We present thirteen epochs of near-infrared ( 0.8-5 µm ) spectroscopic observations of the pre-transitional , “ gapped ” disk system in SAO 206462 ( =HD 135344B ) .
In all , six gas emission lines ( Br \alpha , Br \gamma , Pa \beta , Pa \gamma , Pa \delta , Pa \epsilon , and the 0.8446 \mu m line of O I ) along with continuum measurements made near the standard J , H , K , and L photometric bands were measured .
A mass accretion rate of approximately 2 x 10 ^ { -8 } M _ { \sun } yr ^ { -1 } was derived from the Br \gamma and Pa \beta lines .
However , the fluxes of these lines varied by a factor of over two during the course of a few months .
The continuum also varied , but by only \sim 30 % , and even decreased at a time when the gas emission was increasing .
The H I line at 1.083 \mu m was also found to vary in a manner inconsistent with that of either the hydrogen lines or the dust .
Both the gas and dust variabilities indicate significant changes in the region of the inner gas and the inner dust belt that may be common to many young disk systems .
If planets are responsible for defining the inner edge of the gap , they could interact with the material on time scales commensurate with what is observed for the variations in the dust , while other disk instabilities ( thermal , magnetorotational ) would operate there on longer time scales than we observe for the inner dust belt .
For SAO 206462 , the orbital period would likely be 1-3 years .
If the changes are being induced in the disk material closer to the star than the gap , a variety of mechanisms ( disk instabilities , interactions via planets ) might be responsible for the changes seen .
The He I feature is most likely due to a wind whose orientation changes with respect to the observer on time scales of a day or less .
To further constrain the origin of the gas and dust emission will require multiple spectroscopic and interferometric observations on both shorter and longer time scales that have been sampled so far .