Edge-On Disk Study (EODS) II: Thermal Structure of the Flying Saucer Disk

TL;DR

This study measures the dust and gas temperature profiles of the edge-on Flying Saucer disk, revealing a vertical temperature gradient, CO depletion in the mid-plane, and dust settling, which are crucial for understanding disk chemistry and planet formation.

Contribution

It provides the first detailed temperature profile of the Flying Saucer disk using unique observational constraints and radiative transfer modeling, highlighting vertical gradients and chemical depletion.

Findings

Gas temperature shows a vertical gradient, with 10 K at the mid-plane and 27 K at 100 au.

Evidence of CO depletion below about one scale height, consistent with freeze-out temperatures.

The dust disk is optically thin at 345 GHz with moderate settling.

Abstract

Context. The dust and gas temperature in proto-planetary disks play critical roles in determining their chemical evolution and influencing planet formation processes. Aims. We attempted an accurate measurement of the dust and CO temperature profile in the edge-on disk of the Flying Saucer. Methods. We used the unique properties of the Flying Saucer, its edge-on geometry and its fortunate position in front of CO clouds with different brightness temperatures to provide independent constraints on the dust temperature. We compared it with the dust temperature derived using the radiative transfer code DiskFit and the CO gas temperature. Results. We find clear evidence for a substantial gas temperature vertical gradient, with a cold (10 K) disk mid-plane and a warmer CO layer where T(r) is 27 K at 100 au, dropping with exponent 0.3. Direct evidence for CO depletion in the mid-plane, below about 1 scale height, is also found. At this height, the gas temperature is 15-20 K, consistent with the expected CO freeze out temperature. The dust disk appears optically thin at 345 GHz, and exhibits moderate settling.