adsabs/SciX_UAT_keywords huggingface dataset:
Three-dimensional Analysis of the Minispiral at the Galactic Center: Orbital Parameters, Periods, and the Mass of the Black Hole

In this paper we simultaneously fit the orbits and line-of-sight velocities of the ionized gas around the supermassive black hole, Sagittarius A* (Sgr A*), at the center of the Milky Way. The data we use are taken with the K-band Multi Object Spectrograph (KMOS), presented in Feldmeier-Krause et al., and cover the central ∼2 pc of the Milky Way. From the brightest gas emission line in the K-band, the Brγ line, we derive the spatial distribution and line-of-sight velocities of the gas in the minispiral. Using the flux distribution and the line-of-sight velocity information, we perform a fit to the three main gas streamers in the minispiral, the Northern Arm, Eastern Arm, and Western Arc, using a Bayesian modeling method, and are able to reconstruct the three-dimensional orbits of these gas streamers. With the best-fit orbital parameters and the measured line-of-sight velocities, we constrain the mass of Sgr A*. The orbit of the Eastern Arm is the one that is best constrained using our data. It gives a best-fit orbital period of ${17.4}_{-11.6}^{+31.0}\times {10}^{3}$ yr and results in an enclosed mass of ${14.9}_{-10.4}^{+69.4}\times {10}^{6}{M}_{\odot }.$

Keywords: h ii regions; galactic center
A Search for Light Hydrides in the Envelopes of Evolved Stars

We report a search for the diatomic hydrides SiH, PH, and FeH along the line of sight toward the chemically rich circumstellar envelopes of IRC+10216 and VY Canis Majoris. These molecules are thought to form in high-temperature regions near the photospheres of those stars, and may then further react via gas-phase and dust-grain interactions leading to more complex species, but have yet to be constrained by observation. We used the German Receiver for Astronomy at Terahertz Frequencies spectrometer on the Stratospheric Observatory for Infrared Astronomy to search for rotational emission lines of these molecules in four spectral windows ranging from 600 to 1500 GHz. Although none of the targeted species was detected in our search, we report their upper limit abundances in each source and discuss how they influence the current understanding of hydride chemistry in dense circumstellar media. We attribute the nondetections of these hydrides to their compact source sizes, high barriers of formation, and proclivity to react with other molecules in the winds.

Keywords: astrochemistry; chemical abundances; asymptotic giant branch stars; red supergiant stars; circumstellar envelopes; interstellar molecules
CCAT-prime Collaboration: Science Goals and Forecasts with Prime-Cam on the Fred Young Submillimeter Telescope

We present a detailed overview of the science goals and predictions for the Prime-Cam direct-detection camera-spectrometer being constructed by the CCAT-prime collaboration for dedicated use on the Fred Young Submillimeter Telescope (FYST). The FYST is a wide-field, 6 m aperture submillimeter telescope being built (first light in late 2023) by an international consortium of institutions led by Cornell University and sited at more than 5600 m on Cerro Chajnantor in northern Chile. Prime-Cam is one of two instruments planned for FYST and will provide unprecedented spectroscopic and broadband measurement capabilities to address important astrophysical questions ranging from Big Bang cosmology through reionization and the formation of the first galaxies to star formation within our own Milky Way. Prime-Cam on the FYST will have a mapping speed that is over 10 times greater than existing and near-term facilities for high-redshift science and broadband polarimetric imaging at frequencies above 300 GHz. We describe details of the science program enabled by this system and our preliminary survey strategies.

Keywords: wide-field telescopes; astronomical instrumentation; galaxy evolution; reionization; protogalaxies; time domain astronomy; observational cosmology; interstellar dust; star formation; sunyaev-zeldovich effect; galaxy clusters; recombination (cosmology)
The Robotic Multiobject Focal Plane System of the Dark Energy Spectroscopic Instrument (DESI)

A system of 5020 robotic fiber positioners was installed in 2019 on the Mayall Telescope, at Kitt Peak National Observatory. The robots automatically retarget their optical fibers every 10-20 minutes, each to a precision of several microns, with a reconfiguration time of fewer than 2 minutes. Over the next 5 yr, they will enable the newly constructed Dark Energy Spectroscopic Instrument (DESI) to measure the spectra of 35 million galaxies and quasars. DESI will produce the largest 3D map of the universe to date and measure the expansion history of the cosmos. In addition to the 5020 robotic positioners and optical fibers, DESI's Focal Plane System includes six guide cameras, four wave front cameras, 123 fiducial point sources, and a metrology camera mounted at the primary mirror. The system also includes associated structural, thermal, and electrical systems. In all, it contains over 675,000 individual parts. We discuss the design, construction, quality control, and integration of all these components. We include a summary of the key requirements, the review and acceptance process, on-sky validations of requirements, and lessons learned for future multiobject, fiber-fed spectrographs.

