NGC 4250 is a ring galaxy - new discovery?

[gorann]

3 hours ago, tomato said:

Interesting, the HST image doesn’t look much like it, the star near the centre in Goran’s and the sky survey images doesn’t appear to be there?

Yes, I think even more stars are missing from the HST image - odd!

[Shibby]

Yep, it looks like the star forming regions are concentrated in the outer parts of the spiral arms, which might explain why @gorann's dual-band image (and one of the Hubble images) produces a ring-like appearance.

[symmetal]

2 hours ago, gorann said:

Actually, I found that the "dark ring" is a visual illusion from the bright centre. I used the eyedropper tool in PS and measured the brightness in the dark ring and in the surrounding sky and they are the same.

Interesting. When I said some other features in the image had dark rings too, this was likely an illusion as well. 🙂

Alan

[ONIKKINEN]

Just to sate my curiosity i took to the hubble archive and sorted through the available datasets. Only one wide enough to show the outer regions, and this one is in F300W filter, so near ultraviolet. Just binned it x3 and a really hard stretch to show anything, but there is signal pretty much in the same place as in Göran's image. Being ultraviolet i assume it must be from young stars in the presumed spiral arms producing that? Hard to tell even from this dataset whether its a hollow ring or a spiral arm, but i am leaning towards spiral arms as they do appear to turn inwards a little bit at the corners.

[gorann]

1 hour ago, ONIKKINEN said:

Just to sate my curiosity i took to the hubble archive and sorted through the available datasets. Only one wide enough to show the outer regions, and this one is in F300W filter, so near ultraviolet. Just binned it x3 and a really hard stretch to show anything, but there is signal pretty much in the same place as in Göran's image. Being ultraviolet i assume it must be from young stars in the presumed spiral arms producing that? Hard to tell even from this dataset whether its a hollow ring or a spiral arm, but i am leaning towards spiral arms as they do appear to turn inwards a little bit at the corners.

It is hard to believe that this is actually the same galaxy. It is both lacking the stars and the distinctly oval core seen in my image. Maybe it is the Earth atmosphere that makes my stars much bigger and therefore more obvious.

[wimvb]

1 hour ago, gorann said:

It is hard to believe that this is actually the same galaxy. It is both lacking the stars and the distinctly oval core seen in my image. Maybe it is the Earth atmosphere that makes my stars much bigger and therefore more obvious.

That's why I made my previous comment about having difficulties interpreting the hst image. But I guess you know my standard reply to this, Göran: we need more data . In this case broadband and luminance data.

[ONIKKINEN]

2 hours ago, gorann said:

It is hard to believe that this is actually the same galaxy. It is both lacking the stars and the distinctly oval core seen in my image. Maybe it is the Earth atmosphere that makes my stars much bigger and therefore more obvious.

Hard to compare, since the hubble one is a very short 1000 second shot with ultraviolet. The brightest parts are from young hot stars in star forming regions, other calmer and cooler parts (most of the galaxy) wouldnt show up in this short exposure.

[gorann]

4 hours ago, ONIKKINEN said:

Hard to compare, since the hubble one is a very short 1000 second shot with ultraviolet. The brightest parts are from young hot stars in star forming regions, other calmer and cooler parts (most of the galaxy) wouldnt show up in this short exposure.

Thanks, and yes, of course a short UV shot is something quite different. Also, have a look at this thread which is now focusing on NGC4250 after I posted also there: