[Aavso-photometry] Hot pixels and precision.

[pps at dlsi.ua.es]

Thank you Arne and Michael for your responses,

I have recently purchase my camera (ST-10-XME) and it is not a 
second hand. That Kodak chip seems to be well-known for producing 
many hot pixels. But they are not very hot on average, but many.

The point is I still don't have a clear idea about how to eliminate 
the hot pixels. 

There are 2 kinds: fixed and random located. The majority are fixed, 
but I don't know how to quantify what the proportion is.

1) The fixed (or constant position) hot pixels are easy to suppress: 
just obtaining a good Master Dark-frame.

2) The random hot pixels are the ones I don't know how to suppress. 
If I were processing Pretty images with many luminance frames, I'll 
sigma-combine those frames and the random hot pixels should 
disappear. BUT, I have only one instance of photometric image.

Michael, I'm not sure (I've never done it) but it seems to me that, 
if they are random, doing a defect mask wouldn't help in this 
particular point.

Maybe the answer is: they can not be removed without sigma-rejecting 
several exposures, and as long as they are very few, and few of them 
very hot, it is very rare they could affect the measures.

I would like to know if this is the right answer or there is nay 
other option.

Regards,

Pedro


---- Mensaje Original ----

> You should also be able to create a bad pixel mask and them 
replace 
> those pixel values with an average or median of the surrounding 
pixels. 
> This should not be a no-no in photometry, AFAIK. Both IRAF and 
Mira 
> have capabilities for this.
> 
> Cheers,
> Michael Koppelman
> http://www.lolife.com/astronomy/
> 
> 
> 
> On Feb 16, 2005, at 4:20 AM, Pedro Pastor wrote:
> 
> > I have recently acquired a ST-10 camera and I am in the process 
to get
> > to know how it works.
> >
> > The first thing I did notice is the great number of hot pixels it
> > produces (at least compared with my previous MX916).
> >
> > I’ve tried to eliminate those hot pixels doing many dark frames 
and
> > combining them via “Median combine” or “Sigma reject”. This 
produces a
> > nice Master dark frame, BUT that’s not enough for suppressing 
the hot
> > pixels from the “Light frames”.
> >
> > If I would be doing “post card” CCD images I’d take many light 
frames
> > and I’d Sigma combine them for eliminating hot pixels, BUT 
that’s not
> > the case for photometry.
> >
> > The point is: What would you recommend me to do? (Apart from 
changing
> > the CCD camera ;-). Is there any other ST-10 user out there with 
> > similar
> > problem?
> >
> > On the other hand, I keep my MX916. One of the reasons for 
getting the
> > ST-10 was the anti-blooming built-in system in the MX916. I 
think this
> > system was affecting my measures but I still don't know how (the
> > anti-blooming is only implemented in one specific direction). 
Could
> > someone tell me how MX series anti-bloomming system affect the 
> > precision
> > of the ADU measures? Is there any good strategy for compensating 
(or
> > correcting) that effect?
> >
> >
> > Thank you very much in advance.
> >
> > Pedro
> >
> >
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> 
>