Eta Gemini

[magnahrl]

Yesterday evening/night I for once had very good seeing. 7/10 P.? But it was never 100% clear skies, clouds were coming and going all the time. e and f stars in Trapezium steady and easy at 152X and 270X (not all that common at 57N) with my 8" Classic Cassegrain. 52 Orion had a hint of sep at 270X and a complete sep at 405X. Zeta CNC AB sep at 270X and the whole triple system was gorgious at 347X. Next was Propus (Eta Gem). A double I have split many times during the last two decades with my C8 and 6" Mak as long as the seeing is ok. This time, in a sky I estimated as very good, there was no companion. I tried everything from 152X up to 405X    -nothing! I doublechecked the positions of Mu and Eta so I had not choosen the wrong star. But no it was correct. Very strange. I must recheck this next clear night. I know Eta is a variable star. Can this affect how easy or hard it is to see Eta B? Or maybe the diffraction ring is hiding B in this CC8? I have not had it for more than 7 months and observed with it less than 10X.

Magnus A.

[lunator]

Hi Magnus

I had a quick look back through my records I have split this pair in my 200mm F6 newt so it is doable.

It's central obstruction CO is about 20% maybe slightly more.

These are my comments from my log.

"A tight pair just split at x200. The primary is pale yellow. The secondary a gold/orange A very pretty but tought split."

I gave it a toughness grading of 4 ( I give every pair I view a grading from 1-5) it is a purely subjective number but does give an idea of how hard the split was. 

The only thing I can think is the CO of your scope is adding a lot more light to the airy disc so is making the secondary much harder to spot. 

I will have a try with my OMC250 as it's specs will be closer to your CC when the clouds allow. 

Cheers

Ian

[John]

Nice report Magnus 🙂

I'll give Eta Gem a go, if these cursed clouds ever shift, which they show no signs of doing just yet 🤨

@Nik271 got this one and sketched it back in February with his 127 mak-cass:

 

[magnahrl]

Tried Eta Gem this night as well and no success. I agree with you Ian it may very well have something to do with the fairly large CO on the CC8. On the other hand I am very pleased with this CC8 system. It gives very sharp starimages. It reminds a lot of my Intes MK66 but in a larger version. Next clear night I will bring out my vintage C8 for a try at Eta Gem as I know it rather easely splits it when seeing is good or better. This C8 is good but it doesn`t have those hard, sharp starimages as the CC8. I am a bit confused🙄Oh dear now this starts to be more like a post in an equipment forum. Sorry!

Thanks Ian and John for your feedbacks👍

 

Magnus A.

 

[Nik271]

It was pretty tough in the 127 Skymax :  'a bump' on the diffraction ring is how I saw it. I think this one is currently easier than Zeta Herculis, at least this has been my experience. 

Eta Gem has been reported split with 100mm refractors, so it's surprising that  a 8inch CC could not do it, even with 40% obstruction and slightly reduced aperture. This is what Aberrator simulates for 190mm 40% obstructed scope:

 

Secondary is well outside the first diffraction ring so should be  visible if the seeing is good.

Good luck!

 

[John]

I think my ED120 refractor might be in with a chance on Eta Gem, maybe even my FC100 - I've split Zeta Herc with both those scopes, on decent nights.

[magnahrl]

Nik271 agree Eta Gem is easier than Zeta Her. Indeed Eta should be no trouble in good seeing with the 8" CC. The scope is fully cooled down and collimated as far as I can see. Intressting picture showing B well outside the  diffraction ring. Obviously I am doing something wrong. Is collimation still not 100% spot on? But everything I´ve looked at (apart from Eta Gem) has been so beutiful. Including Mars and Jupiter at 270X-304X.

Magnus A.

PS Thanks for feedbacks👍

Edited December 12, 2024 by magnahrl

[lunator]

The abberrator image might be slightly mis-leading,  the difference in magnitude between the pair looked larger when I viewed it. 

