Discovery of OH in Circumstellar Disks Around Young Intermediate-Mass Stars

TL;DR

This study reports the detection of hydroxyl (OH) emission in the inner regions of circumstellar disks around two young intermediate-mass stars, using infrared spectroscopy, and compares excitation models to interpret the observations.

Contribution

First detection of OH emission in circumstellar disks around Herbig Ae stars, with analysis supporting fluorescence excitation mechanisms.

Findings

OH emission detected at ~1 AU in both stars

Rotational temperatures of 650-800 K derived from models

OH abundances estimated between 10^42 and 10^45 molecules

Abstract

We detect emission from multiple low-excitation ro-vibrational transitions of OH from the two Herbig Ae stars AB Aurigae and MWC 758 in the 3.0 - 3.7 micron wavelength range (L-band), using the NIRSPEC instrument on Keck II. The inner radius for the emitting region in both stars is close to 1 AU. We compare an optically thin LTE model and a thin-wedge fluorescence model, finding rotational temperatures of 650 - 800 K and OH abundances of 10^42 - 10^45 molecules for the two stars. Comparisons with current chemical models support the fluorescence excitation model for AB Aurigae and possibly MWC 758, but further observations and detailed modeling are necessary to improve constraints on OH emission in different disk environments.