10 micron spectra of protostars and the solid methanol abundance.

Abstract

We have searched for the strong C-O stretching absorption of solid methanol near 9.8 micrometers toward the heavily obscured protostars AFGL 961, AFGL 2591, the BN object and Mon R2 IRS 3. There is no clear evidence for this feature in the spectra, resulting in very conservative upper limits to the methanol abundance of 6% to 17% relative to solid H2O toward these objects. This is well below previous estimates of 50%-80% obtained toward W33 A, NGC 7538 IRS 9, AFGL 2136, and W3 IRS 5, which were based on the assignment of the interstellar 6.85 micrometers absorption feature to the methanol C-H bending mode. This study shows that such high methanol abundances are not a characteristic of all interstellar ices.