We have identified the optical counterpart of the isolated, non-pulsing, radio-quiet neutron star RXJ185635-3754 in HST/WFPC2 images as a faint blue object with V=25.6 and U-V = -1.2. The 3000 and 6060A fluxes lie above the extrapolation of the X-ray black body, by factors of 2.4 and 3.7, respectively. The optical points are not consistent with a black body continuum unless the reddening greatly exceeds that suggested by the X-rays. We interpret the spectrum in terms of a latitudinal temperature gradient plus excess emission in the red. If the object lies in front of the CrA molecular cloud, the radius R_infinity < 14 km.
We report on the current status of the investigation. We have obtained
a spectrum near 100 A from the EUVE, and further broadband photometry.
Planned HST observations will
yield the proper motion and parallax. Knowledge of the distance will
permit us to investigate the interior equation of state: we will discuss the
observational constraints on conventional and kaon-condensate
equations of state.
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