(cba:news) stars for february-march

Joe Patterson jop at astro.columbia.edu
Fri Jan 31 15:27:38 EST 2020

Hi CBAers,

Here;s my list of changes in the observing program.  These are all cases 
where we expect to complete observations (i.e., enough to publish) in 
2020.  There are others, worthy targets but not quite in that 
almost-done category.  I'll list them in a fe days.  PLus this list is 
independent of Enrique's (he is working on different stars).

We have enough for V1062 Tau and HZ Pup.  Both difficult stars - but we 
finally battled through to find an ephemeris.

Our biggest faves in recent years have been T Pyx and AM CVn.  The Sun 
has finally gotten out of their way, so let's start up our 2020 effort. 
The prescription for both is basically: as-long-as possible (with <2 
airmasses) and as often as possible.  The main reason for such greed is 
simply that - greed.  We all long to see power spectra with towering 
peaks leaping out of the noise!  But for AM CVn, there's an extra 
reason.  ings are more complicated.  The following is recommended only 
for true AM CVn devotees.

AM CVn's 1028-s orbital signal is quite weak, about 2-5x smaller than 
the superhump signals which are clear in the light curve,  By itself 
that is no great problem; one could just amass enough data to beat down 
the noise.  Around 3 good-quality and closely-spaced nights would 
probably reveal the orbital signal very clearly - amplitude and phase.

The trouble is that the strong superhump signals are at 1051, 525, and 
1011 seconds, plus a few weaker guys... and they're ALL UNSTABLE on a 
timescale of a few weeks.  That instability means that I can't 
accurately remove these contaminating and fairly strong signals, unless 
the data are tightly grouped in time.   This greatly favors the "long 
runs on consecutive days" approach.  But as these signals slowly drift 
in and out of phase with each other, there are intervals when the 
corrupting effects are really maximized.  And that might occur in 
mid-observing -season (Mar-Apr)... so let's pull the trigger now.

WE don't need a lengthy campaign.  After the 2019 season, I already 
wrote most of the paper... but pulled it back for reasons that are 90% 
greed and 10% doubt.  One more season will remove that sliver of doubt 
(re the decades-long change in P_orb).

Whew.  All that arcana applies only to AM CVn.  Everything else, 
certainly including T Pyx, obeys common sense - the more, the better.

One other northern request: QS UMa (H0928+50, as we used to call it). 
It's a 17th mag guy with an eclipse every 20 hours.  Perfectly times for 
northern observers.  And our biggest need is for (brace yourself) V-band 
photometry.  Ideally one orbit in V and one in clear. But the V orbit is 
mainly to *calibrate* the clear.


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