[BAA Comets] magnitude measurements form CCD observations

[Richard Miles]

Dear Uwe,

This is very helpful.  I have a few questions:

In the report by yourself and Bernhard Häusler entitled, "Visuelle und 
CCD-Photometrie von Kometen: Angleich der Messwerte durch die 
Multiapertur-Methode" or "Visual and CCD Photometry of comets: Matching 
measured values using the Multi-aperture Method"

There is the statement:

Die Grenzhelligkeit (m-infinity) und der charakteristische Radius (rho) 
müssen so gewählt werden, dass eine "bestmögliche Passform" erreicht wird 
(Bild 3). Das mathematische verfahren hierzu ist die Ausgleichsrechnung nach 
der Methode der kleinsten Fehlerquadrate, die von Gauß entwickelt wurde. 
Dieser Rechenansatz kann in vielen Lehrbüchern nachgelesen werden, z.B. in 
[3].

which translates to:

The limiting magnitude (m-infinity) and the characteristic radius (rho) must 
be chosen so that a "best fit" is obtained (Fig.3).  The mathematical method 
is the regression analysis using the method of least squares, which Gauss 
developed.  This computational approach can be found in many textbooks, e.g. 
in [3].

Can you say what the form of the equation used to fit the curve?  The 
regression analysis can be used with several different curve equations.  It 
would also help if the algorithms / equations used in the software "Kphot" 
are explicitly stated.

Secondly,

In the plot shown in Fig.3, there are six datapoints plotted (10-60 arcsec 
diameter) and m-infinity is given as 9.7 and the characteristic radius, rho 
is given as 1.82 arcmin.  Is this the radius when 63% of the light flux is 
reached, i.e. 0.502 magnitudes fainter than m-infinity, or mag 10.2?  I am 
not sure where the 63% value has come from - Has it been derived empirically 
from existing data?  In practice the visual observations will vary depending 
on parameters such as focal ratio, magnification and relative sky brightness 
and so this value of 63% may not be the best in all cases.


This looks to be a practical approach to relate visual and CCD measurements 
and may be refined as more examples where we have good data from both CCD 
and visual observations available.

Danke schön,
Richard Miles

----- Original Message ----- 
From: "Uwe Pilz" <piu1958 at uni.de>
To: <comets-disc at britastro.org>
Sent: Tuesday, September 18, 2012 4:37 AM
Subject: [BAA Comets] magnitude measurements form CCD observations


>
>
> Dave Storey wrote
>
> > Or do we need to establish a programme where the whole coma is
> taken into account to derive a magnitude as appears to be happening
> on the COBS web site.
>
> Dear observers,
>
> I wrote a computer programm which calculates the total magnitude
> from multiaperture CCD measurements. At the web pages of the German
> comets' group I publish such values, together with Af(rho) values:
> http://kometen.fg-vds.de/obsaktinh.htm [1]
>
> If somebody is interested in this software please drop me a line.I
> wrote a publication about the mathematic model. Unfortunaltely it is
> only available in German. If there is some interest in this method I
> would perform at least a rought translation into English. The German
> text: http://kometen.fg-vds.de/Publ/ccdphot.pdf [2]
>
> Uwe Pilz, piu1958 at uni.de [3][ Unser Tipp: Tglich Happy Preise bei
> OTTO Live Shopping . Jetzt bei uns im "studentSHOP [4]" auf UNI.DE ]
>
> Links:
> ------
> [1] http://kometen.fg-vds.de/obsaktinh.htm
> [2] http://kometen.fg-vds.de/Publ/ccdphot.pdf
> [3] mailto:piu1958 at uni.de
> [4] http://www.uni.de/shopping