adsabs/SciX_UAT_keywords huggingface dataset:
A New Cosmic-Ray-driven Instability

Cosmic-ray-driven (CR-driven) instabilities play a decisive role during particle acceleration at shocks and CR propagation in galaxies and galaxy clusters. These instabilities amplify magnetic fields and modulate CR transport so that the intrinsically collisionless CR population is tightly coupled to the thermal plasma and provides dynamical feedback. Here, we show that CRs with a finite pitch angle drive electromagnetic waves (along the background magnetic field) unstable on intermediate scales between the gyroradii of CR ions and electrons as long as CRs are drifting with a velocity less than half of the Alfvén speed of electrons. By solving the linear dispersion relation, we show that this new instability typically grows faster by more than an order of magnitude in comparison to the commonly discussed resonant instability at the ion gyroscale. We find the growth rate for this intermediate-scale instability and identify the growing modes as background ion-cyclotron modes in the frame that is comoving with the CRs. We confirm the theoretical growth rate with a particle-in-cell simulation and study the nonlinear saturation of this instability. We identify three important astrophysical applications of this intermediate-scale instability, which is expected to (1) modulate CR transport and strengthen CR feedback in galaxies and galaxy clusters, (2) enable electron injection into the diffusive shock acceleration process, and (3) decelerate CR escape from the sites of particle acceleration, which would generate gamma-ray halos surrounding CR sources such as supernova remnants.

Keywords: galactic cosmic rays; supernova remnants; interstellar medium
Mid-infrared Detections of Type I Supernovae and Unclassified Possible Supernovae with NEOWISE

We describe 238 mid-infrared detections of supernovae and 195 possible supernovae in co-added images of the NEOWISE mission. We find one type Ia supernova (SN 2015cp), which has a mid-infrared evolution that is similar to known type Ia with long-lived mid-infrared detections. We also find long-lived mid-infrared detections in one type Ic (SN 2017dio) and one type Ib (SN 2016ajo). Additionally we provide measured magnitudes for most of our detections. We also find two transients, which we suspect to be TDEs: ASASSN-18ap and ATLAS17jrp.

Keywords: type ia supernovae; type ib supernovae; type ic supernovae; type ii supernovae; tidal disruption; infrared astronomy; infrared sources; massive stars; circumstellar matter
RAIKOU (来光): A General Relativistic, Multiwavelength Radiative Transfer Code

We present a general relativistic radiative transfer code RAIKOU (来光) for multiwavlength studies of spectra and images including the black hole shadows around Kerr black holes. Important radiative processes in hot plasmas around black holes, i.e., (cyclo-)synchrotron, bremsstrahlung emission/absorption, and Compton/inverse-Compton scattering, are incorporated. The Maxwell-Jüttner and single/broken power-law electron distribution functions are implemented to calculate the radiative transfer via both thermal and nonthermal electrons. Two calculation algorithms are implemented for studies of the images and broadband spectra. An observer-to-emitter ray-tracing algorithm, which inversely solves the radiative transfer equation from the observer screen to emitting plasmas, is suitable for an efficient calculations of the images, e.g., the black hole shadows observed by the Event Horizon Telescope, and spectra without Compton effects. On the other hand, an emitter-to-observer Monte Carlo algorithm, by which photons are transported with a Monte Carlo method including the effects of Compton/inverse-Compton scatterings, enables us to compute multiwavelength spectra, with their energy bands broadly ranging from radio to very high energy gamma-ray. The X-ray black hole shadows, which are formed via synchrotron emission and inverse-Compton scattering processes and will be observed in the future X-ray interferometry missions, can be also computed with this algorithm. The code is generally applicable to accretion flows around Kerr black holes with relativistic jets and winds/coronae with various mass accretion rates (i.e., radiatively inefficient accretion flows, super-Eddington accretion flows, and others). We demonstrate an application of the code to a radiatively inefficient accretion flow onto a supermassive black hole.

