[vsnet-chat 7283] Re: [cvnet-discussion] Prioritizing CV targets

[Boris.Gaensicke at warwick.ac.uk]

Dear Mike, and all the observers out there, 

thanks for bringing this up! Indeed, as a professional astronomer I have 
been quite frustrated over the years by the quite exclusive attention that 
SU UMas receive. Don't get me wrong - there is plenty of interesting 
physics we can get out of superhumps, but in terms of overall 
understanding of CVs, we need to get similar amounts of coverage of the 
other CV types. 

One of my recurrent dreams is to get good long-term light curves for a 
large set of all those odd CVs that are often neglected, polars, IPs, nova 
likes. Take e.g. the class of SW Sex stars - most of them are nice & 
bright around 15th magnitude, but some of them drop occasionally into 
2-4mag deep low states - and it is on those occasions that we can learn 
most about these objects from follow-up spectroscopy, as we can directly 
see the white dwarf and secondary star [during the normal "high" state the 
system is completely dominated by light from the accretion disc]. 
Look at the AAVSO archive: (close to) nothing!!! If it was not for 
the dedicated effort of Kent Honeycutts Roboscope, we would know very 
little about these stars. But Roboscope is just one lonely telescope out 
there... 

Then, there are an awful lot of CVs for which we don't even know what they 
are. Novalike, Z Cam stars? Who knows - it needs dedicated monitoring to 
tell, and I have tried to launch some campaign on new CVs from the HQS.

Another example of very useful observations would be regular observations 
of eclipsing CVs, to build up a large data base of eclipse timings, in 
order to (a) establish accurate ephemerides and (b) check for period 
derivatives. Especially the latter point has been done only for very few 
CVs. 

I understand that those topics lack the adrenalin kick of seeing a star 
brightening by many magnitudes, and then a bit later to hump for his life. 
But with sufficient stamina, extremly exciting results can be drawn out of 
such longer term projects.

I know that there are a few observers who have started years ago to 
fdedicate time to polars, e.g. Berto Monard, to name just one, and I hope 
others will follow. 

So, lets see Mikes questions:

> Question #1- is there no interesting science to be gleaned from UGs or 
> UGSS? If not, why are so many papers and investigations done on SS Cyg 
> and U Gem?

Yes, there is, and please don't move from SU UMas to U Gems and think that 
life stops there! See above. 

> Question #2- is the reason superhump recognition and period 
> determination is so popular is because it can be done unfiltered? Isn't 
> there more science that can be done by placing UBVRI filters on CCDs 
> while investigating CVs?

All of the things I've outlined above can be done unfiltered

> Question#3- if you insist on working unfiltered, aren't there a bunch of 
> CVs with no known period that you could work on in quiescence to 
> determine the period?

There are a few brightish CVs which still have no period, and hammering 
away on them in unfiltered photometry for a while might crack their 
secret. But to be fair here - most of the CVs without periods are probably 
too faint. 

> Question #4- isn't there a way to pre-determine the probability 
> somewhat? I don't have an answer. Maybe it takes tools, like 
> spectroscopy, beyond our means to make that determination.

Ehm - I am not sure that I understand what you mean by pre-deterime the 
probability? 

> Question #5- is there a valid scientific reason for continued 
> monitoring?

Absolutely! Look e.g. at the case of RX And - monitored for years and 
years and years, and then, in 1996, it went into a unprecendented 
long-lasting low state *fainter* than the usual quiescence. Such 
observations do challenge quite a bit our understanding of accretion discs 
(e.g. Schreiber et al. 2002, A&A 384, L6). 

Or take the case of EF Eri, that was bright and shiny for 20 years after 
its discovery, and then in the mid-90s switched off - and now, another 10 
years later, came back to life! AM Her is the *only* polar with a really 
good long term light curve. For all the other ones, we just have snipits 
of their behaviour, and it seems that they do quite different things. Why? 
Nobody knows (hint - is QQ Vul ever going to have a low state?). 

> One of the most interesting things any professional has said in a CVnet 
> interview was when Joe Patterson said, "The dwarf-nova outburst itself 
> has become generally well understood -- in the sense that there's a 
> theory which successfully reproduces the observed phenomena.  But it's 
> noteworthy that all of that theory was crafted to fit previously known 
> data -- it has never actually predicted something not known in advance. 
> So that higher standard of scientific worthiness has never been met.  
> In addition, the theory breaks down when applied to dwarf novae in 
> quiescence -- it predicts about a thousand times less accretion than is 
> actually observed!  Plenty of thought needed there."

I agree with the second part of Joe's statement, the theory can't predict 
things. It can't tell when GW Lib will have the next outburst. However, I 
would challenge his first point - yes, the theory can explain outbursts, 
but there is an awful lot of thorny contradictions with the observations. 
Just a simple example: the disc instability model predicts that DN get 
brighter during quiescence, until hitting the next outburst - this has not 
been observed! Unless we really can put to bed DN outbursts and disc 
instabilities, there is sufficient motivation to carry on with monitoring 
DN outbursts (and quiescence!).

> On the other hand, I started doing variable star observing because I 
> wanted to contribute to science. There are a bunch of us out here with 
> talent, enthusiasm, time, money and expertise who want to do good 
> things. Show us the way and we will follow. Empower us and we will amaze 
> you.

You, and all the others, are contributing! Each observations does 
contribute in some way to our understanding of variable stars. But as you 
said, it may take a shift in paradigm, or just more diversity, to get a 
bit more out of the game than some more superhump periods [and again - 
don't take get this wrong, we still need more of them, but not 
exclusively].

Best wishes, 

Boris Gaensicke

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Dr. Boris Gaensicke              www.warwick.ac.uk/staff/Boris.Gaensicke
Lecturer/PPARC Advanced Fellow             Boris.Gaensicke at warwick.ac.uk 
Department of Physics
University of Warwick
Coventry CV4 7AL                                Tel: +44 (0)2476 574741
UK                                              Fax: +44 (0)2476 692016

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