CBA Center for Backyard Astrophysics



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:

  1. Superhumps continued to rage through the light curve at least a week after the eruption ended.

  2. 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!

  3. 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.

  4. 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 1.

IY UMa Figure 2.
IY UMa Figure 2.

IY UMa Figure 3.
IY UMa Figure 3.

IY UMa Figure 4.
IY UMa Figure 4.

IY UMa Figure 5.
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.

Joseph Patterson, CBA New York
Jonathan Kemp, CBA Oracle
Lasse Jensen, CBA Denmark
Tonny Vanmunster, CBA Belgium
David Skillman, CBA East
Brian Martin, CBA Alberta
Robert Fried, CBA Braeside

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