(cba:news) stars for december (Joe Patterson) [2011-11-28T12:32:41Z]
Dear CBAers,
Time for a briefing on results and plans - before the students reappear
after Thanksgiving break!
V378 PEG
I've analyzed the first (and only, so far) week of data. Thanks
mainly to some clear French weather and the determination of Etienne
Morelle, the results confirm Ringwald's fascinating claim - a dominant
signal with nu slightly exceeding nu_orb, the signature of a negative
superhump. The period is 0.1348(2) d, and the full amplitude is a
healthy 0.09 mag. There are 2 important issues left to settle (doubtless
more than 2, but 2 that come to mind immediately):
1. Is there a signal at nu_orb minus nu? On the negative-superhump theory,
this would be the actual precession frequency, and it's usually present
in negative superhumpers. To find out, we need to search the frequency
regime around 0.2 c/day. *Probably* that will have to wait until mid-
season next year... but let's give it the old college try in what's left
of 2011. The enemies of detection efficiency in that frequency regime
are: length of nightly time series (that's why September would be better),
and differential extinction (because we mostly use unfiltered data). To
tame the latter, either observe with a V filter (ideal), keep the airmass
below 2.0, and state the airmass (with a 3rd or 4th column). Differential
extinction is not significant within the ~1000 A bandpass of V... and with
unfiltered data, it can be corrected for if the airmass is known. (Since
I know your locations and observation times, I can calculate airmass too,
but it would help me if you did so.) As most of you know, I usually have
a *great* preference for unfiltered data; with our small scopes, it defines
the timescales of variability much better. The two exceptions are: when
the star is bright (say V<13), and when you're sleuthing the frequency
regime below 1 c/day.
2. How stable is the signal? To study this, we need to keep going for
about a month - then resume in April when Pegasus re-emerges from the Sun.
Great target! I've always wanted to know how stable negative superhumps
are. There's some evidence that they're more stable - maybe even a *lot*
more stable - than positive superhumps (which lose phase over a few-week
baseline). This is an excellent chance to find out - the best one in the
sky yet found.
BW SCL ERUPTION
36 days into the eruption... and we have coverage every day, due mainly
to Josch Hambsch and the perpetually clear Chilean skies of late spring.
The star is now around mag 14.8, and slowly fading. No echoes, much to
my surprise. Superhumps still resounding, and the time series are of
sufficient quality to reveal fine structure: nw-mW, where n and m are
unequal. Too bad no one knows how to interpret such effects - yet.
Hope springs eternal.
The star deserves at least another month of very close scrutiny. To
define the return to quiescence, to watch the dying (or maybe not?)
superhump, and to study/constrain any white-dwarf pulsations that appear
in the light curve (lots of 'em at quiescence).
CD INDI (2115-58)
We took that one off the menu two months ago, and promised to return
in late season. We're a little tardy cuz of the BW Scl hubbub... but it's
*definitely* time to get a couple weeks of coverage. Faint but large
amplitude signal; you can do it - open those floodgates and count every
photon you can lay your hands on! Very important target - we'll clearly
be making the "asynchronous polars" a major subject of study in the next
few years.
BY CAM
We took BY Cam off the menu too, for the same reason (to let time go
by and improve period estimation once coverage resumes). Well, it's
time to resume. Excellent target for those long, clear, crisp December
nights. Another asynchronous polar, and with some serious questions
about interpretation of the star's periods.
PALOMA (RX J0524+42)
Lordy, lordy... what an utterly fascinating star. I didn't think the
star's scientific interest could possibly exceed the quality of its
nickname - but it's at least close! From the first few days (mostly
Enrique and Tom), Paloma appears to have THREE independent periods... and
the smart money says there's more. Maybe this is a complex disk-precession
effect, or an asynchronous polar, or something else altogether. But we
stand a good chance of finding out. It's faint but very large amplitude
(1 mag signal). The dove cries out for your long time series now, and
throughout the winter.
T PYX
After years of being considered a "problem child" by virtue of its
failure to erupt, this star is now a celebrity again. Sic transit gloria
mundi. It's back now, and you've perhaps chopped down those trees
blocking your southeast horizon. So fire away on this star. Arto finds
a weak signal at Porb; everything about the signal will improve as the
season wears on, and it's time to get going. At present, you MUST
observe in V; it's still decently bright (12), and differential extinction
is too problematic for very weak signals.
SOME STARS TO SAY ADIOS TO
...on grounds of lateness of season, and/or sufficiency of data. DQ Her,
AO Psc, FO Aqr, V709 Cas, RX2133+51. Other DQ Hers remain alive, and
RX0704+26 should be especially interesting to small scopes.
SOME NORTHERN EVENING STARS
Many USA CBAers have long clear evening skies in November-December,
and I've talked up mainly midnight, and rather faint, stars. Here are two
evening guys very deserving of coverage: PX And and XSS0056+4548 (V515
And). Both need pretty long coverage; not relevant for time series of
less than a few hours. For shorter pot shots, try IGR0023+61 (V1033 Cas).
Happy observing! Some of you might want to think about the upcoming
late-May meeting of SAS and AAVSO in Big Bear, CA. We'll be there in force -
probably 10-12 CBAers in all.
joe