The first high-resolution near-UV solar spectrum

The Sun is the fundamental stellar standard, the principal calibrator for photometry, spectra, and theoretical investigations of stars and galaxies. Despite its central importance, no high-resolution near-UV spectrum of the Sun exists. This contrasts sharply with the existence of extremely high signal-to-noise solar optical spectra, covering 2958-9250A at a resolution R ~ 350,000-700,000. It is a fundamental tool for wide-ranging investigations. Examples include stellar and Galactic abundances of heavy elements and their implications for nucleosynthesis, the spectral modeling of host stars to better derive the irradiation and the composition of the planets they host, the effects of convection on line strengths and profiles, and the identification of unknown energies and levels of the neutral iron atom. However, below 3000A, a space-based instrument is required.

It is feasible to obtain a solar atlas at resolution of ~50,000 covering 1700-3000A using a small satellite similar to the NASA SMEX IRIS. Instead of filters to isolate individual wavelength regions, this could provide broad spectral coverage by shifting the tilt of the grating to record individual short wavelength segments. Given short exposure times, wide wavelength coverage is feasible. The IRIS instrument has demonstrated pointing stability and the techniques for controlling heat from the solar irradiation. Most of its optical and coating systems are already suitable. A stepping mechanism is required, along with a CCD and optics for pixels of 3.7 rather than 12 microns.