2007ApJ...666L.117M

We present high-resolution spectroscopic mid-infrared observations of the circumstellar disk around the Herbig Ae star HD 97048 with the VLT Imager and Spectrometer for the mid-InfraRed (VISIR). We detect the S(1) pure rotational line of molecular hydrogen (H₂) at 17.035 µm arising from the disk around the star. This detection reinforces the claim that HD 97048 is a young object surrounded by a flared disk at an early stage of evolution. The emitting warm gas is located within the inner 35 AU of the disk. The line-to-continuum flux ratio is much higher than expected from models of disks at local thermodynamic equilibrium. We investigate the possible physical conditions, such as a gas-to-dust mass ratio higher than 100 and different excitation mechanisms of molecular hydrogen (e.g., X-ray heating, shocks), that would explain the detection. We tentatively estimate the mass of warm gas to be in the range from 10^–2 to nearly 1 M_Jup. Further observations are needed to better constrain the excitation mechanisms as well as the mass of gas.