Star Facts: Mintaka

Star Facts: Mintaka
Image Credit: F. Espenak

Mintaka (Delta Orionis), a white-blue star situated 1,200 light years away in the “belt” of the famous constellation Orion, is located so close to the celestial equator that its rising and setting follows an almost exact east and west direction. However, Mintaka is actually a complex multi-star system with a combined apparent visual magnitude of +2.23 or +2.25, which makes it either the 67rd or the 73th brightest star in the entire night sky, depending on the source consulted and the method used to establish the star’s magnitude.

Visibility

Orion is one of the most easily recognized constellations in the night sky, and can be seen by observers located between latitudes of +85° and -75°. A famous asterism within this constellation called Orion’s Belt is one of the straightest lines formed by three or more stars in the night sky, and consists of Alnitak (Zeta Orionis), Alnilam (Epsilon Orionis), and Mintaka. When Orion is close to the meridian, observers in the northern hemisphere looking south can see Mintaka as the right-most star in the “belt”.

Physical Properties

Multi-Star System

Star Facts: Mintaka
Credit: www.researchgate.net

Mintaka (d Ori A) is a rather complex multi-star system whose primary component (Aa1) is a very hot, 09.5-type blue giant star that forms a tight eclipsing binary with Aa2, a 7th magnitude B-class main sequence star located roughly 52 seconds of arc away, with the pair having an orbital period of 5.73 days. There is also an exceedingly faint third member called Ab situated between the primary pair that orbits the system once very 346 years.

Furthermore, Aa2 is a rare type of B-class sub giant that is itself a close spectroscopic binary with a faint 14th magnitude A-type companion that orbits once every 30-days. This faint 14th magnitude star is believed to be located at the same distance that Aa2 is from Aa1, but almost nothing is known about this star, and it is far from certain whether it is related at all to the primary pair or not. To put this into perspective, it must be noted that Mintaka is all but surrounded by a cluster of faint stars that may or may not be part of the larger cluster of stars that surround the nearby star Sigma Orionis.

Distance

While parallax measurements made by the Hipparcos satellite state that the distance to the Mintaka system is 212 ± 30 parsecs (1 parsec = 3.26 light years), other methods to determine the distance, such as spectroscopic studies, comparisons to similar stars, and cluster membership all reveal that the distance to the system should be at least twice the Hipparcos value. However, this kind of irreconcilable difference is not unique to the Mintaka system, although there is as yet no workable explanation as to why these differences occur in the first place.

Quick Facts

Mintaka (d Ori A)

• Constellation: Orion
• Coordinates d Ori A (Aa1 + Aa2 + Ab)): RA 05h 32m 00.40009s|Dec. -00° 17′ 56.7424″
• Distance: ± 1,200 light years
• Apparent Magnitude (d Ori A (Aa1 + Aa2 + Ab)): 2.23 (2.50 + 3.90)
• Luminosity (d Ori A (Aa1 + Aa2 + Ab)): 190,000 sol

The following information applies only to the systems’s three main individual component stars, whose combined details have been noted above:

d Ori Aa1

• Star Type: (O9.5II + B1V +B0IV) + B3V
• Mass: 24 sol
• Radius: 16.5 sol
• Surface Temperature: 29,500
• Rotational Velocity: 130 km/sec
• Age: Undetermined
• Other Designations: d Orionis, 34 Orionis, 88 G. Orionis, FK5 206, HIP 25930, ADS 4134, CCDM J05320-0018, WDS J05320-0018

d Ori Aa2

Mass: 8.4 sol
Radius: 6.5 sol
Luminosity: 16,000 sol
Temperature: 25 600K
Rotational velocity: 150 km/s

d Ori Ab

Mass: 22.5 sol
Radius: 10.4 sol
Luminosity: 63,000 sol
Temperature: 28,400K
Rotational velocity: 220 km/s

History

Collectively, the three “belt stars” have had many names in different cultures. For instance, some old Arabic names include “Al Nijad”, meaning “The Belt”, “Al Nasak, meaning “The Line,” Al Alkat” , meaning “Golden Grains” or “Nuts”, while a modern Arabic name, “Al Mizan al H•akk”, means “The Accurate Scale Beam”. The star also appears in old Chinese mythology as “The Weighing Beam”. In Spain and Portugal, the “belt stars” are known as “The Three Mary’s”, while in some other Christian traditions, the star Mintaka is also known as the third member of the troupe of Wise Men that travelled to the town of Bethlehem.

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