(cba:news) data-taking issues
jop at astro.columbia.edu
Mon Apr 16 11:16:01 EDT 2007
Back in NYC now, anxious to look at that great data for BZ UMa and GW
Lib. Best targets in a couple years, except maybe for the Halloween
Both stars are pretty bright, and you'll need to think about saturation.
Some people are fighting this with filters (generally, V filter
recommended)... some with short exposures... and some with stopped-down
telescopes. One of these should work for you.
In general, superhumps and orbital humps have a color similar to the
star's mean color - hence the amplitude in near-optical passbands (BVRI)
tends to be similar. This is one of the reasons we've tended to
recommend unfiltered photometry: the extra information from filtering
isn't worth the lowered signal-to-noise. But this isn't true for all
stars, and for most stars it has not been studied and hence isn't known
one way or the other. I'd find it very interesting if ANY superhumper
showed a large color effect; superhumps come from heating effects, and
thermal processes at the relevant temperatures (c. 15000 K) are pretty
white. But that's just theory; it is well worth a filtered study if you
have the filters and can still get good signal-to-noise. V-I or B-I are
good choices (we want a good range in central wavelength, but can't
afford the variable atmospheric transmission typical of U).
BTW these pooh-poohs of filtered photometry don't apply to the DQ Her
stars (intermediate polars). There the origin of the pulsed light is
an open question: it could well be a magnetic process (cyclotron
radiation), which can be a very strange color, and is somewhat commonly
very red. PQ Gem is an example of this. Not much is known about this,
because extensive multicolor photometry isn't obtained for most DQ Hers.
An interesting project, perhaps.
Have a wonderful time with these two grand new superhumpers!
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