Evidence for a CO desorption front in the outer as 209 disk

Journal Article · Fri May 20 04:00:00 EDT 2016 · Astrophysical Journal Letters

DOI:https://doi.org/10.3847/2041-8205/823/1/L18· OSTI ID:22869068

Huang, Jane; Öberg, Karin I.

Millimeter observations of CO isotopologues are often used to make inferences about protoplanetary disk gas density and temperature structures. The accuracy of these estimates depends on our understanding of CO freezeout and desorption from dust grains. Most models of these processes indicate that CO column density decreases monotonically with distance from the central star due to a decrease in gas density and freezeout beyond the CO snowline. We present ALMA Cycle 2 observations of {sup 12}CO, {sup 13}CO, and C{sup 18}O J=2−1 emission that instead suggest CO enhancement in the outer disk of T Tauri star AS 209. Most notably, the C{sup 18}O emission consists of a central peak and a ring at a radius of ∼1{sup ′′} (120 au), well outside the expected CO snowline. We propose that the ring arises from the onset of CO desorption near the edge of the millimeter dust disk. CO desorption exterior to a CO snowline may occur via non-thermal processes involving cosmic rays or high-energy photons, or via a radial thermal inversion arising from dust migration.

• OSTI ID: 22869068
• Journal Information: Astrophysical Journal Letters, Journal Name: Astrophysical Journal Letters Journal Issue: 1 Vol. 823; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
CARBON MONOXIDE
COSMIC DUST
COSMIC RADIATION
DESORPTION
DISTANCE
MIGRATION
PHOTONS
PROTOPLANETS
T TAURI STARS
TEMPERATURE INVERSIONS