Dubhe - another really tough one !

[John]

Dubhe / Alpha Ursa Majoris seems to be another double star that comes into the "very hard" category I think. Maybe easier than Procyon though ?

According to the Stella Doppie database, the current split is .81 arc seconds and the A + B components are magnitude 2.02 and 4.95 respectively so a significant brightness difference to add to the challenge. There is a magnitude 7 C component at 370 arc seconds separation as well.

Last time I tried it was with my 130mm refractor and I thought that I might be seeing indications of the B star but it was very vague and pressed right up against the airy disk of the A star - inside the diffraction ring. 

I have recently washed the primary mirror of my 12 inch dob so I'm hoping that will give be a better chance with this one, if the clouds ever clear that is

 

[Mr Spock]

I think this might be a good one for my 250mm. Another one I've not seen, so, added to my list 

[iapa]

1 hour ago, John said:

Dubhe / Alpha Ursa Majoris seems to be another double star that comes into the "very hard" category I think. Maybe easier than Procyon though ?

According to the Stella Doppie database, the current split is .81 arc seconds and the A + B components are magnitude 2.02 and 4.95 respectively so a significant brightness difference to add to the challenge. There is a magnitude 7 C component at 370 arc seconds separation as well.

Last time I tried it was with my 130mm refractor and I thought that I might be seeing indications of the B star but it was very vague and pressed right up against the airy disk of the A star - inside the diffraction ring. 

I have recently washed the primary mirror of my 12 inch dob so I'm hoping that will give be a better chance with this one, if the clouds ever clear that is

 

If you want to push things further, then, according to Sky and Telescope, there is a 4th component.

https://skyandtelescope.org/astronomy-news/meet-dubhe-giant-star-big-dipper/

 

 

[Nik271]

6 hours ago, John said:

Dubhe / Alpha Ursa Majoris seems to be another double star that comes into the "very hard" category I think. Maybe easier than Procyon though ?

According to the Stella Doppie database, the current split is .81 arc seconds and the A + B components are magnitude 2.02 and 4.95 respectively so a significant brightness difference to add to the challenge. There is a magnitude 7 C component at 370 arc seconds separation as well.

Last time I tried it was with my 130mm refractor and I thought that I might be seeing indications of the B star but it was very vague and pressed right up against the airy disk of the A star - inside the diffraction ring. 

I have recently washed the primary mirror of my 12 inch dob so I'm hoping that will give be a better chance with this one, if the clouds ever clear that is

 

I've been waiting for Dubhe to be  higher in the sky to give it a serious try with my 180 Skymax. These days  Dunhe is almost directly overhead in the early hours of the morning,and  hopefully this weekend there will be some clear sky to give it a shot. 

[Nik271]

I tried Dubhe early in the moring, both yesterday and today but the seeing was very poor. Yesterday was a bit better and I think I saw some disturbance in the diffraction rings north at x350 but very far from a sure split. Hoping for a steady still night once this weather front passes. I started to leave the telescope out overnight covered under BBQ cover so it's ready to go at 6am.

Edited November 22, 2021 by Nik271

[markse68]

I’ve given up on Dubhe for this year. It’ll be better positioned in February so i’ll try again then 🤞

Mark

[lunator]

I have never split this but it is one I should try a bit harder with 😉

I have a look through my spreadsheet and the nearest comparable split I have is with STF2900.

At the time it was ~0.7" and the delta M was about 3.

The pair are much fainter than Dubhe. It took x450 mag to split. So I think Dubhe may take something similar.

Cheers

Ian

[Mr Spock]

The magnitude difference make the difference in splitting close pairs like this. In the C9.25 an 0.7" equal pair was an easy split; I expect Dubhe to be a lot more difficult. Challenge accepted!

[John]

Although the seeing was quite good last night and the primary star well defined I could not get any indications of Dubhe B with my ED120 refractor last night even at 300x plus.

Theta Aurigae A & B on the other hand (and a much easier pair) was beautifully split by the scope at 300x. The 2 fainter and further off stars in the group showed well too.

 

Edited November 23, 2021 by John

[Mr Spock]

I'll get those in a couple of month's time. I'm limited to south to west from my patio 

[Nik271]

I managed to spot Dubhe's secondary this morning with my Skymax 180 at x450 magnification 🙂

Last night the seeing was OK but nothing special so I didn't even plan for anything difficult. In the morning however it was very still and a bit misty, a good sign.

Luckily I didn't dismantle the scope last night, just capped and covered it on the mount with a BBQ cover and the corrector plate stayed dry and clear.

Dubhe was quite high in the northern sky at 7am and it was still dark. This was as good a chance as ever so I went directly for the 6mm EP giving x450. The seeing was good, but not the best. The diffraction pattern of the orange primary was shimmering a bit, there were moments of stillness and in these I could  see a  faint bump on the first diffraction ring. I noted the position as north west and stayed at the scope for half an hour waiting in moments of clarity. The bump kept appearing and disappearing, always in the same position. It was also noticeable at x340 with the 8mm Starguider. I would not call this a clean split since I didn't see a well defined secondary airy disc, just a dim hump on the diffraction ring. I checked with stelle doppie and PA is 330 degrees which tallies with my observation. I'm very happy about this one, it was one of my 'bucket list' doubles. I'm very confident that in better seeing this double is doable with even smaller aperture. Not my 127 Mak perhaps but certainly a 5 inch refractor or above should show it. The separation is about  0.8'' and stays like this for several more years.

Clear skies!

Nik

 

[John]

Great going Nik

I forgot to try Dubhe when I had my 12 inch scope out the night before last

 

 

[chiltonstar]

I've managed a split a couple of times now with my 180 Mak at x375 and x450. The secondary appears as a slightly distorted blob on the first diff ring of the primary, and with dark space so it is actually split. Not an easy one though, needs excellent seeing.

Chris

[Nik271]

1 hour ago, chiltonstar said:

I've managed a split a couple of times now with my 180 Mak at x375 and x450. The secondary appears as a slightly distorted blob on the first diff ring of the primary, and with dark space so it is actually split. Not an easy one though, needs excellent seeing.

Chris

Great results, Chris! I still have to have a clear split of the secondary. Obstructed scopes like the Mak suffer from poor seeing more: the first diffraction ring keeps shifting and pulsing, so to split anything on the diffraction limit of the scope requires a very good seeing condition indeed.

[chiltonstar]

Yes, agreed. At their best in good seeing, Maks can be truly "refractor like" but if the seeing is poor or the scope not equilibrated, the view is less good. However, I have found that sometimes going to a higher mag just shows the Airy disks without the diffraction mess which is of course fainter.

The main point being I suppose that most of us could not afford or lift a 7" frac with a 2.7 m focal length.

Chris