Cool Stars 14 - Submitted Abstract # 154
This version created on 05 October 2006

Spitzer:  A search for Weather in late-L Brown dwarfs


Maria Morales-Calderon, LAEFF-INTA
John R. Stauffer, SSC-Caltech
J.Davy Kirkpatrick, IPAC-Caltech
Sean Carey, SSC-Caltech
Chris Gelino, SSC-Caltech
David Barrado y Navascues, LAEFF-INTA
Luisa Rebull, SSC-Caltech
Mark Marley, NASA Ames Research Center

We have conducted a photometric monitoring program of 3 field late-L
brown dwarfs looking for temporal variability due to the existence of
clouds in their atmospheres.  The observations were performed using
Spitzer/IRAC 4.5 and 8 um bandpasses and were designed to cover at
least one rotational period of each object.  One-sigma RMS (root mean
squared) uncertainties of less than 3 mmag at 4.5 um and around 9 mmag
at 8 um were achieved.  This observations provide the most sensitive
search to date for structure in the photospheres of late-L dwarfs at
mid-IR wavelengths, and our photometry provides stringent upper limits
to the extent to which the photospheres of these transition L dwarfs
are structured.  Two out of the three objects studied exhibit some
modulation in their light curves at 4.5 um -but not 8 um- with periods
of 7.4 and 4.6 hr and peak-to-peak amplitudes of 10  mmag 8 mmag.

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