GeminiFocus July, 2015 | Page 7

(CN), and ethynide (C2H). Protoplanetary disks also contain carbonaceous and silicate dust grains, which coagulate over time, grow in size, and settle towards the disk midplane. Present theories hold that giant planet formation in disks likely occurs via one of two mechanisms: core accretion or gravitational instability. In the core accretion scenario, ice-covered dust particles collide and stick together, growing into ever-larger rocky bodies; planetesimals form from this buildup of rocky material, and their collisions eventually build super-Earth-mass planetary “cores.” Such massive cores can then rapidly collect gas from the disk to form giant planets. In contrast, the gravitational instability theory holds that planets form when a perturbation in the disk causes a large amount of disk material to collapse and form a planet essentially all at once. Hence, this rapid process is similar to that by which a young central star forms from its birth cloud. Under either scenario, once a massive planet forms, co-orbiting material either accretes onto the planet or is accelerated radially in the disk via spiral density waves, which cause material approaching them to speed up — until they reach the perturbed regions, where they slow down and linger. These mechanisms result in ring-like or spiral structures in the disk characterized by sharp radial gradients in both surface density and particle size. Our team is interested in studying planet formation around young nearby stars within ~ 30 AU, where we can search for evidence for gas giant planet formation on scales similar to that of our Solar System. We do so by focusing on a handful of solar mass stars within ~ 300 light years (ly) of Earth that are surrounded by, and actively accreting material from, gas-rich circumstellar disks. Target: V4046 Sagittarii Our team has been closely scrutinizing one such star-disk system: V4046 Sagittarii (Sgr). )1她