron CL detections. We posit that the bulk of the iron CLs are destroyed by dust grains in the galaxies with the highest [O III] luminosities in our sample, and that AGNs in the galaxies with low [O III] luminosities are possibly too weak to be detected using traditional techniques.

Keywords: active galactic nuclei; photoionization; emission line galaxies; astrophysical dust processes
High Accuracy Photodissociation Rates in VULCAN with MCRT

Photochemical processing is a key influence on the chemical compositions of exoplanet atmospheres. We develop a 1D plane-parallel Monte Carlo radiative-transfer (MCRT) path length method to calculate actinic fluxes for photochemical modeling, which we couple to the VULCAN photochemical model. Due to the flexible nature of MCRT methods, this enables accurate calculation of photodissociation rates for complex multiple scattering scenarios encountered in exoplanet atmospheres such as high altitude haze layers.

Keywords: exoplanet atmospheres; radiative transfer; chemical kinetics
The Mass of the Milky Way from the H3 Survey

The mass of the Milky Way is a critical quantity that, despite decades of research, remains uncertain within a factor of two. Until recently, most studies have used dynamical tracers in the inner regions of the halo, relying on extrapolations to estimate the mass of the Milky Way. In this paper, we extend the hierarchical Bayesian model applied in Eadie & Juri to study the mass distribution of the Milky Way halo; the new model allows for the use of all available 6D phase-space measurements. We use kinematic data of halo stars out to 142 kpc, obtained from the H3 survey and Gaia EDR3, to infer the mass of the Galaxy. Inference is carried out with the No-U-Turn sampler, a fast and scalable extension of Hamiltonian Monte Carlo. We report a median mass enclosed within 100 kpc of $M(\lt 100\,\mathrm{kpc})={0.69}_{-0.04}^{+0.05}\times {10}^{12}\,{M}_{\odot }$ (68% Bayesian credible interval), or a virial mass of ${M}_{200}=M(\lt {216.2}_{-7.5}^{+7.5}\,\mathrm{kpc})={1.08}_{-0.11}^{+0.12}\times {10}^{12}\,{M}_{\odot }$ , in good agreement with other recent estimates. We analyze our results using posterior predictive checks and find limitations in the model's ability to describe the data. In particular, we find sensitivity with respect to substructure in the halo, which limits the precision of our mass estimates to ~15%.

Keywords: astrostatistics; astrostatistics tools; bayesian statistics; computational methods; galaxy dark matter halos; galaxy kinematics; halo stars; milky way dark matter halo; milky way mass
Simulating the Space Weather in the AU Mic System: Stellar Winds and Extreme Coronal Mass Ejections

Two close-in planets have been recently found around the M-dwarf flare star AU Microscopii (AU Mic). These Neptune-sized planets (AU Mic b and c) seem to be located very close to the so-called "evaporation valley" in the exoplanet population, making this system an important target for studying atmospheric loss on exoplanets. This process, while mainly driven by high-energy stellar radiation, will be strongly mediated by the space environment surrounding the planets. Here we present an investigation of this last area, performing 3D numerical modeling of the quiescent stellar wind from AU Mic, as well as time-dependent simulations describing the evolution of a highly energetic coronal mass ejection (CME) event in this system. Observational constraints on the stellar magnetic field and properties of the eruption are incorporated in our models. We carry out qualitative and quantitative characterizations of the stellar wind, the emerging CMEs, as well as the expected steady and transient conditions along the orbit of both exoplanets. Our results predict extreme space weather for AU Mic and its planets. This includes sub-Alfvénic regions for the large majority of the exoplanet orbits, very high dynamic and magnetic pressure values in quiescence (varying within 102-105 times the dynamic pressure experienced by Earth), and an even harsher environment during the passage of any escaping CME associated with the frequent flaring observed in AU Mic. These space weather conditions alone pose an immense challenge for the survival of exoplanetary atmospheres (if any) in this system.

Keywords: stellar magnetic fields; stellar coronal mass ejections; stellar winds; space weather; exoplanets; m stars; red dwarf flare stars; magnetohydrodynamical simulations; star-planet interactions; plasma astrophysics; high energy astrophysics
Charting Galactic Accelerations with Stellar Streams and Machine Learning

