The Astrophysical Journal
Latest articles in this journal
The Astrophysical Journal, Volume 885; doi:10.3847/2041-8213/ab5119
The Astrophysical Journal, Volume 885; doi:10.3847/1538-4357/ab48e0
Abstract:Coronal and solar wind physics have long used plasma fluid models to motivate physical explanations of observations; the hypothesized model is introduced into a fluid simulation to see if observations are reproduced. This procedure is called Verification of Mechanism (VoM) modeling; it is contingent on the self consistency of the closure that made the simulation possible. Inner corona VoMs typically assume weak gradient Spitzer–Braginskii closures. Four prominent coronal VoMs in place for decades are shown to contradict their closure hypotheses, demonstrably shaping coronal and solar wind research. These findings have been possible since 1953. This unchallenged evolution is worth understanding, so that similarly flawed VoMs do not continue to mislead new research. As a first step in this direction, this paper organizes four a posteriori quantitative tests for the purpose of easily screening the physical integrity of a proposed VoM. A fifth screen involving the thermal force, the tandem of the heat flux, has been shown to be mandatory when VoMs involve species-specific energy equations. VoM modeling will soon be required to advance Parker Solar Probe and Solar Orbiter science. Such modeling cannot advance the physical understanding sought by these missions unless the closures adopted (i) are demonstrated to be self consistent for the VoM plasma Knudsen numbers, (ii) are verified a posteriori as possessing nonnegative VDFs throughout the simulated volume, and (iii) include the physical completeness of thermal force physics when the VoM requires species-specific energy equations.
The Astrophysical Journal, Volume 885; doi:10.3847/2041-8213/ab518d
Abstract:We have detected the submillimeter-wave fine-structure transition (3P 1–3P 0) of 13C, [13C i], in the gaseous debris disk of 49 Ceti with the Atacama Large Millimeter/submillimeter Array (ALMA). Recently, the [C i] 3P 1–3P 0 emission has been spatially resolved in this source with ALMA. In this data set, the F = 3/2–1/2 hyperfine component of [13C i], which is blueshifted by 2.2 km s−1 from the normal species line, [C i], has been identified in the outer part of the 49 Ceti disk, thanks to the narrow velocity widths of the gas components. The [C i]/[13C i] line intensity ratio is found to be 12 ± 3, which is significantly lower than the 12C/13C abundance ratio of 77 in the interstellar medium. This result clearly reveals that the [C i] emission is optically thick in 49 Ceti at least partly, as speculated by the previous work. As far as we know, this is the first detection of [13C i] 3P 1–3P 0 emission at 492 GHz not only in debris disks but also in the interstellar medium.
The Astrophysical Journal, Volume 885; doi:10.3847/1538-4357/ab4882
Abstract:A Steady Electron Runaway Model (SERM) is formulated describing plasmas in the astrophysical "condition" having finite (rather than infinitesimal) Knudsen number, , suggesting an omnipresent leptokurtic, nonthermal, and heat-conducting electron velocity distribution function (eVDF) as the replacement for the Maxwellian ansatz typically made. The shape parameters of SERM's eVDFs are functionals of the local dimensionless electric field, , shown to be nearly interchangeable with the pressure Knudsen number, . The eVDF is determined by the total density and pressure, heat flux, and with the Maxwellian as a special case when . The nonthermal part of the eVDF is caused by local and global runaway physics and its density fraction is monotonically dependent on . SERM explains the distinguishable conduction band of suprathermal electrons to be the result of the inhomogeneities of astroplasmas that require to enforce quasi-neutrality. SERM shows that the direction of the heat flow should be that of . Almost all reported space age correlations among the shape parameters of the solar wind eVDF are reproduced by this modeling, including scaling of: (i) nonthermal spectral break energy, and (ii) partition of suprathermal density and partial pressure, with solar wind speed. SERM, together with eVDF observations, indirectly bracket , producing a steady-state eVDF, consistent with in situ (i) heat flows, (ii) strahl pitch angle features in high-speed winds, (iii) , and (iv) non-negative probability at all velocities. Because finite is the identified prerequisite for SERM modeling, nonthermal eVDF's are expected nearly everywhere in astrophysics where .
The Astrophysical Journal, Volume 885; doi:10.3847/2041-8213/ab50bd
Abstract:The turbulence and spatial nonuniformity of the guide magnetic field cause two competitive effects, namely, the scattering effect and the adiabatic focusing effect, respectively. In this work, we numerically solve the five-dimensional Fokker–Planck transport equation to investigate the radial evolutions of these important effects undergone by the solar energetic particles (SEPs) propagating through interplanetary space. We analyze the interplay process between the scattering and adiabatic focusing effects in the context of three-dimensional propagation, with special attention to the scenario of the outer heliosphere, in which some peculiar SEP phenomena are found and explained. We also discuss the radial dependence of the SEP peak intensities from the inner through the outer heliosphere, and conclude that it cannot be simply described by a single functional form such as R −α (R is radial distance), which is often used.
The Astrophysical Journal, Volume 885; doi:10.3847/1538-4357/ab43c2
Abstract:With the aim of characterizing the dynamical processes involved in the formation of young protostars, we present high-angular-resolution ALMA dust polarization observations of the Class 0 protostellar cores Serpens SMM1, Emb 8(N), and Emb 8. With spatial resolutions ranging from 150 to 40 au at 870 μm, we find unexpectedly high values of the polarization fraction along the outflow cavity walls in Serpens Emb 8(N). We use 3 mm and 1 mm molecular tracers to investigate outflow and dense-gas properties and their correlation with the polarization. These observations allow us to investigate the physical processes involved in the radiative alignment torques (RATs) acting on dust grains along the outflow cavity walls, which experience irradiation from accretion processes and outflow shocks. The inner core of SMM1-a presents a polarization pattern with a poloidal magnetic field at the bases of the two lobes of the bipolar outflow. To the south of SMM1-a we see two polarized filaments, one of which seems to trace the redshifted outflow cavity wall. The other may be an accretion streamer of material infalling onto the central protostar. We propose that the polarized emission we see at millimeter wavelengths along the irradiated cavity walls can be reconciled with the expectations of RAT theory if the aligned grains present at <500 au scales in Class 0 envelopes have grown larger than the 0.1 μm size of dust grains in the interstellar medium. Our observations allow us to constrain the magnetic field morphologies of star-forming sources within the central cores, along the outflow cavity walls, and in possible accretion streamers.
The Astrophysical Journal, Volume 885; doi:10.3847/1538-4357/ab4814
The Astrophysical Journal, Volume 885; doi:10.3847/1538-4357/ab43e5
The Astrophysical Journal, Volume 885; doi:10.3847/1538-4357/ab46b6
The Astrophysical Journal, Volume 885; doi:10.3847/1538-4357/ab4795