A HIRES/KECK SPECTROSCOPIC INVESTIGATION OF THE MEASUREMENT OF SODIUM IN THE ATMOSPHERE OF HD 209458b

We present high-resolution High Resolution Echelle Spectrometer (HIRES)/Keck spectra of HD 209458, and a Monte Carlo variation on the basic method used by other workers, to look for the excess in-transit absorption in the NaD doublet at 5893 angstrom due to the extrasolar planet. The HIRES data, binned by bandpass, allow a direct comparison with previous results. We find >3 sigma results in most test bandpasses around the NaD doublet, including relative absorption of (-108.8 +/- 25.7) x 10(-5) in the narrow bandpass used by other workers. This is approximate to 4.7 times larger than the narrow results reported by Charbonneau et al. for HD 209458b. However, >2 sigma absorption is detected in some weak Fe I and Ni I lines that were tested for comparison, raising concern about the uncertainties introduced by continuum-fitting and terrestrial atmosphere subtraction.