APOD: Stars and Dust in Corona Australis (2015 Jan 08)

[Ann]

I'm clearly rubbish at spotting things in some APOD images as I cannot definitely see two presumably separate blue reflection nebulae NGC 6726 and 6727 that are marked in the labelled version of the wider field-of-view image as NGC 6726-7 that is brought up through the 'NGC 6726, 6727, and IC 4812' link in the explanation to the APOD (and also through the CHART32 website link in the credit). It all looks like only one nebula to me

In the labelled image it marks Bernes 157 of which in the CHART32 website it states "Bernes 157, a boomerang -shaped dark nebula partly seen in the bottom left corner is 520 light years distant. It stretches around the Corona Australis Nebula like a huge, draping black scarf". Even knowing that I still don't see it and if it had not been mentioned I would never have given the area marked as Bernes 157 a second glance!

In this image from www.spiegelteam.de you can see what I believe is NGC 6726 and NGC 6727. These two nebulas are simply the brightest, rather white-looking parts of the reflection nebulas surrounding the two embedded stars. I believe NGC 6726 is to the lower right, and NGC 6226 is to the upper left.

As for Bernes 157, this (unfortunately large, 678kb) labelled image by Martin Pugh shows this dark nebula a bit more clearly.

I find it interesting that the two stars HD 176269 and HD 176270, that I talked so much about earlier in this thread, are called a double star in Martin Pugh's image. The double star even has its own name, BRS 014.

Ann

[Nitpicker]

I find it interesting that the two stars HD 176269 and HD 176270, that I talked so much about earlier in this thread, are called a double star in Martin Pugh's image. The double star even has its own name, BRS 014.

Double stars are so called because they appear close together to us. But they might not be gravitationally bound. They might just be a chance alignment from the position of Earth, as suggested by the HIP catalogue, which would make them an optical double. But if the HIP parallax angles are not reliable in this case, then it might be a binary system.

[JuanAustin]

Thank you Nitpicker!

[DavidLeodis]

Thank you Ann for your helpful reply to my post .

[starsurfer]

I'm clearly rubbish at spotting things in some APOD images as I cannot definitely see two presumably separate blue reflection nebulae NGC 6726 and 6727 that are marked in the labelled version of the wider field-of-view image as NGC 6726-7 that is brought up through the 'NGC 6726, 6727, and IC 4812' link in the explanation to the APOD (and also through the CHART32 website link in the credit). It all looks like only one nebula to me

I think this is an instance of the same object being catalogued twice in the NGC and given two separate catalogue numbers. You also have to remember that nearly all the objects in the NGC were discovered through visual observation. I don't know the 19th century history of this area but it might have been observed as two bright separate patches whereas a modern photograph shows it as one large nebula.
Other objects that have two NGC numbers include the galaxy NGC 1344 (also NGC 1340), the galaxy NGC 4517 (also NGC 4437) and the galaxy NGC 1291 (also NGC 1269) to name a few examples.

[DavidLeodis]

Thanks for that explanation starsurfer .