15 replies to this topic

[Irido]

While looking through the Digitized Sky Survey, I saw a tiny hint of what looked like HII. It was invisible with a linear stretch applied to the survey image. With a hyperbolic arcsine stretch applied and the image brightness turned up, a small "blob" of what looks to be HII appears, about 5' by 5' in angular size. It's in the constellation Cepheus at 22 44 51.350 +60 49 03.41 (J2000). The star in the middle of the attached image is HD 215575 (I haven't been able to tell if it's just co-located with the HII region or if it's actually inside it.)

 

I initially thought this object was quite probably catalogued, so I checked SIMBAD and the VizieR databases. Nothing turned up. I searched the Sharpless catalog, as it's intended to be a comprehensive survey of all HII regions north of -27 degrees declination. While there are several Sharpless objects in the region, including one only about a degree south, this object is not in the Sharpless catalog. I searched for any references of an HII region/any nebula near HD 215575, and nothing turned up. I looked at all the papers that SIMBAD stated referenced HD 215575, and there was no mention of this HII region. 

 

I am somewhat doubtful that this region is truly undiscovered, on account of its size and brightness. I would have thought that it would be in the Sharpless catalog. Perhaps it is just part of another HII region, a part that just happens to be centered around HD 215575. Still, I am unable to find any reference to this object. Any help in tracking it down, or in determining if it truly is uncatalogued, would be appreciated.

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Edited by Irido, 05 December 2024 - 02:04 AM.

[Jiashuo Zhang]

This seems to be a very interesting target.

There are no known nebulae or HII regions listed near HD 215575.

The WISE image confirms that this object is real and quite extensive. I believe there may be a close relationship between this region and HD 215575, so whether this target is part of the nearby Sharpless catalog object needs further evaluation. At the same time, I haven't found any records of HII regions near HD 215575.

 

Perhaps for cases like this, Deep Sky Hunters (DSH, https://groups.io/g/deepskyhunters) would be a good choice. I believe friends like Victor would further investigate this location. 

[Irido]

This seems to be a very interesting target.

There are no known nebulae or HII regions listed near HD 215575.

The WISE image confirms that this object is real and quite extensive. I believe there may be a close relationship between this region and HD 215575, so whether this target is part of the nearby Sharpless catalog object needs further evaluation. At the same time, I haven't found any records of HII regions near HD 215575.

 

Perhaps for cases like this, Deep Sky Hunters (DSH, https://groups.io/g/deepskyhunters) would be a good choice. I believe friends like Victor would further investigate this location. 

 

Yes, I checked ALLWISE as well, which seemed to show some IR-emitting nebulosity around HD 215575. When I first viewed HD 215575 in the Pan-STARRS data, it almost appeared as though it had a small reflection nebula near it, though it is quite difficult to tell. This object I've found is certainly quite interesting---if it turns out to be novel, I will probably rent some time on a large remote telescope to image it better. (Unless any of you all would be interested in helping!)

Edited by Irido, 05 December 2024 - 02:05 AM.

[Bob4BVM]

Possibly an IFN, like around M31 area ?

[twoc]

Very nice find! I downloaded some IPHAS data and indeed you can see the Ha nebulosity around HD 215575 well. I couldn't find any reference to it in the optical. In VizieR there are two catalogues listing it as a star-forming region from IR survey data, if you do a 30" radius search around 22:44:54.62 +60:48:55.6 and ctrl+f page search 'star-forming' they should show up.

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[Irido]

Very nice find! I downloaded some IPHAS data and indeed you can see the Ha nebulosity around HD 215575 well. I couldn't find any reference to it in the optical. In VizieR there are two catalogues listing it as a star-forming region from IR survey data, if you do a 30" radius search around 22:44:54.62 +60:48:55.6 and ctrl+f page search 'star-forming' they should show up.

Interesting. Those star-forming regions seem to be tagged everywhere though. Is that process largely automated (like the cataloguing of stars), or is it human-reviewed?

[twoc]

Interesting. Those star-forming regions seem to be tagged everywhere though. Is that process largely automated (like the cataloguing of stars), or is it human-reviewed?

Yeah it's largely automated and by no means a detailed study of one object. Looks like the data comes from IRAS, as well as radio observations of the water maser and CO lines. Two independent kinematic distances from CO observations put it at 0.83kpc and 0.63kpc, meanwhile the GAIA distance to HD 215575 is 0.76 kpc so it very likely is the ionizing source.

[Irido]

Yeah it's largely automated and by no means a detailed study of one object. Looks like the data comes from IRAS, as well as radio observations of the water maser and CO lines. Two independent kinematic distances from CO observations put it at 0.83kpc and 0.63kpc, meanwhile the GAIA distance to HD 215575 is 0.76 kpc so it very likely is the ionizing source.

Beat me to it! Should have checked CO. Not particularly surprising to see that it's likely the ionizing source, given its location, but it's good to have more concrete evidence of it.

Edited by Irido, 05 December 2024 - 01:59 AM.

[Irido]

Beat me to it! Should have checked CO. Not particularly surprising to see that it's likely the ionizing source, given its location/spectral type/luminosity, but it's good to have more concrete evidence of it.

Actually, I'm not so sure I'd jump to that conclusion. I was a little "weirded out" by the apparent size of the H II region relative to the luminosity of HD 215575, so I did some quick napkin math. It seems to suggest that the Stromgen sphere for a type B8e star with its absolute magnitude should be about 100 times smaller than the nebula, which is approximately 1.5 parsecs in diameter. I'm thus a bit skeptical that HD 215575 really is the sole ionization source. It's totally possible that I'm missing something, but I haven't been able to figure out what that could be.

Edited by Irido, 05 December 2024 - 01:59 AM.

