Wednesday, June 03, 2020

freebie double

On the forum, after my double star post, Chris asked:
Can you post what you consider to be Delta Draconis’ secondary?  Is it the red star a couple of arc-minutes from Altais, or a faint star that’s much tougher to see?
I dig a bit of digging and shared my findings.

Lots of alternate designations: Altais, Nodus Secundus, 57 Dra, BUP 186, SAO 18222, or HIP 94376.

The separation is a whopping 87.7". That datum from SkyTools 3 (and dated 1914 curiously). ST3 only notes it as a two-star system.

From my life list (doubles page 1 of 2): Simple double. Very bright, yellow component with the dim nearby white star to the north. In a lovely, busy field.

Checked Stelle Doppie for BUP 186: It reports a “triple system.”

AB, 342°, 81.0", 3.17, 12.58
AC, 22°, 135.4", 3.07, 12.00

So, again B is 80+ arc-seconds from A. C is further out, about 50% further. B is dim with a mag between 12 and 13. C is a smidgen brighter. B is almost due north while C is near a 45 degree angle from the AB line.

I imaged delta Dra on 21 Jul '17 while collecting data on SLE 235.

double star delta Draconis

North is up, east is left.

In the image, B is the nearest medium bright star, slightly right of north.

I found that C is up and left, slightly brighter than B.

Begs the question why the star to the right, same intensity as B, about the same separation as C, is not considered part of the system…

So, thanks, Chris. You just helped me “split” another star!


All of this was interesting. I learned the Altais is officially a triple in the Washington Double Star catalogue and that, happily, I had captured the third star in my imaging run. Added a new row to the the life list.

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