[Aavso-photometry] Cosmic Rays

[arne]

I've looked at thousands of CRs in my days.  The overriding feature
is that they are pointlike, affecting only one pixel, or form a line
that is one pixel wide and so easily distinguished from the seeing
profile of stellar objects.  They are usually, though not always, very
bright. With a TEC-cooled CCD, I would believe Michael's
observation that undercorrected hot pixels would be a "contaminant"
in searching for CRs, and would be very hesitant on accepting
the CR-theory for events that are only marginally above the background
noise level.

Your best source of information is Jim Janesick's book,
"Scientific Charge Coupled CCDs", especially the discussion in
section 7.1.7 (page 670 and following).  The usual rate is about
100 events per cm2 per hour at sea level.
Arne

Ben Davies wrote:
> I looked at your mexdev image. ... there are a lot of low angle CR's. 
> Not every bright thing you see is a CR. The vast majority of those 
> single points look to me like shot noise from under-corrected hot 
> pixels.... So you may be sitting near something radioactive---that's no 
> joke. Are you in Colorado? Got any other ideas?
>  >>>>>>>>>>>>>>>>>
> 
> Hello Michael,
> 
> I'm in San Francisco, but who knows?
> 
> The single, seemingly symmetrical, points you see on the jpeg are really 
> not symmetrical.  If you trace them back to the originating image, they 
> are linelike, about 3 pixels thick, with pixel values (to take one 
> example) like this
> 125(noise)   176   1066   506   421   283   288   134(noise)
> 
> What I suspect, is that I am seeing low level cosmic rays that go 
> unnoticed in an image just because they are not big and bright.  I 
> expect my flux levels to be what anyone will see.
> 
> The idea that I am sitting near something radioactive needs to be tested.
> I will go down to San Jose soon and make the same test at the same time, 
> 7-12pm pacific std time.  That of course will not eliminate the camera 
> itself as a source.
> 
> Ben
> http://ben.davies.net/cosmicrays1.htm
> 
> send me the ftp location and I'll send you the whole lot to look at.  
> Your experienced eye will probably be able to sort something out.
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