(cba:news) V1101 Aql... BK Lyn... and friends?

[Joe Patterson]

                                                 24 October 2013
Hi CBAers,

Grinding away at the write-up of our V1101 Aql campaign, I'm struck with 
the glaring similarities to BK Lyn.  Both have very strong credentials 
as Z Cam stars, both have negative superhumps, both have what we call 
"precession" periods (at least until we learn otherwise, which of course 
might someday come to pass)... and both superhumps are basically 
characteristics of quiescence rather than outburst.  Because they're 
clearly signatures of quiescence, the superhumps' origin must be 
drastically different from that of the common superhumps we have come to 
regard as practically universal among short-Porb CVs in their high 
states (SU UMas and novalikes).  What is that origin?

Well, there are some guesses in the literature, but basically we don't 
know.  It's possible that the superhumps are intimately connected to the 
cause of the Z Cam phenomenon - or vice versa (we've never found 
superhumps in U Gem stars).  Both ideas conflict mightily with today's 
understanding of what Z Cam stars are - but the superhumps are quite 
big, and it feels uncomfortable to attribute them to some minor and 
accidental feature of the binary.

So let's see - with a similar global photometry campaign - what 
relatives of these stars might be out there, waiting to be discovered. 
Two stars with light curves similar to V1101 Aql, and well-placed in the 
sky, are IW And (14-17.5) and V513 Cas (15.5-17.5). Both stars spend 
most of their time near the brighter end of their range, and I think 
they're great CBA targets.  V513 Cas comparison stars were studied by 
Misselt (1996 AJ), and his stars 5 and 6 appear to be good comparison 
stars, with sufficiently neutral colors (not particularly red).

Let's start the proverbial ball rolling on these stars!  Another star 
interesting in this regard - but more of a long shot since we've tried 
before and failed - is FY Per.  A mysterious hardly-studied bright CV,
with two discrepant periods - but the photometric one (1.5 hours?) has 
never been firmly established or discredited.  Perhaps it's transient. 
It's embarrassing not to know something like that in so bright a CV.

A little later in the season, we'll try this with CN Ori.  I've long 
suspected this star as a two-period guy.

As many of you know, Mike Simonsen has been cheerleading and leading (he 
always does both) an AAVSO campaign on Z Cam stars (the "ZCampaign"). 
In my opinion, this has already greatly expanded what we know about this 
class, and I suspect will soon lead to wholesale tearing-up of what we 
thought we knew about these stars. His stuff can be found on the AAVSO 
website.  Fred Ringwald's article on Z Cams also deserves its #1 rating 
on google:

https://sites.google.com/site/thezcamlist/why-observe-z-cam-stars

Buena suerte!

joe p

P.S. When adding stars to our menu, it's only responsible to take some 
away.  In this case, I recommend removing V339 Del and V1294 Tau (as 
well as V1101 Aql of course).  Both V339 and V1294 have given uncertain 
results; the former won't get better (because the season is getting 
late, and the variability is small), and the latter can be reinstated 
later if warranted.  I imagine that first looks at the new stars will be 
more rewarding.  I also think a brief break from the DQ Hers 
(intermediate polars) is fine, although these stars may still be the 
best choice for *short* time series.
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