Keywords: black hole physics; general relativity; radiative transfer; accretion; relativistic jets; high energy astrophysics; computational methods
Eclipsing Binaries in the Open Cluster Ruprecht 147. III. The Triple System EPIC 219552514 at the Main-sequence Turnoff

Spectroscopic observations are reported for the 2.75 day, double-lined, detached eclipsing binary EPIC 219552514 located at the turnoff of the old nearby open cluster Ruprecht 147. A joint analysis of our radial-velocity measurements and the K2 light curve leads to masses of ${M}_{1}={1.509}_{-0.056}^{+0.063}\,{M}_{\odot }$ and ${M}_{2}={0.649}_{-0.014}^{+0.015}\,{M}_{\odot }$ for the primary and secondary, along with radii of ${R}_{1}={2.505}_{-0.031}^{+0.026}\,{R}_{\odot }$ and ${R}_{2}={0.652}_{-0.012}^{+0.013}\,{R}_{\odot }$ , respectively. The effective temperatures are 6180 ± 100 K for the F7 primary and 4010 ± 170 K for the late K secondary. The orbit is circular, and the stars' rotation appears to be synchronized with the orbital motion. This is the third eclipsing system analyzed in the same cluster, following our earlier studies of EPIC 219394517 and EPIC 219568666. By comparison with stellar evolution models from the PARSEC series, we infer an age of ${2.67}_{-0.55}^{+0.39}$ Gyr that is consistent with the estimates for the other two systems. EPIC 219552514 is a hierarchical triple system, with the period of the slightly eccentric outer orbit being 463 days. The unseen tertiary is either a low-mass M dwarf or a white dwarf.

Keywords: eclipsing binary stars; fundamental parameters of stars; stellar evolution; open star clusters; stellar ages
Calibrating the Davis-Chandrasekhar-Fermi Method with Numerical Simulations: Uncertainties in Estimating the Magnetic Field Strength from Statistics of Field Orientations

The Davis-Chandrasekhar-Fermi (DCF) method is widely used to indirectly estimate the magnetic field strength from the plane-of-sky field orientation. In this work, we present a set of 3D MHD simulations and synthetic polarization images using radiative transfer of clustered massive star-forming regions. We apply the DCF method to the synthetic polarization maps to investigate its reliability in high-density molecular clumps and dense cores where self-gravity is significant. We investigate the validity of the assumptions of the DCF method step by step and compare the model and estimated field strength to derive the correction factors for the estimated uniform and total (rms) magnetic field strength at clump and core scales. The correction factors in different situations are cataloged. We find the DCF method works well in strong-field cases. However, the magnetic field strength in weak-field cases could be significantly overestimated by the DCF method when the turbulent magnetic energy is smaller than the turbulent kinetic energy. We investigate the accuracy of the angular dispersion function (ADF; a modified DCF method) method on the effects that may affect the measured angular dispersion and find that the ADF method correctly accounts for the ordered field structure, the beam smoothing, and the interferometric filtering, but may not be applicable to account for the signal integration along the line of sight in most cases. Our results suggest that the DCF methods should be avoided to be applied below ~0.1 pc scales if the effect of line-of-sight signal integration is not properly addressed.

Keywords: magnetic fields; radiative transfer simulations; magnetohydrodynamical simulations; star formation
Dwarf Galaxy Formation with and without Dark Matter-Baryon Streaming Velocities

We study how supersonic streaming velocities of baryons relative to dark matter-a large-scale effect imprinted at recombination and coherent over ~3 Mpc scales-affect the formation of dwarf galaxies at z ≳ 5. We perform cosmological hydrodynamic simulations, including and excluding streaming velocities, in regions centered on halos with M vir(z = 0) ≈ 1010 M ⊙; the simulations are part of the Feedback In Realistic Environments (FIRE) project and run with FIRE-3 physics. Our simulations comprise many thousands of systems with halo masses between M vir = 2 × 105 M ⊙ and 2 × 109 M ⊙ in the redshift range z = 20-5. A few hundred of these galaxies form stars and have stellar masses ranging from 100 to 107 M ⊙. While star formation is globally delayed by approximately 50 Myr in the streaming relative to nonstreaming simulations and the number of luminous galaxies is correspondingly suppressed at high redshift in the streaming runs, these effects decay with time. By z = 5, the properties of the simulated galaxies are nearly identical in the streaming versus nonstreaming runs, indicating that any effects of streaming velocities on the properties of galaxies at the mass scale of classical dwarfs and larger do not persist to z = 0.

