The lack of spectral variability in 51 Pegasi: Confirmation of the planet hypothesis

We present-high resolution (R > 200,000), high signal-to-noise spectral dat a for 51 Pegasi spanning a complete orbital period of the purported planeta ry companion. A detailed examination of the line bisectors from eight spect ral lines as well as the ratio of the line depth of the V I 6251 Angstrom l ine to the Fe I 6253 Angstrom line were performed. The changes in the mean bisector velocity span and curvature are about 1 m s(-1) and 4 m s(-1), res pectively. These variations are an order of magnitude less than the variati ons reported by Gray and are small enough to exclude all nonradial sectoral pulsation modes. The line-depth ratio of V I/Fe I also shows no significan t variations, and a least-squares sine fit using the planet period of 4.23 days yields an amplitude of 0.00038 for any line-depth ratio variations. Th is corresponds to a disk-integrated temperature variation (peak-to-peak) of less than 1.7 K. We conclude that the radial velocity variations are not d ue to a dynamical stellar atmosphere and that a planetary companion remains as the only viable explanation for the observed radial velocity variations . The lack of bisector variability in our data indicates that the contribut ion to the observed spectra due to reflected light from the planet is at le ast 2000 times less than that of the primary light. Assuming a planetary al bedo of unity, this places an upper limit of 0.2 R. for the radius of the p lanet.