FAR-INFRARED OBSERVATIONS OF THE VERY LOW LUMINOSITY EMBEDDED SOURCE L1521F-IRS IN THE TAURUS STAR-FORMING REGION

We investigate the environment of the very low luminosity object L1521F-IRS using data from the Taurus Spitzer Legacy Survey. The MIPS 160 mu m image shows both extended emission from the Taurus cloud and emission from multiple cold cores over a 1 degrees x 2 degrees region. Analysis shows that the cloud dust temperature is 14.2 +/- 0.4 K and the extinction ratio is A(160)/A(K) = 0.010 +/- 0.001 up to A(V) similar to 4 mag. We find kappa(160) = 0.23 +/- 0.046 cm(2) g(-1) for the specific opacity of the gas-dust mixture. Therefore, for dust in the Taurus cloud we find that the 160 mu m opacity is significantly higher than that measured for the diffuse interstellar medium, but not too different from dense cores, even at modest extinction values. Furthermore, the 160 mu m image shows features that do not appear in the IRAS 100 mu m image. We identify six regions as cold cores, i.e., colder than 14.2 K, all of which have counterparts in extinction maps or C(18)O maps. Three of the six cores contain embedded young stellar objects, which demonstrates the cores are sites of current star formation. We compare the effects of L1521F-IRS on its natal core and find there is no evidence for dust heating at 160 or 100 mu m by the embedded source. From the infrared luminosity L(TIR) = 0.024 L(circle dot) we find L(bol_int) = 0.034 -0.046 L(circle dot), thus confirming the source's low luminosity. Comparison of L1521F-IRS with theoretical simulations for the very early phases of star formation appears to rule out the first core collapse phase. The evolutionary state appears similar to or younger than the class 0 phase, and the estimated mass is likely to be substellar.