  We have searched for a methane signature in the infrared spectrum of tau
Bootis, produced by the planetary companion. The observations comprise 598
low-noise, high resolution spectra near 3.28 microns, which we analyze by
cross-correlating with a modeled planetary spectrum based on the work of
Burrows and Sharp (1999), and Sudarsky et al. (2000). The 3-sigma random noise
level of our analysis is 0.00006 stellar continuum flux units, and the
confusion noise limit - measuring the resemblence of a cross-correlation
feature to the spectrum of methane - is 0.00025.
  We find a significant cross-correlation amplitude of 0.00033 continuum units
at a velocity near that of the star. This is likely due to methane from a
low-mass companion in a long-period orbit. Fischer, Butler and Marcy (2000)
report a long-term velocity drift indicative of such a companion. But the
system is known to be a visual binary with an eccentric orbit, and is rapidly
approaching periastron. Whether the visual companion can account for our
observations and the Fischer et al. velocity drift depends on knowing the orbit
more precisely. The stability of planetary orbits in this system also depends
crucially on the properties of the binary orbit. A second cross-correlation
feature, weaker and much more diffuse, has intensity amplitude 0.0002 continuum
units and occurs at a velocity amplitude of 71 +/-10 km/sec, in agreement with
the orbit claimed for the planet by Cameron et al. (1999). Like the first
feature, it has passed several tests designed to reject systematic errors. We
discuss the possibility that this second feature is due to the planet.