The difference of 3 magnitudes is significant. The secondary has 6% the brightness of the primary. 

Also the primary is very red so the Airy disc and rings will be larger, the first ring is 7% the brightness of the disc without any brightening due to the CO. This all might add up to making it more tricky than it first appears. 

I am sure you can split the pair. Make sure everything is collimated and on a night of good seeing go for a minimum of x200.

Cheers

Ian

[magnahrl]

Very informative post, Ian. Thanks!

I just came in from trying my C8 at Eta Gem. Seeing not quite as good as the latest 2 evenings I´ve been out with the CC8. I used 222, 250, 286 and 333X. First I could not see the Eta secondary. Noticed the collimation was a tiny bit off. So I collimated the C8 as perfect as I could and it helped. Suddenly Eta B was there in the magnifications I mentioned. But it was best in 222X, quite pretty actually! I could not see e and f in Trapezium as I did the other night with the CC8 but failed to split Eta Gem.

I have read my logbooks this evening and noticed that in 2016 I had wonderful splits of Eta with my 8"f/6 Newton and 120ED refractor at 200X.....

Cheers

Magnus A.

[John]

Prompted by this thread (thanks Magnus) we have had the first clear night since the original post so I've had a look at Eta Gem / Propus with my Tak FC100 refractor.

At medium magnifications Propus showed as strong orange coloured star - an attractive sight in it's own right. 

As I increased the magnification, I started to make out a faint greyish companion star very close to the much brighter primary but clearly separated. It seemed to rest gently against the outer rim of the thin, faint diffraction ring around Propus. At 300x this secondary star was more obvious (although never what I would call easy). The faint companion star seemed to be positioned more or less to the west of the primary - it led the brighter star as the pair drifted across the undriven field of view.

@Nik271's sketch in this thread seems spot on:

https://stargazerslounge.com/topic/418615-eta-geminorum-a-gem-in-gemini/

A very nice pair to split and as far as I can recall, a first for me. 

Thanks again for raising it's profile Magnus and for the further info, Nik 👍

 

 

Edited December 16, 2024 by John

[magnahrl]

Thanks John for your Propus/Eta Gem observation report👍 Indeed it`s a nice and, sometimes, challenging pair.  Glad you enjoyed it!

Magnus A.

[magnahrl]

Once again a try at Eta Gem/Propus with my CC8 this moonlight and very steady night. 7, sometimes maybe even 8/10 P. At first no succes again, hmm! As I have, the other night, seen "e" and "f" in Trapezium, split the triple Zeta CNC and 52 Orion among other rather tight doubles and Jupiter and Mars showed wonderful details I didn`t worry about that collimation thing.🙄 But when I looked at Eta Gem A in 405X and 486X  it was obvious the diffraction ring was not uniform. So I did a very , very small collimation of the secondary and thanks to the excellent seeing I could achieve a very good view of Eta Gem A. The diffraction ring was now quite uniform and steady. At once I saw Eta B just outside the diff ring in the correct pos angle. Started again at 152X were I could see a hint of the companion but I don`t think I would have seen it if I didn`t know were to look. In 270X it Eta was easy, in 304X it was a beutiful view. A star orange-yellow and B somewhat greyish-green. So once again I have learned to be sure my collimation is not just good; it must be better than good. Perfect won`t hurt! I now pray the CC8 collimation will hold!

After I had separeted Eta Gem I went to 47 Taurus for a test. It`s rather similar to Eta. Delta mag 2 sep 1.3". I could separate it at 270X and in 347X it was really fine, though I couldn`t notice any colors.

I also did quick observations of 52 Orion, 32 Orion, "e" and "f" Trap, seen at 101X, now and than in 152X but at 270X and above they were gone. Positive obs of Zeta CNC, soo beutiful at 405X. After that I turned my scope to Jupiter, the moon and Mars. Thats another story but I enjoyed that  part of the session as well!

