(cba:news) stars for Dec-Jan 2018/9

[Joe Patterson]

Hi CBAers,

In the north, long nights.  In the south, our juiciest targets.  Great 
time for long time series of CVs.

Much of our recent work has been on novae (in particular, "old novae"). 
The reason is that we're testing the theory that classical novae may 
have a dominant effect on long-term CV evolution - basically by 
destabilizing (by heating) their secondaries.  Our BK Lyn paper of 2013 
explored this, and it needs to be tested by application to other stars. 
That's why I keep harping on T Pyx and CP Pup, where it's most likely to 
apply (because their secondaries are *feeble*).

These two stars are back in the night sky, and merit close observation. 
CP Pup merits INTENSE observation - round-the-world if possible.  Why? 
Because its period structure - the key to measuring the mass ratio - 
appears to contain 2 significant, closely spaced periods.  At least one 
of these periods has low coherence, and is possibly the rarest of 
superhumps - arising from the 2:1 orbital resonance, rather than the 3:1 
as is common for superhumps.  Testing that would be a coup!

The other well-placed old nova for coverage is V959 Mon.  Its 7-hour 
orbital light curve should change as this 2012 nova fades.  Let's find 
out how!

Our many-year campaigns on AM CVn stars are finally yielding dP_orb/dt, 
which has been the long-term goal.  We published the results on ES Cet, 
which "confirmed" (i.e. were consistent with) the prediction from GR. 
But having produced a long-term ephemeris, we need to check if the star 
is now obeying it.  (We need not only laws, but also police!)

And that brings us to AM CVn itself.  Almost every year, I say "just one 
more year" to nail the long-term ephemeris.  And, to my embarrassment, 
I'm back saying that again.  But this time, I PROMISE to publish the 
long-term ephemeris no matter what.  I've been bashful about it because 
its shape appears to signify negative dP/dt, which is incompatible with 
the commonly held theory that it's a double white dwarf.  This year, 
I've decided to go with the data no matter what the "commonly held" 
theories say.  But now that Can Ven has rolled around again, let's wrap 
it up with 2018-9 coverage.  Unfiltered coverage *definitely* OK for 
this one.

There's an abundance of DQ Her stars filling the Dec-Jan northern sky.
V405 Aur, V418 Gem, DW Cnc, HT Cam, and AO Psc are all CBA program stars 
which need a season (at least a month, anyway) of coverage.  Most are 
fairly easy targets; but HT Cam is faint... and DW Cnc requires LONG 
nightly coverage because the spin period is long.

And AT Cnc is a promising applicant to this club.  Its credentials are 
still mixed.  If you want to do it a favor, select it as your "star for 
the season".

We're JUST about to send the ASASSN-18ey paper off.  Can anyone squeeze 
in a few V-band measures in the evening twilight?  Just to nail it shut 
for the year... and bridge to the early-season observations next March.
No time-series needed - just a few points will be fine.

As usual, unfiltered light is generally OK, and slightly preferred, for 
CBA light curves.  But if you have a lot of photons, pop in the V filter 
(better for archival purposes).  Another good approach is: unfiltered 
time series plus a few V-band measures to establish the level of mean 
light in a calibrated system (V is calibrated, unlike unfiltered*).

Happy observing!

joe

*But watch out if your CCD has good UV response.  UV light is mildly 
terrible, since its extinction coefficient is so high.  Not welcome! 
The best variety of "unfiltered" system uses a glass filter to block the 
UV.

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