Other
Scientific paper
Dec 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997hst..prop.7288v&link_type=abstract
HST Proposal ID #7288
Other
Hst Proposal Id #7288 Binary Stars
Scientific paper
We propose STIS observations of the X-ray binary pulsar system Hercules X-1/HZ Herculis. We will resolve the UV emission lines, and use Doppler shifts to map the system {normal star, disk, gas stream}. A previous HST observation revealed separate narrow and broad emission components of the strongest emission line, the N V doublet at 1240 Angstrom, but the dramatic spectral changes over orbital phases 0.6-0.9 do not yet have a unique interpretation. With the STIS, we can also resolve similar structure in the other strong UV lines, O VLambda1371, Si IVLambdaLambda1393, 1403, C IVLambdaLambda1548, 1550, and He IILambda1640. The O IV lines near 1400 Angstrom provide a density diagnostic which will allow us to test models for the ionization of the emitting gas. The constraints from the additional lines obtained over a full binary orbit should enable us to distinguish between the possible interpretations as well as to construct a physical image of the system using Doppler tomography. Using the Time-Tag mode, we will search for pulsations at the 1.24 second X-ray pulsar period throughout the lines and continuum. We will apply models of the continuum emission to infer the mass-accretion rate of the neutron star. We will set limits on the size, shape, rotation, and precession of the disk, the effects of X-ray illumination of the disk and star, and possible mass-loss from winds in the system. The weak residual lines present during eclipse may reveal a disk wind or other gas within the system.
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