Re: GSC 748-1618

[Michael Koppelman <lolife@bitstream.net>]

What do you mean by "raw TASS magnitudes"? From the ensemble 
photometry? Also, you say the second plot is the difference -- I'm just 
curious why it's plotted in the V=11 range when it should be <1? Is 
that just a label or relative offset issue? That seems like quite a lot 
of scatter. Is it tighter within a night and we are just seeing 
night-to-night difference? The scatter on the brighter TASS stars I've 
worked on is much less than this. Is the (what seems to me) increased 
scatter just due to the dimmer nature of this batch of stars?

Thanks Chris!

Michael Koppelman

On Tuesday, February 18, 2003, at 03:25 PM, Chris Lloyd wrote:

> Michael,
>
> I normally use the differential magnitudes when working with TASS data 
> but
> in this case they are certainly no better and probably worse. I 
> enclose two
> plots. The first shows the light curve of GSC748 relative to number 
> 89632 in
> the big list.
>
> The filled symbols are the raw TASS magnitudes while the open symbols 
> are
> the differential magnitudes plus the mean of the comparison. In reality
> there is very little to choose between them but to me the differential 
> mags
> have more scatter.
>
> The second plot is the difference between two comparisons, 89632 and 
> 89725
> using the same phasing. The symbols are the same as before. Apart from 
> the
> few outliers I can see no obvious difference but the standard 
> deviations are
> 0.023 and 0.029 for the raw and differential mags respectively. There 
> is
> clearly something afoot here because my experience is that the 
> differential
> magnitudes are usually significantly more reliable than the raw mags. 
> I have
> most of a technical note on this which I really must finish off. I 
> suspect
> that there is something up with the TASS data which generally 
> increases the
> noise but that doesn't explain why parts of the curve are 
> systematically
> different.
>
> GSC 748-1618
>  89720  135 103.5564   7.9413  2286.72869 11.406 0.130 0 10.645 0.074 0
>  89632  194 103.4339   7.9736  2286.70740 10.477 0.017 0  9.050 0.027 0
>  89725  143 103.5627   7.9019  2286.74822 10.878 0.023 0  9.665 0.014 0
>
> Cheers,
>
> Chris
>
> <gsc748_f1.png><gsc748_f2.png>