The Spitzer Survey of Interstellar Clouds in the Gould Belt. IV. Lupus V and VI Observed with IRAC and MIPS

TL;DR

This study uses Spitzer IRAC and MIPS data to identify and analyze young stellar objects in Lupus V and VI clouds, revealing a high proportion of diskless stars likely due to their older age compared to other Lupus regions.

Contribution

It provides the first detailed infrared survey of Lupus V and VI, highlighting their unique YSO population characteristics and exploring the reasons behind their high Class III star fraction.

Findings

43 YSO candidates in Lupus V and 45 in Lupus VI identified.

High fraction (~80-87%) of Class III (diskless) YSOs compared to other regions.

Gas surface densities below star-formation threshold, suggesting older stellar populations.

Abstract

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; ~79% in Lupus V and ~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 (AV {\eqsim}8.6 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