(cba:news) stars for september

[Joe Patterson]

A new menu for the month...
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Dear CBAers,

The seasonal change looms... time for a new menu of stars.

V407 Lup.  Our data, from Gordon and Berto, show this recent classical
nova to be a 3.3 hour binary (common enough) and a 9.5 minute DQ Her
star (very rare for a classical nova).  Great... but we started too late
in the season to complete the study, and we'll suspend until next April
rolls around.

WZ Sge. Great coverage this year, especially by Geoff Stone.  I've analyzed
all the runs until Sept. 7, and was really happy with the accuracy.  The
eclipses can be timed to an accuracy of +-8 s, although the integration
times are typically 25-45 seconds... and despite their shallowness (~0.15
mag, similar to the flickering).  This is because of the square walls of
the eclipse - and, of course, because we get many eclipses and thus can
average them.

The campaign was called to check on the surprising result by Han et al.
(2017) that the orbital period was decreasing, and pretty fast too.
Our data are clearly inconsistent with this conclusion.  The timings do
show a slow (~25 year?) up-and-down wander of around 25 s, like several
other short-period CVs.  This result is no stunner, but is worth publishing
since WZ Sge is a celebrity star and the alleged period change has attracted
a lot of attention.  In a few weeks I'll send around a draft to the
(numerous) CBA co-authors.  Meanwhile, take it off your 2017 menu.

I've been working hard on eclipse timings this summer.  In principle we can
learn the direction and rate of evolution from changes in the orbital
period, and we're the best show in town for such data since we have been
acauiring lots of time-series data for many years.  Here are the
seasonally-appropriate stars which probe these matters:

QR And (especially!  but long runs only, the period is very long)
ES Cet - once in a while
V617 Sgr - finished for the year; thanks Josch!
WX Cen - (long since) finished for the year
BW Scl - just a few nights; we'll promote if it looks interesting
V Sge - done for the year, thanks for all the great data!

Another category in which the world relies on us is: the changing orbital
light curve of novae after they erupt (a few years, decades, centuries, and
even millennia).  These seasonally-appropriate stars are:

V Per - getting optimistic here (V=18.5... but we're desperate)
T Aur
V339 Del
V1974 Cyg - David Cejudo has been carrying out a great vigil... but we
           desperately need a USA observer to complement his Euro coverage
V1500 Cyg - unless Enrique says we have enough
DQ Her - but here we are quite interested in the fast (71 s) period, as
         well as the orbit.  I recommend you keep your cycle time (integration
         + read) below 25-30 seconds. The season is getting late, so a
         good 14.5 mag target now (rather than, say, a month from now).
                                             
+ 2 other bookended stars - north and south - which are tantalizing but so
far resisted our efforts to torture their secrets out of them.  They are:

GD 552 = "Cep 1" in Downes & Shara
VZ Scl

Let's try harder on these guys!

A big menu.  Choose a couple of stars and concentrate on them.  If any
star looks particularly good or unpromising, I'll jump it up in the
menu.

Enrique will likely follow with comments and suggestions, esp. re the
DQ Her stars (intermediate polars).

joe




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