(cba:news) V1101 Aql... BK Lyn... and friends?
jop at astro.columbia.edu
Thu Oct 24 09:03:49 EDT 2013
24 October 2013
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
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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