CR Boo again

(vsnet 645, Joe Patterson)


We have been observing this star intensively from six observatories during may 5-29. During the first half of this interval, the star cycled between magnitude 13.9 and 15.3 on a timescale of about 0.8 days. It's possible that this represents the repetition time for ordinary dwarf nova eruptions. Since May 19 the star has been stuck in a high state (mag 14.3), though it's now declining at a rate of 0.1 mag/day. "Superhumps" appeared in the light curve starting on May 22. Over the last week the period has smoothly evolved from 1493 s to 1485 s. The period change and the association of the humps with the long bright state provide a significant clue that this is essentially a supermaximum of an SU UMa-type dwarf nova.

Such stars are common, but this one is special because it is dominated by helium rather than hydrogen. If we could thoroughly learn the amplitudes and timescales of the "eruptions", it would provide a wonderful and unique test for dwarf nova theories.

We expect to continue the campaign until the end of the observing season in late July. Our observing run in Chile has ended so we're all the more anxious to find other observers around the world with whom to pool data. The "normal" variations occur extremely rapidly (<1 day), and it requires observation at different longitudes to define this timescale. Even quite rough accuracy (0.2 mag) can be very useful in solving this problem.

Joe Patterson
Dept. of Astronomy, Columbia Univ.

CR Boo (1)

CR Boo (2)

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