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Re: Flashers


In all cases that I am considering both the V and I CCDs see a simultaneous 
increase in brightness.  It is not always necessarily the same increase in 
each channel.  We only measure stars which have detections at the same 
location in the sky within 7 arc seconds made simultaneously with two 
cameras.  Same location in the sky does not mean same CCD pixel 
coordinate.  This rules out some kinds of electronic problems.

There are 4 million pixels.  There are of order 20 cosmic ray hits on each 
of the two CCDs during a typical exposure.  The probability of a 
simultaneous hit in the same star on the two chips is pretty low.  I give 
it 2 x 10E-11 but I have probably computed it wrong.  This exceeds by a lot 
the number of measurements in my catalog.

I tried to make this computation before on a different project and left out 
a factorial in the numerator.  Still, the probability is quite low, though 
I suspect not as low as above.

Tom Droege

At 10:55 AM 5/18/03 -0500, you wrote:

>a cosmic ray hit into the star during the exposure
>george wm turner
>uits/rats @ indiana university
>812 855 5156
>On Sun, 18 May 2003, Tom Droege wrote:
> > Are there many stars that flash?  I keep finding stars with one bright
> > point.  I assume that these are airplanes flying by that happen to 
> flash on
> > top of a measured star.  This especially if the bright point is at a
> > slightly different position.  But sometimes the bright point is at the
> > exact same position as all the others which I think unlikely for an 
> airplane.
> >
> > Tom Droege
> >
> >
> >