Other
Scientific paper
Dec 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994aas...185.1106m&link_type=abstract
American Astronomical Society, 185th AAS Meeting, #11.06; Bulletin of the American Astronomical Society, Vol. 26, p.1325
Other
Scientific paper
The old nova DQ Herculis was observed with the Hubble Space Telescope (HST) Faint Object Spectrograph in the lambda lambda 1150--2500 Angstroms range, over three orbits of the satellite, as part of the FOS team's GTO program. These observations were carried out in the ``rapid" mode, with a time resolution of 4.08 s, allowing us to search for pulsations of the UV light at the 71-s white-dwarf spin period, analogous to the low amplitude oscillations long known to be present in visible light. The integrated spectrum shows strong line emission in Lyalpha , NV, SiIV/OIV], CIV and HeII. The flux of all of these lines drops during the eclipse of the white dwarf by the late-type star, indicating that most of the emission is not nebular, geocoronal, or from an extended wind. The SiIV/OIV] complex is marginally resolved, with OIV] perhaps surprisingly contributing the majority of the flux. Furthermore, none of 300 simple photoionization models examined yields SiIV/OIV] as strong as that observed. During the first and second HST orbits, we detect coherent 71-s pulsations in the continuum, with amplitudes of 9% and 4%, respectively. This is the first report of pulsed UV emission from DQ Her. The amplitude is clearly time-variable, also known to be the case in visible light, as no pulsations are seen during the third orbit, with an amplitude upper limit of 2%. Most interesting, however, is the behavior of the emission lines. During the second HST orbit, the strong Lyalpha emission is seen to pulse with a 12% amplitude, and the phase of maximum light is displaced 0.3 later than that of the continuum pulse. No pulsations were detected in any other emission line, nor in Lyalpha during the other two orbits. The line and continuum pulsations clearly hold great promise as an aid in unraveling the complexities of this well-studied but still poorly understood system. This work has been supported by NASA Grant NAG5-1630.
Anderson Scott F.
Downes Ronald A.
Margon Bruce
Silber Andrew
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