ALMA observations of complex organic molecules, water, and ion molecules in protostellar objects V883 Ori and IRAS 4C

When: Friday, July 24, 2026, 2:30 PM - 3:30 PM
Where: G. O. Jones, Room 610, Mile End

Speaker: Shota Notsu - The University of Tokyo

Title:  ALMA observations of complex organic molecules, water, and ion molecules in protostellar objects V883 Ori and IRAS 4C

Abstract:  We present recent ALMA observations of molecular lines toward two young protostellar systems: V883 Ori and IRAS 4C.

In the V883 Ori disk, we observed complex organic molecules (COMs) and water at several different wavelengths with ALMA. The COMs abundances relative to methanol are much higher than in the surrounding gas of younger, more deeply embedded protostars like IRAS 16293-2422, and instead resemble ratios seen in comet 67P — suggesting COMs can efficiently re-form within disks rather than simply surviving from earlier stages. We also made the first measurements of 12C/13C ratios for disk organics, finding values of ~20–30, notably lower than the standard interstellar ratio of ~69, pointing to strong carbon isotope fractionation in CO. Separately, new ALMA observations at 7 mm reveal a steep rise in methanol emission within 40 au of the star — direct evidence of warm methanol gas in the disk's innermost region, previously hidden by thick dust at (sub-)mm

The IRAS 4C disk/envelope system is nearly edge on disc around a very young protostar (still deeply embedded in its natal envelope). Dense-gas tracers (C18O, H2CO) are concentrated near the disk midplane, while tracers of UV-driven chemistry (CCH, c-C3H2) occupy the lower-density upper layers — a layered structure that differs from the similar source L1527. Using H13CO+ and C18O emission, we estimate the HCO+/CO ratio as a proxy for ionization, finding that both the ionization degree and rate increase toward the outer disk and envelope.