(cba:news) "Winter" stars for Dec-Jan

Joe Patterson jop at astro.columbia.edu
Thu Nov 28 10:25:59 EST 2019

Dear CBAers,

Many IPs lurking in the sky these nights.  There are a few new ones to 
report...  plus some old ones which have now revealed or should reveal a 
period change (due to the torques exerted by the accreting gas).  The 
latter take at least a few years to detect (white dwarfs have a decently 
large moment of inertia), but we've been pounding away for a while, and 
the pulses eventually start to arrive EARLY by measurable elements 
("early" since most of the white dwarfs are spinning up from the torques).

So I'm preparing a history-of-period-change paper.  Some well-placed 
stars these days are: V418 Gem*, V902 Mon*, HT Cam*, HZ Pup*, WX Pyx*, 
BG CMi, V647 Aur, V1062 Tau*, V405 Aur.  I've asterisked the stars I 
consider to be not yet "properly published", and therefore I guess 
deserving of somewhat higher priority.  But the best single measure of 
priority is probably determined by the match to your individual 
circumstances: brightness, time of night, quality of night, crowded 
field, suitable comp, etc.

It's best to choose 1, 2, or 3 of these stars - and specialize in them. 
Since the main interest here is *periods*, a clear filter is fine.  A 
few LONG runs are very desirable, but runs as short as 2 hours are 
plenty useful too.

The only really short period here ia 4 minutes (V418 Gem - though it has 
a menagerie of other periods which have never been clarified).  On that 
one, you need to keep the cycle time (observing + readout) below one 
minute.  This star has a raft of periods - fast and slow - and they've 
never been adequately identified, much less understood.

Nearly all of these stars are in Koji Mukai's ("NASA's") page on 
intermediate polars, and Lew Cook's re-ordering of it.

I didn't manage to make it to Las Cruces for the AAVSO meeting (been 
hobbling around with a torn Achilles)... but maybe someone could write 
with a summary of relevant goings-on?

joe p

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