[BAA Comets] Visual Equivalent Magnitude (VEM) software - Test dataneeded

[Roger Dymock]

Hi Nick,

Will send you the data probably next week - busy decorating. Perhaps someone in the Computing
Section might be able to do the Windows coding. 

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: 07 November 2015 19:22
To: Comets-disc at britastro.org
Subject: [BAA Comets] Visual Equivalent Magnitude (VEM) software - Test dataneeded

As some of you know I have been working on some software to simplify the 
extraction of Visual Equivalent Magnitudes (VEMs) from CCD images. I now 
have an approach which I believe is robust over a wide range of 
circumstances from faint comets in large telescopes to bright comets 
with wide-field systems.

I would like to test this with images from as wide a range of systems as 
possible and compare the results with magnitude estimates made by other 
methods. I would therefore ask that if you have submitted multi-box 
reports or VEMs that you send me example images to analyze as set out 
below along with the estimates that you made.

The analysis needs two images. One is stacked on the stars and solved 
astrometrically and photometrically using a suitable catalogue (UCAC-4 
recommended) and the other is stacked on the comet's motion using the 
same stacking settings. For particularly bright comets where no stacking 
is required a single image can be used twice.

To generate the pair of images you can use the track-and-stack feature 
of Astrometrica. You need to check the setting "Auto-save FITS with WCS" 
in Settings->CCD and ensure that you use average stacking. First do an 
offset stack and save it, then do a non-offset stack (select restack 
images and set the speed to 0) and save it.

Now load the non-offset stack and solve it against UCAC-4 (I suggest 
using R mags for most unfiltered CCDs). This adds a magnitude zero point 
tag to the file along with astrometric information that is used by the 
program.

Send the two images to me at the email address below along with the 
original multi-box/VEM report.

An example output from the program using one of my 67P observations is 
shown below. The program is told the names of the two FITS files and a 
rough position of the comet in the image. It then does all of the 
calculations automatically. At present it is a Linux command line 
program but, once it is working, I'd be looking for someone to take the 
code and develop a Windows version.

===========================================
[ndj at jupiter proc]$ comphot 67p_ofs_0000.fit 67p_noofs_0000.fit 163 219 
# Date: 2015-09-25T03:36:04
# Telescope: C11 Edge HD
# Observer: Nick James
# Object: 67P_Churyumov-Gerasimenko
# Total exposure: 1324.0 s
# Image scale: 1.54 arcsec/pix, FoV 13.2 x 13.2 arcmin, ZP: 24.88 mags
# Sky background from fixed stack: 1982.3
# Residual sky background in offset stack: 0.2, RMS sky 16.1
# Centroid at 163 220, Max pixel is 951.7
# SKY: 0.0 (0 -> 20) 1201 0 47.5
# SKY: 30.0 (20 -> 39) 3524 0 8.1
# SKY: 60.0 (39 -> 59) 5968 0 1.7
# Sky estimation annulus inner radius 60.0 arcsec, skylevel 1.7
# Total pixels requested but outside frame: 0
                                    10x10  20x20  30x30  40x40  50x50  60x60
COMET         UTC                    +/-    +/-    +/-    +/-    +/-    +/-
                                    13.78  13.01  12.70  12.50  12.37  12.28
                                    13.78  13.06  12.71  12.53  12.42  12.34
Total integrated magnitude: 12.14
[ndj at jupiter proc]$
===========================================


Nick James. Director, BAA Comet Section
ndj at nickdjames.com
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