Astronomy and Astrophysics – Astronomy
Scientific paper
May 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993aas...182.0706a&link_type=abstract
American Astronomical Society, 182nd AAS Meeting, #07.06; Bulletin of the American Astronomical Society, Vol. 25, p.802
Astronomy and Astrophysics
Astronomy
Scientific paper
The Faint Object Spectrograph aboard Hubble Space Telescope has observed HZ Her, the companion of the prototypical binary X-ray pulsar Her X-1, in its high spectral resolution mode (lambda /Delta lambda ~ 1200). The spectra encompass the 1150--3300 Angstroms range at binary orbital phases 0.5 and 0.0, corresponding to X-ray maximum and mid-X-ray eclipse, respectively. The maximum light spectra are dominated by strong, narrow NV, CIV, and HeII emission, confirming and extending previous IUE results. The OIII Bowen resonance fluorescence line at lambda3133 is particularly prominent, confirming that the Bowen mechanism is most certainly the source of the strong lambda lambda4640 , 4650 emission complex. Most remarkable, however, are the minimum light spectra, where the object is too faint for reasonable observations from IUE. Despite the total eclipse of the X-ray-emitting neutron star, our spectra show strong emission at NV lambda 1240, SiIV lambda 1400, NIV] lambda1488 , and CIV lambda1549 . (The situation at Lalpha is ambiguous due to geocoronal contamination). In a little-cited observation almost two decades ago, Koo & Kron (PASP, 89, 285) reported an incident of HeII lambda4686 in emission on a glass plate obtained in 1973 at mid-eclipse in a heroic 6 hr exposure by R. Kraft. However, very few ground-based spectra of HZ Her have been published in the last decade, and it does not seem commonly appreciated that strong, high excitation emission is indeed present, probably routinely, when the neutron star is occulted. Although the hot gas might be associated with the ``accretion disk corona" (inferred to be present through very weak X-ray emission during eclipse), more likely the source is somewhat cooler blobs above and around the disk, also thought to be responsible for the occasional odd ``X-ray dips," as well as features in the optical light curve. This work has been supported by NASA Grant NAG5-1630.
Anderson Scott F.
Downes Ronald A.
Margon Bruce
Wachter Stefanie
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