Kitt Peak Vacuum Telescope: New Data and New Web Page

The NSO Kitt Peak Vacuum Telescope, operated in collaboration with the NASA Goddard Space Flight Center and the NOAA Space Environment Center produces full-disk solar maps of various quantities of use to the solar research community every clear day. Starting in 1973, we have made maps of the line-of- sight component of the photospheric magnetic field. In 1974, the strength of the He I 1083-nm line was added to the daily products. In 1993, the old instrument was replaced and additional quantities such as Doppler shift and line depth have been regularly measured.

From time to time, the KPVT has been used to make magnetic field measurements using chromospheric spectrum lines such as H, the infrared Ca II triplet, and He I 1083 nm. Stimulated by the recent discovery of apparent outflow from polar coronal holes observed with He I 1083 nm (Dupree, Penn and Jones, ApJ in press), D. Branston and J. Harvey made a full-disk map using Ca II 854.2 nm. This chromospheric map showed a number of surprises. It reveals magnetic fields near the limb (and especially the poles) much more clearly than when using photospheric lines. Closer to disk center, it is less affected by the clutter of small-scale background fields and appears to show very large-scale patterns of fields better than when using photospheric lines. It is also sensitive to prominences above the limb. (A technical problem is currently suppressing off-disk measurements). There appear to be diffuse unipolar patches covering several supergranules visible occasionally at high latitudes (prominence fields projected against the disk?).

Because of these differences with photospheric measurements and also because of the beautiful results becoming available from instruments on the SOHO spacecraft, we have added the chromospheric full- disk observations as a regular daily data product. Experiments are underway using the 849.8-nm line instead of 854.2 nm to try to obtain simultaneous photosphere and chromosphere observations. The 849.8-nm line is also more sensitive to magnetic fields.

Although the KPVT data were among the earliest solar images available on the World Wide Web, our web pages were not effective in getting data to the community. J. Harvey has overhauled automated reduction scripts and prepared a new page to access the most current popular KPVT data more effectively. This page displays tiny images and allows the user to obtain larger gif versions as well as to ftp research-quality versions of the data. The page can be accessed through NSO's home page, http://www.nso.noao.edu. Access to older data is under development.

Jack Harvey