Re: Why no superhumps on V358 Lyr?

From: Joe Patterson <*jop_at_astro.columbia.edu*> Date: Wed, 10 Dec 2008 18:03:50 -0500 · jop_at_astro.columbia.edu

Hi Tom,

What an interesting question.  No one knows for sure... or even for 
probably... but here's my take on it.

One, the coverage on V358 has not been up to our usual standards - it's 
just too far over in the west for really good runs.  Nevertheless, I 
share your conclusion - that there haven't been superhumps.  It does 
mean that we should look somewhat askance on our earlier expectation 
that this is an SU UMa/WZ Sge star.  However, while being uncomfortable 
about it, I still think the smart money is on SU/WZ.

Which brings me to 2. There are a few (2-4) other stars which are 
seemingly SU/WZ and yet failed to show superhumps for a very long time, 
or ever.  All have a very large max-min magnitude range, and that means 
WZ class.  Theorists used to tell us (before we started boxing their 
ears) that the eccentric-disk instability exists in the q(=M2/M1) range 
of 0.05 to 0.20.  Observations tell us that the upper limit is more like 
0.35... but WE'VE NEVER REALLY TESTED THE LOWER LIMIT.  I think we've 
managed to see superhumps down to about 0.04... but not lower, so far.
The physical reason for such a lower limit (assuming one exists) is that 
the disk is very weakly perturbed by such a puny secondary.  The 
practical reason it's very hard to explore is that the predicted Psh 
would be only *slightly* different from Porb... and also that Porb would 
often be hard to measure, since all known candidates are very faint at 
quiescence.

So testing that lower limit - probably by finding eruptions of stars of 
known very low q - is a mighty worthy goal.  RX1050-14, GD 552, 
RE1255+266, and PQ And are particularly luscious targets in that regard.

For the moment, our goal should be to examine how good is our evidence 
that V358 Lyr is a non-superhumper.  I'll take a shot at that in a few 
days.

joe

Tom Krajci wrote:
> Has anyone announced superhumps on V358 Lyr?
> 
> If not, why not?  Is the star another type?  Or are we viewing it 
> face-on instead of edge-on?
> 
> Thanks in advance.
> 