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Session 67 - Stars: Evolution, Atmospheres, Intrinsic.
Display session, Thursday, June 11
The recent addition of ``NEWSIPS"-processed echellograms to the IUE archives permits the analysis of apparent radial velocities (RVs) via cross-correlation techniques, both with respect to old-generation (``IUESIPS") processings and relative to different instruments. We report here on a comparison of apparent RVs, mainly for the short-wavelength (SWP) camera with respect to time, wavelength, aperture-type, and cameras. We also compare RVs from IUE data relative to RVs from the Copernicus and Orfeus missions. (See also http://archive.stsci.edu/iue/newsips/radvel/.)
Although residual zeropoint errors still exist for NEWSIPS SWP data, both with respect to apparent RVs from images from the LWP and LWR cameras and relative to RVs derived from optical studies, most NEWSIPS-processed SWP images are to be greatly preferred over IUESIPS data because of their far greater stability with time. Differences in apparent RVs from large- (LGAP) and small-aperture (SMAP) images arise for all three cameras for *bright* stars because of a systematic centering error resulting from the procedure adopte for guiding on bright stars. The LGAP - SMAP difference amounts to -5 to -6 km s^-1 for SWP images. In addition, centering errors for individual large-aperture images generally cause RV differences of several km s^-1.
One of the most interesting systematics found in this study is a wavelength-dependent errors in NEWSIPS SWP images, both respect to IUESIPS processings and the Copernicus Atlas of \tau Sco. We show that this systematic is robust and is likely to arise from a 1990 revision of the laboratory wavelengths of the PtNe calibration source used by IUE (NEWSIPS) and GHRS. This fact may have broad implications for comparisons of velocities from satellites launched before and after this date.
Program listing for Thursday