This image shows the disc around the young star AB Aurigae in polarized near-infrared light as seen with the European Very Large Telescope’s SPHERE instrument. Measurements of the molecular components of the disk at millimeter wavelengths reveal several unexpected properties including a warmer temperature, more dust, and a deficiency of sulfur.
Credit: ESO/Boccaletti et al.

Planets are formed from the disk of gas and dust around a star, but the mechanisms for doing so are imperfectly understood. Gas is the key driver in the dynamical evolution of planets, for example, because it is the dominant component of the disk (by mass). The timescale over which the gas dissipates sets the timescale for planet formation, yet its distribution in disks is just starting to be carefully measured. Similarly, the chemical composition of the gas determines the composition of the future planets and their atmospheres, but even after decades of studying protoplanetary disks, their chemical compositions are poorly constrained; even the gas-to-dust ratios are largely unknown.

The detailed characterizations of individual sources provide insights into the physical and chemical nature of protoplanetary disks. The star AB Aurigae is a widely studied system hosting a young transitional disk, a disk with gaps suggestive of clearing by newly forming planets. Located 536 light-years (plus-or-minus 1%) from the Sun, it is close enough to be an excellent candidate in which to study the spatial distribution of gas and dust in detail.

CfA astronomer Romane Le Gal was a member of a team that used the NOrthern Extended Millimeter Array (NOEMA) to observe the AB Aur gas disk at high spatial resolution in the emission lines of CO, H2CO, HCN, and SO; combined with archival results, their dataset includes a total of seventeen different spectral features.

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