Uncatalogued planetary nebula (?)

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IO_12
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Uncatalogued planetary nebula (?)

Postby IO_12 » Wed Dec 28, 2016 10:56 am

Hi everybody!
A couple of days ago we took this image centered on the reflection nebula VdB 48 and covering an area 1.93 x 1.28 deg. just a few arc minutes north from Alnilam (ε Orionis)
Click to view full size image 1 or image 2

There is an object on this image (please see the annotated mouseover), looking like a planetary nebula, partially covered by VdB 48. Although this object is clearly seen on DSS plates, we couldn't find it catalogued in any catalogue. Could somebody identify the object (as well as its nature)? We'll highly appreciate your help!
For more info and hi-res images please visit the website
We whish to all of you a great New Year, full of clear skies!
Velimir and Emil

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Ann
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Re: Uncatalogued planetary nebula (?)

Postby Ann » Wed Dec 28, 2016 4:00 pm

IO_12 wrote:Hi everybody!
A couple of days ago we took this image centered on the reflection nebula VdB 48 and covering an area 1.93 x 1.28 deg. just a few arc minutes north from Alnilam (ε Orionis)
Click to view full size image 1 or image 2

There is an object on this image (please see the annotated mouseover), looking like a planetary nebula, partially covered by VdB 48. Although this object is clearly seen on DSS plates, we couldn't find it catalogued in any catalogue. Could somebody identify the object (as well as its nature)? We'll highly appreciate your help!
For more info and hi-res images please visit the website
We whish to all of you a great New Year, full of clear skies!
Velimir and Emil


Sure looks like a PN. You should definitely ask starsurfer about this. If he doesn't know if this planetary nebula has been catalogued or not, no one does!

Lovely image, full of blue light! Thank you so much from a grateful Color Commentator! :D

Ann
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Re: Uncatalogued planetary nebula (?)

Postby starsurfer » Wed Dec 28, 2016 6:32 pm

Erm I'm not the only planetary nebula expert on the planet for thanks for your kind words!

While it could look like an ancient evolved PN interacting with the ISM, it is very likely to be part of the dust of the Orion Molecular Cloud. A lot of dust clouds in the Orion area also have ionized Ha emission, which is ionized by many of the hot stars in the area.

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Re: Uncatalogued planetary nebula (?)

Postby Chris Peterson » Wed Dec 28, 2016 7:00 pm

IO_12 wrote:Hi everybody!
A couple of days ago we took this image centered on the reflection nebula VdB 48 and covering an area 1.93 x 1.28 deg. just a few arc minutes north from Alnilam (ε Orionis)
Click to view full size image 1 or image 2

There is an object on this image (please see the annotated mouseover), looking like a planetary nebula, partially covered by VdB 48. Although this object is clearly seen on DSS plates, we couldn't find it catalogued in any catalogue. Could somebody identify the object (as well as its nature)? We'll highly appreciate your help!
For more info and hi-res images please visit the website
We whish to all of you a great New Year, full of clear skies!
Velimir and Emil

It could be a distinct object (like a PN) as opposed to structure in the surrounding molecular cloud (which seems very possible, especially since the circular shape may be an optical illusion, with the actual structure being an arc-shaped front that sort of merges with surrounding clouds in a way that we process as a circle). If it is a PN, it is certainly not cataloged. Using Vizier, Simbad, and Aladin it's clear that the only cataloged objects within the apparent region are a few IR sources and a few galaxies.
Chris

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Ann
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Re: Uncatalogued planetary nebula (?)

Postby Ann » Thu Dec 29, 2016 5:51 am

Chris Peterson wrote:
IO_12 wrote:Hi everybody!
A couple of days ago we took this image centered on the reflection nebula VdB 48 and covering an area 1.93 x 1.28 deg. just a few arc minutes north from Alnilam (ε Orionis)
Click to view full size image 1 or image 2

There is an object on this image (please see the annotated mouseover), looking like a planetary nebula, partially covered by VdB 48. Although this object is clearly seen on DSS plates, we couldn't find it catalogued in any catalogue. Could somebody identify the object (as well as its nature)? We'll highly appreciate your help!
For more info and hi-res images please visit the website
We whish to all of you a great New Year, full of clear skies!
Velimir and Emil

It could be a distinct object (like a PN) as opposed to structure in the surrounding molecular cloud (which seems very possible, especially since the circular shape may be an optical illusion, with the actual structure being an arc-shaped front that sort of merges with surrounding clouds in a way that we process as a circle). If it is a PN, it is certainly not cataloged. Using Vizier, Simbad, and Aladin it's clear that the only cataloged objects within the apparent region are a few IR sources and a few galaxies.


