(cba:news) AM CVn, clarified

Joe Patterson jop at astro.columbia.edu
Tue Apr 30 06:27:11 EDT 2019

Hi CBAers,

In my previous message, I said AM CVn is still a good target.  Let ne 
clarify!  The main project for 2019 was to clarify the Pdot - the rate 
of orbital period change,  That part is done.  There's a secondary goal:
to compare the slow phase wanderings of the positive (525 s) and 
negative (1011 s) superhump.  They wander on a timescale of months, so 
they require *months* to compare their wanderings.  I've always wondered 
whether those wanderings are ~180 degrees out of phase - which one might 
expect if they're both affected by small variations in disk radius. 
Those variations must be quite tiny, but on the other hand, our 
long-baseline measurements of period are very, very sensitive.

That side of the project still requires more data.  However, the two 
superhumps are easy to measure, not requiring all-night coverage (or 
anything close).  So AM CVn is still a good 2-hour target in the evening 
sky; with a few observers on the case, that'll suffice for a phase 
measurement of the superhumps (if continued for a few more weeks).

After that, it's HP Lib and CR Boo.


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