We present a data-driven method for reconstructing the galactic acceleration field from phase-space (position and velocity) measurements of stellar streams. Our approach is based on a flexible and differentiable fit to the stream in phase-space, enabling a direct estimate of the acceleration vector along the stream. Reconstruction of the local acceleration field can be applied independently to each of several streams, allowing us to sample the acceleration field due to the underlying galactic potential across a range of scales. Our approach is methodologically different from previous works, as a model for the gravitational potential does not need to be adopted beforehand. Instead, our flexible neural-network-based model treats the stream as a collection of orbits with a locally similar mixture of energies, rather than assuming that the stream delineates a single stellar orbit. Accordingly, our approach allows for distinct regions of the stream to have different mean energies, as is the case for real stellar streams. Once the acceleration vector is sampled along the stream, standard analytic models for the galactic potential can then be rapidly constrained. We find our method recovers the correct parameters for a ground-truth triaxial logarithmic halo potential when applied to simulated stellar streams. Alternatively, we demonstrate that a flexible potential can be constrained with a neural network, and standard multipole expansions can also be constrained. Our approach is applicable to simple and complicated gravitational potentials alike and enables potential reconstruction from a fully data-driven standpoint using measurements of slowly phase-mixing tidal debris.

Keywords: galaxy dynamics; stellar streams; galaxy mass distribution; galaxy stellar halos; milky way dark matter halo; galaxy structure
Discovery of One Neutron Star Candidate from Radial-velocity Monitoring

We report the discovery of one possible neutron star binary (P orb = 0.8666 days) by using LAMOST low-resolution spectroscopic data. The visible companion is a late A-type dwarf (T eff = 7900 ± 200 K; logg = 4.3 ± 0.2; M = 1.7 ± 0.1 M ⊙; R = 1.7 ± 0.2 R ⊙) at a distance of 1.11 ± 0.03 kpc. No double-lined feature can be seen from the Gran Telescopio Canarias/HORuS high-resolution spectra; thus the radial-velocity variation indicates an invisible object hiding in the binary. The system's optical light curves show clear ellipsoidal variability, suggesting that the visible companion is tidal distorted. By fitting the multiband light curves with the eclipsing light-curve (ELC) code and the Wilson-Devinney (WD) code, we constrain the mass of the invisible star to be 1.1-1.3 M ⊙. Spectral disentangling shows no additional component with optical absorption spectra, supporting the idea that the system contains one compact object. No X-ray or UV emission is detected in the ROSAT archive observations. Therefore, we suspect the invisible object is more likely a neutron star rather than a white dwarf. Our finding suggests the ability of LAMOST spectroscopic survey to discover X-ray-quiescent compact objects.

Keywords: ellipsoidal variable stars; compact binary stars; neutron stars
Dynamical Simulations of the First Globular Clusters

A Milky Way-like halo is simulated with tidally limited star clusters inserted in the dark matter halos present at high redshift. An n-body code augmented with velocity relaxation in the star clusters evolves the system. The stripped stars and remnant clusters that began in the lower mass subhalos have a distribution somewhat more extended than the dark matter halo, with a mean galactic radius of about 60 kpc inside 150 kpc, whereas the distribution of all stripped stars and clusters is more centrally concentrated than the dark matter. The clusters from low mass subhalos, those with a peak circular velocity of 12-18 $\,\mathrm{km}\,{{\rm{s}}}^{-1}$ , also produce most of the population's thin stellar streams. Together these suggest a search strategy for extremely metal-poor cluster stars and their remnants. The dependence of the stellar population distribution on subhalo mass is not seen in simulations that start clusters at lower redshift. The half mass radii of the clusters are set by the tidal fields of the initial subhalo, "dwarf galaxy" location, which causes the average half mass-radius to decrease with increasing redshift of formation. Starting clusters at greater than redshift 4 leads to cluster half mass radii approximately as seen in the Milky Way.

Keywords: globular star clusters; milky way stellar halo; milky way formation
Quasi-conservative Integration Method for Restricted Three-body Problem

The simplest restricted three-body problem, in which two massive points and a massless point particle attract one another according to Newton's law of inverse squares, has pulsating Hill's regions where the massless particle moves inside the closed regions surrounding only one of the massive points. Until now, no numerical integrator is known to maintain these regions, making it challenging to reproduce the phenomenon of gravitational capture of massless particles. In this article, we propose a second-order integrator that preserves Hill's regions to accurately simulate this phenomenon. Our integrator is based on a logarithmic Hamiltonian leapfrog method developed by Mikkola and Tanikawa and features a parameter that is adjusted to preserve a second-order approximation of an invariant integration relation of this restricted three-body problem. We analytically and numerically clarify that this integrator has the following properties: (i) it retains the collinear and triangular Lagrangian solutions regardless of the eccentricity of the relative orbit of the two massive points, (ii) it has the same Hill stability criterion for satellite-type motion of the massless point particle as the original problem, and (iii) it conserves the Jacobi integral for zero eccentricity.

