We present Gould ’ s Belt ( GB ) Spitzer IRAC and MIPS observations of the Lupus V and VI clouds and discuss them in combination with near-infrared ( 2MASS ) data .
Our observations complement those obtained for other Lupus clouds within the frame of the Spitzer “ Core to Disk ” ( c2d ) Legacy Survey .
We found 43 Young Stellar Object ( YSO ) candidates in Lupus V and 45 in Lupus VI , including 2 transition disks , using the standard c2d/GB selection method .
None of these sources was classified as a pre-main sequence star from previous optical , near-IR and X-ray surveys .
A large majority of these YSO candidates appear to be surrounded by thin disks ( Class III ; \sim 79 % in Lupus V and \sim 87 % in Lupus VI ) .
These Class III abundances differ significantly from those observed for the other Lupus clouds and c2d/GB surveyed star-forming regions , where objects with optically thick disks ( Class II ) dominate the young population .
We investigate various scenarios that can explain this discrepancy .
In particular , we show that disk photo-evaporation due to nearby OB stars is not responsible for the high fraction of Class III objects .
The gas surface densities measured for Lupus V and VI lies below the star-formation threshold ( A _ { V } \approx 8.6Â mag ) , while this is not the case for other Lupus clouds .
Thus , few Myrs older age for the YSOs in Lupus V and VI with respect to other Lupus clouds is the most likely explanation of the high fraction of Class III objects in these clouds , while a higher characteristic stellar mass might be a contributing factor .
Better constraints on the age and binary fraction of the Lupus clouds might solve the puzzle but require further observations .