We obtained 238 spectra of the close orbiting extrasolar giant planet HD 189733b with resolution R \sim 15 , 000 during one night of observations with the near infrared spectrograph , NIRSPEC , at the Keck II Telescope .
We have searched for planetary absorption signatures in the 2.0 µm - 2.4 \micron region where H _ { 2 } O and CO are expected to be the dominant atmospheric opacities .
We employ a phase dependent orbital model and tomographic techniques to search for the planetary absorption signatures in the combined stellar and planetary spectra .
Because potential absorption signatures are hidden in the noise of each single exposure , we use a model list of lines to apply a spectral deconvolution .
The resulting mean profile possesses a S/N ratio that is 20 times greater than that found in individual lines .
Our spectral timeseries thus yields spectral signatures with a mean S/N = 2720 .
We are unable to detect a planetary signature at a contrast ratio of log _ { 10 } ( F _ { p } / F _ { * } ) = -3.40 , with 63.8 per cent confidence .
Our findings are not consistent with model predictions which nevertheless give a good fit to mid-infrared observations of HD 189733b .
The 1 - \sigma result is a factor of 1.7 times less than the predicted 2.185 µm planet/star flux ratio of log _ { 10 } ( F _ { p } / F _ { * } ) \sim - 3.16 .