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DSC-60 – Visiting Mintaka, an old and comfortable friend

This is a DSC-60 Project observation –  for project details go here.
Splitting Tools for Mintaka: Yields easily to 50mm scope at low power.

Data from Double Star Club list

  ] 20 Delta Orionis 05h 32m.0 -00° 18′ 2.2, 6.3 52.6″ 359

Mintaka (Delta (δ) Orionis)
RA: 5h 32m  Dec: -00° 18′
Magnitudes –   2.2,  6.8
Separation –   52.8″
Postion Angle –   0°
Distance:  915 LY
Spectral Classification –  B4

A couple bonus points to note about those stats – first, the declination – this star is just 18 minute south of the celestial equator. In fact, it’s the brightest star that close to the celestial equator.  Combine that with the PA of 0° – due north – and it’s a good way to help get yourself oriented. Oh – and that separation – 52.8 seconds – that’s just a tad more than the width of Jupiter as it appears in our sky when we’re closest to it, as is the case as I write this. So Jupiter could just fit between the two stars!

Click image for larger version. (Prepared from Starry Nights Pro screenshot.)

OK, I really should admit it – I don’t get out to Mintaka – Delta (δ) – often enough.  It’s one of those easy doubles I’ve known forever, but it’s in one of the best parts of the best neighborhood in the best universe – well, the only universe I know, although this multiverse idea is beginning to make some sense to me 😉

So this morning I found myself heading west on Orion’s belt, certainly one of the best known asterisms in the sky. Who can miss three perfectly spaced stars of almost even brightness (1.71, 1.68, and 2.2)  and straddling the celestial equator where they can be seen from almost any location in the world?  And Mintaka, a charming double, is one of those three – the western most. But it’s easy to ignore because the belt itself is embedded in a huge open cluster. what’s more, when you look at the other end of the belt  you get  the famous, but nearly invisible, Horsehead Nebula, not to mention the Flame Nebula and the delectable quadrupal star, Sigma Orionis.

But Mintaka is #20 on the Double Star Club list and I just had to see how it looked in a 60mm scope – well, at least my  8-inch SCT masked to 60mm. And it didn’t disappoint. This is not even close to being a challenge, even with a 60mm, but it has it’s own charm. While there’s quite a gap in magnitude between the two, the large angular separation makes this a good object to try to capture with binoculars. In physical terms given the angular separation and distance from us the faint companion orbits the primary at about a quarter of a light year.

What the 8-inch shows is a silver star with a smaller blue star tagging long. Stopped down to 60mm with the off-axis mask, the blue star turns to a steely grey, while the primary remains silvery.  Haas  saw the secondary as “very bluish white” and the primary  as “yellow white” and quotes Smyth and Webb as seeing the companion as “violet.”

Whatever color you see, there’s a lot more to this star that you don’t see.  Jim Kaler writes on his web site that the primary is “ALSO double, and consists of a hot (30,000 Kelvin) class B, slightly evolved, giant star and a somewhat hotter class O star, each radiating near 90,000 times the solar luminosity (after correction for a bit of interstellar dust absorption), each having masses somewhat over 20 times the solar mass. This pair is too close to be separated directly.” In addition, he notes the two stars orbit each other about every six days causing a slight dip of about .2 magnitudes.

Mintaka is another example of how Bayer made things up as he went when it comes to Greek letter designations. Usually the stars in a constellation follow the Greek alphabet starting wiht “alpha” being the brightest. But Mintake is Delta Orionis, yet Mintaka is the seventh brightest stars in Orion. Again, Kaler comes to the rescue here, saying Mintaka “received the Delta designation from Bayer, who lettered the belt stars in order from west to east before dropping down to Orion’s lower half to continue the process.”

Oh – and those two closely matched super stars we know as Mintaka. They’re heading for a short life and fiery doom.  Kaler notes that given their size “their only fate is to explode violently as supernovae.”  Hmmm… and a twin supernovae at that – wouldn’t that be something? What does happen when one star goes supernovae right next to another?

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