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Old 08-12-2008, 01:56 PM
Coen
"Doc"

Coen is offline
 
Join Date: Oct 2008
Location: Adelaide, Australia
Posts: 180
70mm refractor - some doubles+extras in Gru

Hello All,

November has been a shocking month regarding having any clear skies. While we are in drought, the clouds that come to block observing do not drop rain so nobody wins. So when at last a clear night out came the little telescope and time to do some observing. I decided to pick a constellation and as part of getting to know it, tour the various doubles within it. I planned a list using Taki's Double Star Atlas and the CNebulaX program so had plenty to keep me amused. The constellation of choice this time is Grus, it rides high at this time of year, around altitude 77 degrees give or take.

My telescope is a base model Skywatcher 70mm refractor and I was using a 15mm GSO 68 deg eyepiece, the 10mm that came with the scope and a 6mm Plossl to give me 60x, 90x and 150x. I decided to keep the 25mm Plossl and 25mm eyepiece (36x) that came with scope in their box as the 15mm GSO gave almost identical field of view although admittedly a little less contrast and some minor distortion near the edges of the field of view. Seeing was good with plenty of sky-glow; a combination of suburbia and day-light savings. The date is 26 November 2008, the sky does not get all that dark until around 2200 local with Sun set approximately 2000.

Set up the telescope and handed over controls to my daughter so that she could find and have a look at a few things before she headed off to bed. She is becoming adept and particularly enjoys globular clusters not understanding my fascination with doubles. Her favourites include M22, the cluster in Pavo and 47 Tuc; she has not been introduced to Omega Cen yet. I digress, after her bed time it was onto doubles.

Some of the following stars are not necessarily "true" doubles but thought they might be worth a look anyway. Default eyepiece, when not mentioned, is the 15mm GSO giving a real field of view of about 68 arc minutes. I purposely do not look up PA (plus I do not get exicted about which way North and West are in general when viewing) and if I have doubt about whether I am viewing the right thing a quick sketch and consultation with a star atlas later is usually enough to confirm or deny.

Sky still bright, so start with a brighter one.

Delta 2 Gru 2118 local time
Easily split with the 60x, main star is orange (mag 4.3), companion is faint as sky still bright (mag 9.7), colour hard to distinguish, perhaps grey. Able to see other very faint stars in the field via direct and averted vision. Consulting StarCalc, CNebulaX and Ciel whilst compiling these notes indicates that I was seeing stars to 11.6 magnitude - pretty happy with that. Nice field with Delta 1 present. No chance of splitting Delta 1.

Rho Gru 2137 local time
Cleanly split with a very faint companion (10.3) located in a nice star field.

Sigma 1 & 2 Gru 2145 local time
With the 60x and 90x there was a hint of a companion to sigma 1, nothing for sigma 2. The companion was very faint and averted vision helped although by no means definitive. A quick sketch with some orientation stars and later consultation indicated that I had seen the 11.8 magnitude companion as well as some 11 to 11.8 magnitude stars. A further consultation with the documentation indicates sigma 2's companion is at 2.7" and is magnitude 11 so no surprise I could not split it. The star viewed near sigma 1 is unrelated and nearly 2' away.

Pi 1 & 2 Gru 2155 local time
No indications of being able to split in 60x or 90x

BSO 15 2203 local time
Nice and easily uneven pair with a yellow primary, colour hard to tell on secondary.

HJ5319 2227 local time
Took a while to find and confirm that I was looking at the right location. Could not split it with 60x. Hint of a "peanut" shape at 90x and this was confirmed with the 150x with perhaps a split, subsequent consultation with the tables indicates a 6.9 and a 7.8 magnitude star separated by 2.1" in the orientation noted at the eyepiece.

JC19 2232 local time
Nice double with a yellow primary (6.7) and a hint of red to the companion (8.1) separated by about 18".

