  We have obtained deep Adaptive Optics (AO) images of Vega and epsilon Eri to
search for planetary-mass companions. We observed at the MMT in the L' (3.8
micron) and M (4.8 micron) bands using Clio, a recently commissioned imager
optimized for these wavelengths. Observing at these long wavelengths represents
a departure from the H band (1.65 microns) more commonly used for AO imaging
searches for extrasolar planets. The long wavelengths offer better predicted
planet/star flux ratios and cleaner (higher Strehl) AO images, at the cost of
lower diffraction limited resolution and higher sky background. We have not
detected any planets or planet candidates around Vega or epsilon Eri. We report
the sensitivities obtained around both stars, which correspond to upper limits
on any planetary companions which may exist. The sensitivities of our L' and M
band observations are comparable to those of the best H-regime observations of
these stars. For epsilon Eri our M band observations deliver considerably
better sensitivity to close-in planets than any previously published results,
and we show that the M band is by far the best wavelength choice for attempts
at ground-based AO imaging of the known planet epsilon Eri b. The Clio camera
itself with MMTAO may be capable of detecting epsilon Eri b at its 2010
apastron, given a multi-night observing campaign. Clio appears to be the only
currently existing AO imager that has a realistic possibility of detecting
epsilon Eri b.
