Moderate-Resolution Spitzer Infrared Spectrograph Observations of M, L, and T Dwarfs

June 2007 • 2007ApJ...662.1245M

Authors • Mainzer, A. K. • Roellig, Thomas L. • Saumon, D. • Marley, Mark S. • Cushing, Michael C. • Sloan, G. C. • Kirkpatrick, J. Davy • Leggett, S. K. • Wilson, John C.

Abstract • We present 10-19 μm moderate-resolution spectra of 10 M dwarfs, one L dwarf, and two T dwarf systems obtained with the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope. The IRS allows us to examine molecular spectroscopic features/lines at moderate spectral resolution in a heretofore untapped wavelength regime. These R=λ/Δλ~600 spectra allow for a more detailed examination of clouds and nonequilibrium chemistry, as well as the molecular features of H2O, NH3, and other trace molecular species that are the hallmarks of these objects. A cloud-free model best fits our mid-infrared spectrum of the T1 dwarf ɛ Indi Ba, and we find that the NH3 feature in ɛ Indi Bb is best explained by a nonequilibrium abundance due to vertical transport in its atmosphere. We examined a set of objects (mostly M dwarfs) in multiple systems to look for evidence of emission features, which might indicate an atmospheric temperature inversion, as well as trace molecular species; however, we found no evidence of either.


IPAC Authors


Davy Kirkpatrick

Senior Scientist