EUVE photometry of SS Cygni: Dwarf nova outbursts and oscillations Page: 8 of 13
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5
C. W. Mauche: EUVE Photomeiry of SS Cygni
FIGURE 2. DS count rate (filled circles with error bars) and pulsation period (diamonds) as
a function of time from (a) 1993 August and (b) 1994 June/July. The size of the diamonds
correspond to the relative size of the x2 statistic (see text).
To present the results of these calculations, we show in Figure 2 the X2 statistic in
the form of a pseudo-contour diagram along with the log of the DS count rate. It is
apparent from this figure that coherent oscillations exist in the DS count rate for both
outbursts. For the 1993 outburst, randlom jp, ks in the x2 surface are present very early
in the outburst, but the oscillation does not Stabilize until MJD 9219 when the count
rate is 2.8 counts s-. The period of the oscillation is initially : 8.6 s, falls over the
next day or so to 7.8 s, and then asymptotically approaches ~ 7.5 s over the next few
days. For the 1994 outburst, the oscillation turns on during the fast rise to outburst on
a MJD 9528 when the count rate is ~ 2.3 counts s-1. The period of the oscillation is
initially ; 8.9 s, falls to ; 7.2 s (the shortest period ever observed in SS Cyg, or in any
other dwarf nova) within a day, and rebounds to N 7.4 s by the end of the observation
on MJD 9529.8. When observations resume N 3 days later, the period of the oscillation
is a 7.6 s and rises slowly over the next few days to ~ 8.0 s.
Other quantitative aspects of the oscillations are as follows. First, as is evident from
Figure 2, the period of the oscillation correlates with the count rate, being long when the
count rate is low and short when the count rate is high. Furthermore, it appears from
the 1994 outburst that at a given count rate the period on the rise to outburst is to first
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Mauche, C.W. EUVE photometry of SS Cygni: Dwarf nova outbursts and oscillations, report, May 15, 1995; California. (https://digital.library.unt.edu/ark:/67531/metadc793210/m1/8/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.