Keywords: dark energy; astronomical instrumentation; spectrometers; galaxy spectroscopy
Constraints on the Mass Accretion Rate onto the Supermassive Black Hole of Cygnus A Using the Submillimeter Array

We present the first detailed polarimetric studies of Cygnus A at 230 GHz with the Submillimeter Array (SMA) to constrain the mass accretion rate onto its supermassive black hole. We detected the polarized emission associated with the core at a fractional polarization of $0.73\pm 0.15 \% $ . This low fractional polarization suggests that the polarized emission is highly depolarized. One of the possible explanations is due to a significant variance in the Faraday rotation measure within the synthesized beam. By assuming the Faraday depolarization caused by inhomogeneous column density of the magnetized plasma associated with the surrounding radiatively-inefficient accretion flow within the SMA beam, we derived the constraint on the mass accretion rate to be larger than 0.15 ${M}_{\odot }$ yr-1 at the Bondi radius. The derived constraint indicates that an adiabatic inflow-outflow solution or an advection-dominated accretion flow should be preferable as the accretion flow model in order to explain the jet power of Cygnus A.

Keywords: galaxy accretion disks; galaxy accretion; galaxy physics; active galaxies; active galactic nuclei; radio galaxies; astronomical techniques; polarimetry; submillimeter astronomy; radio astronomy
Blazar Radio and Optical Survey (BROS): A Catalog of Blazar Candidates Showing Flat Radio Spectrum and Their Optical Identification in Pan-STARRS1 Surveys

Utilizing the latest and the most sensitive radio and optical catalogs, we completed a new blazar candidate catalog, Blazar Radio and Optical Survey (BROS), which includes 88,211 sources located at decl. δ > -40° and outside the galactic plane ( $| b| \gt 10^\circ $ ). We list compact flat-spectrum radio sources of α > -0.6 (α is defined as Fν ∝ να) from 0.15 GHz TGSS to 1.4 GHz NVSS catalogs. We further identify optical counterparts of the selected sources by cross-matching with Pan-STARRS1 photometric data. Color-color and color-magnitude plots for the selected BROS sources clearly show two distinct populations, a "quasar-like" population consisting of both flat-spectrum radio quasars and BL Lac type objects. On the other hand, an "elliptical-like" population of mostly BL Lac type objects is buried in the elliptical galaxy. The latter population is also reported in previous catalogs, but the BROS catalog provided a new larger sample of this population, due to the lower radio flux threshold of our selection. Model calculations show that the "elliptical-like" population consists of elliptical galaxies located at redshift z ≲ 0.5, which is also supported by the logN-logS distribution of the power-law index of 1.49 ± 0.05. This BROS catalog is useful for identifying the electromagnetic counterparts of ultra-high-energy cosmic rays and PeV neutrinos recently detected by IceCube, as well as nearby BL Lac objects detectable by future high-sensitivity TeV telescopes, such as the Cherenkov Telescope Array.

Keywords: blazars; radio active galactic nuclei; catalogs
The X-Ray Reactivation of the Radio Bursting Magnetar SGR J1935+2154

A few years after its discovery as a magnetar, SGR J1935+2154 started a new burst-active phase on 2020 April 27, accompanied by a large enhancement of its X-ray persistent emission. Radio single bursts were detected during this activation, strengthening the connection between magnetars and fast radio bursts. We report on the X-ray monitoring of SGR J1935+2154 from ∼3 days prior to ∼3 weeks after its reactivation, using Swift, the Nuclear Spectroscopic Telescope Array (NuSTAR), and the Neutron Star Interior Composition Explorer (NICER). We detected X-ray pulsations in the NICER and NuSTAR observations, and constrained the spin period derivative to $| \dot{P}| \lt 3\times {10}^{-11}$ s s-1 (3σ c.l.). The pulse profile showed a variable shape switching between single and double-peaked as a function of time and energy. The pulsed fraction decreased from ∼34% to ∼11% (5-10 keV) over ∼10 days. The X-ray spectrum was well fit by an absorbed blackbody model with temperature decreasing from kTBB ∼ 1.6 to 0.45-0.6 keV, plus a nonthermal power-law component (Γ ∼ 1.2) observed up to ∼25 keV with NuSTAR. The 0.3-10 keV X-ray luminosity increased in less than 4 days from $\sim 6\times {10}^{33}{d}_{6.6}^{2}$ erg s-1 to about $3\times {10}^{35}{d}_{6.6}^{2}$ erg s-1 and then decreased again to $2.5\times {10}^{34}{d}_{6.6}^{2}$ erg s-1 over the following 3 weeks of the outburst, where d6.6 is the source distance in units of 6.6 kpc. We also detected several X-ray bursts, with properties typical of short magnetar bursts.