The reason why I think it is a planetary nebula is partly the shape, but mostly the color of the object. Velimir and Emil's mystery object is green (not blue) on the inside and red on the outside. It is an OIII kind of green, not too far from blue, yet even so distinct from blue. Nowhere else in the picture do I detect this green color.

As a color nerd, I always look at and note the color of any object in an RGB image. I am not aware of any other objects than planetary nebulas that are OIII green on the inside and red on the outside. Typical emission nebulas like the Orion Nebula hardly ever look green inside, because there is such a wealth of ions emitting light at the same time there, so that the central part of the nebula often looks whitish, light pink, or yellowish. Fainter, less "concentrated" emission nebulas often look "all red". But not green. Only PNs are rarefied enough to be clearly green inside.

As a color commentator, I must say that this looks like a planetary nebula. Can I be certain that this is what if is? No, of course not. I can only say what it looks like.

Ann
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Re: Uncatalogued planetary nebula (?)

Postby Ann » Thu Dec 29, 2016 7:22 am

I have a suggestion for Velimir and Ivan, however. Can you search for a central star of your possible planetary nebula? Any true planetary nebula must have a central star ionizing it. If the green and red arc in your image is really a PN, there must be a central star ionizing it. Such a star would be quite faint, but strikingly blue.

The Medusa Nebula.
Al and Andy Ferayorni/Adam Block/NOAO/AURA/NSF
Take a look at this picture of an old planetary nebula, the Medusa Nebula. To the right of the main arcs of it is a small star that is noticeably bluer than any other star in the picture. The unique color and small size of it is a dead giveaway that this is the central star of the planetary.

I checked your image, but I couldn't spot any strikingly blue small star to the left of the elegant green-and-red arc. But there has to be such a star there, if this is a planetary nebula.

It is possible that the there is a central star there, but it might be reddened by dust, so that its blue color is obscured. But in any case, this is my advice to you: Search for a blue central star.

Ann
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Re: Uncatalogued planetary nebula (?)

Postby IO_12 » Thu Dec 29, 2016 10:37 am

Hi guys!
Many thanks for your comments, especially to Ann for her comprehensive analysis!
Yes, that about the central star is absolutely right. The problem is, from one part this star (if any) can be immersed in the shine of VdB 48, which is blue, therefore (the star) will be hardly detectable. From the other part, the image hasn't very good resolution. It was taken in bin x2, and the seeing wasn't that great. We can do another image of this region in x1 binning (and hoping for better seeing).
Do you think it will make sense imaging in OIII ?
We have also a diffraction grid with 200 lines per mm, thus we can get a low dispersion spectrum (not sure that the brightness of the object will permit this, but we can try). If we can detect an absorption in OIII, this will be a clue. What do you think about?
Thanks again for taking your time!
V. & E.

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Re: Uncatalogued planetary nebula (?)

Postby Ann » Thu Dec 29, 2016 3:04 pm

IO_12 wrote:Hi guys!
Many thanks for your comments, especially to Ann for her comprehensive analysis!
Yes, that about the central star is absolutely right. The problem is, from one part this star (if any) can be immersed in the shine of VdB 48, which is blue, therefore (the star) will be hardly detectable. From the other part, the image hasn't very good resolution. It was taken in bin x2, and the seeing wasn't that great. We can do another image of this region in x1 binning (and hoping for better seeing).
Do you think it will make sense imaging in OIII ?
We have also a diffraction grid with 200 lines per mm, thus we can get a low dispersion spectrum (not sure that the brightness of the object will permit this, but we can try). If we can detect an absorption in OIII, this will be a clue. What do you think about?
Thanks again for taking your time!
V. & E.


I think it is a very good idea to image this area in OIII. If the green-looking arc is indeed OIII emission, it will show up beautifully through an OIII filter.

I don't think you should search for the central PN star in blue light. As you said, the reflection nebula van den Bergh 48 scatters a lot of blue light across this region, and the star you're looking for is faint.

If at all possible, you should search for the central star in UV light. The reflection nebula is not going to be overwhelmingly bright in UV, but a white dwarf ionizing a planetary nebula should stand out like a sore thumb.

Ann
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Re: Uncatalogued planetary nebula (?)

