Re: Ensemble analysis: "new variables"

[Andrew Bennett <andrew.bennett@ns.sympatico.ca>]

On Wed, 30 Jan 2002 08:51:54 -0700, you wrote:

>Andrew, my automatic ensemble pipeline does not use
>the 60 brightest stars, but some smaller number of well-exposed stars.
>When you use the brightest ones, they tend to be saturated

I'm already selecting out any even close to saturation.

>  A well-exposed star is one that is no more than half-well.
>Within a half degree (I assume that is radius, so you are
>talking a degree-sized area) you typically have 300 Tycho2
>stars, all of which should be well-exposed.

True.
>  I don't know
>why an average of 60 such stars should give you poor
>statistics;

But I don't end up with 60 - that's the problem. My
simple minded selection routine throws out a star if
on even one image it falls too near a bad pixel or
gets a cosmic ray hit that screws up the fit to the PSF.
All rare events ... but not rare enough!

> sqrt(60) is a big factor and they should all
>have Poisson statistics under one percent.
>Arne

But still contrive to have a noise floor of 0.008 mag
in V and 0.004 mag in I. And it only gets that good
after throwing out images with any trace of oddities.

Andrew Bennett, Avondale Vineyard