(cba:news) stars for september (Joe Patterson) [2011-09-02T18:51:03Z]
Dear CBAers,
September 1. Time for a review of in-progress projects.
Josch Hambsch now has a 16" telescope in Chile, and is getting very
frequent coverage of CD Ind, an "asynchronous polar". Since we also have
very proficient observers in South Africa (Berto), Perth (Greg Bolt),
and New Zealand (numerous, including Jennie M and Bob Rea), we really
ought to extend the longitude range. That's not fully needed for the
principal goal (phase of Porb and Prot), but it will *greatly* help in
defining the other subtle periods in the star (the complex fine structure
of the main signals).
The Arkansas Dynamic Duo (Tut Campbell and George Roberts) has been
observing up a storm on XSS0056+4548 (now V515 Andromedae). This star
also has subtle fine structure in the periods, and multi-site time
series are extremely desirable to define that structure. Jim Jones's
contributions from Oregon help a lot, but we really need contributions
from an ocean away. The Atlantic definitely comes to mind! (And Enrique
is marooned in, of all places, New York City.)
Now for the various DQ Her stars on our radar screen.
1. FO Aqr can be left until end-of-season observations in Nov-Dec.
2. AO Psc is a good target for intensive time series with the smaller scopes.
In our program are numerous stars with V~16 with fairly small pulse
amplitudes; these are a challenge for the small scopes - AO Psc is s good
alternative.
3. V2306 Cyg = WGA1958+32 and V2069 Cyg = RX2123+42. Coverage from Bob Koff,
Steve Brady, and David Boyd. Observations over the next two months are
needed to nail down the cycle count. We need some long observations, as
well as the 2-3 hour guys ("pulse timings") which usually suffice to
specify cycle count.
4. RX J2133.7+5107. One of the many "Cyg"s in the Downes catalog. We've
never done this star (to any serious degree). It's time to remedy this
oversight! Decently bright, and very well placed for us borealites.
5. IGR0023+61 = V1033 Cas. Time to start the new season on this star.
The main need is pulse timings.
6. V4743 Sgr. Great target for the australites; not well placed, but
no one else seems to be observing this fascinating star. How about a
few end-of-season time series?
More on the overall DQ Her project. Some of you know all this, chapter
and verse. But CBA membership changes over the years, so I'll recite
it again. Along with most of the CV-photometry community, we love our
dwarf novae - but the DQ Hers flash fast periodic signals all the time,
supplying both entertainment and science every night of every year.
For several years we have been collecting time series on the DQ Her stars -
CVs which sport basically permanent, coherent, and fast periodic signals
in their light curves. Most - though not all - of these binaries also show
strong X-ray pulses at the same (or similar) period. This signal is
attributed to the rapid rotation of an underlying magnetic white dwarf -
hence "white-dwarf pulsars". These stars have been very popular in
recent years, especially among X-ray observers since their since their
pulses and spectra show quite interesting features. But most of the papers
report only a few days of study. A few days is usually enough to
establish a stable period, and is any case all that can be obtained on
highly competitive X-ray telescopes. Ideally one would like a study
based on years of data; that would yield a much more sensitive test of
stability, and would allow messurement of accretion torques (given a
white-dwarf moment of inertia and a plausible accretion rate, about 5
years are required for that measurement). To accomplish the latter, you
need a collaborative network, focus, and patience. And multiple
longitudes, to eliminate problems with aliasing.
Oops, that would be us... and that's our goal. We should be able to do
this for all the DQs which are sufficiently bright (say V<17.5) and have
decent pulse amplitudes (>0.01 mag for P<10 min, or >0.02 mag for P=10-30
min). No one else is stepping up to the plate (baseball lingo) for this,
so let's us do it. It calls for our usual observations: fairly long time
series - scattered over the observing season, but also with a few dense
clusters to yield the fine-structure of the periodic signals.
joe