The Spitzer c2d survey of nearby dense cores.: II.: Discovery of a low-luminosity object in the "evolved starless core" L1521F

We present Spitzer Space Telescope observations of the "evolved starless core" L1521F that reveal the presence of a very low luminosity object (L < 0.07 L-circle dot). The object, L1521F-IRS, is directly detected at mid- infrared wavelengths (> 5 mu m), but only in scattered light at shorter infrared wavelengths, showing a bipolar nebula oriented east- west that is probably tracing an outflow cavity. The nebula strongly suggests that L1521F-IRS is embedded in the L1521F core. Thus, L1521F-IRS is similar to the recently discovered L1014-IRS and the previously known IRAM 04191 in its substellar luminosity and dense core environment. However, these objects differ significantly in their core density, core chemistry, and outflow properties, and some may be destined to be brown dwarfs rather than stars.