The McDonald Observatory serendipitous UV/blue spectral survey of asteroids

Spectra of 14 asteroids of varying classes were acquired using a moderate resolution spectrograph (dispersion 3.5 [Angstrom]/pixel) at the McDonald Observatory 2.7-m telescope as random targets of opportunity over the past 6 yr. The utility of high-quality measurements of asteroid reflectance in the 3200-5500 [Angstrom] wavelength range was demonstrated by the presence of subtle absorption features and the confirmation of the broad spectral properties of asteroids in this region. Notably, the sharp increase in reflectance with increasing wavelength for 5145 Pholus was confirmed, extending to the short wavelength of 3200 [Angstrom]. The NEAR target 253 Mathilde shows an absorption feature centered at 4300 [Angstrom] similar to features attributed to an [Fe.sup.3+] spin forbidden transition in the iron sulfate jarosite, a product of aqueoous alteration. Subtle absorption features near 4300 and 5065 [Angstrom] attributed to [Fe.sup.2+] spin-forbidden transitions in pyroxenes are apparent in the spectrum of 4 Vesta. Examples of the effects of signal loss due to differential refraction in the UV/blue, and the effects of slight misregistration of the sharper spectral features present in the solar spectrum at these wavelengths are presented and discussed.