Keywords: population iii stars; dwarf galaxies; early universe; primordial galaxies
Identification of a Group III CEMP-no Star in the Dwarf Spheroidal Galaxy Canes Venatici I

CEMP-no stars, a subclass of carbon-enhanced metal-poor (CEMP) stars, are one of the most significant stellar populations in galactic archeology, because they dominate the low end of the metallicity distribution function, providing information on the early star formation and chemical-evolution history of the Milky Way and its satellite galaxies. Here we present an analysis of low-resolution (R ∼ 1800) optical spectroscopy for a CEMP giant, SDSS J132755.56+333521.7, observed with the Large Binocular Telescope (LBT), one of the brightest (g ∼ 20.5) members of the classical dwarf spheroidal galaxy, Canes Venatici I (CVn I). Many CEMP stars discovered to date have very cool effective temperatures (Teff < 4500 K), resulting in strong veiling by molecular carbon bands over their optical spectra at low/medium spectral resolution. We introduce a technique to mitigate the carbon-veiling problem to obtain reliable stellar parameters, and validate this method with LBT low-resolution optical spectra of the ultra-metal-poor ([Fe/H] = -4.0) CEMP-no dwarf, G 77-61, and seven additional very cool CEMP stars, which have published high-resolution spectroscopic parameters. We apply this technique to the LBT spectrum of SDSS J132755.56+333521.7. We find that this star is well described with parameters Teff = 4530 K, log g = 0.7, [Fe/H] = -3.38, and absolute carbon abundance A(C) = 7.23, indicating that it is likely the first Group III CEMP-no star identified in CVn I. The Group III identification of this star suggests that it is a member of the extremely metal-poor population in CVn I, which may have been accreted into its halo.

Keywords: metallicity; carbon stars; chemical abundances; chemically peculiar stars; dwarf galaxies; population ii stars; spectroscopy
The Strength of the Dynamical Spiral Perturbation in the Galactic Disk

The mean Galactocentric radial velocities $\langle {v}_{R}\rangle (R,\varphi )$ of luminous red giant stars within the midplane of the Milky Way reveal a spiral signature, which could plausibly reflect the response to a nonaxisymmetric perturbation of the gravitational potential in the Galactic disk. We apply a simple steady-state toy model of a logarithmic spiral to interpret these observations, and find a good qualitative and quantitative match. Presuming that the amplitude of the gravitational potential perturbation is proportionate to that in the disk's surface mass density, we estimate the surface mass density amplitude to be ${{\rm{\Sigma }}}_{\max }({R}_{\odot })\approx 5.5\,{M}_{\odot }\,{\mathrm{pc}}^{-2}$ at the solar radius when choosing a fixed pattern speed of ${{\rm{\Omega }}}_{{\rm{p}}}=12\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{kpc}}^{-1}$ . Combined with the local disk density, this implies a surface mass density contrast between the arm and inter-arm regions of approximately ±10% at the solar radius, with an increase toward larger radii. Our model constrains the pitch angle of the dynamical spiral arms to be approximately 12°.

Keywords: milky way disk; galaxy structure; spiral arms; spiral pitch angle; stellar kinematics; milky way dynamics; stellar distance; stellar parallax
FN8-23-7179: A Low-temperature Circumstellar Shell?

In the course of a narrow-band imaging survey for dwarf emission-line galaxies in a nearby void, we serendipitously discovered a low-excitation nebula that fits the profile of a shell surrounding a low-temperature star. The star has a parallax of 0.47 ± 0.34 mas with a most likely distance of 1686 pc. It has apparent magnitudes in $r^{\prime} $ and g of 18.5 and 19.54, absolute magnitudes ${M}_{r^{\prime} }$ and M g of 7.4 and 8.41, and a redshift of 140 km-1. The color and magnitude are consistent with a K6V dwarf. A lack of forbidden emission suggests that the nebular electron temperature is < 3500° K.

Keywords: circumstellar shells; emission line stars; stellar spectral lines
Deep Hubble Space Telescope Photometry of Large Magellanic Cloud and Milky Way Ultrafaint Dwarfs: A Careful Look into the Magnitude–Size Relation

We present deep Hubble Space Telescope photometry of 10 targets from Treasury Program GO-14734, including six confirmed ultrafaint dwarf (UFD) galaxies, three UFD candidates, and one likely globular cluster. Six of these targets are satellites of, or have interacted with, the Large Magellanic Cloud (LMC). We determine their structural parameters using a maximum-likelihood technique. Using our newly derived half-light radius (r h ) and V-band magnitude (M V ) values in addition to literature values for other UFDs, we find that UFDs associated with the LMC do not show any systematic differences from Milky Way UFDs in the magnitude–size plane. Additionally, we convert simulated UFD properties from the literature into the M V –r h observational space to examine the abilities of current dark matter (DM) and baryonic simulations to reproduce observed UFDs. Some of these simulations adopt alternative DM models, thus allowing us to also explore whether the M V –r h plane could be used to constrain the nature of DM. We find no differences in the magnitude–size plane between UFDs simulated with cold, warm, and self-interacting DM, but note that the sample of UFDs simulated with alternative DM models is quite limited at present. As more deep, wide-field survey data become available, we will have further opportunities to discover and characterize these ultrafaint stellar systems and the greater low surface-brightness universe.

