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According to some recent studies, the star Mintaka in Orion's belt ($\delta$ Orionis) is a multiple star system consisting of 6 stars in total:

  • the triple system $\delta$ Ori A, with $\delta$ Ori Aa1, $\delta$ Ori Aa2 and $\delta$ Ori Ab;
  • the single component $\delta$ Ori B;
  • the spectroscopic binary component $\delta$ Ori C (or HD 36485).

The studies I'm referring to are mainly a 2023 study by Oplištilová et al., which quotes a 2010 study by Leone et al. with respect to $\delta$ Ori C being a binary star, and states that the system has 6 components overall:

The bright star δ Ori (HR 1852, HD 36486, HIP 25930, ADS 4134) is a multiple stellar system consisting of six components: Aa1, Aa2, Ab, B, Ca, and Cb, more specifically, the eclipsing binary Aa1+Aa2, the interferometric binary (Aa1+Aa2)+Ab, the faint visual companion B, and the spectroscopic binary Ca+Cb

(from the Introduction)

This 2024 study by Malkov et al confirms that $\delta$ Ori C is a spectroscopic binary. On page 2, they say (emphasis mine):

HD 36486 has remote companions B and C at separation ρ = 33" (V = 14.m 2, O9V) and ρ = 56" (V = 6.m 83, B2Vsn), respectively. Companion C (=HD 36485, B2Vsn) is itself a spectroscopic (SB1) binary

The Simbad database also seems to consider $\delta$ Ori C as a spectroscopic binary, if I'm not mistaken.

However, this 2015 article by NASA says that $\delta$ Ori B and C are single stars, while $\delta$ Ori A is a triple system, which would bring the total number of components to 5 instead of 6. They cite studies conducted by the Chandra X-Ray observatory (a series of papers starting with this one by Nichols et al.). These studies, though, seem more concerned with $\delta$ Ori A than with the other components, but I could be mistaken.

Can you explain why there is this discrepancy in the total number of stars in the system? Are there more recent studies that report $\delta$ Ori C as a single star and not a spectroscopic binary?

I'm asking this because it seems that the doubt relates only to the C component, while A and B are established as triple and single, respectively.

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    $\begingroup$ You nicely reference your findings - that's awesome and very well done, and it's a good question. The question will be even nicer to read, if you use the authors' names instead of "this" in the visible text :) $\endgroup$
    – planetmaker
    Commented Aug 28 at 13:46
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    $\begingroup$ @planetmaker I've added authors' names where missing, thanks. $\endgroup$
    – user3764418
    Commented Aug 28 at 14:05

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If I understood your explanation of the problem correctly, in earlier papers, Star C was identified as a spectroscopic binary, while in the later paper based on X-ray data, it was classified as a single star. The first thing that comes to mind is that if subsystem C is a spectroscopic binary, it’s quite possible that one component has X-ray emissions while the other does not. If they are spectroscopic binaries in the sense that it's a close binary system, having X-rays from one star and not from the other is quite common.

Therefore, the question is in which range the star is considered single or binary, but I might not have fully understood your question

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  • $\begingroup$ Yes, the earliest reference I could find for delta Ori C to be a spectroscopic binary is the cited 2010 paper, I don't know if there's anything earlier than that. The X-ray study was published in 2015, while the papers mentioning component C as binary are more recent (2023 and 2024). If as you say the X-ray survey could have missed the binary nature of delta Ori C (due to only one component emitting X-rays), could one say that the spectroscopic result is more reliable in this regard? The question is essentially whether the C component is actually a binary system or not. $\endgroup$
    – user3764418
    Commented Aug 28 at 14:13
  • $\begingroup$ yes, spectroscopic result is more reliable (if we speak in the say of existing two objects at all). The absence of X-ray from the secondary does not mean that there is no secondary at all. To sum up (from your words), we can say: - Ori C is a spectroscopically binary - only one component emits X-ray You can find the same thoughts in the latest papers (dedicated to X-ray from Ori C) – if it is, you will see references and discussions about the binary nature of Ori C. You can also ask ChatGPT to help you in analyzing :) $\endgroup$
    – Stephan Panarin
    Commented Aug 28 at 19:28

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