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Theta 2 Orionis?

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#1 Gschnettler

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Posted 24 February 2021 - 08:48 PM

I was observing M42 last night and saw the A-F stars in the Trapezium.  It was my first time seeing the E and F stars  - it was really cool to pick them out!  

 

It looks like those 6 stars comprise what they call Theta 1 Orionis.  But then what is Theta 2?  Is it all three of the stars that are in a line to the bottom left of the Trapezium?  Or just the first 2?  Which orbit one another?  The “Turn Left at Orion” book just points to the first two and labels them both as Theta 2.  And says that they are a double.  

 

But Sky Safari only labels the first as Theta 2 and calls the second one HD 37042 and the third one V361 Ori (HD 37062).  It says that Theta 2 is a double and the separation is 52.4”.  It says that the second one is also a double and the separation is 76.6”. And it says that the third one is a double too with a separation of 78.2”.   So, I’m not really sure what’s going on here and I would like to know since it’s more interesting when you know what you are looking at.  

 

If you know the answer, or know of some better sources to look up this type of data I would really appreciate it if you shared!

 

 712B35D3-EBD1-468A-89CE-4E6C4A2162D3.jpeg

 

(I borrowed this photo from another post on Cloudy Nights.  Hopefully no copyright infringement!)



#2 payner

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Posted 24 February 2021 - 09:09 PM

Theta-1 Orionis is what comprises the Trapezium. Take a look at this article https://skyandtelesc...ions-trapezium/

 

Theta-2 Orionis is the three bright star system in the lower left of your photo. It is a multiple system where A (HD 37041) is a spectroscopic binary, B (HD 37042) is a variable star and C (HD 37062) is a binary system.

 

Congrats on seeing the A - F components. You obviously had steady skies.

 

Randy


Edited by payner, 24 February 2021 - 09:24 PM.

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#3 cildarith

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Posted 24 February 2021 - 09:28 PM

Yes, Theta 2 is the three stars in a line to the left of the Trapezium in your photo.

Attached Thumbnails

  • Theta Ori.jpeg


#4 Gschnettler

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Posted 25 February 2021 - 12:45 AM

Thank you. That helps. Not sure why the Turn Left Orion book shows all 3 stars but only indicates that the first 2 are Theta 2.

Referring to them as A, B and C as in the above picture, it’s easy to think of them being born one after another and traveling through space together. But, Sky Safari shows them at very different distances from Earth:

A - 1500 LY
B - 650 LY
C - 4,600 LY

So, first of all, do these distances seem right to you? And if they are, what is the relationship between these 3 stars? Are they considered to be on their own if they are that far away from each other?

#5 Tony Flanders

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Posted 25 February 2021 - 06:30 AM

Thank you. That helps. Not sure why the Turn Left Orion book shows all 3 stars but only indicates that the first 2 are Theta 2.
<…snip…>

This is interesting; for some reason I also thought of only the two brighter stars as being Theta 2. But I see that the Washington Double Star Catalog does indeed list the third as Theta2 C. That pleases me, because from a visual perspective they all seem obviously related.

 

I'm always a little annoyed and perplexed that people mention Theta2 so rarely. Granted, it may pale in comparison to the Trapezium, at least in big scopes. But in small scopes and binoculars, those three stars are a huge part of the overall visual impression, especially in bright skies where the nebulosity is impressed.

 

As for the questions above, the distances probably aren't worth the pixels they're printed with. Too much visual confusion in the area. Judging by their brightness and spectral types, they're obviously all related to Theta1. But no, they do not orbit each other, nor do the stars of the Trapezium. Like the Trapezium, they are still close to each other because they were born together and very recently, and haven't had time to disperse.




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