[Aavso-photometry] Re: VV will be a fairly lonely Pup!

[Berto Monard]

Arne and Co,

I was very realistic in what I wrote before the week-end..

Even in unfiltered mode, a 'humping' system at 17.5 will not yield a precise lightcurve with a CCD system on a 12" telescope (which is near the max size of amateur instrumentation). I refer to my own experience on U Sco and some other CVs of similar magnitude. Going V filtered will bring the S/N further down (about 6x?) with the equivalent of about 2 magnitudes. The R filter will loose something like 1.5 mag...

If you want to jack up the S/N you'll do that at the cost of time resolution. With orbital periods of less than 2h there will be not much signature left.

My remark 
'At decl -19, VV Pup is very much equatorial, which means that longer
> exposures (more than 30 sec) will produce significant star trailing on
> most of the images with the commercal type telescopes. This will firmly
> reduce the magnitude reach in filtered photometry.'
ought to be clear in the context. Production scopes show a serious periodic error, even when corrected. The maximum amplitude of trailing occurs at decl 0, eg for equatorial targets. Since cos 19° = 0.95, it is very much equatorial in that regard..
I apply about 30 sec exposure time for most of my observations, since it gives about 90% acceptable images in most parts of the sky. Observations near the South pole can stand significantly longer exposures (much less star trailing, since cos 70 =0.34 ..).
Who is doing autoguiding on timeseries?

I hope that VV Pup strikes some active behaviour during the observing windows. That will help a lot for the cause.

BTW my most recent observation saw VV Pup at 15.8CR (UT 050212.764). Hmm, who knows?

Regards,

Berto


>>> Arne Henden <aah at nofs.navy.mil> 11/02/2005 22:46:20 >>>
Expanding on Aaron's reply to Berto...

Berto Monard wrote:
> Recent 'unfiltered' observations show VV pup evolving around 17.5CR. I
> wonder if, at this faint level, any precise timeseries photometry via
> filtered observations can be done by the usual amateur instrumentation.
> 
Depends on the size of the telescope, the desired signal/noise, the
bandpass and the required time resolution.  It may be true that only
the larger amateur telescopes will do good time resolution, but you
don't know for sure until you try.  We already consider this; the
announcement suggested red filters for the smaller telescopes and
B/V for the larger ones.
> 
> But if VV Pup is a polar, it will give a reasonably good signal over
> the unfiltered CCD band while measurements in the different bands will
> likely show a similar light curve. 
> 
Polars look quite different depending on the wavelength.  This is
why Steve is requesting filtered observations.

> At decl -19, VV Pup is very much equatorial, which means that longer
> exposures (more than 30 sec) will produce significant star trailing on
> most of the images with the commercal type telescopes. This will firmly
> reduce the magnitude reach in filtered photometry.
> 
I don't follow this.  Dec = -19 is not equatorial by my definition.  The
30sec comment doesn't make sense; many telescopes will go longer
unguided, and if you are autoguiding, you can certainly do very long
exposures.  So Brad, you are not the only person confused by this
statement!

> If someone were (in addition to unfiltered runs, produced by others
> perhaps) to make (by means of stackings) 'deep' snapshot observations in
> the different filters, the overall information can still be had. From
> past experience I am not a strong believer in the quality of timeseries
> derived from stacked images...
> 
"Deep snapshots" is essentially what we are asking for; the difference
in your description, I think, is that you are planning a single snapshot
per filter per night and we want as many such exposures as you can take
for each night (that is, a coarse time series).  Please do not observe
unfiltered for Steve's project.

Tim, the f-scale chart is an image from the DSS, with the variable pretty
easily visible.  We have a hundred high-resolution images taken with the
1.55m telescope of this field, since it was on our parallax program.
However, there is a blowup with the variable marked in the
Downes Living Edition catalog that will be useful for identification:
http://icarus.stsci.edu/~downes/cvcat/ 

Arne