Searching for molecular hydrogen mid-infrared emission in the circumstellar environments of Herbig Be stars

TL;DR

This study used high-resolution mid-infrared spectroscopy to search for warm molecular hydrogen in the circumstellar environments of Herbig Be stars, finding no emission and setting upper limits on warm gas mass.

Contribution

First high-resolution mid-infrared search for H2 in Herbig Be stars' circumstellar environments, providing stringent upper limits on warm gas content.

Findings

No H2 emission detected at 17.0348 microns.

Upper limits on warm gas mass are less than 1-10 Jupiter masses.

Constraints on warm gas presence in Herbig Be star disks.

Abstract

Context: Molecular hydrogen (H2) is the most abundant molecule in the circumstellar (CS) environments of young stars, and is a key element in giant planet formation. The measurement of the H2 content provides the most direct probe of the total amount of CS gas, especially in the inner warm planet-forming regions of the disks. Aims: Most Herbig Be stars (HBes) are distant from the Sun and their nature and evolution are still debated. We therefore conducted mid-infrared observations of H2 as a tracer of warm gas around HBes known to have gas-rich CS environments. Methods: We report a search for the H2 S(1) emission line at 17.0348 microns in the CS environments of 5 HBes with the high resolution spectroscopic mode of VISIR (ESO VLT Imager and Spectrometer for the mid-InfraRed). Results: No source shows evidence for H2 emission at 17.0348 microns. Stringent 3sigma upper limits on the integrated line fluxes are derived. Depending on the adopted temperature, limits on column densities and masses of warm gas are also estimated. These non-detections constrain the amount of warm (>150 K) gas in the immediate CS environments of our target stars to be less than 1-10 Jupiter masses.