Keywords: astronomical simulations; celestial mechanics; three-body problem; analytical mathematics; lagrangian points; roche limit
Assessing the Distribution of Water Ice and Other Volatiles at the Lunar South Pole with LUVMI-X: A Mission Concept

The search for exploitable deposits of water and other volatiles at the Moon's poles has intensified considerably in recent years, due to the renewed strong interest in lunar exploration. With the return of humans to the lunar surface on the horizon, the use of locally available resources to support long-term and sustainable exploration programs, encompassing both robotic and crewed elements, has moved into focus of public and private actors alike. Our current knowledge about the distribution and concentration of water and other volatiles in the lunar rocks and regolith is, however, too limited to assess the feasibility and economic viability of resource-extraction efforts. On a more fundamental level, we currently lack sufficiently detailed data to fully understand the origins of lunar water and its migration to the polar regions. In this paper, we present LUVMI-X, a mission concept intended to address the shortage of in situ data on volatiles on the Moon that results from a recently concluded design study. Its central element is a compact rover equipped with complementary instrumentation capable of investigating both the surface and shallow subsurface of illuminated and shadowed areas at the lunar south pole. We describe the rover and instrument design, the mission's operational concept, and a preliminary landing-site analysis. We also discuss how LUVMI-X fits into the diverse landscape of lunar missions under development.

Keywords: the moon; lunar science; lunar surface; lunar mineralogy; lunar craters; cosmic rays; solar radiation; space weather; lunar probes; rovers; space vehicle instruments
Dust Properties of Comets Observed by Spitzer

As comets journey into the inner solar system, they deliver particulates and volatile gases into their comae that reveal the most primitive materials in the solar system. Cometary dust particles provide crucial information for assessing the physicochemical conditions in the outer disk from which they formed. Compared to the volatiles and soluble organics, the refractory dust particles are more robust and may be traceable to other small bodies. Using data from the Spitzer Heritage Archive, we present thermal dust models of 57 observations of 33 comets observed spectroscopically with the NASA Spitzer Space Telescope. This comet spectral survey offers the opportunity to study comets with data from the same instrument, reduced by the same methods, and fitted by the same thermal model using the same optical constants. The submicron dust tends to be dominated by amorphous carbon, and the submicron silicate mass tends to be dominated by amorphous silicate materials. We discuss the implications of these findings as they relate to Mg-rich crystalline silicates, which are high-temperature condensates, as well as to potential ion irradiation of amorphous Mg:Fe silicates prior to their incorporation into comets. These results impact our understanding of the protoplanetary disk conditions of planetesimal formation. Lastly, we cannot definitively conclude that a distinct difference exists in the dust composition between the Oort cloud and Jupiter-family comet dynamical population as a whole.

Keywords: long period comets; short period comets; comet origins; dust composition; infrared spectroscopy
A Photometric and Spectroscopic Study of the Short-period Algol EW Boötis with a δ Sct Pulsator

In this paper, we present Transiting Exoplanet Survey Satellite (TESS) photometry and high-resolution spectra of the short-period Algol EW Boo. We obtained double-lined radial velocities (RVs) from the time-series spectra and measured the effective temperature of the primary star as T eff,1 = 8560 ± 118 K. For the orbital period study, we collected all times of minima available for over the last 30 yr. It was found that the eclipse timing variation of the system could be represented by a periodic oscillation of 17.6 ± 0.3 yr with a semiamplitude of 0.0041 ± 0.0001 day. The orbital and physical parameters were derived by simultaneously analyzing the TESS light and RV curves using the Wilson-Devinney (WD) binary star modeling code. The component masses and radii were showed over 3% precision: M 1 = 2.67 ± 0.08 M ⊙, M 2 = 0.43 ± 0.01 M ⊙, R 1 = 2.01 ± 0.02 R ⊙, and R 2 = 1.35 ± 0.01 R ⊙. Furthermore, multiple frequency analyses were performed for the light-curve residuals from the WD model. As a result, we detected 17 pressure-mode pulsations in the region of 40.15-52.37 day-1. The absolute dimensions and pulsation characteristics showed that the δ Sct pulsator was the more massive and hotter primary star of the EW Boo.

