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Re: [AAVSO-DIS] IO Aurigae and the STARE eclipser Aur0 3503
When grilled further on (Mon, 30 Aug 2004 18:29:07 -0300),
"Sebastian Otero" <varsao@fullzero.com.ar> confessed:
> > > TASS data have a +/-0.2 mag. scatter so there is no way to tell if there
> > are
> > > eclipses or not since the amplitude discovered by STARE is only 0.07
> mag.
> >
> > Could you explain how you arrived at the scatter above since it does not
> > appear to be consistent with the data in our S&T note 10 at
> > http://www.tass-survey.org/tass/showtell/st0010.html
>
> Tom,
>
> Brian has already answered the question.
> This happens all the time in different fields (not crowded).
> TASS observations for some stars are good and for others are useless. I
> don't know how this comes to be and why it happens. In the example above it
> becomes pretty evident what makes the errors to stand out easily: almost
> simultaneous measurements giving very different results. It's not a cirrus
> thing or the like because it happens all the time and the pattern is : one
> observation bright , the following 0.2 or even 0.3 mag. fainter and so on.
> The big problem with this is that when there is a single observation per
> night... how can we believe in its value? It becomes more a matter of faith
> than anything else.... Something must be happening and maybe it can be
> corrected.
>
It's interesting. I just took some data for Michael Sallman, and had the exact
same problem. I take 11 images of a field (generally), and one of the images
came up with .3 mag dimmer than the others, at least for the stars in the
vacinity. I have not yet looked for a reason, but the stars were right on the
edge of the frame (y around 2012). The instrumental magnitude (from DAOPHOT) is
also .3 mag dimmer.
And I don't use the same reduction pipeline as Tom does... But I do suspect my
color calculations.
Cheers,
Rob
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