Sigma Orionis

rcheshire (Rowland) · #1 04-01-2011, 08:49 PM

Comparison of wide field images (Flame Nebula to M42), over two nights, (edit: 29th Dec and 1st and 2nd Jan) (ongoing project), the lens (200mm f/2.8L II) was able to resolve the binary stars.

Crops showing the location of Sigma Ori (upper right corner), and the star system on separate nights. The movement of the Sigma Ori companion star is evident, and one of the pair upper most left from Sigma Ori, or so it appears.

edit: added a screenshot from stellarium.

Geoff45 (Geoff) · #2 04-01-2011, 09:10 PM

Interesting. I suspect it's a random--perhaps an asteroid.

OICURMT · #3 04-01-2011, 11:08 PM

I agree with Geoff... asteroid is the most likely, as the SigOri main pair have an orbital period of 170 years. Alternatively, could be turbulence.

OIC!

rcheshire (Rowland) · #4 05-01-2011, 06:37 AM

Thanks. I've not had much time to research this, but I am aware of the rotational period. The only reference I could find is this, that comes anywhere close to the difference over a day.

http://www.astro.wisc.edu/~townsend/

I'll have another look over the images to see if there is any difference. The posts are composites of each nights viewing.

hotspur (Chris) · #5 05-01-2011, 07:38 AM

Great work,well done,is the horse head neb in pic one?

Cheers Chris

rcheshire (Rowland) · #6 05-01-2011, 09:07 AM

Hi Chris. Early days yet. Still more data to get and improve on the technique.

Addressing the other issue. I stand corrected - short term memory loss assw aging

- images were taken 29th Dec, 1st and 2nd Jan.

I audited the image collection - there are over 200 in the set with different exposure times - selecting images at random from each subset and did not find the 'artefacts' in the images shown in post 1. I then viewed each subset integration and found no anomolies. I think this is a processing artefact.

EDIT: Looking at the first nights image, there is no evidence of the artefact. It seems to have been introduced when integrating the images from the second and third night with those of the first.

rcheshire (Rowland) · #7 05-01-2011, 12:41 PM

I've narrowed the issue down to 3 sets of images that probably have inadequate SNR to process adequately - alignment of the images appears problematic evidenced by the pixel rejection maps, showing misalignment. Mixed with the image sets at large, these shorter exposure images would not align.

I think mixing the images one night from the other might be the problem. A better technique would be to combine similar image sets and then integrate together.

So, those stars that appeared out of nowhere are misaligned. Closer inspection of the image concerned shows the same all over - but I didn't pick it up at first. Lesson learned.

Possibly this should be in the beginners section as it seems no longer relevant to this forum.

rcheshire (Rowland) · #8 06-01-2011, 06:20 AM

May be this should be moved to the beginners section. May as well finalise this for info.

Anyway. The offending images were throughout the 10 and 15 second sets.

Basically, during the image run on the first night I tried different f/stops, down to 6.3 the difference in SNR was significant as should be expected, but I didn't anticipate the problems assw processing.

I have settled on f/5.6 as a good setting, although 6.3 and longer exposure time gives nice sharp stars - even at 5.6 a little bloating begins to show after 30 seconds.