HERSCHEL Suborbital Program: 3-D Applications for the STEREO Mission

The HERSCHEL (HElium Resonance Scatter in the Corona and HELiosphere) Suborbital Program is an international collaborative program between a consortium of Italian Universities & Observatories led by Dr. E. Antonucci (and funded by the Italian Space Agency, ASI), the French IAS (funded in part by CNES) and the Solar Physics Branch of NRL (by NASA SEC and the Office of Naval Research). HERSCHEL will: investigate the slow and fast solar wind, determine the helium distribution and abundance in the corona, and test solar wind acceleration models; by obtaining simultaneous observations of the electron, proton and helium solar coronae. HERSCHEL will also establish proof-of-principle for the Ultra-Violet Coronagraph, which is in the ESA Solar Orbiter Mission baseline. The HERSCHEL launch date has been linked to the STEREO launch date to allow coordinated science between the two missions. One aspect of this scientific coordination is establishing the 3-D structure of the inner corona. HERSCHEL provides a third viewpoint for the inner corona covered by the A&B STEREO SECCHI COR-1. HERSCHEL is the only scheduled, space-based asset that could provide this third viewpoint for the critical inner corona viewed by STEREO COR-1 (although lower resolution, ground-based cononagraphs will make a contribution). A third viewpoint dramatically increases one's ability to establish the 3-D structure of an optically thin object (e.g. the metric in Fig. 7 of Davila 1994, ApJ 423, 871). HERSCHEL will provide at least a snapshot of that viewpoint, plus a wide range of additional information on the H and He composition of the inner corona.