(cba:news) Equinox!

Joe Patterson jop at astro.columbia.edu
Tue Mar 18 02:40:34 EST 1997

Dear CBAers,                                            March 18, 1997.

     We've just finished a very dense stretch of data on DW UMa, I
think 18 of 20 straight days, with multiple longitudes represented.  I
haven't seen all of it yet, but I've seen most of it, and it's enough
to convince me that the DW UMa campaign should be closed.

     Here are three reasons.

One, we did the best job we could.  It's unlikely that we will do
better or as well in the future, with more divided loyalties.

Two, we're now up to ~400 hr of coverage (counting last year).  That's
my rule of thumb borderline for feeling that we've gotten all there
is to get out of the star.

Three, I've been disappointed by this year's superhump.  Weaker than
last year, at a significantly different period, and probably less
coherent too.  A sufficiently poor clock that it is hard to follow from
night to night (whereas it was a breeze last year).  Not the Rosetta
Stone that I had hoped.

Add 'em up, and I think DW UMa should be gracefully retired.  I'll be
happy to send the merged light curve to anyone who's interested (though
I think there are about 4-5 runs still not included).

So what's on the marquee now?  For the coming weeks, there are southern
stars taking center stage.  We have three straight weeks of South
Africa time (March 25-April 14), and ten days of Chile time (April 9-
18).  So naturally, right about now, we are tremendously interested in
our (few but valued) Australasian friends!

A prime target which everyone can get (except the northern Europeans I
guess) is EC1533-1403.  This star is reliably magnitude 13.6, and it
superhumps away at a period of 1119 s.  Lovely for time series.  Still
slightly early in the season, but definitely important to do now.
Good for small telescopes to track the slowly wandering superhump,
and for the bigger ones to detect fine structure (if any) in
the main signal.

V803 Cen (1323-42).  Prime southern star for this three-week spell,
assuming it does not "go south" (uh... north?) on us by diving into an
extended low state.

T Pyx (0900-32).  This will be our early-evening target from South
Africa.  At magnitude 15.6 and with that dec and a small hump amplitude
(0.07 mag), it is probably out of reach for all CBAers.  But the
Arizonans, Cap'n Bob and Dave West, are just possible.  Alternatively,
there are Chileans reading this.  Are you there, Thomas?

Finally, there's V485 Cen.  Definitely a fishing expedition.  Haven't
seen it yet this year (usually at 18-19 I think), but I wanna keep
looking in case it erupts.  Thomas, can you tell us more about this
star?  You seem to be the only one who really knows anything about it.

     What about the borealites?  I recommend AM CVn and EC1533 as
the stars for prime coverage in the next two months.  Long time series
will bring much happiness.  CBA charts available at the Web site and by
mail if requested (maybe you got 'em already?).  If you don't like the
dec of EC1533, try LX Ser, another probable SW Sexer on the immediate
menu.  We need some pilot runs on Mister LX to decide whether to
promote him or not.

     As always, we enormously prefer long time series.  But actually
quite short time series can be useful for AM CVn and EC1533, since
their periods are so short (525 and 1119 s).  I've found that two
hours will often give an acceptable pulse timing, though longer is
certainly much better.

     Happy Spring, oops March, Equinox in two days.  My best address
for correspondence remains jop at astro.columbia.edu, but data is better sent
to Columbia.


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