ON THE USE OF SUPERNOVAE AS RADIO-OPTICAL ASTROMETRIC FIDUCIAL POINTS

Abstract

ABSTRACT The high accuracy radio astrometric reference frame is based on extragalactic radio sources which are optically faint (mV > 15), while the most accurate optical astrometric reference frame is made up of bright galactic stars which are almost all radio quiet to current sensitivity limits. The HIPPARCOS mission is establishing positional accuracies for these bright stars at the several millarcsecond level of precision, and advancements in space-based observations should eventually allow precisions at the submilliarcsecond level. However, the relationship between the two reference frames is difficult to directly establish to a level consistent with the internal precision of the two independent frames. The compact extragalactic radio sources are too faint for most optical astrometric techniques, and the bright stars which are active radio sources are often in binary or extended envelope systems where the radio and optical photocenters may be related at accuracies of only a few millarcseconds. This difficulty may be alleviated by using the occasional optically and radio bright supernovae as point-like fiducial marks for establishing relationships between the two reference frames. These independent reference frame relationships can be accomplished from currently available ground-based platforms.