Keywords: neutron stars; magnetars; radio pulsars; x-ray bursts; x-ray transient sources
Uranus's Influence on Neptune's Exterior Mean-motion Resonances

Neptune's external mean-motion resonances play an important role in sculpting the observed population of trans-Neptunian objects (TNOs). The population of scattering TNOs is known to "stick" to Neptune's resonances while evolving in semimajor axis (a), though simulations show that resonance sticking is less prevalent at a ≳ 200–250 au. Here we present an extensive numerical exploration of the strengths of Neptune's resonances for scattering TNOs with perihelion distances q = 33 au. We show that the drop-off in resonance sticking for the large a scattering TNOs is not a generic feature of scattering dynamics but can instead be attributed to the specific configuration of Neptune and Uranus in our solar system. In simulations with just Uranus removed from the giant planet system, Neptune's resonances are strong in the scattering population out to at least ∼300 au. Uranus and Neptune are near a 2:1 period ratio, and the variations in Neptune's orbit resulting from this near-resonance are responsible for destabilizing Neptune's resonances for high-e TNO orbits beyond the ∼20:1 resonance at a ≈ 220 au. Direct interactions between Uranus and the scattering population are responsible for slightly weakening Neptune's closer-in resonances. In simulations where Neptune and Uranus are placed in their mutual 2:1 resonance, we see almost no stable libration of scattering particles in Neptune's external resonances. Our results have important implications for how the strengths of Neptune's distant resonances varied during the epoch of planet migration when the Neptune–Uranus period ratio was evolving. These strength variations likely affected the distant scattering, resonant, and detached TNO populations.

Keywords: resonant kuiper belt objects; orbital resonances; celestial mechanics; trans-neptunian objects
The Absolute Magnitudes of 1991T-like Supernovae

1991T-like supernovae are the luminous, slow-declining extreme of the Branch shallow-silicon (SS) subclass of Type Ia supernovae. They are distinguished by extremely weak Ca II H & K and Si II λ6355 and strong Fe III absorption features in their optical spectra at pre-maximum phases, and have long been suspected to be over-luminous compared to normal Type Ia supernovae. In this paper, the pseudo-equivalent width of the Si II λ6355 absorption obtained at light curve phases from ≤ +10 days is combined with the morphology of the i-band light curve to identify a sample of 1991T-like supernovae in the Carnegie Supernova Project II. Hubble diagram residuals show that, at optical as well as near-infrared wavelengths, these events are over-luminous by ~0.1-0.5 mag with respect to the less extreme Branch SS (1999aa-like) and Branch core-normal supernovae with similar B-band light-curve decline rates. * This paper includes data gathered with the 6.5 meter Magellan telescopes at Las Campanas Observatory, Chile.

Keywords: supernovae; type ia supernovae; observational cosmology
The Novel Obscured State of the Stellar-mass Black Hole GRS 1915+105

GRS 1915+105 is a stellar-mass black hole that is well known for exhibiting at least 12 distinct classes of X-ray variability and correlated multi-wavelength behavior. Despite such extraordinary variability, GRS 1915+105 remained one of the brightest sources in the X-ray sky. However, in early 2019, the source became much fainter, apparently entering a new accretion state. Here, we report the results of an extensive, year-long monitoring campaign of GRS 1915+105 with the Neil Gehrels Swift Observatory. During this interval, the flux of GRS 1915+105 gradually diminished; the observed count rate eventually dropped by two orders of magnitude. Simple but robust spectral fits to these monitoring observations show that this new state results from the combination of a dramatic and persistent increase in internal obscuration, and a reduced mass accretion rate. The internal obscuration is the dominant effect, with a median value of NH = 7 × 1023 cm-2. In a number of observations, the source appears to be Compton-thick. We suggest that this state should be identified as the "obscured state," and discuss the implications of this new (or rarely observed) accretion mode for black holes across the mass scale.

