Hi Terry et al.,This is a good opportunity to comment on filters... though it's somewhat specialized to TT Ari.
Because of the star's extremely strange and unprecedented state - with cool secondary and hot WD dominating in the non-flaring phases - it really is true that multicolor data can be of enormous help in decoding the relative contributions to the light. (And this is rare: most CVs, i.e. their disks, are so broadband that there is seldom much advantage in using filters.) However, this presupposes that the multicolor data has high statistical accuracy... and there is practically no chance of achieving that with small telescopes on a flickering 16th magnitude star.
So one lesson is a general one: improve S/N by observing clear (or roughly clear; a little blue block can help with differential-extinction
issues). This is almost always optimum for period-finding issues... andshortening exposures to ~60 s will help with time-resolution and possibly data quality (if your drive is problematic).
But here's an important consideration that cuts the other way. This is a landmark event in the history of humanity's acquaintance with TT Ari. The light curves are something I've never even dreamt of; and here they are, rolling off our little telescopes. Since TT Ari is the brightest CV in the sky, that's nothing to sneeze at. So our observations have solid archival value - except for unfiltered data, which doesn't, since the bandpass is not defined. Personally I tend to prefer data of high statistical quality (unfiltered), since that helps me get science from it in the short run; but I could imagine filtered data being equally or more productive for other studies down the road.
For brighter stars and/or bigger scopes, V has much to commend it, because it is excellent (ideal) for archival purposes, has low extinction, and you can often get decent S/N. (Of course, if our stars weren't rapid variables, we could always get a desired S/N by just observing longer... but we don't have that luxury!)
Sorry for going on so long... but in my opinion, 300 sec is too long. When the star flares, significant changes take place in 300 sec. Anything over about 120 s is difficult to recommend for CVs, unless you know - as we never do - that no rapid state changes are occurring.
Fortunately, some CBAers ignore my advice and observe in V. That greatly helps in calibration. If everyone observed unfiltered, our
calibration would be really pathetic.For people who have been observing this star for a while now, I don't recommend changes in filters or comp stars. I've measured the offsets between different observers; and while they change slightly (and somewhat inexplicably) from night to night, they are of great use in splicing light curves. If you do change, announce it prominently in the message!
joe Terry Bohlsen wrote:
I took 2 hours of R filter data last night from the east of Australia before it clouded in.Hopefully this will help a bit. What exposures are OK?I tried 120 secs and 180 secs but the SN is still a bit low. Is a 300sec exposure too long?Cheers Terry Bohlsen Armidale NSW Australia