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Gemini Doubles

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#1 WRAK

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Posted 31 January 2013 - 07:38 AM

As Gemini stands high now I have made a list of doubles selected from the WDS catalogue per 05/2012 with separations between 0.6 and 10 arcseconds sorted by suggested apertures for resolution with refractor scopes and mild light pollution with NEML +4.5mag.
Any positive or negative observation reports on any of these doubles with apertures around the suggested value would be highly appreciated.
Wilfried
PS: Beware - there are several Jonckheere doubles on the list with most probably wrong magnitudes

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#2 R Botero

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Posted 31 January 2013 - 09:25 AM

Thank you for posting this. I have taken the liberty of creating a SkySafari list for those stars visible in apertures of up to 175mm. See the attached.

Thanks again! :ooo:

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#3 WRAK

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Posted 31 January 2013 - 11:47 AM

Great. Just for info: SkySafari shows only objects existing in its own data base, so may be not all doubles on the list will be available in SkySafari.
Wilfried

#4 R Botero

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Posted 31 January 2013 - 01:52 PM

You are right Wilfried. The Pro version has the whole WDS catalog as I understand. Also only the Pro and below version allow the user to create and import lists.

Your list is nevertheless a nice observation project regardless of the format!
:jump:

#5 fred1871

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Posted 31 January 2013 - 09:17 PM

Wilfried, likewise my thanks for your list. Given my southern latitude, I'll tend to work on the more southerly parts of Gemini, so as to keep stars a useful altitude above the horizon.

I'm inclined to think the later part of the list too optimistic, especially the fainter objects that are also close, which make up a lot of the above 200mm part of the list.

You'll notice a high proportion of TDS doubles there - and while a few of them were no doubt closer during the northern sky surveys, I suspect some were missed by Aitken (36-inch) and Couteau (30-inch) in their surveys. Because they're very very difficult and even with large scopes might not show readily. Tycho got them because there's no atmosphere limitation in space.

Quite a few of them fit the numbers for tougher doubles found by Aitken and Couteau in the north, and by Rossiter (26.5-inch refractor) in the south.

To go back to Lewis's listings, which I extracted some details from in another thread - Doolittle (18-inch) averages 1.0" at mags 9.6 and 10.1; Hough (18.5-inch) averages 0.9" at mags 9.6 and 10.0.

I'm also inclined to accept the reality of Couteau's 10th magnitude barrier. Yes, a few observers (including Couteau) sometimes breach it, but that's typically with 'scopes in the 26-inch to 36-inch range. I can't see it happening as readily with scopes around 10-inch (240-269mm). As said above - Tycho is not atmosphere limited, and the basis of Couteau's barrier effect is atmospheric seeing, as his description makes clear.

And my own observing experience in the past, when I had a good number of nights with a C14 with good optics, makes me doubt seeing pairs with a ~10-inch such as HEI 50 (mags 10.9 and 11.7 at 0.7") or TDS 4196 (mags 10.95 and 11.25 at 0.6").

I suspect most observers with typical sizes of telescope will find they do better on the somewhat brighter uneven pairs (when conditions allow) than on the very close and quite faint pairs.

One comparison that I noticed. HO 250 is listed for 224mm, mags 7.32 and 9.46 at 0.7". I'd expect to see this one double with less aperture, quite likely it'd be double, though not a clean split, with the 180mm refractor I've used. Near it is TDS 4625, listed for 236mm aperture - mags 10.7 and 11.0 at 0.7" also. That's not one I'd expect to see split with the 180mm; and I'd be pleasantly surprised if 236mm (such as my C9.25) could show it.

So I think there are still some issues with the modelling, which show up when comparing brighter uneven with dimmer even pairs. And the un-cooperative atmosphere that makes things much harder around 10th magnitude and fainter.

More positively - those are issues largely with the dim-and-close part of the list. We'll see if it works as suggested at that end - I'd be happy to be wrong on this. :)

And with a couple of nights partly cloud-free I've managed to see a few more doubles from your Orion list - I'll describe my observations in another thread.

#6 WRAK

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Posted 01 February 2013 - 02:20 AM

...So I think there are still some issues with the modelling, which show up when comparing brighter uneven with dimmer even pairs...

More positively - those are issues largely with the dim-and-close part of the list. We'll see if it works as suggested at that end - I'd be happy to be wrong on this...


Fred, you are certainly right and I am aware of this weakness of the current model. I have several ideas how to repair this weakness for pairs coming near the TML of small scopes but most of all I need more observation reports in this area.
Wilfried

#7 R Botero

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Posted 18 February 2013 - 06:10 PM

I have been going through this list and on Saturday evening bagged quite a few. Seeing wasn't the best but I still managed to split HR2711. Lovely pair of 6.5 mag stars just under the arms of the twins. Separated by 1.0" they almost kiss against the dark sky. Apparently one of the stars is yellowish whist the other is white. I could not detect any colour but this may be due to me using a Baader Mark IV zoom which is quite colourless. May try it next with a barlowed EO RKE which is a lot warmer.

#8 WRAK

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Posted 19 February 2013 - 04:49 AM

SkySafari has a lot of very nice features - the possibility to highlight the objects from a list is one of them.
What makes me a bit uneasy are the frequent differences in the advertised data in comparison with WDS - I just wonder about the reasons because WDS is freely accessible and as far as I know the best source for double stars.
Wilfried






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