Keywords: x-ray binary stars; x-ray astronomy; accretion; stellar mass black holes; low-mass x-ray binary stars
Atmosphere Models of Brown Dwarfs Irradiated by White Dwarfs: Analogs for Hot and Ultrahot Jupiters

Irradiated brown dwarfs (BDs) provide natural laboratories to test our understanding of substellar and irradiated atmospheres. A handful of short-period BDs around white dwarfs (WDs) have been observed, but the uniquely intense UV-dominated irradiation presents a modeling challenge. Here, we present the first fully self-consistent 1D atmosphere models that take into account the UV irradiation's effect on the object's temperature structure. We explore two BD-WD systems, namely WD-0137-349 and EPIC-212235321. WD-0137-349B has an equilibrium temperature that would place it in the transition between hot and ultra-hot Jupiters, while EPIC-212235321B has an equilibrium temperature higher than all ultra-hot Jupiters except KELT-9b. We explore some peculiar aspects of irradiated BD atmospheres and show that existing photometry can be well-fit with our models. Additionally, the detections of atomic emission lines from these BDs can be explained by a strong irradiation-induced temperature inversion, similar to inversions recently explored in ultra-hot Jupiters. Our models of WD-0137-349B can reproduce the observed equivalent width of many but not all of these atomic lines. We use the observed photometry of these objects to retrieve the temperature structure using the PHOENIX ExoplaneT Retrieval Algorithm and demonstrate that the structures are consistent with our models, albeit somewhat cooler at low pressures. We then discuss the similarities and differences between this class of irradiated brown dwarf and the lower-mass ultra-hot Jupiters. Lastly, we describe the behavior of irradiated BDs in color-magnitude space to show the difficulty in using otherwise well-tested methods for isolated objects to classify irradiated BDs.

Keywords: brown dwarfs; binary stars; stellar atmospheres; exoplanet atmospheres; theoretical models; infrared photometry; broad band photometry; spectroscopy
BASS. XXIV. The BASS DR2 Spectroscopic Line Measurements and AGN Demographics

We present the second catalog and data release of optical spectral line measurements and active galactic nucleus (AGN) demographics of the BAT AGN Spectroscopic Survey, which focuses on the Swift-BAT hard X-ray detected AGNs. We use spectra from dedicated campaigns and publicly available archives to investigate spectral properties of most of the AGNs listed in the 70 month Swift-BAT all-sky catalog; specifically, 743 of the 746 unbeamed and unlensed AGNs (99.6%). We find a good correspondence between the optical emission line widths and the hydrogen column density distributions using the X-ray spectra, with a clear dichotomy of AGN types for N H = 1022 cm‑2. Based on optical emission-line diagnostics, we show that 48%–75% of BAT AGNs are classified as Seyfert, depending on the choice of emission lines used in the diagnostics. The fraction of objects with upper limits on line emission varies from 6% to 20%. Roughly 4% of the BAT AGNs have lines too weak to be placed on the most commonly used diagnostic diagram, [O III]λ5007/Hβ versus [N II]λ6584/Hα, despite the high signal-to-noise ratio of their spectra. This value increases to 35% in the [O III]λ5007/[O II]λ3727 diagram, owing to difficulties in line detection. Compared to optically selected narrow-line AGNs in the Sloan Digital Sky Survey, the BAT narrow-line AGNs have a higher rate of reddening/extinction, with Hα/Hβ > 5 (∼36%), indicating that hard X-ray selection more effectively detects obscured AGNs from the underlying AGN population. Finally, we present a subpopulation of AGNs that feature complex broad lines (34%, 250/743) or double-peaked narrow emission lines (2%, 17/743).

