Spitzer Space Telescope spectra of the low mass young stellar object ( YSO ) IRS 46 ( L _ { { bol } } \approx 0.6 { L } _ { \odot } ) in Ophiuchus reveal strong vibration-rotation absorption bands of gaseous C _ { 2 } H _ { 2 } , HCN , and CO _ { 2 } .
This is the only source out of a sample of \sim 100 YSO ’ s that shows these features and the first time they are seen in the spectrum of a solar-mass YSO .
Analysis of the Spitzer data combined with Keck L - and M - band spectra gives excitation temperatures of \gtrsim 350 K and abundances of 10 ^ { -6 } -10 ^ { -5 } with respect to H _ { 2 } , orders of magnitude higher than those found in cold clouds .
In spite of this high abundance , the HCN J = 4 - 3 line is barely detected with the James Clerk Maxwell Telescope , indicating a source diameter less than 13 AU .
The ( sub ) millimeter continuum emission and the absence of scattered light in near-infrared images limits the mass and temperature of any remnant collapse envelope to less than 0.01 { M } _ { \odot } and 100 K , respectively .
This excludes a hot-core type region as found in high-mass YSO ’ s .
The most plausible origin of this hot gas rich in organic molecules is in the inner ( < 6 AU radius ) region of the disk around IRS 46 , either the disk itself or a disk wind .
A nearly edge-on 2-D disk model fits the spectral energy distribution ( SED ) and gives a column of dense warm gas along the line of sight that is consistent with the absorption data .
These data illustrate the unique potential of high-resolution infrared spectroscopy to probe organic chemistry , gas temperatures and kinematics in the planet-forming zones close to a young star .