(cba:news) FO Aquarii, keep the faith
jop at astro.columbia.edu
Sat Nov 18 09:13:17 EST 2017
Some of you still have FO Aqr in your observing programs - for
occasional coverage - despite the unfavorable sky location. For our
time-series photometry, an equatorial star 6 hours out of season is
usually a no-fly zone! But this year is different. The usual dominant
signals are still present, but the mean light has been fading throughout
the season. Now at 14.9, and seemingly still diving. Over the years it
has averaged about 13.7, so it's not exactly a call-911 deal. Since it
was comparably low early in the previous season (2016), I'd call it a
"somewhat low but somewhat unstable" state. Accurate, but not real catchy.
In a CV, is this *significant*? Hard to say, since most of the previous
35 years (mostly ours) used differential photometry, so the constancy of
mean light over this interval is only good to around +-0.4 mag. I would
have noticed anything more than that. So it's somewhat significant...
but the more interesting question is, is it useful?
The answer is YES. In theory, the magnetic WD spins "up" (period
decreasing) when in a high-accretion state, and spins down in a
low-accretion state. Of course, HOW LOW is an important and probably
unanswerable question. But we do the best we can! In this case, we can
track spin-up/down by studying the 21-minute signal, which is strong as
ever. The fainter the star, and the longer the duration of faintness,
the more convincing is this test.
Northern observers are now favored, because of the long nights. Another
month of coverage would be great. Our usual advice of "not more than
2.0 airmasses" doesn't quite apply here, since we're tracking a 21
minute signal. On a clear night, you can probably stretch it out to 3.0
airmasses. Beyond that, you're almost certainly in the regime of "bad
data driving out the good".
No one biting yet on DN Gem. This is likely to be a real winner!
Center for Backyard Astrophysics (CBA) mailing lists
More information about the cba-public