2011ApJ...738...12T

We present high-resolution near-infrared spectra of β Pictoris–a nearby young star with a debris disk. Fundamental low-J CO absorption lines are detected and strict upper limits are placed on the flux of v = 2-1 low-J CO emission lines. The limit on the UV fluorescent emission flux in the v = 2-1 lines is used to place a tight constraint on the inner extent of the CO gas. Assuming H I is the primary collision partner, the sub-thermal population of the low-J v = 0 rotational levels constrains the density of the gas in the disk to n_H= (2.5^+7.1_- 1.2_)x10⁵/cm3. If the distribution of hydrogen follows that of the other metals in the disk, we find that the mass of the gas in the disk is 0.17^+0.47_- 0.08_M⊕_. We compare this mass to the gas mass necessary to brake the metals in the disk through ion-neutral reactions.