(cba:news) March stars, volume 1; AM CVn & friends

Joe Patterson jop at astro.columbia.edu
Wed Mar 11 11:16:06 EDT 2020

Hi CBAers,

Time for an update.  As many of you know, many colleges have decided to 
go online-only, and we're all scrambling to do this here in NYC.  Quite 
a challenge to do so with only a few days notice!

So this is just volume 1 of the seasonal target list.

AM CVn.  El Magnifico.  The 2020 coverage has confirmed the period 
change we strongly suspected with all the earlier data.  That was the 
main goal... and hallelujah, ee got there!  But now there is a new 
challenge, which we can meet by extending the observing season another 
1-2 months.

AM CVn has superhumps at 1011 s and 1051 s (most of the power at 525.5 
s).  Being superhumps, they flail around somewhat in phase (in contrast 
to the stable 1028 s ORBITAL signal).  Since both superhumps are present 
nearly all the time, one can study their phase wanderings relative to 
each other.  In "theory", they should be anti-correlated; one period 
lengthens while the other shortens.  But theory always yields to data, 
and in this case even more than usual; when it comes to accretion-disk 
precession, "theory" is too respectful a word.

The phase wanderings of the 1011 and 1051 s signals can be readily 
tracked with a few (5 would be great) months of time-series photometry. 
Long runs are helpful, but not usually necessary.  See if you can grab a 
3-4 hour run on AM CVn over the next ~2 months, when it will be 
well-placed in the northern sky.

Attached is last year's paper (a prelim version of what we will submit 
to the regular journals in a few weeks).

All this beautiful data has made me hungry to try similar analysis on CR 
Boo and V803 Cen - the other two bright helium-disk stars. We've 
published on each before, but never extensively.  So those are 
high-priority stars for the next month!

We've had a good year on HZ Pup - definitely enough to publish (for the 
first time, re this star).  But just to make sure we can bridge to the 
next observing season, try to get a few more runs over the next 2 weeks 
or so.

FULL MOON SPECIAL.  SW Sex should be a prime candidate for superhumps, 
yet has never shown them.  We ought to keep looking - it's getting very 
annoying that the star doesn't show them... and also annoying that we've 
never done a really thorough search.

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