 

Magnus A.

[John]

Great report Magnus 👍

I have found the same with Trapezium E & F - you have to find the right magnification to pull them out of the M42 nebulosity.

I got 32 Orionis last night with my 100mm but could not split 52 - just got an elongated touching pair with a narrow "waist" where they touched.

It's fun pushing the optics, observer and conditions with these tight doubles 🙂

[IB20]

Currently observing Propus with the Tak 76Q. The secondary appears as a grey bulge in the first diffraction ring. Seeing isnt the best but it has popped out once as a notched pair. Using the 3-8mm zoom at full mag.

An excellent target and easy to locate too, many thanks for this!

Think this is my new favourite double!

 

Edited December 20, 2024 by IB20

[magnahrl]

Great catch with 76 mm aperture refractor👍 And yeas easy to find. 

Magnus A.

[IB20]

5 minutes ago, magnahrl said:

Great catch with 76 mm aperture refractor👍 And yeas easy to find. 

Magnus A.

I will get the Tak 100DL and StellaMira 125ED on it next time I get the opportunity. I would hope both will give me a full or hairline split, seeing permitting. Propus will be added to my forever list of double targets that I spend an obscene amount of time trying to split e.g. Sirius, Antares, Zeta Herc. 😄

[magnahrl]

So glad you like Propus! I am convinced at least your 125ED will give you a hairline split and probably also TAK 100DL. When seeing is good. For me I wish to have a Sirius A-B split ( never had one in my life) but it`s hard here at 57N, Antares is out of the question and I love to wrestle with Zeta Herc. - sometimeses I win and sometomes I lose. But it`s great fun!

Magnus A.

[John]

I managed a split of Propus with my Tele Vue 85 a couple of nights back. It was hard work but in the steadier moments the dim secondary star was clearly visible embedded in the diffraction ring around the brighter star.

With my Tak FC100-DL the secondary was easier to spot and appeared to be touching the outer side of the diffraction ring. I've not tried with the ED120 yet.

I'm at 51N here and can split Sirius with the ED120 and FC100 (on good nights) and I've split Antares occasionally with the ED120. 

I'd like to have a try at Zeta Herc with the TV 85. When I first observed it, more than a decade ago, it was hard work with the ED120 but familiarity with the star means that I can get it more often than not with the FC100 now. 

32 and 52 Orionis are nice challenges and well placed currently 🙂

With some of these it is the small separation that is the challenge, with others it's that and uneven brightness components and with Sirius and Antares it's the massive uneven brightness AND their low altitude from the UK.

I tend to use these categories, defined by David Knisely, when considering what I've managed to see:

 

Edited December 21, 2024 by John

[magnahrl]

Before clouds came this evening (18:30UT) I tried my 120 S-W Equinox ED refractor on Eta Gem. At 200X (9mm eyepiece + 2X TV barlow) I had a beutiful "split". I would call it easy. Sadly enough I didn`t have the time to try higher mag. Clouds were quicker than me. Also I did not have the time to estimate seeingconditions but it must have been well above average!  On occasions like this I fully understand people who are refractorfans. I must use my refractor more often. It was a dreamlike view.....

Magnus A.

[IB20]

Not great seeing tonight but the 125ED is showing Propus as two entities more often than not. Isn’t quite a full black gap split but a thin “hair”. Best mag is ~195-240x.

[IB20]

Managed the cleanest split yet with the Tak 100DL in good seeing conditions and the 2.5mm TOE. The secondary sat bulging off the first diffraction ring.

Edited January 10 by IB20

[John]

Nice illustration. The DL's just soak up the power when the seeing co-operates 🙂

[John]

12 minutes ago, John said:

Nice illustration. The DL's just soak up the power when the seeing co-operates 🙂

You just tempted me out with my Tak FC100-DL to try the same - with similar results !

(and I was going to have an evening in tonight !) 😁