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Re: Re:[APML] orion mosaic
Rob,
Thanks for the description. It puts a bit of "depth" into the picture we
always see in our images. What kind of project are you working on? Is it
some outreach type program?
Dave
> Dave,
>
> The nebulosity that comprises IC2118 probably forms the outer
>
> boundary of the huge Orion-Eridanus bubble which explains the
>
> subtle emission component. I believe this bubble being a sphere
>
> has some of its boundary much closer than the emission cloud
>
> which makes up Barnards loop.See below for a description I put
>
> together fior a project I'm involved in.
>
>
>
> A classic reflection nebula, IC 2118 lies 2 degrees northwest of the
>
> bright Class B supergiant Rigel which is thought to be the source of
>
> illumination for the nebula. The distance to IC2118 has been reported
>
> to be 210 pc's based on its proximity to Rigel. Radio observations
>
> show substantial carbon monoxide emission throughout parts of IC 2118
>
> an indicator of the presence of molecular clouds and star formation in the
>
> nebula. In fact candidates for pre-main sequence stars and some classic
>
> T-Tauri stars have been found deep within the nebula. The molecular
> clouds
>
> of IC 2118 are probably juxtaposed to the outer boundaries of the vast
>
> Orion-Eridanus bubble, a giant supershell of molecular hydrogen blown
>
> by the high mass stars of the Orion OB1 association. As the supershell
>
> expands into the interstellar medium favorable circumstances for star
>
> formation occur. IC 2118 is located in one such area.
>
>
>
> The wind blown appearance and cometary shape of the bright reflection
>
> nebula is highly suggestive of a strong association with the high mass
>
> luminous stars of Orion OB1. The fact that the heads of the cometary
>
> clouds of IC2118 point northeast towards the association is strong
>
> support of that relationship.
>
>
>
> On a much larger scale the Orion molecular cloud is a component of a
>
> more vast expanding supershell or superbubble of molecular gas
>
> called the Orion Eridanus bubble. The immense superbubble has been
>
> inflated over the last 10 million years by the radiation of only 10 to 20
> high
>
> mass O and B type stars of the Orion OB association. This immense cloud
>
> complex spans 15 degrees (120pc) in diameter north-south and 40 degrees
>
> (320pc) east-west to encompass the constellations of Orion and Eridanus.
>
> The eastern boundary of the bubble is marked by Barnard's Loop.
>
>
>
>
>
> Rob Gendler
> email: robgendler@att.net
> Web Site: http://www.robgendlerastropics.com
> ----- Original Message -----
> From: "D. Kodama" <kodama@alumni.caltech.edu>
> To: "Wei-Hao Wang" <whwang@gmail.com>; "Discussion of Film
> Astrophotography"
> <astro-photo@seds.org>
> Sent: Friday, April 01, 2005 2:35 AM
> Subject: Re: Re:[APML] orion mosaic
>
>
>> Wei-Hao,
>>
>> It would be interesting to see if someone has a CCD image of the Witch
>> Head taken through a 10 or 20 nm H-alpha filter to see if it is really a
>> significant emission source.
>>
>> Is everything in the Orion complex at the same distance? It may be old
>> data I'm looking at but Rigel's distance is listed at 250 pc and I'd
>> guess
>> the Witch Head must also be at about the same distance. The belt stars
>> and Orion nebula are listed at distances somewhat farther away than
>> Rigel.
>> Meanwhile Betelgeuse is listed as being "nearby" at 150 pc. I'm just
>> wondering what is the distance to the veil of H-alpha that seems to run
>> through the whole area and if Rigel is a contributing ionization source.
>>
>> At any rate, I think it is the general tint of the H-alpha background
>> that
>> throws color adjustments off when they are based on assuming black or
>> dark-gray backgrounds. One really needs these deep wide field shots to
>> get close to the correct colors or one needs to use a strictly
>> calibrated
>> color adjustment procedure which probably will only work with CCD
>> images.
>>
>> Thanks for the info on what you used for the Registar reference. I was
>> wondering if you might have used a computer-generated star map for that
>> purpose.
>>
>> Dave
>>
>>
>>
>> > Hi Dave,
>> >
>> > About the redness of the Witch Head, I have two explanations.
>> > First, indeed no reflection nebulas are purely blue. The dust
>> > clouds reflect light at all wavelengths. However, the reflection
>> > in blue is stronger than red. Thus if the nearby star has blue or
>> > average colors, the reflection nebula appears blue. But it's not
>> > pure blue. There is still green and red light reflected. If the
>> > nearby star is very red, then it is possible to have red reflection
>> > nebula. The yellow nebula next to Antares is of this kind.
>> >
>> > The above is continuous light. On the other hand, it is possible
>> > for a reflection nebula to have emission line (like Ha) as well.
>> > In a very intensive UV radiation field (like Orion), molecular
>> hydrogen
>> > will be broken into atomic hydrogen by the powerful UV photon and
>> > the H atom will then be ionized to produce line emission. However,
>> > if a cloud is so dense that the UV photons cannot penetrate it,
>> > it can stay in the molecular form and remains dark. If this is the
>> > case, only the surface layer of that cloud is ionized and emitting
>> > a little Ha emission. This picture is a good example:
>> > http://www.ifa.hawaii.edu/~wang/gallery/picutres/sco_oph_complex.htm
>> > The dark clouds to the upper left of Antares are covered by thin red
> skin.
>> > This is Ha emission coming from the surface of the clouds. I believe
>> > the Witch Head also has this kind of weak Ha emission. But since
>> > itself also reflect blue light, the Ha is not as apparent.
>> >
>> > I just used an old picture taken by a 50mm lens as the reference.
>> >
>> > Cheers,
>> >
>> > Wei-Hao
>> >
>> >
>> > On Thu, 31 Mar 2005 06:40:38 -0800 (PST), D. Kodama
>> > <kodama@alumni.caltech.edu> wrote:
>> >> Wei-Hao,
>> >>
>> >> Fantastic mosaics! It's amazing to me that you can turn out these
>> >> mosaics
>> >> while pursuing a PhD!
>> >>
>> >> It's interesting that the Witch Head shows up quite well in your
>> >> R-channel
>> >> shot. Most people reproduce that as an almost pure blue object, but
> for
>> >> a
>> >> long time I've felt that wasn't quite accurate. It could be that
>> they
>> >> are trying to color-balance the background and losing the red because
> of
>> >> so much h-alpha emission in the general area.
>> >>
>> >> When registering the components of a large mosaic covering a large
>> part
>> >> of
>> >> the sky, what are you using as an overall registration reference?
>> >>
>> >> Dave Kodama
>> >>
>> >
>> > --
>> > ________________________________________________________________
>> > Wei-Hao Wang :)
>> >
>> > Institute for Astronomy at University of Hawaii
>> >
>> > Address:
>> > 2680 Woodlawn Drive Personal Website:
>> > Honolulu, HI 96822 http://www.ifa.hawaii.edu/~wang
>> > ________________________________________________________________
>> > _______________________________________________
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>> > http://seds.org/mailman/listinfo/astro-photo
>> >
>> >
>> >
>>
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>
>
>
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