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Millimeter observations of disks around young stars reveal substructures indicative of gas pressure traps that may aid grain growth and planet formation. We present Submillimeter Array observations of HD 34700: two Herbig Ae stars in a close binary system (Aa/Ab, ∼0.25 au), surrounded by a disk presenting a large cavity and spiral arms seen in scattered light, and two distant, lower-mass companions. These observations include 1.3 mm continuum emission and the 12CO 2–1 line at ∼0.″5 (178 au) resolution. They resolve a prominent azimuthal asymmetry in the continuum and Keplerian rotation of a circumbinary disk in the 12CO line. The asymmetry is located at a radius of 155+11−7 au, consistent with the edge of the scattered-light cavity, being resolved in both radius (72 +14−15 au) and azimuth (FWHM = 64°+8−7). The strong asymmetry in millimeter continuum emission could be evidence for a dust trap, together with the more symmetric morphology of 12CO emission and small grains. We hypothesize an unseen circumbinary companion responsible for the cavity in scattered light and creating a vortex at the cavity edge that manifests in dust trapping. The disk mass has limitations imposed by the detection of 12CO and nondetection of 13CO. We discuss its consequences for the potential past gravitational instability of this system, likely accounting for the rapid formation of a circumbinary companion. We also report the discovery of resolved continuum emission associated with HD 34700B (projected separation ∼1850 au), which we explain through a circumstellar disk. [ABSTRACT FROM AUTHOR]

Exocomets are small bodies releasing gas and dust which orbit stars other than the Sun. Their existence was first inferred from the detection of variable absorption features in stellar spectra in the late 1980s using spectroscopy. More recently, they have been detected through photometric transits from space, and through far-IR/mm gas emission within debris disks. As (exo)comets are considered to contain the most pristine material accessible in stellar systems, they hold the potential to give us information about early stage formation and evolution conditions of extra solar systems. In the solar system, comets carry the physical and chemical memory of the protoplanetary disk environment where they formed, providing relevant information on processes in the primordial solar nebula. The aim of this paper is to compare essential compositional properties between solar system comets and exocomets to allow for the development of new observational methods and techniques. The paper aims to highlight commonalities and to discuss differences which may aid the communication between the involved research communities and perhaps also avoid misconceptions. The compositional properties of solar system comets and exocomets are summarized before providing an observational comparison between them. Exocomets likely vary in their composition depending on their formation environment like solar system comets do, and since exocomets are not resolved spatially, they pose a challenge when comparing them to high fidelity observations of solar system comets. Observations of gas around main sequence stars, spectroscopic observations of "polluted" white dwarf atmospheres and spectroscopic observations of transiting exocomets suggest that exocomets may show compositional similarities with solar system comets. The recent interstellar visitor 2I/Borisov showed gas, dust and nuclear properties similar to that of solar system comets. This raises the tantalising prospect that observations of interstellar comets may help bridge the fields of exocomet and solar system comets. [ABSTRACT FROM AUTHOR]

The Vega planetary system hosts the archetype of extrasolar Kuiper belts and is rich in dust from the sub-astronomical unit region out to hundreds of astronomical units, suggesting intense dynamical activity. We present Atacama Large Millimeter/submillimeter Array (ALMA) millimeter observations that detect and resolve the outer dust belt from the star for the first time. The interferometric visibilities show that the belt can be fit by a Gaussian model or by power-law models with a steep inner edge (at 60–80 au). The belt is very broad, extending out to at least 150–200 au. We strongly detect the star and set a stringent upper limit to warm dust emission previously detected in the infrared. We discuss three scenarios that could explain the architecture of Vega's planetary system, including the new ALMA constraints: no outer planets, a chain of low-mass planets, and a single giant planet. The planetless scenario is only feasible if the outer belt was born with the observed sharp inner edge. If, instead, the inner edge is currently being truncated by a planet, then the planet must be and at to have cleared its chaotic zone within the system age. In the planet chain scenario, outward planet migration and inward scattering of planetesimals could produce the hot and warm dust observed in the inner regions of the system. In the single giant planet scenario, an asteroid belt could be responsible for the warm dust, and mean motion resonances with the planet could put asteroids on star-grazing orbits, producing the hot dust. [ABSTRACT FROM AUTHOR]