Keywords

We obtained the first maps of Jupiter at 1–3 mm wavelength with the Atacama Large Millimeter/Submillimeter Array (ALMA) on 2017 January 3–5, just days after an energetic eruption at 165S jovigraphic latitude had been reported by the amateur community, and about two to three months after the detection of similarly energetic eruptions in the northern hemisphere, at 222–230N. Our observations, probing below the ammonia cloud deck, show that the erupting plumes in the South Equatorial Belt bring up ammonia gas from the deep atmosphere. While models of plume eruptions that are triggered at the water condensation level explain data taken at uv–visible and mid-infrared wavelengths, our ALMA observations provide a crucial, hitherto missing, link in the moist convection theory by showing that ammonia gas from the deep atmosphere is indeed brought up in these plumes. Contemporaneous Hubble Space Telescope data show that the plumes reach altitudes as high as the tropopause. We suggest that the plumes at 222–230N also rise up well above the ammonia cloud deck and that descending air may dry the neighboring belts even more than in quiescent times, which would explain our observations in the north.

We present new determinations of disk surface density, independent of an assumed dust opacity, for a sample of seven bright, diverse, protoplanetary disks using measurements of disk dust lines. We develop a robust method for determining the location of dust lines by modeling disk interferometric visibilities at multiple wavelengths. The disks in our sample have newly derived masses that are 9%–27% of their host stellar mass, substantially larger than the minimum mass solar nebula. All are stable to gravitational collapse, except for one that approaches the limit of Toomre-Q stability. Our mass estimates are 2–15 times larger than estimates from integrated optically thin dust emission. We derive depleted dust-to-gas ratios with typical values of ∼10⁻³ in the outer disk. Using coagulation models, we derive dust surface density profiles that are consistent with millimeter dust observations. In these models, the disks formed with an initial dust mass that is a factor of ∼10 greater than is presently observed. Of the three disks in our sample with resolved CO line emission, the masses of HD 163296, AS 209, and TW Hya are roughly 3, 115, and 40 times more massive than estimates from CO respectively. This range indicates that CO depletion is not uniform across different disks and that dust is a more robust tracer of total disk mass. Our method of determining surface density using dust lines is robust even if particles form as aggregates and is useful even in the presence of dust substructure caused by pressure traps. The low Toomre-Q values observed in this sample indicate that at least some disks do not accrete efficiently.

We present spatially resolved millimeter maps of Neptune between 95 and 242 GHz taken with the Atacama Large Millimeter/submillimeter Array (ALMA) in 2016–2017. The millimeter weighting functions peak between 1 and 10 bar on Neptune, lying in between the altitudes probed at visible/infrared and centimeter wavelengths. Thus, these observations provide important constraints on the atmospheric structure and dynamics of Neptune. We identify seven well-resolved latitudinal bands of discrete brightness temperature variations, on the order of 0.5–3 K in all three observed ALMA spectral bands. We model Neptune's brightness temperature using the radiative-transfer code Radio-BEAR and compare how various H₂S, CH₄, and ortho-/para-H₂ abundance profiles can fit the observed temperature variations across the disk. We find that observed variations in brightness temperature with latitude can be explained by variations in the H₂S profile that range from sub- to supersaturations at altitudes above the 10 bar pressure level, while variations in CH₄ improve the quality of fit near the equator. At the south polar cap, our best-fit model has a depleted deep atmospheric abundance of H₂S from 30 to only 1.5 times the protosolar value, while simultaneously depleting the CH₄ abundance. This pattern of enhancement and depletion of condensible species is consistent with a global circulation structure where enriched air rises at the midlatitudes (32°–12°S) and north of the equator (2°–20°N), and dry air descends at the poles (90°–66°S) and just south of the equator (12°S–2°N). Our analysis finds more complex structure near the equator than accounted for in previous circulation models.

We study the nonthermal emission from the interaction between magnetized Jupiter-like exoplanets and the wind from their host star. The supersonic motion of planets through the wind forms a bow shock that accelerates electrons that produce nonthermal radiation across a broad wavelength range. We discuss three wind mass-loss rates: ${\dot{M}}_{{\rm{w}}}\sim {10}^{-14}$, 10⁻⁹, ${10}^{-6}\,{M}_{\odot }\,{\mathrm{yr}}^{-1}$ corresponding to solar-type, T Tauri, and massive O/B-type stars, respectively. We find that the expected radio synchrotron emission from a Jupiter-like planet is detectable by the Jansky Very Large Array and the Square Kilometre Array at $\sim 1\mbox{--}10\,\mathrm{GHz}$ out to a distance of ∼100 pc, whereas the infrared emission is detectable by the James Webb Space Telescope out to a similar distance. Inverse Compton scattering of the stellar radiation results in X-ray emission detectable by Chandra X-ray Observatory out to ∼150 pc. Finally, we apply our model to the upper limit constraints on V380 Tau, the first star–hot Jupiter system observed in radio wavelength. Our bow-shock model provides constraints on the magnetic field, the interplanetary medium, and the nonthermal emission efficiency in V380 Tau.

Dust grains emit intrinsic polarized emission if they are elongated and aligned in the same direction. The direction of the grain alignment is determined by external forces, such as magnetic fields, radiation, and gas flow against the dust grains. In this Letter, we apply the concept of the grain alignment by gas flow, which is called mechanical alignment, to the situation of a protoplanetary disk. We assume that grains have a certain helicity, which results in the alignment with the minor axis parallel to the grain velocity against the ambient disk gas and discuss the morphology of polarization vectors in a protoplanetary disk. We find that the direction of the polarization vectors depends on the Stokes number, which denotes how well grains are coupled to the gas. If the Stokes number is less than unity, the orientation of polarization is in the azimuthal direction because the dust velocity against the gas is in the radial direction. If the Stokes number is as large as unity, the polarization vectors show a leading spiral pattern because the radial and azimuthal components of the gas velocity against the dust grains are comparable. This suggests that if the observed polarization vectors show a leading spiral pattern, it would indicate that the Stokes number of dust grains is around unity, which is presumably radially drifting.

