
Dear CBAers,

It's time to shake up the cast of characters.  WZ Sge has been flashing
its familiar quiescent light curve; the attached 2-cycle average of ~120
orbits shows the double-hump (*really* equal!) and the sharp eclipse.
What was interesting to me was: no other periodic features near Porb or
longer (which might, for example, be associated with disk precession).
Quite a few CVs of extreme mass ratio show such phenomena at quiescence,
though the origin is still mysterious - we'd like to explore all of 'em
that we can reach with our little telescopes.  WZ Sge is a no.  So let's
take it off the menu.

Also off the menu now are two bright DQ Her stars (intermediate polars):
FO Aqr and AO Psc.  I've extracted all the 1981-2010 pulse timings for each
(>200 timings over a 30-year baseline), and traced the exact evolution of
the period behavior: basically spin-up on a timescale of a million years.
That was the main goal of these studies - and for FO Aqr, the only new
finding.  AO Psc shows some other interesting effects (a possible superhump),
but it too has been sufficiently covered to kiss goodbye for the rest of
the season.  We'll likely take a year off and revisit these guys in 2012.

Ditto for V1223 Sgr. Although this one, oddly enough, shows a steady period
*increase* over its 30-year baseline.  Let a hundred flowers bloom.  Also
deserves a rest until around 2012.

This type of work is really ideal for CBA scopes.  The large telescopes
mainly look at these stars for a few nights in their year of discovery,
then abandon them.  So basically all further knowledge about period
changes is up to us; a few professional astronomers sometimes venture
into this topic, but usually get the cycle count wrong, since they have
little and very scattered data.  This is a job for us Army Ants.

So let's focus the time-series photometry on other DQ Hers.  About half of
these have been on CBA menus in previous years (and hence the data are
ripening); the rest are new to us.  All are very likely DQ Hers (a few
still haven't had that last nail in the coffin... but are still mighty
good bets).  The best references for these are Downes's catalogue (lacks
the newest objects, but still the basic CV bible), and Koji Mukai's
intermediate-polar webpage.  The newest objects are treated by Retha
Pretorius (MNRAS 395, 386).  In these you'll find exact positions and
finding charts, and lots of useful data.

We usually like to observe targets in mid-season, i.e. transiting near
local midnight.  The reason is to get long runs, which are normally vital
to our enterprise.  This is somewhat true for DQ Hers as well - it's by
far the best way to ferret out subtle features in the power spectrum.
However, there's an additional wrinkle that applies specially to the DQs:
the need for pulse timings in early and late season - ~3 months either side
of midnight transit.  Only short runs are then possible, but these pulse
timings then make it possible to link up the cycle count from year to year.
Roughly 3 hour runs usually yield a decent pulse timing, and it's an
efficient way to make use of partial nights.

So pick out a few of these that look appropriate in terms of position and
brightness, and also period.  For the slowest rotators, make sure you observe
for at least 5 cycles; that's really the bare minimum to identify the
pulse (and a lot more, if it's weak).  For the fastest rotators, it's easy
to accumulate >100 cycles... but you have to make sure the time resolution
is adequate to resolve the pulse.  Rule of thumb: make sure you have (at
least) 3 integrations per rotation period.  Formally the "Nyquist theorem"
requires only 2, but give yourself some margin.  On the other hand, don't
shy away from these fast guys, if you can master that technical challenge
(of the short cycle times).

Mid season

V2306 Cyg  WGA1958+32  16.3    24 min (most power at 8 min)
V709 Cas               15     313 s
IGR0023+61 (Cas)       15     563 s
V455 And   HS2331+39   16     several! (fastest = 34 s)
RX2133+51              15.8   570 s
XSS 0056+46 (UMa)      15     470 s
V4743 Sgr              16      24 min


Late season

RX1803+40 (Her)  17.5     25 min
RX1730-05 (Oph?) 16.3    128 s
RX1509-66         15     810 s  
RX1654-19 (Oph)   15     546 s  <-- do this one!
NY Lup (1548-45)  15     693 s
DQ Her (1806+45)  14.7    71 s
IGR 1719-41       15.3    19 min


Early season

V405 Aur (0558+53) 13.5    545 s
MU Cam (RX0625+73) 14.5   1187 s
V1062 Tau          16       63 min
RX0636+35 (Aur)    15
RX0704+26 (Gem)    15   480/240 s

Except for a few garish guys like FO Aqr and RX0704+26, DQ Her amplitudes
are usually low enough that you can't really spot the individual pulses.
If you have a suitable analysis program (something like PERANSO), you can
tell at night's end whether you have a detection.

Good luck!

joe



