AX Cap and V825 Her

From: Joe Patterson <*jop_at_astro.columbia.edu*> Date: Tue, 20 Jul 2004 06:02:18 -0400 (EDT) · jop_at_astro.columbia.edu

Dear CBAers,

Just back from the Strasbourg CV conference.  Went a lot better than my
last overseas conference adventure!

And returning gave me a chance to dig into the week's CBA data - with very
interesting results. Lew Cook and Dave Messier (and Tom Krajci before
moving back to the USA) have been observing V825 Her, a decently bright
(14) and little-studied novalike.  The published radial-velocity period is
4.9 hours - but the light curve shows a large-amplitude modulation at 8.6
hours.  Quite an oddity!  And very well suited to the CBA, since with a
distribution over terrestrial longitude we can get very long nightly
observing runs.

Rod Stubbings found an eruption of AX Cap, and Berto's time-series
photometry revealed large-amplitude waves at 2.8 hours.  Thus it is a new
SU UMa star, and at this Porb it really merits quite a bit of interest.
The superhumps just started, and AX Cap is well positioned for all but our
most northerly observers.

So there's a big shakeup of target stars this month.  We'll postpone the
V1315 Aql campaign, and cease the campaigns on V1186 Sco, Var Her 2004,
V4633 Sgr, V4743 Sgr, V4744 Sgr, V4745 Sgr. V603 Aql is definitely worth
continuing, and now, but takes a back seat to AX Cap. AX Cap and V825 Her
are the stars for the next few weeks!

AX Cap is 15-16 so may present some problems on poor nights.  Those would
then be suitable for V603 Aql (at 11.7).  V825 Her is bright enough, but
this period can be awkwardly long.  Above about 1.8 airmasses,
differential extinction can be pretty important... and you will need
somewhat long runs to help define this 8-9 hour modulation.  A V filter
will reduce or eliminate differential extinction (since it keeps the
effective wavelengths of variable and comparison stars equal to within 200
A or so)... but this assumes you have enough photons to pay the price.

There's no conventional understanding of stable periods much longer than
Porb, and it's nearly always the case that Pspec=Porb.  So at this point
V825 Her is a mystery - let's try to dispel it!

joe