[BAA Comets] CCD astrometry and photometry

[Roger Dymock]

Hi Nick,

Are you sure this is the correct link? I get a 404 page not found error and then a page headed
nickdjames.com opens. McAfee didn't seem to like it and I couldn't find the images, etc you mention.

Regards

Roger Dymock
Email: roger.dymock at ntlworld.com
Tel: 023 92647986
Skype: rogerdymock67 or
Skype: rjvdymock
Project Alcock http://www.britastro.org/projectalcock/


-----Original Message-----
From: Comets-disc [mailto:comets-disc-bounces at britastro.org] On Behalf Of Nick James
Sent: 24 January 2015 18:24
To: BAA Comets discussion list
Subject: Re: [BAA Comets] CCD astrometry and photometry

Roger,

Example files (offset and nonoffset stacks + Astrometrica config for 
this system) are here if you want to have a go.

http://www.nickdjames.com/Transfers/photom/

These were taken under rather grotty conditions. I get a zero point of 
22.85 using Astrometrica using the nonoffset image. I then load the 
offset image into IRIS and use "noffset 0" to set the sky background to 
zero (this uses a global median estimate). Stretch the image to estimate 
the size of the coma (I get 250 pixels radius = 21.5 arcmin diameter). I 
then used concentric apertures of 250,350,500 radius and the previously 
measured zero point to get a magnitude of 4.2 (2015-01-22, 20:07).

Nick.

> Nick, could you let me have the images you used plus the necessary config file for Astrometrica so
I
> can work through the process and then write it up for the Project Alcock website?
>
> I am reasonably familiar with IRIS so shouldn't be too much of a problem but could you please
> explain (from your previous posting);
>
> 3 - I then used a median estimator to get the sky background and
> stretched the image around this point to show the size of the coma.
>
> Not sure what a 'median estimator' is.
>
> I have done some work with a DSLR attached to a telescope and the astrometry and photometry looked
> quite reasonable but guess I need to do same for DSLR standalone.
>

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