[Irido]

Actually, I'm not so sure I'd jump to that conclusion. I was a little "weirded out" by the apparent size of the H II region relative to the luminosity of HD 215575, so I did some quick napkin math. It seems to suggest that the Stromgen sphere for a type B8e star with its absolute magnitude should be about 100 times smaller than the nebula, which is approximately 1.5 parsecs in diameter. I'm thus a bit skeptical that HD 215575 really is the sole ionization source. It's totally possible that I'm missing something, but I haven't been able to figure out what that could be.

Checked some of my assumptions and re-did the math better, hopefully it's all correct (I think I dropped a zero or two somewhere). If I assume a density of hydrogen of about 100 atoms per cubic centimeter that uniformly surrounds HD 215575, the Stromgren sphere is about 1.1 parsec across, nearly identical to the diameter of the nebula. It seems reasonable to suggest that it is the ionization source after all.

Edited by Irido, 05 December 2024 - 10:36 PM.

[twoc]

Checked some of my assumptions and re-did the math better, hopefully it's all correct (I think I dropped a zero or two somewhere). If I assume a density of hydrogen of about 100 atoms per cubic centimeter that uniformly surrounds HD 215575, the Stromgren sphere is about 1.1 parsec across, nearly identical to the diameter of the nebula. It seems reasonable to suggest that it is the ionization source after all.

Guess there are always things like stellar winds and non-uniform density that can result in a difference from the static Stromgren model. I was only going off circumstantial evidence / gut feeling (HII region with a hot star at the structure centre, well agreeing CO kinematic and star distances). Recent StarHorse2 and SHBoost temperature estimates from E/DR3 data are around 17000K so perhaps the spectral type is earlier than B8. There are similar HII regions nearby like Sh2-141,165,166,169 so would be interesting how well the model works with those also. 

The attachment shows the location of HD215575 from the wonderful interactive galaxy map https://gruze.org/dr3_app/. It appears to be in the vicinity of Cep OB3, slightly closer to us than the cave nebula.

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[Irido]

Guess there are always things like stellar winds and non-uniform density that can result in a difference from the static Stromgren model. I was only going off circumstantial evidence / gut feeling (HII region with a hot star at the structure centre, well agreeing CO kinematic and star distances). Recent StarHorse2 and SHBoost temperature estimates from E/DR3 data are around 17000K so perhaps the spectral type is earlier than B8. There are similar HII regions nearby like Sh2-141,165,166,169 so would be interesting how well the model works with those also. 

The attachment shows the location of HD215575 from the wonderful interactive galaxy map https://gruze.org/dr3_app/. It appears to be in the vicinity of Cep OB3, slightly closer to us than the cave nebula.

That is hotter than typical for a B8 star, and only strengthens the idea that it's the ionizing source. I really want to get a better look at the nebula itself, but its surface brightness is exceedingly low, it has to be under something ridiculous like 25 mag/arcsec². My biggest scope is a Super C8 Plus on its original Byers drive mount , so I'm not going to be able to image it myself. I was considering renting a remote scope but they're crazy expensive. Any advice on how to get this thing imaged? I don't think most astrophotographers take requests.

[twoc]

That is hotter than typical for a B8 star, and only strengthens the idea that it's the ionizing source. I really want to get a better look at the nebula itself, but its surface brightness is exceedingly low, it has to be under something ridiculous like 25 mag/arcsec². My biggest scope is a Super C8 Plus on its original Byers drive mount , so I'm not going to be able to image it myself. I was considering renting a remote scope but they're crazy expensive. Any advice on how to get this thing imaged? I don't think most astrophotographers take requests.

I had a look on Astrobin and Gary Imm has a lovely image of the area with the nebula appearing at the bottom right https://app.astrobin.com/i/2thrlh. Funny to read that he also could not find an ID for it. With all the clouds and light pollution I have I don't think I will get round to imaging this any time soon, though if I do I will let you know. Not too sure what else to suggest other than asking people. It will be there for as long as we are around so perhaps it will be a rewarding future target for you after some upgrades.

[Irido]

I had a look on Astrobin and Gary Imm has a lovely image of the area with the nebula appearing at the bottom right https://app.astrobin.com/i/2thrlh. Funny to read that he also could not find an ID for it. With all the clouds and light pollution I have I don't think I will get round to imaging this any time soon, though if I do I will let you know. Not too sure what else to suggest other than asking people. It will be there for as long as we are around so perhaps it will be a rewarding future target for you after some upgrades.

Cool to find a good image of it! A little sad that I got scooped by roughly 10 months on the discovery; looks like I won't be adding this to my catalog! At the same time, it's quite large, so I suppose this is expected.

Edited by Irido, 07 December 2024 - 01:33 AM.

[Bob4BVM]

Looks like classic IFNs to me. They are all over the place, extremely faint and extended, very easily (usually ) overlooked. Here's a small sampling:

 

https://www.cloudyni...n#entry13824538

 

CS
Bob

[Jiashuo Zhang]

That is hotter than typical for a B8 star, and only strengthens the idea that it's the ionizing source. I really want to get a better look at the nebula itself, but its surface brightness is exceedingly low, it has to be under something ridiculous like 25 mag/arcsec². My biggest scope is a Super C8 Plus on its original Byers drive mount , so I'm not going to be able to image it myself. I was considering renting a remote scope but they're crazy expensive. Any advice on how to get this thing imaged? I don't think most astrophotographers take requests.

After a brief discussion, I added this target to our group's observation list.

To ensure there is no moonlight interference, we will photograph it at the end of the month. Although we still have observation plans for some asteroids, variable stars, and other objects, I think allocating some time to this interesting target is a very engaging thing to do.