Postby Chris Peterson » Thu Dec 29, 2016 3:09 pm

IO_12 wrote:Yes, that about the central star is absolutely right. The problem is, from one part this star (if any) can be immersed in the shine of VdB 48, which is blue, therefore (the star) will be hardly detectable. From the other part, the image hasn't very good resolution. It was taken in bin x2, and the seeing wasn't that great. We can do another image of this region in x1 binning (and hoping for better seeing).
Do you think it will make sense imaging in OIII ?

Do you have an instrument other than the astrograph you could use? What you need is two or three times the focal length, and no binning. If you could get your data at around 1"/pixel you'd have much more to work with, and better hope of detecting the central star. You could search the catalogs for an already identified blue star, or try subtracting your blue and green data to approximate a B-V value for candidate stars. For the nebula, I'd shoot the entire thing using Ha and OIII filters only (at the higher resolution, of course). Straight RGB isn't so useful for looking at emission structures.
Chris

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Re: Uncatalogued planetary nebula (?)

Postby neufer » Thu Dec 29, 2016 4:38 pm

Ann wrote:
IO_12 wrote:
Do you think it will make sense imaging in OIII ?
We have also a diffraction grid with 200 lines per mm, thus we can get a low dispersion spectrum (not sure that the brightness of the object will permit this, but we can try). If we can detect an absorption in OIII, this will be a clue. What do you think about?

I think it is a very good idea to image this area in OIII. If the green-looking arc is indeed OIII emission, it will show up beautifully through an OIII filter.

I agree. It resembles the Helix Nebula in size and thus should be brighter on the inside in OIII:

https://www.howardastro.org/halgal/main ... emId=19342
http://www.astrosurf.com/luxorion/Scien ... mar48i.jpg

Otherwise it is just a piece of the Orion Molecular Cloud Complex running into a reflection nebula.
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Re: Uncatalogued planetary nebula (?)

Postby starsurfer » Thu Dec 29, 2016 6:13 pm

IO_12 wrote:Hi guys!
Many thanks for your comments, especially to Ann for her comprehensive analysis!
Yes, that about the central star is absolutely right. The problem is, from one part this star (if any) can be immersed in the shine of VdB 48, which is blue, therefore (the star) will be hardly detectable. From the other part, the image hasn't very good resolution. It was taken in bin x2, and the seeing wasn't that great. We can do another image of this region in x1 binning (and hoping for better seeing).
Do you think it will make sense imaging in OIII ?
We have also a diffraction grid with 200 lines per mm, thus we can get a low dispersion spectrum (not sure that the brightness of the object will permit this, but we can try). If we can detect an absorption in OIII, this will be a clue. What do you think about?
Thanks again for taking your time!
V. & E.

Take an OIII image with an exposure of 1-3 hours. If anything shows up, at the very least it is an ionized nebula and not a reflection nebula.

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Re: Uncatalogued planetary nebula (?)

Postby IO_12 » Thu Dec 29, 2016 10:46 pm

Ann wrote:If at all possible, you should search for the central star in UV light. The reflection nebula is not going to be overwhelmingly bright in UV, but a white dwarf ionizing a planetary nebula should stand out like a sore thumb.

Yes, we have such filters and definitely will give a try.
Chris Peterson wrote:Do you have an instrument other than the astrograph you could use? What you need is two or three times the focal length, and no binning. If you could get your data at around 1"/pixel you'd have much more to work with, and better hope of detecting the central star. You could search the catalogs for an already identified blue star, or try subtracting your blue and green data to approximate a B-V value for candidate stars. For the nebula, I'd shoot the entire thing using Ha and OIII filters only (at the higher resolution, of course). Straight RGB isn't so useful for looking at emission structures.

The scope with the image was taken can get resolution of 1.7 arcsec/pixel, the other - 0.98arcsec/pixel. Changing the reducers/correctors we can acheive even better resolution, but since the telescopes are remotely controlled, we cannot do it right now. Good idea to search the catalogs for an already identified blue star! Thanks!
Ann wrote:I think it is a very good idea to image this area in OIII. If the green-looking arc is indeed OIII emission, it will show up beautifully through an OIII filter.

neufer wrote:I agree. It resembles the Helix Nebula in size and thus should be brighter on the inside in OIII:
https://www.howardastro.org/halgal/main ... emId=19342
http://www.astrosurf.com/luxorion/Scien ... mar48i.jpg
Otherwise it is just a piece of the Orion Molecular Cloud Complex running into a reflection nebula.

starsurfer wrote:
Take an OIII image with an exposure of 1-3 hours. If anything shows up, at the very least it is an ionized nebula and not a reflection nebula.

We are clouded up right now, but as soon as possible we'll take OIII images.
Thanks a lot to all of you. We'll keep you in touch.
V&E


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