(cba:news) QR And, WZ Sge, mostly
jop at astro.columbia.edu
Sun Oct 1 07:39:22 EDT 2017
Some great (northern) fall weather this year, and a lotta work keeping
up with all the CBA data. Fortunately I have my every-7-years
sabbatical this semester, so I can do a better job.
Our paper on WZ Sge is about ready for circulation (to the numerous
authors - you know who you are out there). It spans many years, but
another couple of weeks would really help nail things down for 2017.
It's a tough target - 15.5 with a neighbor star ~7 arcsec away - and
calls for (somewhat) fast integrations, since eclipse ingress and egress
are brief. I recommend a 20-30 s cycle time, but I notice that slower
is usually OK too.
The bottom line won't change. The eclipse times wander very slightly on
a timescale of decades. This prevents a measurement of long-term
evolution (systematic orbital-period increase or decrease), but the
timings seem to wander on the ~25 year ERUPTION cycle. That would be
pretty interesting... although we can't prove it since we only have 55
years of data. I look forward to another 55.
Of all CVs, WZ Sge is the nearest, brightest in eruption, most studied,
possibly oldest, and a dozen other distinctions. It's the Andromeda
Galaxy of CVs. But the fast variations in light mean that only the
larger CBA scopes (14 inch and up) can contribute substantially.
We can definitely quit on QR And. Some really great data - long and
top-quality runs - has been arriving on this 12th mag eclipsing binary.
Jim Sergeant, Joe Ulowetz, Stephen Brincat, and James Boardman have been
leading the way. I'm just about to do the period-change analysis, but
am sure that we have enough for 2017.
Some morning-target talk, on BRIGHT stars...
FY Per is a total mystery star. A well-determined spectroscopic period
of 0.2585 d, but every so often, a 90-minute photometric period pops up
-just a few hundredths of a magnitude, but not particularly difficult to
study since the star is 12th mag. One of these years, we should figure
GK Per has a 351-second signal - an intermediate polar (DQ Her star).
But it's *really* difficult to spot in quiescence, which is 95% of the
time. So no one has figured out its long-term ephemeris; and this
matters a lot, because it has by far the highest accretion rate among
all DQs (and thus should spin up fast). The reason for failure is that
there's a K subgiant in the binary, overwhelming the light from the
white dwarf. This can be subdued with ULTRAVIOLET photometry. If you
have an ultraviolet filter (and CCD with decent UV sensitivity), you can
be the hero with a long program of UV time series. Calibration is of no
importance - you just want to make sure a lot of UV photons, and not
many others, reach your CCD. It's just a timing project.
Airmass is usually a big problem with UV photometry - but less so here,
since the point of interest is a 6-minute *periodic* signal.
Don't fall in love with your U filter, though. Accurate UV photometry
is famously tricky, for many reasons (extinction, low sensitivity,
weirdness of the filter itself, etc.) For nearly all purposes - except
maybe this one - it's a tool to AVOID.
The AAVSO fall meeting is in Nashville this year (Nov 2-4), and it looks
like a pretty good collection of CBAers will be there. So I guess I
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