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Eta Cassiopeiae colours

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2 weeks 6 days ago #106882 by flt158
flt158 created the topic: Eta Cassiopeiae colours
Last Wednesday night (27th December) I had a clear sky in south Dublin.
So I thought I should set up my scope.
As you all know I have a William Optics 158 mm F/7 apochromatic refractor on a Berlebach altazimuth mount.
I had a 9 day old Gibbous Moon visible and I observed it for a while.
To its east, Alpha Piscium (Alrischa) was nicely split at 140X. Its 2 components are white.
But here is my mysterious star for today.
Quite a few people have been discussing the colours of the true binary star Eta Cassiopeiae whose name is Achird on www.cloudynights.com
A is 3.5 in magnitude. B is 7.4. The separation is 13.3". The PA is 325 degrees.
There are not part of the W or M pattern of Cassiopeia.
The single star is a bit faint to our own eyes -but easy to find nonetheless.
The primary has a spectral class G0 and it is a yellow star -the same as our Sun. No debate for that one.
It's the secondary that causes much debate. What is its true colour?
Lots of spectral classes have been listed down through the centuries by some of the greatest astronomers who have ever lived. K3, K5, M0 and M1 have all been given. We all know K is orange and M is red.
But when I google the secondary star today, K7 seem to be the new official spectra.
So it could be a mixture of orange or red? Normally a K-class star, say K 1 to 5, describes an orange star.
But the new description of K7 is a little bit rarer. There are less than 100 such stars in northern hemisphere skies.
Sissy Haas states in her excellent book "Double Stars for small telescopes" that both Webb and Smyth saw the companion as purple. But they had much older telescopes than we have today. I cannot say I saw any purple tint on Wednesday night.
William Sadler Francks (1851- 1935) observed it as a pale garnet and I would like to agree with his judgement.
Meanwhile, Sissy Haas herself describes it as almond brown and it appears that I completely agree with her assessment.
This surely is the only brown star I have ever observed. True orange, red or purple are out for me.
As you know, apochromatic refractors reject false colours because of their triple lenses.

So have any of you observed Achird at any time in the past?
I will be delighted to hear from you -especially if your colours are very different to mine.

Clear skies from Aubrey.
The following user(s) said Thank You: michael_murphy, lunartic, Fermidox, mariosi

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2 weeks 3 days ago #106888 by stevie
stevie replied the topic: Eta Cassiopeiae colours
Both myself and others in our group have observed this star many times over the years and it always appears brown to us, no matter which scopes we have used.

stevie

Secretary NIAAS
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2 weeks 3 days ago #106889 by flt158
flt158 replied the topic: Eta Cassiopeiae colours
Happy New Year, Stevie.
And a huge thank you for describing your observations of Eta Cassiopeiae.
It is very interesting that you agree with my brown colour.
I wonder can you give a little bit of detail as to what scopes they were? Reflectors, refractors or SCT's?
I would be quite keen to find out.

What do you say if any double star enthusiast would have a look at Eta Cassiopeiae over the next couple of months? After all it is high in the northern sky right now.

Thank you from Aubrey.

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2 weeks 1 day ago #106898 by stevie
stevie replied the topic: Eta Cassiopeiae colours
Hi Aubrey

Here's some notes from my old double star observing diary. I'm afraid I haven't done much specific double star observing in recent times

23/11/06 - Tal100R 4" refractor - Eta Cassiopeiae - Lovely pair, split at 40x, but best at 160x, yellow primary with brown companion

20/8/07 - Celestron C6SGT + 12.5mm ortho - Eta Cassiopeiae - Pale yellow primary, brown secondary, spectacular

22/8/08 - Orion Optics 10" reflector - Eta Cassiopeiae - particularly good view, brown companion very vivid.

stevie

Secretary NIAAS

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2 weeks 1 day ago #106899 by lunartic
lunartic replied the topic: Eta Cassiopeiae colours
Looking back at a sketch I did of Eta back in 2007, I noted that it appeared to be more of a reddish colour, this was using a 80mm refractor.

Next clear night I will check it out with my MCT.

Paul

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2 weeks 40 minutes ago #106903 by flt158
flt158 replied the topic: Eta Cassiopeiae colours

stevie wrote: Hi Aubrey

Here's some notes from my old double star observing diary. I'm afraid I haven't done much specific double star observing in recent times

23/11/06 - Tal100R 4" refractor - Eta Cassiopeiae - Lovely pair, split at 40x, but best at 160x, yellow primary with brown companion

20/8/07 - Celestron C6SGT + 12.5mm ortho - Eta Cassiopeiae - Pale yellow primary, brown secondary, spectacular

22/8/08 - Orion Optics 10" reflector - Eta Cassiopeiae - particularly good view, brown companion very vivid.


Hello again, Stevie.

That sure is a most interesting bunch of instruments you have used on Eta Cassiopeiae.
And they all give the same results not matter which one you used throughout the years 2006-2008,
Thank you very much for taking the time to informing the rest of us.

Valerie and I had another look at Achird on New Year's night. She agrees that the B star is almond brown and not pale garnet.

Kindest regards from Aubrey.

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2 weeks 36 minutes ago - 2 weeks 7 minutes ago #106904 by flt158
flt158 replied the topic: Eta Cassiopeiae colours

lunartic wrote: Looking back at a sketch I did of Eta back in 2007, I noted that it appeared to be more of a reddish colour, this was using a 80mm refractor.

Next clear night I will check it out with my MCT.

Paul


Hello Paul.

I do hope you will get another look at Achird once again very soon.
Yes - I can see where you get your reddish colour from.
But I am looking forward to your next observation of this fascinating binary.
I was able to go up to 225X last New Year's Night.
The double looks truly brilliant as I up the power!

Clear skies for 2018,
Aubrey.
Last Edit: 2 weeks 7 minutes ago by flt158.

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