Guest1 wrote:Hello. After studying this picture, I have found a curious green object in the upper middle of the picture. I don't know if this picture is a color enhanced photo or not. Anyway I was just wondering if anyone else noticed it.
The cluster image consists of a number of filtered images overlaid in artificial colours. This is the case with the majority of modern astronomical images. Here we have two visual filters, plus IR plus H-alpha. At full scale it shows a number of artefacts that I can't imagine are purely optical.
The colors in this picture are probably less "artificial" than the colors in many other astronomy images. The filters used for this picture are blue, green, H-alpha(red) and infrared. That is not far from how the human eye sees color, since we have receptors for blue, green and red light. We can be certain that the picture of NGC 3292 taken through the blue filter has been shown as blue, the "green-filter-image" has been shown as green, and the Ha and infrared-filter images have both been mapped as red. That's not too far from "reality".
I wasn't able to spot a green object in the upper middle of the picture, but it is true that one star, at about 8 o'clock, has a curious green halo around it. This is somewhat baffling, since the color of the star (HD 92121) is unremarkable, about +0.2. However, one thing sets this star apart from all the other bright stars in this image, and that is that HD 92121 belongs to spectral class A. All the other bright stars here are either bluer than spectral class A (spectral classes O and B) or redder than spectral class A (K and M). Since HD 92121 belongs to spectral class A its "energy distribution" will be different than the really hot and really cool stars here, and it will emit more of its energy in the form of green light. But surely there must be stars of spectral class A inside NGC 3293? Oh, absolutely, but the main sequence A-type stars are not so bright, and they don't have any obvious halos in this image. Chances are that HD 92121 may belong to NGC 3293, but if so it is probably an older and somewhat evolved member.
In any case the green halo is an artifact. HD 92121 has four well separated and distinct halos: a large green one, centered on the star, a smaller blue one moderately well centered on the star, a blue ring to the upper right, and a small, sharp red ring to the right of the star. The rings are very obvious artifacts, and the distinct green halo is, too.