july stars

From: Joe Patterson <*jop_at_astro.columbia.edu*> Date: Thu, 05 Jul 2007 06:54:29 -0400 · jop_at_astro.columbia.edu

Dear CBAers,

Time for a major overhaul of targets.  GW Lib has been center stage, and 
  has continued to flash superhumps to the present, even 3 months after 
outburst.  But the data are getting ratty and the signal isn't changing 
much - so the returns are diminishing.  Those of you who have been 
observing it a lot might want to keep visiting it for another month or 
so... but I'm going to demote it to secondary.

No dwarf nova cries out for immediate attention, so we pass to novae and 
the novalikes...

We have a long baseline of data on V1494 Aql.  I dunno how bright it is 
now (17?), but it would be *great* to see what has happened to its 3.4 
hr orbital signal.  The latter is powered by the white dwarf's 
underlying supersoft X-ray emission, which is not directly observable - 
but can still be probed by a proxy signal (the reflected light in the 
orbital signal).  This would give us an 8-year baseline for supersoft 
study - by far the best available.  The star sits on the celestial 
equator and transits near midnight.  Very, very tempting target, if you 
can handle the faintness.

Another equatorial target that has been good to us is V1432 Aql.  This 
is an asynchronous AM Her star, in which rotation has been slightly 
de-synched from orbit, possibly from the effect of a (putative) nova 
eruption.  We've been tracking it for some years, but missed the last 
two.  Time to re-establish the rotation ephemeris (another 3.4 hr wave).

Lotta DQ Her stars on the menu too.  These are perhaps more suitable if 
you don't do much observing - on the grounds that observations yield 
mainly a pulse timing (mean pulse arrival time of the rapid signal), and 
  scattered pulse timings usually suffice to establish a yearly 
ephemeris.  For most of our program stars, though (as you well know if 
you've been reading these missives!!), we need many long runs on 
consecutive nights.
Anyway, the relevant and easy DQ Hers are AO Psc and V1223 Sgr.  Others 
that are not so easy are DQ Her and RX1730-05 (=Oph); these require 
pretty fast photometry (time resolution better than 20 s for sure) to 
resolve the fast pulses.  And another tough one is RX1803+40, mainly 
because it's pretty faint.

DQ Hers haven't been so popular among CBAers, but you might want to 
adopt one of these stars and try it out.

Two key northern stars this month are MV Lyr and V533 Her.  The former 
is in a low state and possibly invisible to CBAers; but if you can see 
it, it's a great target to study for a possible orbital signal (which 
would constrain the existence of an underlying undetectable supersoft 
source).  It's mighty faint though (18?), so might need special 
techniques.  V533 Her is plenty bright at ~15, and we want to study it 
for orbital/superhump signals (your job) and for rapid pulsations (my job).

We start an observing run on Kitt Peak on July 12, and some quick 
re-arranging of priorities may occur around then.  Plus of course for 
the latest greatest star that pops off up there...

joe

btw this replaces all the stars on our page-one, which has been getting 
mighty brown around the edges...

Happy observing!