(cba:news) almost-pi-day cba-news

Joe Patterson jop at astro.columbia.edu
Sun Mar 12 08:32:12 EDT 2017


in both pdf and .txt format

joe p
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                                                             March 12, 2017.
Hi CBAers,

Unless Christian or Enrique protests mightily, time to end the YZ Cnc
campaign, or demote to once-a-week status.

CN Ori is also at the end of the line.  Time to quit.  Nice result: all the
previously published orbital periods appear to be wrong (in the third
decimal place).  The reason is subtle: in this ever-on-the-move
star, the phasing of the orbital wave is not completely stable - it depends
on brightness.  Could this be a consequence of changes in disk size?  A
tempting interpretation... but one which awaits more careful analysis.

We have long-term programs going om FS Aur and BY Cam.  Many others too of
course, but these are at the end of their observing seasons... and end-of-
season runs are of special value because they help bridge the gap to the
next observing season.  So on some clear nights when you can get a
long-ish run, have a go at these stars.  This self-expires about April
1 (can't get blood from a turnip).

Shawn Dvorak has started up the AM CVn season, and that's definitely a star
for high-priority coverage over the next month.  We need just one more
high-quality timing to get a superb 24-year ephemeris.  But each good-
quality timing takes a week or more of coverage, because there are two
stronger signals - the 1051 s and 1011 s superhumps - which have to be
subtracted in order to isolate the 1028 s orbital signal.  It's not that
difficult to do this, but it does require a lot of concentrated runs -
as long as you can go on it, and for a few weeks on end.

I've written up our paper on the recurrent nova IM Nor.  It appears to be
a great match for T Pyx, which is mighty encouraging since T Pyx otherwise
stands alone - no relatives! - in the CV zoo.  But now that Norma season
has rolled around again, I really want to get a few 2017 timings of the
eclipse.  It's 19th magnitude, so is probably a project for Gordon and Berto
only (who have been able to get good data on it in the past).

T Pyx.  Now near the end of its observing season... and for the same
reason cited above, a good time to get some long runs, to pin down the
cycle count.  Not that it's uncertain, but since the period is changing
(mirabile dictu!), we have to keep vigilance on it.  Berto has gotten
one late-season run - another 3-5 will end its observing season nicely.

NY Lup. Beginning of observing season for this DQ Her star.  Beginnings
are just as critical as endings, for the same reason.  A few runs now
would be great.  Watch out for the contaminating neighbor star.

Consider this list to be ADDITIVE to Enrique's list.  He's more up-to-date
than me concerning current targets, especially the DQ Her stars, which he
tracks closely.  I heartily concur in recommending EI UMa as a great
northern target now.

I've got the AAVSO/SAS June meeting on my travel schedule, and hope to
see a bunch of you there!  

joe p
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