Re: (IAAC) Markarian 205 - 8inch F/10
I have followed this discussion with some interest and I am surprised that
Jeff has not jumped in yet.
Anyway when observing planetaries you have to have some knowledge of the
type of object that you are looking at before using the OIII filter. Jack
Marling and Steve Gottleib always recommended using both the OIII and
H-beta filter and comparing the brightness at both wavelengths as some
objects have low OIII emission due either to the temperature of the central
star or due to the density of the object quenching the OIII emission.
Popular targets in this state are NGC 40 and Campbells star.
Colour perception is such an individual thing that it is difficult to
compare between observers, witness the comments from Penny and Sue earlier
on this list. PN's in the visible do not have much, if any, continuum
emission so that is not likely to be the explanation for colour variations.
Both the objects mentioned have very high surface brightness's though so
this will stimulate the colour receptors of the eye.
NGC2392 appears to have a normal emission spectrun form the numbers in the
ESO-Strasbourg catalogue so its colour should be green/blue from the
NGC6543 a does not have a meausred line spectrun for the OIII lines which I
find slightly strange. recorded observations of it beeing blinked with an
H-beta filter suggest it has no response to that filter so it must be a
normal type object but the line values just have not been recorded.
It is also perhaps true that the use of the OIII filter for instance on
very bright objects can sometimes worsen the view although from UK skies
the use of the UHC filter on 2392 with the 20" does show up in th internal
parka detail better than without.
I like your project idea to try and map the reflection vs emission
component of diffuse nebulae using the UHC filter. Perhaps if you get any
results you could write it up for the Webb magazine. You might also try and
use the H-beta filter to map out the extended low excitation nebulosity.
>At 09:42 AM 6/11/98 -0400, you wrote:
>>Welcome back, Nick!
>>You are right - the views of many objects are worsened by narrowband
>>guess I was proposing that the reason for those worsened views was
>>just reduced light transmission overall - rather than any reduced
>>the object/feature relative to background. But I wonder if there may be
>>of some of these nebulae (Cat's Eye in particular) which do in fact emit
>>light mainly at wavelengths outside the Hbeta and OIII regions?
>It is possibly significant that both the Catseye and Eskimo nebulae are both
>quite highly coloured so they must be emitting at other wavelenghts apart
>from any continuum reflection.
>>One thing for certain, there are lots of "emission" nebulae whose light is
>>actually more than half reflected (continuum) starlight: using even a
>>filter on these can make them disappear entirely (or make many of their
>>features - the primarily reflected ones - disappear from the object).
>>As a matter of fact, one of my favorite observing projects is trying to
>>distinguish and map out the complex, intermingled dust- and gas-heavy
>>components of brighter nebulae, using nothing but "UHC blinking".
>I also find it a very interesting exercise when I try it.
>Nick Martin, Bonnyton house, By Ayr, Ayrshire KA6 7EW ,Scotland, UK.
> Longitude 55 24'56" Latitude 4 26' 00".
>"Thou star of evening's purple dome
> That lead'st the nightingale abroad,
> And guid'st the pilgrim to his home."
> To the Evening Star by T.Campbell