Keywords: supermassive black holes; active galactic nuclei; x-ray active galactic nuclei; agn host galaxies; quasars
Kinetic Simulations of Radiative Magnetic Reconnection in the Coronae of Accreting Black Holes

We perform 2D and 3D particle-in-cell simulations of reconnection in magnetically dominated e± plasmas subject to strong Compton cooling. Magnetic reconnection under such conditions can operate in accretion disk coronae around black holes, which produce hard X-rays through Comptonization. Our simulations show that most of the plasma in the reconnection layer is kept cold by Compton losses and locked in magnetically dominated plasmoids with a small thermal pressure. Compton drag clears cavities inside plasmoids and also affects their bulk motions. These effects, however, weakly change the reconnection rate and the plasmoid size distribution from those in nonradiative reconnection. This demonstrates that the reconnection dynamics is governed by similar magnetic stresses in both cases and weakly affected by thermal pressure. We examine the energy distribution of particles energized by radiative reconnection and observe two distinct components: (1) A mildly relativistic peak, which results from bulk motions of cooled plasmoids. This component receives most of the dissipated reconnection power and dominates the output X-ray emission. The peak has a quasi-Maxwellian shape with an effective temperature of ∼100 keV. Thus, it mimics thermal Comptonization used previously to fit hard-state spectra of accreting black holes. (2) A high-energy tail, which receives ∼20% of the dissipated reconnection power. It is populated by particles accelerated impulsively at X-points or "picked up" by fast outflows from X-points. The high-energy particles immediately cool, and their inverse Compton emission explains the MeV spectral tail detected in the hard state of Cyg X-1. Our first-principle simulations support magnetic reconnection as a mechanism powering hard X-ray emission from magnetically dominated regions of accreting black holes.

Keywords: astrophysical black holes; stellar accretion disks; accretion; solar magnetic reconnection; relativistic jets; relativistic disks
The Tilt of the Velocity Ellipsoid of Different Galactic Disk Populations

The tilt of the velocity ellipsoid is a helpful tracer of the gravitational potential of the Milky Way. In this paper, we use nearly 140,000 red clump (RC) stars selected from LAMOST and Gaia to make a detailed analysis of the tilt of the velocity ellipsoid for various populations, as defined by stellar ages and chemical information, within 4.5 ≤ R ≤ 15.0 kpc and ∣Z∣ ≤ 3.0 kpc, respectively. The tilt angle of the velocity ellipsoid of the RC sample stars is accurately described as α = α 0 $\arctan $ (Z/R) with α 0 = (0.68 ± 0.05). This indicates the alignment of the velocity ellipsoid is between cylindrical and spherical, implying that any deviation from the spherical alignment of the velocity ellipsoid may be caused by the gravitational potential of the baryonic disk. The results of various populations suggest that α 0 displays an age and population dependence, with values α 0 = (0.72 ± 0.08) and α 0 = (0.64 ± 0.07) for the thin and thick disks, respectively, and α 0 displays a decreasing trend as age (and [α/Fe]) increases, meaning that the velocity ellipsoids of the kinematically relaxed stars are mainly dominated by the gravitational potential of the baryonic disk. We determine the α 0 -R relation for various populations, finding that α 0 displays oscillations with R for the different populations. The oscillations in α 0 appear in both kinematically hot and cold populations, indicating that resonances with the Galactic bar are the most likely origin for these oscillations.

Keywords: stellar abundances; stellar kinematics; milky way disk; milky way formation; milky way evolution
A Swing of the Pendulum: The Chemodynamics of the Local Stellar Halo Indicate Contributions from Several Radial Merger Events

We find that the chemical abundances and dynamics of APOGEE and GALAH stars in the local stellar halo are inconsistent with a scenario in which the inner halo is primarily composed of debris from a single massive, ancient merger event, as has been proposed to explain the Gaia-Enceladus/Gaia Sausage (GSE) structure. The data contain trends of chemical composition with energy that are opposite to expectations for a single massive, ancient merger event, and multiple chemical evolution paths with distinct dynamics are present. We use a Bayesian Gaussian mixture model regression algorithm to characterize the local stellar halo, and find that the data are fit best by a model with four components. We interpret these components as the Virgo Radial Merger (VRM), Cronus, Nereus, and Thamnos; however, Nereus and Thamnos likely represent more than one accretion event because the chemical abundance distributions of their member stars contain many peaks. Although the Cronus and Thamnos components have different dynamics, their chemical abundances suggest they may be related. We show that the distinct low- and high-α halo populations from Nissen & Schuster are explained by VRM and Cronus stars, as well as some in situ stars. Because the local stellar halo contains multiple substructures, different popular methods of selecting GSE stars will actually select different mixtures of these substructures, which may change the apparent chemodynamic properties of the selected stars. We also find that the Splash stars in the Solar region are shifted to higher v ϕ and slightly lower [Fe/H] than previously reported.

Keywords: galactic archaeology; stellar astronomy; milky way stellar halo; gaussian mixture model