Sunday, April 24, 2016

researched Arrakis

Did a deeper dive into μ (mu) Draconis (or Alrakis or Arrakis) in an attempt to figure out what's going on. A key issue for me is that I have not been able to, after a few attempts, to spot the C star.

Checked the info in the Washington Double Star database. The AB and AC data is very similar to the numbers I'm seeing in SkyTools 3 Professional. Both show the magnitude is around 13 to 14. Quite doable in many of the instruments that I have access to. The position angle and separation values, again, are very consistent. The dim C star should be south of the AB pair, opposite B, but well away, 4 or 5 times the distance of AB.

Viewed on 3 Aug 2009. That appears to be the first ever. But then, I was only going after the AB pair, from the Sky & Tel list. Probably did not even know there was a C then... (didn't have SkyTools that summer). Viewed on 31 May 2014, 6 Jul 2014, and on 17 Apr 2016. Never spotted the C.

The WDS has a very strange entry by Burnham for the BC pairing.

date:    1889    1958
theta (PA) °:    191    186
rho (sep.) ":    12.3    13.6

That makes no sense at all. I visually checked the numbers using Visio.

diagram showing angles between A, B, C stars

The dashed lines are the first observations (some of which are over 200 years old). The solid lines should be the current (or recent) positions and distances. The lower 2 lines are for the BC entry, that is, the PA and sep between B and C. Clearly the angle and separation are wrong/different. Finally, I loaded in the screen snapshot from SkyTools and pushed it to the background. The dots above the A and B labels along with the C near the top-left indicate how the ST3P software is plotting the star positions. Again, not too far off. I made no attempt to scale the snap to the diagram. Regardless, the PA for A and B looks spot-on.

[ed: Could it be that Burnham was looking at A and C?! The separation values are very consistent although the angles are different.]

I also the checked Aladin image and SIMBAD data. The AC pair angle looks very good. B looks like it is OK in terms of separation but the angle is different—B is more counter-clockwise than in the graphic above. Still, quite good correspondence. Sadly, the Aladin image is not useful visually as the A and B stars overwhelmed the sensor.

Wonder if I should image this area...




Tried again visually to spot C on the evening of 3 July with a big Dob... No joy.

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