(cba:news) V455 And and CD Ind...
jop at astro.columbia.edu
Wed Sep 19 08:12:23 EDT 2007
Pardon me for the brevity. The start of the school year has set me
back! Still, I have been analyzing all the data coming in... and here's
V455 And = HS2331, as you all know, is having an outburst for the ages.
The coverage is almost as good as that of WZ Sge in 2001, and vastly
better than any other dwarf nova in history. It's great to have bright
eruptions from stars transiting near local midnight, and in this case
with many periodic clocks to study the effects of outburst.
A few of you are obtaining multicolor data; except possibly for the very
beginning of outburst, there appear to be no significant color effects
in the star. It's basically a big blue light bulb, and the main reasons
for observing it filtered are these:
(1) Archival. With V data, it's possible to say meaningfully "how
bright it is".
(2) (Differential) extinction. Through a very wide or no filter, a CV's
extinction always exceeds that of the comparison star, introducing
unwanted waves in long light curves.
(2) is an item of some consequence, and worth doing if you can afford
the roughly 6x loss of photons (in which case V is probably the best
choice). But I tend to be skeptical about (1). CVs are forever
variable anyway, and there is likely no significance to their exact
brightness. *Someone* needs to do V measurements; and everyone - even
unfiltered diehards - needs to make an estimate of the brightness level.
But the sensitivity of time series to periodic signals is greatly
improved by a healthy count rate. So for our purposes, unfiltered
generally wins. Exceptions are a very bright star (like V455 And the
last 2 weeks!) and an interest in timescales natural to extinction (say
There's another very specialized reason that applies to this star. It
has strong 68 and 34 second signals at quiescence. Their origin is
still unclear, but we FERVENTLY would like to measure how they are
affected by the outburst. So we need quite short integrations. To
resolve both, you need a cycle time (integration + dead time) of <17 s,
or let's say 13 s to be more comfortable. Can you do that? I think for
most of you the answer is no; if that's true, try for ~20 s, which will
fail to resolve the harmonic properly, but do a decent job on the
fundamental. Avoid, however, cycle times very close to 17 s and 34 s;
when the period is an exact multiple of the sampling time, terrible
things happen! (Like trying to measure the Earth's rotation period with
brightness measures at noon and midnight every day!)
For the moment, V455 And is certainly the best northern object. To say
In the south, it's time to quit on V1432 Aql. We've covered 1.2 cycles
of its 50-day supercycle, done very well (primarily due to Berto), and
the data clarify the ephemerides and timescale for synchronization.
It's also time to quit on EC2117 ("Ind"). This is a great eclipsing
binary, with hardly anything yet published on it; we have excellent
data, and one or more of you southerners might want to write something
up - I'll be happy to send you all the data and a preliminary analysis.
Apart from its faintness, CD Ind is a great, great target this month and
next. This too is an "asynchronous polar", and our data (mainly Bob
Rea's) show many effects cycling on the six-day beat between Porb and
Prot. They also specify the long-term ephemeris, which has never yet
been published. This star may well be the most revealing of this small
class of CVs (only five known) - revealing of the magnetic torques
present in this "asynchronous" geometry. Try hard for CD Ind!
Not so brief... but in a few days, I hope to make up more detailed
Please keep up the cba-chat, it's working very well I think!
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