[BAA Comets] Comet Section Programmes

Mon May 21 19:16:51 BST 2012

Hi Roger,

Thanks for your interests of the CARA procedure. It should be very
interesting to make a study of the 2 procedures, Spanish and Italian.  Why
use of a filter ? We use this filter to just give a idea of the
dust-continuum and not the gas tail components.  Read more on the CARA
website: http://cara.uai.it/filters .  So you can see bigger differences in
af(rho) results with comets with a more explicit gas-tail, also depending on
the gases were gastail consisted and their emmission are located whether or
not in the range of the pass band of the R or I filter. With gas-rich comets
(like in the past comet C/2009 P1 ) I usually take 2 images R and I filter.

About your question regarding the exposuretime, I have not exactly the
correct value for increasing the exposuretime, but you must think on about
3x for the R-filter, for I-filter in the region of 6x depends of the
CCD-chip you are using, like you know some are more sensitive in the red
region like a ST-10XME camera (KAF-3200ME). 

You can find the procedure on the website of CARA. We use a selection of
reference stars for differential photometry in the respective order from the
Hipparcos and TYCO Main catalog with a B-V index of between 0.5 ... 0.7.  (
read more on
http://cara.uai.it/determining-reference-stars-erik-bryssink-version-2 ). 
Also you need the wafrho-software or you can use Astroart or other software
but this is much more time consuming. 
On the other hand, we do not only af(rho) but also a study of the morphology
of the coma, this is also a result of the wafrho software.

Is Af(rho) now 'the' method ?? not exactly, af(rho) has also
disadvantages... read more -> very interesting paper to understand more
about af(rho) -> from Marco Fulle :
http://www.lpi.usra.edu/books/CometsII/7006.pdf

Hope this helps, if you have questions remarks... don't hesitate to ask...
via mailinglist or privat.

___________________________________
regards,

Erik Bryssinck 

BRIXIIS Observatory (MPC:B96)
http://www.astronomie.be/erik.bryssinck/
___________________________________
CARA - Cometary Archive for Af(rho) : http://cara.uai.it
VVS - Belgian association for amateur astronomers : http://www.vvs.be

-----Oorspronkelijk bericht-----
Van: comets-disc-bounces at britastro.org
[mailto:comets-disc-bounces at britastro.org] Namens Roger Dymock
Verzonden: maandag 21 mei 2012 16:30
Aan: 'BAA Comets discussion list'
Onderwerp: Re: [BAA Comets] Comet Section Programmes

Hi Eric,

I have just emailed CARA with a request to join the project. I will image
some comets using both the Spanish and Italian approaches and compare
results. As you know the Spanish method does not require a filter so could
you please give me some idea of the increase in exposure time required for R
and I filters compared with imaging in the clear.

Regards

Roger Dymock
Email: roger.dymock at ntlworld.com
Tel: 023 92647986
Skype: rjvdymock
MPC Observatory Code: 940

-----Original Message-----
From: comets-disc-bounces at britastro.org
[mailto:comets-disc-bounces at britastro.org] On Behalf Of Erik Bryssinck
Sent: 20 May 2012 15:28
To: 'BAA Comets discussion list'
Subject: Re: [BAA Comets] Comet Section Programmes

Hi Roger,

They use narrowband filters as well, this kind of narrow-band can only be
used for larger telescopes and the brightest comets en when they in the
brightest part of the appearance. Indeed, as you may know, narrow band
filters let barely 2% of the total light trough .... But let say that 95% of
the observations of CARA are made with the R and I filter of the BVRI-set.
And for me are this 100% of the observations made with these filters. A
small advantage is that you can use a I-filter when you live in a light
polluted area like mine backyard observatory. So, the amateurastronomers can
do Af(rho) work.

Best regards,
Erik

-----Oorspronkelijk bericht-----
Van: comets-disc-bounces at britastro.org
[mailto:comets-disc-bounces at britastro.org] Namens Roger Dymock
Verzonden: zondag 20 mei 2012 15:15
Aan: 'BAA Comets discussion list'
Onderwerp: Re: [BAA Comets] Comet Section Programmes

Hi Eric,

Thanks for the CARA info. I had (wrongly it seems) assumed that narrowband
filters were required and they are expensive. The SSON robotic telescope
does have BVRI filters available so I can try out the CARA method.

Regards

Roger Dymock
Email: roger.dymock at ntlworld.com
Tel: 023 92647986
Skype: rjvdymock
MPC Observatory Code: 940

-----Original Message-----
From: comets-disc-bounces at britastro.org
[mailto:comets-disc-bounces at britastro.org] On Behalf Of Erik Bryssinck
Sent: 20 May 2012 10:30
To: 'BAA Comets discussion list'
Subject: Re: [BAA Comets] Comet Section Programmes

Hi Roger et all,

very interesting discussion on vision and observing comets. We find in
Belgium similar questions, comments, etc.

>1) For some time now I have been submitting data to the Spanish group. 
>Analysing the images with Astrometrica and Focas (developed by them) is 
>very easy and to be encouraged.
>I didn't go down the Italian route as the filters are quite expensive 
>and not available on SSON telescopes.

I had a comment regarding the use of expensive filters for the Italian CARA
approach on comet observations, particularly Af(Rho) measurements. The
filters are that be used are, the R and I from the Cousins/Bessel BVRI
filterset, which are also used for the photometry of stars. You're right
that they are not cheap, but still quite affordable as you can see the total
amount of your investment in the telescope setup. It is true that the more
"work" calls for subsequently process the data and determine the afrho,
while the Spanish approach to the data obtained very quickly after using
astrometrica. 
I apply these two methods, the Spanish-approuch (with FOCAS-II software)  as
the CARA approach (with Wafrho-software  - developed by CARA). Only recently
aaply af(rho) to comets were a particular activity is expected and retrieve
magnitude brighter than magnitude 12. Only then it is interesting to apply
Af(rho) values. I checked both approaches in terms of Af(rho) and compared,
and still see the occasional differences. Meanwhile I have already a lot of
experience with the CARA approach. I would recommend it for comets who are
observable for a while and fluctuations are possible or bright comets (eg
comet 29P) and now, for example comet C/2011 L4 (PANSTARRS), unfortunately
the latter will usually only detectable by the southern hemisphere. A nice
example in the past was comet C/2009 P1 (Garradd) were I have made a lot of
observations, it gives interesting data for Af(rho) ! But indeed, every
comet observer does what he wants or where he is interested.

___________________________________
Kind regards,

Erik Bryssinck
BRIXIIS Observatory (MPC:B96)
http://www.astronomie.be/erik.bryssinck/
___________________________________
CARA - Cometary Archive for Af(rho) : http://cara.uai.it VVS - Belgian
association for amateur astronomers : http://www.vvs.be