Keywords: dwarf galaxies; hst photometry; galaxy structure; local group
On the Evidence for Molecular Outflows in High-redshift Dusty Star-forming Galaxies

Galactic-scale outflows of molecular gas from star-forming galaxies constitute the most direct evidence for the regulation of star formation. In the early Universe (z > 4), such outflows have recently been inferred from gravitationally lensed dusty star-forming galaxies (DSFGs) based on ubiquitous detections of OH absorption extending to more blueshifted velocities than [C II] or CO emission in spatially integrated spectra. Because these lines are redshifted to submillimeter wavelengths, such measurements require careful corrections for atmospheric absorption lines, and a proper accounting of sometimes large variations in measurement uncertainties over these lines. Taking these factors into consideration, we reanalyze OH and [C II] data taken with the Atacama Large Millimeter/submillimeter Array for five sources where such data are available, of which four were categorised as exhibiting outflows. Based on their spatially integrated spectra alone, we find statistically significant (≥3σ) OH absorption more blueshifted than [C II] emission in only one source. By contrast, searching channel maps for signals diluted below the detection threshold in spatially integrated spectra, we find evidence for a separate kinematic component in OH absorption in all five sources in the form of (i) more blueshifted OH absorption than [C II] emission and/or (ii) a component in OH absorption exhibiting a different spatio-kinematic pattern than in [C II] emission, the latter presumably tracing gas in a rotating disk. Providing a more complete and accurate assessment of molecular outflows in gravitationally lensed DSFGs, we suggest methods to assess the precision of corrections for atmospheric absorption better and to measure the source continuum in future observations more accurately.

Keywords: galactic winds; early universe; stellar feedback; radio interferometry
Identification of the Top TESS Objects of Interest for Atmospheric Characterization of Transiting Exoplanets with JWST

JWST has ushered in an era of unprecedented ability to characterize exoplanetary atmospheres. While there are over 5000 confirmed planets, more than 4000 Transiting Exoplanet Survey Satellite (TESS) planet candidates are still unconfirmed and many of the best planets for atmospheric characterization may remain to be identified. We present a sample of TESS planets and planet candidates that we identify as "best-in-class" for transmission and emission spectroscopy with JWST. These targets are sorted into bins across equilibrium temperature T eq and planetary radius R p and are ranked by a transmission and an emission spectroscopy metric (TSM and ESM, respectively) within each bin. We perform cuts for expected signal size and stellar brightness to remove suboptimal targets for JWST. Of the 194 targets in the resulting sample, 103 are unconfirmed TESS planet candidates, also known as TESS Objects of Interest (TOIs). We perform vetting and statistical validation analyses on these 103 targets to determine which are likely planets and which are likely false positives, incorporating ground-based follow-up from the TESS Follow-up Observation Program to aid the vetting and validation process. We statistically validate 18 TOIs, marginally validate 31 TOIs to varying levels of confidence, deem 29 TOIs likely false positives, and leave the dispositions for four TOIs as inconclusive. Twenty-one of the 103 TOIs were confirmed independently over the course of our analysis. We intend for this work to serve as a community resource and motivate formal confirmation and mass measurements of each validated planet. We encourage more detailed analysis of individual targets by the community.

Keywords: exoplanet astronomy; exoplanet atmospheres; transit photometry; james webb space telescope; exoplanets
The Volatile Composition of the Inner Coma of Comet 46P/Wirtanen: Coordinated Observations Using iSHELL at the NASA-IRTF and Keck/NIRSPEC-2

The 2018 perihelion passage of comet 46P/Wirtanen afforded an opportunity to measure the abundances and spatial distributions of coma volatiles in a Jupiter-family comet with exceptional spatial resolution for several weeks surrounding its closest approach to Earth (Δmin ∼0.078 au on UT December 16). We conducted near-infrared spectroscopic observations of 46P/Wirtanen using iSHELL at the NASA Infrared Telescope Facility on UT 2018 December 18 in direct coordination with observations using the newly upgraded NIRSPEC-2 instrument at the W. M. Keck Observatory, and securely detected fluorescent emission from CH3OH, C2H6, and H2O. This coordinated campaign utilizing the two premier near-infrared facilities in the northern hemisphere enabled us to sample distinct projections of the coma into the plane of the sky simultaneously, and provided an unprecedented view into the inner coma of 46P/Wirtanen near closest approach. We report rotational temperatures, production rates, and abundance ratios (i.e., mixing ratios) for all sampled species and compare our iSHELL results to simultaneous (or near-simultaneous) measurements taken with NIRSPEC-2. We demonstrate the extraordinary synergy of coordinated measurements using iSHELL and NIRSPEC-2, and advocate for future cometary studies that jointly leverage the capabilities of these two facilities.

