The Spitzer c2d Survey of Large, Nearby, Interstellar Clouds. XI. Lupus Observed With IRAC and MIPS

TL;DR

This study uses Spitzer IRAC and MIPS data to analyze the stellar and disk properties of the Lupus molecular clouds, revealing a large, diverse population of young stars and disks, with implications for star formation processes.

Contribution

First comprehensive Spitzer IRAC and MIPS survey of Lupus clouds, expanding the sample size and characterizing disk properties and star formation activity.

Findings

70-80% disk fraction indicating young age

20% optically thick accretion disks

Star formation rates of 2-10 M_sun/Myr

Abstract

We present c2d Spitzer/IRAC observations of the Lupus I, III and IV dark clouds and discuss them in combination with optical and near-infrared and c2d MIPS data. With the Spitzer data, the new sample contains 159 stars, 4 times larger than the previous one. It is dominated by low- and very-low mass stars and it is complete down to M $\approx$ 0.1M$_\odot$. We find 30-40 % binaries with separations between 100 to 2000 AU with no apparent effect in the disk properties of the members. A large majority of the objects are Class II or Class III objects, with only 20 (12%) of Class I or Flat spectrum sources. The disk sample is complete down to ``debris''-like systems in stars as small as M $\approx$ 0.2 M$_\odot$ and includes sub-stellar objects with larger IR excesses. The disk fraction in Lupus is 70 -- 80%, consistent with an age of 1 -- 2 Myr. However, the young population contains 20% optically thick accretion disks and 40% relatively less flared disks. A growing variety of inner disk structures is found for larger inner disk clearings for equal disk masses. Lupus III is the most centrally populated and rich, followed by Lupus I with a filamentary structure and by Lupus IV, where a very high density core with little star-formation activity has been found. We estimate star formation rates in Lupus of 2 -- 10 M$_\odot$ Myr$^{-1}$ and star formation efficiencies of a few percent, apparently correlated with the associated cloud masses.