FIRST RESULTS OF THE SUMER TELESCOPE AND SPECTROMETER ON SOHO .1. SPECTRA AND SPECTRORADIOMETRY

SUMER - the Solar Ultraviolet Measurements of the Emitted Radiation in strument on the Solar and Heliospheric Observatory (SOHO) - observed i ts first light on January 24, 1996, and subsequently obtained a detail ed spectrum with detector B in the wavelength range from 660 to 1490 A ngstrom (in first order) inside and above the limb in the north polar coronal hole. Using detector A of the instrument, this range was later extended to 1610 Angstrom. The second-order spectra of detectors A an d B cover 330 to 805 Angstrom and are superimposed on the first-order spectra. Many more features and areas of the Sun and their spectra hav e been observed since, including coronal holes, polar plumes and activ e regions. The atoms and ions emitting this radiation exist at tempera tures below 2 x 10(6) K and are thus ideally suited to investigate the solar transition region where the temperature increases from chromosp heric to coronal values. SUMER can also be: operated in a manner such that it makes Images or spectroheliograms of different sizes in select ed spectral lines. A detailed line profile with spectral resolution el ements between 22 and 45 m Angstrom is produced for each line at each spatial location along the slit. From the line width, intensity and wa velength position we are able to deduce temperature, density, and velo city of the emitting atoms and ions for each emission line and spatial element in the spectroheliogram. Because of the high spectral resolut ion and low noise of SUMER, we have been able to detect faint lines no t previously observed and, in addition, to determine their spectral pr ofiles. SUMER has already recorded over 2000 extreme ultraviolet emiss ion lines and many identifications have been made on the disk and in t he corona.