Keywords: eclipsing binary stars; algol variable stars; pulsating variable stars
NICMOS Kernel-phase Interferometry. II. Demographics of Nearby Brown Dwarfs

Star formation theories have struggled to reproduce binary brown dwarf population demographics (e.g., frequency, separation, and mass ratio). Kernel-phase interferometry is sensitive to companions at separations inaccessible to classical imaging, enabling tests of these theories at new physical scales below the hydrogen burning limit. We analyze the detections and sensitivity limits from our previous kernel-phase analysis of archival HST/NICMOS surveys of field brown dwarfs. After estimating physical properties of the 105 late-M to T dwarfs using Gaia distances and evolutionary models, we use a Bayesian framework to compare these results to a model companion population defined by log-normal separation and power-law mass-ratio distributions. When correcting for Malmquist bias, we find a companion fraction of $F={0.11}_{-0.03}^{+0.04}$ and a separation distribution centered at $\rho ={2.2}_{-1.0}^{+1.2}$ au, smaller and tighter than seen in previous studies. We also find a mass-ratio power-law index that strongly favors equal-mass systems: $\gamma ={4.0}_{-1.5}^{+1.7}-{11}_{-3}^{+4}$ depending on the assumed age of the field population (0.9-3.1 Gyr). We attribute the change in values to our use of kernel-phase interferometry, which enables us to resolve the peak of the semimajor axis distribution with significant sensitivity to low-mass companions. We confirm the previously seen trends of decreasing binary fraction with decreasing mass and a strong preference for tight and equal-mass systems in the field-age substellar regime; only ${0.9}_{-0.6}^{+1.1}$ % of systems are wider than 20 au and $\lt {1.0}_{-0.6}^{+1.4}$ % of systems have a mass ratio q < 0.6. We attribute this to turbulent fragmentation setting the initial conditions followed by a brief period of dynamical evolution, removing the widest and lowest-mass companions, before the birth cluster dissolves.

Keywords: brown dwarfs; l dwarfs; t dwarfs; direct detection interferometry; direct imaging; hubble space telescope; infrared astronomy; binary stars; star formation
Jules Verne's Formulation of the Fermi Question

Jules Verne's novel Around the Moon envisions the circumlunar flight of a crewed projectile around the lunar farside ending with a safe return to Earth. The novel is justifiably famous, partly because of certain parallels it contains to the U.S. Apollo program a century later. What is less appreciated is that the novel contains a rather direct statement of what would later become known as the Fermi Question or Fermi Paradox.

Keywords: history of astronomy; sociology of astronomy; astrobiology
Strong Post-merger Gravitational Radiation of GW170817-like Events

The post-merger gravitational-wave (GW) radiation of the remnant formed in the binary neutron star (BNS) coalescence has not been directly measured yet. We show in this work that the properties of the BNS involved in GW170817, additionally constrained by PSR J0030+0451, the lower limit on the maximum gravitational mass of nonrotating neutron star (NS), and some nuclear data, are in favor of strong post-merger GW radiation. This conclusion applies to the mergers of Galactic BNS systems as well. Significant post-merger GW radiation is also preferred to improve the consistency between the maximum gravitational mass of the nonrotating NS inferred from GW170817/GRB170817A/AT2017gfo and the latest mass measurements of pulsars. The prominent post-merger gravitational radiation of GW170817-like events are expected to be detectable by advanced LIGO/Virgo detectors in the next decade and then shed valuable light on the properties of the matter in the extremely high density.

Keywords: gravitational waves; neutron stars; gravitational energy
A New Physical Picture for Active Galactic Nuclei Lacking Optical Emission Lines

In this work, we use ~500 low-redshift (z ~ 0.1) X-ray active galactic nuclei (AGNs) observed by XMM-Newton and the Sloan Digital Sky Survey (SDSS) to investigate the prevalence and nature of AGNs that apparently lack optical emission lines ("optically dull AGNs"). Although one quarter of spectra appear absorption-line dominated in visual assessment, line extraction with robust continuum subtraction from the MPA/JHU catalog reveals usable [O III] measurements in 98% of the sample, allowing us to study [O III]-underluminous AGNs together with more typical AGNs in the context of the L [O III]-L X relation. We find that "optically dull AGNs" do not constitute a distinct population of AGNs. Instead, they are the [O III]-underluminous tail of a single, unimodal L [O III]-L X relation that has substantial scatter (0.6 dex). We find the degree to which an AGN is underluminous in [O III] correlates with the specific star formation rate or D 4000 index of the host, which are both linked to the molecular gas fraction. Thus the emerging physical picture for the large scatter seems to involve the gas content of the narrow-line region. We find no significant role for previously proposed scenarios for the presence of optically dull AGNs, such as host dilution or dust obscuration. Despite occasionally weak lines in SDSS spectra, >80% of X-ray AGNs are identified as such with the Baldwin-Phillips-Terlevich diagram. More than 90% are classified as AGNs based only on [N II]/Hα, providing more complete AGN samples when [O III] or Hβ are weak. X-ray AGNs with LINER spectra obey essentially the same L [O III]-L X relation as Seyfert 2s, suggesting their line emission is produced by AGN activity.

Keywords: active galaxies; liner galaxies; emission line galaxies; seyfert galaxies; x-ray active galactic nuclei; active galactic nuclei