THE SOLAR UV CONTINUUM 1440-1680-ANGSTROM AND ITS CENTER-TO-LIMB VARIATION

The solar UV continuum has been derived from intensity-calibrated obse rvations with the High-Resolution Telescope and Spectrograph - HRTS - on its second rocket flight in 1978. A has been constructed using the spatially-resolved solar spectrum 1180-1700 angstrom along a slit exte nding from near disk center to the solar limb and crossing a sunspot a nd two active regions. The angular resolution is approximately 1.8''. The data consist of 1772 spectral scans in the full center-to-limb ran ge, including both quiet and active solar regions. The distribution of solar UV intensities has been derived and the center-to-limb variatio ns of the continuum intensities in the quiet Sun are studied. Both qua ntities show spectral variations, particularly across the Si I continu um edge at 1521 angstrom. The spectra have been fitted to curves of co nstant color temperature above and below the Si I edge. The derived ce nter-to-limb variations have been compared to the values of Samain (19 79) which are frequently referred to in the literature. A relatively l arge discrepancy may be explained by the higher spectral and angular r esolution of the HRTS as compared to the rocket instrument used by Sam ain. Comparisons with the VAL M model calculations by Vernazza, Avrett , and Loeser (1981) show discrepancies between the observations and th e model predictions, particularly with regard to the sip and amount of the intensity change across the Si i continuum edge. It is noted that some of the results presented, i.e., absolute intensities and brightn ess temperatures may change, pending confirmation of the SUSIM Spacela b 2 irradiance results (VanHoosier et al., 1988).