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J. K. Miller (Villanova University), S. G. Korzennik, P. Nisenson (Harvard-Smithsonian Center for Astrophysics)
We present the results of our efforts to develop a procedure to determine the velocity shifts between the pre- and post-upgrade stellar reference spectra observed with the Advanced Fiber Optic Echelle (AFOE). The AFOE spectrograph was upgraded to increase its efficiency in measuring radial velocities by rearranging the physical set-up of the optical system. While observing roughly the same wavelength range, the post-upgrade spectra have a different ratio of wavelength to pixels and gaps in the data where pieces of the spectrum were not projected onto the CCD. These differences necessitated taking new stellar references of each star system. All velocity measurements for a star are made relative to this reference. However, there is an unknown velocity shift between every pair of new and old stellar reference spectra simply because they were observed on different nights. The differences in the spectra prevent us from recalculating all of the velocities relative to one reference or the other. To overcome this problem, we have been developing a procedure that models the new stellar reference with a parameterized function of the old reference, and the velocity shift is one parameter of the model. We independently model each wavelength range of the new spectrum that overlaps the old spectrum, which gives us twelve measurements of the velocity shift. The spread in these results gives us an idea of the precision of our calculations, and our goal precision is ~ 1 ms-1.
This work was supported in part by the SAO intern program under NSF grant AST-9731923.
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.