A detailed study of the L1641N star formation region
  We search for young stellar objects (YSOs) in the L1641N cluster and characterize the star formation activity through determination of the age distribution, mass function, spatial distribution, and the star formation history.   We detect a total of 216 (Spitzer or $I$ band) sources in L1641N, 89 of which are YSO candidates. Most of the spectra are of M-type with H$\alpha$ strongly in emission, and many have Li 6707 in absorption. The four brightest $I$ band sources (F and G stars) are suggested as foreground stars, and the L1641N IRAS source is shown to be the combined flux of at least four sources. We find that the interstellar extinction is well-fit in the optical and near-IR by a power law with an exponent of 1.58, although in the mid-IR the Spitzer observations show a higher extinction than expected from theory. The median age of the YSO sample is $\sim$1 Myr and the resulting MF has a flat distribution for low masses down to the completeness limit. There is evidence of a constant star formation rate of one star in 3.7 $\times$ 10$^4$ yr during the past few Myr. We find 11 sources older than 10 Myr and a spatial separation between younger and older YSOs, suggesting that many of the older stars formed in L1641N could have left the cluster, giving the appearance of an increased star formation rate with time. 
M.Gaalfalk, G.Olofsson