Geminga as Seen by the HST

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Session 21 -- Pulsars
Oral presentation, Monday, 30, 1994, 2:00-3:30

[21.07] Geminga as Seen by the HST

Giovanni F. Bignami (IFC-CNR,Milano), Patrizia A. Caraveo (IFC-CNR,Milano), Sandro Mereghetti (IFC-CNR,Milano), Roberto Mignani (Universita' di Milano), Laurence Taff (STScI)

The crucial piece of information still lacking for the understanding of Geminga is the object's distance. Comparing the measured gamma-ray flux with the known neutron star rotational energy loss, one obtains values anywhere between few pc to 300 pc, an upper limit not too far from the one derived from the IS X-ray absorption. \\Exploiting the post-refurbishment capabilities of the HST instruments, we plan to measure (or to put limit on) Geminga's parallactic displacement. This will be done in Cycle 4 with three sets of WFPC2 observations already scheduled near the spring and fall equinoxes, when the expected parallactic displacement is maximum. The program started on March 18, and the results of the first observations will be reported. \\Meanwhile, ground based optical observations, taken fron the New Technology Telescope of the European Southern Observatory, also in 1994, have confirmed the high proper motion of the optical counterpart.

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