TAKAMIZAWA V85 = IY UMA HITS THE BIG-TIME
In January 2000, the variable star Takamizawa V85 went into
eruption, first spotted by Patrick Schmeer. Within two days Lasse Jensen
kicked off the CBA photometric campaign. And what a star it has turned
out to be! At Ouda Observatory on the first night, Uemura and Kato found
superhumps and eclipses, attesting to the star's identity as a deeply
eclipsing SU UMa-type dwarf nova. Jonathan was just starting an
observing run at Kitt Peak then, so was able to keep the North American
coverage long and excellent, even while the usual CBA heavyweights
(Daves East and West, and Cap'n Bob) were off attending to other parts
of life. We even had two telescopes (the 1.3 and 2.4 m)
working in tandem for some of that time, which enabled strictly
simultaneous multicolor measurement.
We have coverage over 17 straight days. As if on script, the star
fell to a "quiescent" (let's rather call it post-superoutburst, as it
was still ~1 mag above apparent true quiescence) state right in the
middle; so we have long, excellent time series in both states. There
were four conclusions of considerable interest:
- Superhumps continued to rage through the light curve at least a
week after the eruption ended.
- A sharp white dwarf eclipse appeared in the light curves as soon as
the star went faint. Ingress and egress times were 27±6 s. Outside
the humps, the white dwarf is responsible for about 60% of the light in
the binary. Folks, that's a hot white dwarf. It'll be fascinating to see
(from continued photometry) if it now cools!
- When the "hot spot" at disk edge emerged again at 17th magnitude,
it was very strong (about 0.6 mag). The evolving brightness of the hot
spot will be a tracer of how the mass transfer rate varies between
eruptions.
- In addition to the orbital frequency w and the main superhump at
w-W (where W is the putative precession frequency), there are also
signals at 3w-W, 4w-W, and 5w-W. Such complexities in the superhump
spectrum have popped up before, but never in a dwarf nova.
In addition, the clearest reason for studying eclipsing systems
has not yet been properly exploited: to use the eclipses to map out the
light sources in the binary (beyond the obvious ones revealed by the
sharp eclipses). Project for later.
Tak V85 is off our small-scope radar screens
now, but it is turning out to be a bountiful season for eclipsing dwarf
novae!
(click figures for larger versions)
IY UMa Figure 1.
IY UMa Figure 2.
IY UMa Figure 3.
IY UMa Figure 4.
IY UMa Figure 5.
Figure 5. Sample blow-ups of individual eclipses. All this data
(in contrast to the above V-band data) was obtained through a
Schott BG38 filter, which for an intrinsically blue star has an
effective "wide B" passband. Eclipse numbers are shown at upper
right. The differential photometry is rendered on an intensity scale.
Each eclipse has four rapid phases (white dwarf ingress, bright spot
ingress, white dwarf egress, bright spot egress), plus a more gradual
event (disk eclipse?). Phase zero is defined as the white dwarf's
mid-eclipse, which can be timed to very high accuracy (~3 s); the bright
spot's center of light is displaced to much later phase, as can easily be
seen. The points are at ~17 s intervals.
