The initial conditions of isolated star formation – VII. Spitzer mapping of pre-stellar cores

We have retrieved Spitzer archive data of pre-stellar cores taken with the Multiband Imaging Photometer for Spitzer (MIPS) at a wavelength of 160 μm. Seventeen images, containing 18 cores, were constructed. Flux densities were measured for each core, and background estimates were made. Mean off-source backgrounds were found to be 48 ± 10 MJy sr -1 in Taurus and 140 ± 55 MJy sr -1 in Ophiuchus. Consistency was found between the MIPS 170-μm and ISOPHOT 160-μm calibrations. Fourteen cores were detected both by MIPS and by our previous submillimetre surveys. Spectral energy distributions were made for each core, using additional 24- and 70-μm data from the Spitzer data archive, as well as previous infrared and submillimetre data. Previous temperature estimates were refined, and new temperature estimates were made where no Infrared Space Observatory (ISO) data exist. A temperature range of 8-18 K was found for the cores, with most lying in the range 10-13 K. We discount recent claims that a large number of pre-stellar cores may have been misclassified and in fact contain low-luminosity protostars detectable only by Spitzer. We find no new protostars in our sample other than that previously reported in L1521F. It is shown that this has a negligible effect on pre-stellar lifetime estimates.