I138 2252 local time
No split with either 60x or 90x

HJ5362 2256 local time
Averted vision brings this one out with a 6.6 main and 9.9 companion. The main is yellow, and the secondary is perhaps a dark green. Colour is a challenge on most of the doubles so far, not sure why.

Theta Gru 2309 local time
This is a triple star but only the A&C components split (A&B are too close for the 70mm). Colours are yellow and darker yellow.

HJ5390 2313 local time
Nothing at 60x or 90x.

COO 252 2320 local time
Seems to be too easily seen from documentation on hand at the telescope, split neatly by the 60x. A quick sketch and later consultation with some atlases indicates that what was seen was an unrelated nearby magnitude 9.5 star to the COO252 pair. COO252 consists of a 6th and 11th magnitude separated by about 8". The 9.5 magnitude star is about 47" away.

Dun 246 2328 local time
Nice double with yellow primary (6.3) and greenish/blue secondary (7.0) also nearby is a fainter double on the way to Zeta consisting of a pair of about 9.6 magnitude stars (TYC 8454-1352-1 or TYC 8454-963-1 or TDSC 63084, mag 9.5 and 9.7). Probably the choice double so far.

Dun 248 2339 local time
Uneven pair split at 60x with yellow primary (6.1) and murky green secondary (8.9) separated by 17". This is very different to the documentation in Taki's atlas which has two even stars (6.1 & 6.6) separated by 17" and the 6.1 mag star having a 1" 8.9 magnitude companion. Upping the power does not split the 6 magnitude star (150x). Consultation with an atlas confirms that what was seen is "true" and that either I am not reading Taki's atlas information correctly for multiple stars or I found an error.

Dun 250 2344 local time
This pair is located near Dun 248 and technically not in Gru, also known as TDSC 63929 and consists of a 7.6 primary and 8.5 secondary separated by about 30". The colours appear to be yellow and reddish and is nicely framed on either side by some brighter stars.

Dun 249 2349 local time
Nice uneven pair with a white (6.1) primary and green (7.0) secondary separated by about 27". A nice view.

HJ5349 2357 local time
Star located by unable to locate the secondary at 60x or 150x. Listed as 6.7 and 11.5 separated by 34".

HDO 298 0007 local time (27 November)
Star located but failure to locate the secondary at either 60x, 90x or 150x. Listed as 5.4 and 9.7 separated by 5".

Summary on telescope:

After viewing the double stars I concluded that the 70mm is a nice portable scope (can lift it with one hand and is easily taken outside being always set up). As always tempting to go bigger etc and may well do at some point but the 70mm fits the bill for portability and teaching kids (both schools and my own). My previous second-hand 60mm eventually gave up the ghost after 20 years and numerous trips to schools etc. Plus the cost of the 70mm means not worried about the kids learning. The optics of the 70mm are nice and the match to the 15mm GSO seems to work. I think I need a decent 9 or 10mm eyepiece to fill out the range and replace the basic one that came with the scope. A barlow and an improved diagonal would not go astray either. The good thing about eyepieces is that they go between scopes . I borrowed an 18mm ortho by university optics and that was also a very nice match and I can see what the extra dollars on an eyepiece can get you even in a cheap scope.

What seems to be a challenge with the scope is that the colours of doubles does not seem that strong.

With some of the doubles of Gru under the belt thought it would be good to try for a few DSO's. I was not holding my breath as the sky was still bright.

NGC 7213 0014 local time.
Unable to see.

IC5201 & IC5267 0018 local time
Indications that each seen although not convinced. A "fog" in the eyepiece moved when the telescope was tapped.

Did not try for IC1459, suspect should have seen something.

By this stage Orion is riding high, so lost myself in the nebula and had a look at the multiple sigma Orion as well as theta. Checked out M1. Had a look at the beautiful double HJ3945 in Canis Majoris. Then it was time to check some open clusters in Carina which was rising, finishing with the eta Carina nebula and the globular NGC 2808. The open clusters near eta Carina are just something and I am looking forward to showing my daughters them. Finished up around 1:30am.

Now which constellation next...
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