(cba:news) the multitude of intermediate polars, mostly

[Joe Patterson]

Hi CBAers,

Lots of data coming in these days, especially on the IPs, which are 
abundant in the northern winter skies.  I'd like to parse them out in 
more detail here.

GOOD ENOUGH.  For these stars, we have enough for the 2019 season: V1033 
Cas, AO Psc, V405 Aur, and probably V418 Gem

MORE NEEDED: V515 And, MU Cam, V647 Aur, HT Cam

MORE NEEDED, AND HIGH PRIORITY: HZ Pup, V902 Mon, WX Pyx, V1062 Tau*

*Mister V1062 is sui generis.  With P_spin ~1 hour and P_orb ~10 hours, 
it's ideally suited to test the theory of accretion torques (since 
10-hour secondaries transfer a lot of matter, and 1-hour wds are easy to 
spin up).  However, the star presents challenges: high flickering, low 
pulse amplitude, and only 3-4 pulse cycles per night.  So, although the 
rewards are high, this star is mainly suitable for people who can give 
it LONG runs - say 6 hours or so.

Enrique will follow up, and probably supplement or amend this list.  He 
has been tracking these somewhat more steadily than I have.

Now for some other targets, which have achieved or deserve "old 
favorite" status.  Two are studies of orbital-period changes.  Such 
changes, IF SUSTAINED, reveal to us the timescale of evolution - always 
a big prize in astronomy!

1. T Pyx.  Still tracking its changing 1.7 hour orbital period.  There 
was some indication last year that the rate of change was levelling off. 
  Not good for the simple explanation we've been touting (binary blowing 
itself apart, sine fine)!  But good coverage this year, especially early 
in the season, will clarify it.

2. AM CVn.  We have a paper on the dP/dt ready to ship out.  But the 
star is back in the northern morning sky, and 2019-20 coverage would be 
great.  (You have to feel better about an ephemeris which predicts 
*future* observations.)  If you can get 3-4 runs in Dec-Jan, that would 
be great.

3. V598 Pup.  Confusing star. We have some good data establishing a 
70-minute period, and some good data showing no sign of it (but 
suggesting some other signals).  Just a really confusing situation.  It 
will probably only be resolved with very long runs at widely spaced 
longitudes.  Good for Berto-Josch-Gordon over something like a 3-night 
stretch - that would very likely clear things up!

That's my menu.  BTW, integration times in the range 30-60 s are about 
right for nearly all our targets.  That's sort of a midrange which 
yields decent S/N and time resolution.  Flavor it as needed for 
individual stars (extra bright or extra faint, e.g.).  A clear (or, 
slightly better, a minus-blue) filter is usually fine.  V is fine too, 
of course, but usually exacts a high price in S/N.  And try to avoid 
airmasses >2.0 unless you have a special purpose in mind (e.g. timing 
*fast* signals, which will survive extinction changes to some extent).

joe p

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