Dubhe

[John]

I seem to recall that we have discussed Dubhe / Alpha Ursae Majoris sometime in the past ?

It is a double star and seems to be considered to be a really tough one to split. According to Stelle Doppie the brighter component is magnitude 2.02 and the fainter one magnitude 4.95. Add to that a separation of just .81 arc seconds and we have a challenge for most scopes I think 😬

Despite Dubhe being rather low tonight, the seeing was very steady so I had a look with my 130mm F/9.2 refractor. I was not hopeful of getting a clear split of this pair but I thought it might be possible to see some indications of elongation. I had not researched the position angle of the pair so I think I went into this with a reasonably open mind. 

I gradually ramped up the magnification through 300x, 400x and found a "sweet spot" image of the star tonight at 480x. I studied the star for a good 30 minutes and during the most settled moments of seeing I was consistently detecting a bulge on the side of the airy disk of the brighter star. Sometimes this took the form of a brightening / thickening at one point in the 1st diffraction ring. At other times more of a "lump" which appeared to be stuck on the side of the airy disk.

As I became more certain that I was seeing something over and over, I made a quick & dirty sketch of a heavily enlarged airy disk with the position of the lump / bulge shown. My estimated position angle for the centre of this "feature" was around 330 degrees or on the north west side of the main star.

Once the sketch was made I consulted the sources / references that I could find on the web (including the Stelle Doppie database) and found that my PA estimate was in the right ball park for the secondary star of the Dubhe pair. 

Not a split or resolution of course but perhaps a fair indication that this is indeed a very close double star.

I've included my very crude sketch below and would be interested to hear from anyone else who has observed Dubhe looking for this split and how they got on 🙂

I'm definitely coming back for more when the star is higher in the sky 👍

 

 

 

 

[Mr Spock]

Nice observation. I've not tried it yet. Should be a good target for the 12".

[RobertI]

Good catch John, perseverance paid off. 👍

[bosun21]

Will now be having a good look at Dubhe the next time I have the 12" out again. I didn't even know that Dubhe was indeed a double star.

[Nik271]

Well done, John! Your 130mm refractor seems a very impressive instrument. After many attempts last year I managed to spot the companion of Dubhe with a 180mm Skymax Pro Mak at x450 magnification. Dubhe was near the zenith at the time. Even with 180mm aperture it was tough, the secondary is on the first diffraction ring and is three magnitudes fainter.

The seeing was excellent last night, I just had fun with my Skymax 127, nothing very serious just some classic doubles and a quick look at the ring M57. Now I wish I had the big Mak out and tried something harder. Tonight also looks promising, the humidity is bad for deep sky but  doubles tend to look good on muggy nights. 

[lunator]

Hi John very well done. The Dawes limit on your scope would be around 0.9 so a brightening on the first ring sounds about right. 

I haven't tried for B component but it is something I should put on my to do list. :).

I have found for close pairs that for a magnitude difference of around 2 you can get pretty close to the Dawes limit. This pair has a delta M of ~3 so I think you were pretty close to the limit of what is achievable.

Cheers

Ian

[Franklin]

Sub-arcsecond pairs are out of the range of my scopes but if you have enough aperture it's worth a try, though the seeing will play a major role in success.

@John your observation reports are, as always, an inspiration👍.

[lunator]

I've has a quick look at the orbit and it is at apastron in 2023. It is at 0.819" and will begin to close later this year.. The orbit is graded 2 so is pretty good. 

Cheers

Ian

[Mr Magoo]

On 10/08/2023 at 16:23, Nik271 said:

Well done, John! Your 130mm refractor seems a very impressive instrument. After many attempts last year I managed to spot the companion of Dubhe with a 180mm Skymax Pro Mak at x450 magnification. Dubhe was near the zenith at the time. Even with 180mm aperture it was tough, the secondary is on the first diffraction ring and is three magnitudes fainter.

This gives me encouragement to try for Dubhe with my 178mm Intes Micro Mak. It's a double I've not considered before now.

[Neil_104]

On 10/08/2023 at 01:26, John said:

would be interested to hear from anyone else who has observed Dubhe looking for this split and how they got on

Bear with me and I'll check it out in my 60mm next time I'm out 😂

Enjoyed your report, it's always fun going on little adventures like this 👍

[Mr Magoo]

14 hours ago, Neil_104 said:

Enjoyed your report, it's always fun going on little adventures like this 👍

Agreed. I'm looking for inspiration in my observing. On a recent overnight excursion to observe some Perseid meteors, I spent most of the night asleep! I Didn't even unpack my scope. Lack of observation planning came into it, there was no list of interesting, or challenging targets.

I did see one impressive fireball streak across the sky for some distance, that alone reminds why I do this. Out of this world!

 

[Neil_104]

4 hours ago, Mr Magoo said:

I did see one impressive fireball streak across the sky for some distance, that alone reminds why I do this. Out of this world!

Nice! You saw more than me - totally clouded out. At one point I was out putting something in the bins, and there was a gap in the clouds. I followed that gap from the North west to the South east hoping to see something, but nothing. 

[Gonariu]

Nice result, a double resolution start.

[chiltonstar]

On 11/08/2023 at 20:34, Mr Magoo said:

This gives me encouragement to try for Dubhe with my 178mm Intes Micro Mak. It's a double I've not considered before now.

Certainly splits with my 180 Mak. The secondary touches the 1st diff ring, but if the seeing is good, it can be seen as a separate disk (see other posts here re Dubhe).

Chris

[Mr Magoo]

6 minutes ago, chiltonstar said:

Certainly splits with my 180 Mak. The secondary touches the 1st diff ring, but if the seeing is good, it can be seen as a separate disk (see other posts here re Dubhe).

I will try tomorrow evening or Wednesday.  Here in the South the forecast is clear sky and low winds for a few nights. With a new Moon conditions for observing look to be very good.