In order to reveal variations of days to weeks in the brightness distribution of Jovian Synchrotron Radiation (JSR), we made simultaneous radio and ultraviolet observations using the Giant Metrewave Radio Telescope (GMRT) and the Hisaki EXtreme ultraviolet spectrosCope for ExosphEric Dynamics (EXCEED). It is known from visible and ultraviolet observations that Io plasma torus (IPT) has dawn–dusk asymmetry, and that this asymmetry is believed to be due to the dawn-dusk electric field. Continuous ultraviolet observation by Hisaki reveals that dawn–dusk asymmetry of IPT changes in days to weeks, therefore, if this global electric field around Io's orbit (5.9 Jovian radii) could penetrate the radiation belt region (<2 Jovian radii), the variations in brightness distribution of JSR and IPT are expected to be correlated. The GMRT observations were made from 2013 December 31 to 2014 January 16 at 610 MHz and 2016 March 14–June 23 at 1390 MHz, while Hisaki continuously monitored IPT. The statistical analysis indicates that JSR and IPT do not have a significant correlation. Although these results do not support our hypothesis, we cannot rule out the possibility that the dawn-dusk electric field was masked by some other process, including the conductivity variation and/or the time-variable longitudinal asymmetry of JSR.

The search for exoplanets in the radio bands has been focused on detecting radio emissions produced by the interaction between magnetized planets and the stellar wind (auroral emission). Here we introduce a new tool, which is part of our MHD stellar corona model, to predict the ambient coronal radio emission and its modulations induced by a close planet. For simplicity, the present work assumes that the exoplanet is stationary in the frame rotating with the stellar rotation. We explore the radio flux modulations using a limited parameter space of idealized cases by changing the magnitude of the planetary field, its polarity, the planetary orbital separation, and the strength of the stellar field. We find that the modulations induced by the planet could be significant and observable in the case of hot Jupiter planets— above 100% modulation with respect to the ambient flux in the 10–100 MHz range in some cases, and 2%–10% in the frequency bands above 250 MHz for some cases. Thus, our work indicates that radio signature of exoplanets might not be limited to low-frequency radio range. We find that the intensity modulations are sensitive to the planetary magnetic field polarity for short-orbit planets, and to the stellar magnetic field strength for all cases. The new radio tool, when applied to real systems, could provide predictions for the frequency range at which the modulations can be observed by current facilities.

Electric dipole emission from rapidly spinning polycyclic aromatic hydrocarbons (PAHs) is widely believed to be an origin of anomalous microwave emission (AME), but recently it has encountered a setback owing to the noncorrelation of AME with PAH abundance seen in a full-sky analysis. Microwave observations for specific regions with well-constrained PAH features would be crucial to test the spinning dust hypothesis. In this paper, we present physical modeling of microwave emission from spinning PAHs from protoplanetary disks (PPDs) around Herbig Ae/Be stars and T Tauri stars where PAH features are well observed. Guided by the presence of 10 μm silicate features in some PPDs, we also model microwave emission from spinning nanosilicates. Thermal emission from big dust grains is computed using the Monte Carlo radiative transfer code (radmc-3d). Our numerical results demonstrate that microwave emission from either spinning PAHs or spinning nanosilicates dominates over thermal dust at frequencies ν < 60 GHz, even in the presence of significant grain growth. Finally, we attempt to fit millimeter–centimeter observational data with both thermal dust and spinning dust for several disks around Herbig Ae/Be stars that exhibit PAH features and find that spinning dust can successfully reproduce the observed excess microwave emission (EME). Future radio observations with ngVLA, SKA, and ALMA Band 1 would be valuable for elucidating the origin of EME and potentially open a new window for probing nanoparticles in circumstellar disks.

We present archival Atacama Large Millimeter/submillimeter Array (ALMA) observations of the HD 141569 circumstellar disk at 345, 230, and 100 GHz. These data detect extended millimeter emission that is exterior to the inner disk. We find through simultaneous visibility modeling of all three data sets that the system's morphology is described well by a two-component disk model. The inner disk ranges from approximately 16–45 au with a spectral index of 1.81 (q = 2.95), and the outer disk ranges from 95 to 300 au with a spectral index of 2.28 (q = 3.21). Azimuthally averaged radial emission profiles derived from the continuum images at each frequency show potential emission that is consistent with the visibility modeling. The analysis presented here shows that at ∼5 Myr, HD 141569's grain size distribution is steeper and therefore possibly more evolved in the outer disk than in the inner disk.

We present a new set of measurements obtained with the Combined Array for Research in Millimeter-wave Astronomy (CARMA) of Jupiter's microwave thermal emission near the 1.3 cm ammonia (NH₃) absorption band. We use these observations to investigate the ammonia mole fraction in the upper troposphere, near 0.3 < P < 2 bar, based on radiative transfer modeling. We find that the ammonia mole fraction must be ∼2.4 $\,\times \,{10}^{-4}$ below the NH₃ ice cloud, i.e., at 0.8 < P < 8 bar, in agreement with results by de Pater et al. We find the NH₃ cloud-forming region between 0.3 < P < 0.8 bar to be globally sub-saturated by ∼55% on average, in accordance with the result in Gibson et al. Although our data are not very sensitive to the region above the cloud layer, we are able to set an upper limit of $2.4\times {10}^{-7}$ on the mole fraction here, a factor of ∼10 above the saturated vapor curve.