Evidence for CO depletion in the inner regions of gas-rich protoplanetary disks

TL;DR

This study uses high-resolution spectra to analyze CO gas distribution in two protoplanetary disks, revealing evidence of CO depletion in the inner regions, which impacts our understanding of disk chemistry and planet formation.

Contribution

It provides the first detailed spatial and spectral analysis of CO in these disks, demonstrating CO depletion in inner regions through modeling and spectro-astrometry.

Findings

CO emission regions are located at 11 AU and beyond 100 AU in HD 97048.

HD 100546 shows a lower limit of 8 AU for CO emission region.

Gaseous [OI] emission at smaller radii suggests CO destruction in inner disk layers.

Abstract

We investigate the physical properties and spatial distribution of Carbon Monoxide (CO) gas in the disks around the Herbig Ae/Be stars HD 97048 and HD 100546. Using high-spectral-resolution 4.588-4.715 $\mu$m spectra containing fundamental CO emission taken with CRIRES on the VLT, we probe the circumstellar gas and model the kinematics of the emission lines. By using spectro-astrometry on the spatially resolved targets, we constrain the physical size of the emitting regions in the disks. We resolve, spectrally and spatially, the emission of the $^{13}$CO v(1-0) vibrational band and the $^{12}$CO $v=1-0, v=2-1, v=3-2$ and $v=4-3$ vibrational bands in both targets, as well as the $^{12}$CO $v=5-4$ band in HD 100546. Modeling of the CO emission with a homogeneous disk in Keplerian motion, yields a best fit with an inner and outer radius of the CO emitting region of 11 and $\geq$ 100 AU for HD 97048. HD 100546 is not fit well with our model, but we derive a lower limit on the inner radius of 8 AU. The fact that gaseous [OI] emission was previously detected in both targets at significantly smaller radii suggests that CO may be effectively destroyed at small radii in the surface layers of these disks