[Aavso-photometry] When to submit "Fainter Than" versus actualnumbers.

[BailyHill at aol.com]

Hello Jeff;

You asked about "time series".  We use this term to describe an observation 
of a single object, many times, on the same nite.  So the particular time 
series of BZ Uma that I was referring to, had 95 images, of 2 minute exposure, over 
a 4 hour period, done continuously.  So I have an estimate of the Target 
about every 2.5 minutes, allowing for downloading, etc.  This allows us to study 
flares, superhumps in CV, and any other time varying behavior that a target 
star may be exhibiting.

So as a result, we get a light curve of the target or object, and also the 
light curves of any other stars which appear in all images.  This allows us to 
plot the time variation of the check stars, which should be constant, and any 
variation is a measure of the noise of the process.  It also gives us a basis 
of comparison.

As an example, BZ Uma had a Std Dev of ,192, which you commented was not very 
good.  On the contrary, since the check stars of the same magnitude as BZ Uma 
were much more constant, with std devs of .045 to .066.  In fact, examination 
of the BZ Uma light curve shows a broad brightening in 16 of the 95 frames 
that drives its std dev higher.  The same brightening is not seen in the check 
stars.  Since this is so, it gives us confidence that the brightening of BZ Uma 
is real, and not an artifact of our process, clouds, aurora, etc.  

These errors are very driven by the magnitude.  As an example, in the same 
time series on BZ Uma, the check stars around 13th mag had std devs of .017 to 
,024 mag, which is much more typical.  I am sure that if there were brighter 
check stars in the field, the std dev could be driven down to a few milli mags.  


I was wondering, on the targets that you collect 10 million photons, how 
bright are they typically?  You say you collect for 3-10 seconds.  How do you read 
out the total?  Do you know how it is done?

Clear Skies
Gary