Keywords: molecular spectroscopy; high resolution spectroscopy; near infrared astronomy; comae; comets
Correction to the Photometric Colors of the Gaia Data Release 2 with the Stellar Color Regression Method

The second Gaia data release (DR2) delivers accurate and homogeneous photometry data of the whole sky of an exquisite quality, reaching down to the unprecedented millimagnitude (mmag) level for the G, GRP, and GBP passbands. However, the presence of magnitude-dependent systematic effects at the 10 mmag level limits its power in scientific exploitation. In this work, using about a half million stars in common with the LAMOST DR5, we apply the spectroscopy-based stellar color regression method to calibrate the Gaia G - GRP and GBP - GRP colors. With an unprecedented precision of about 1 mmag, systematic trends with G magnitude are revealed for both colors in great detail, reflecting changes in instrument configurations. Color-dependent trends are found for the GBP - GRP color and for stars brighter than G ∼ 11.5 mag. The maximum correction term of the calibration is about 20 mmag in general and varies by a few mmag/mag. A revised color-color diagram of Gaia DR2 is given, and some applications are briefly discussed.

Keywords: stellar photometry; astronomy data analysis; fundamental parameters of stars
Do Afterglow Synchrotron Radiations Follow the Lp,iso-Ep,z-Γ0 Relation of Gamma-Ray Bursts? The Cases of GRBs 190114C, 130427A, and 180720B

Bimodal spectral energy distributions (SEDs) of gamma-ray burst (GRB) afterglow of GRBs 190114C, 130427A, and 180720B confirm that they are originated from the synchrotron emission (Syn) and synchrotron self-Compton scattering (SSC) process of electrons accelerated in the jets. The radiation mechanism and the physics of the observed spectrum-luminosity/energy relations of GRBs remain as open questions. By extracting the Syn component through fitting their early afterglow SEDs with the Syn+SSC model, we find that their luminosity (Lsyn), peak energy (Ep,syn,z), and the Lorentz factor of the afterglow fireball (Γt) follow the Lp,iso-Ep,z-Γ0 relation of prompt gamma rays, where Lp,iso is the isotropic luminosity, Ep,z is the peak energy of the $\nu {f}_{\nu }$ spectrum in the burst frame, and Γ0 is the initial Lorentz factor of the fireball. To examine whether late afterglows are consistent with this relation, we calculate the synchrotron component at late afterglows. It is found that they also follow the same Lp,iso-Ep,z-Γ0 relation, albeit they are not consistent with the Lp,iso-Ep,z relation. Our results may imply that the Lp,iso-Ep,z-Γ0 relation would be a universal feature of synchrotron radiations of electrons accelerated in GRB jets throughout the prompt and afterglow phases among GRBs. Its origin is not fully understood, and possible explanations are briefly discussed.

Keywords: gamma-ray bursts; non-thermal radiation sources
Fermi/GBM View of the 2019 and 2020 Burst Active Episodes of SGR J1935+2154

We present temporal and time-integrated spectral analyses of 148 bursts from the latest activation of SGR J1935+2154, observed with the Fermi/Gamma-ray Burst Monitor from 2019 October 4 through 2020 May 20, excluding an ∼130 s segment with a very high burst density on 2020 April 27. The 148 bursts presented here are slightly longer and softer than bursts from earlier activations of SGR J1935+2154, as well as from other magnetars. The long-term spectral evolution trend is interpreted as being associated with an increase in the average plasma loading of the magnetosphere during bursts. We also find a trend of increased burst activity from SGR J1935+2154 since its discovery in 2014. Finally, we find no association of typical radio bursts with X-ray bursts from the source. This contrasts the association of FRB 200428 with an SGR J1935+2154 X-ray burst, which is to-date unique among the magnetar population.

Keywords: magnetars; soft gamma-ray repeaters