Tabit (Pi³ Orionis)

Tabit, Pi³ Orionis (π³ Ori) is an F-type main sequence star located 26.32 light-years away in the constellation Orion. With an apparent magnitude of 3.16, it is visible to the unaided eye. The star forms Orion’s Shield (or Orion’s Bow) with five other stars and star systems that share the Bayer designation Pi Orionis.

Star type

Tabit is a yellow-white main sequence star of the spectral type F6 V. It has a mass of 1.288 solar masses and a radius 1.317 times that of the Sun. With a surface temperature of 6,518 K, it is 2.816 times more luminous than the Sun. The star spins at 17 km/s. It has an estimated age of 104 billion years.

Pi³ Orionis is believed to be a single star. It has a visual companion, a magnitude 8.8 star, and is listed as CCDM J04499+0657A in the Catalog of Components of Double & Multiple Stars. The Washington Visual Double Star Catalog lists other companions, also likely optical.

Even though researchers reported detecting a periodicity of 73.26 days, this is believed to be linked with stellar activity and not to the presence of a planet. No planets have been detected orbiting the star to date.

Tabit (Pi³ Orionis), image credit: ESO/Digitized Sky Survey 2 (CC BY 4.0)

Facts

Tabit is the ninth brightest star in Orion, after Rigel (Beta Orionis), Betelgeuse (Alpha Orionis), Bellatrix (Gamma Orionis), Alnilam (Epsilon Orionis), Alnitak (Zeta Orionis), Saiph (Kappa Orionis), Mintaka (Delta Orionis), and Hatysa (Iota Orionis). On average, Pi³ Orionis is the 207th brightest star in the sky. It is about as bright as Haedus (Eta Aurigae), Epsilon Leporis, and Xami (Alpha Circini).

Tabit has served as a spectral standard for its class (F6 V) since 1943. The star’s spectrum is one of the stable anchor points used to classify other stars.

Tabit (Pi³ Orionis) shares the Bayer designation Pi Orionis with five unrelated stars and star systems: Pi¹ Orionis, Pi² Orionis, Pi⁴ Orionis, Pi⁵ Orionis, and Pi⁶ Orionis. Tabit is the brightest and nearest of the five stars. It is also the only one that has a proper name.

Pi¹ and Pi² Orionis are A-type main sequence stars located 116 and 224 light-years away, Pi⁴ and Pi⁵ Orionis are hot blue B-type giants located 1,050 and 1,300 light-years away, and Pi⁶ Orionis is an orange giant located 950 light-years away. Pi⁴ and Pi⁵ Orionis are binary stars, while others are believed to be solitary.

The six stars and star systems form Orion’s Shield (or Orion’s Bow), one of three prominent asterisms in the constellation Orion, along with the brighter Orion’s Belt and Orion’s Sword. In depictions of the Hunter constellation, the stars that share the Bayer designation Pi Orionis represent either Orion’s shield, Orion’s bow, or the lion’s hide held by the mythical hunter. Pi¹ Orionis lies almost 9 degrees north of Pi⁶ Orionis.

Orion’s Shield, image: Stellarium

In Persian astronomy, the stars of Orion’s Shield were known as Al Taj (“the crown” or “the tiara”). In Arabic astronomy, they were called Al Kumm (“the sleeve”) and Al Dhawain (“anything pendent”).

The 10th century Persian astronomer Al Sufi called the stars Manica, referring to a sleeve in heraldry.

Name

The name Tabit (pronunciation: /ˈteɪbɪt/) comes from the Arabic al-thābit, meaning “the endurer” or “the fixed one (the constant one).” The name was approved by the International Astronomical Union’s (IAU) Working Group on Star Names (WGSN) on September 5, 2017.

Pi³ Orionis traditionally shared the name Tabit (or Thabit) with the fainter Upsilon Orionis, a hot blue star in the region of Orion’s Sword.

In traditional Chinese astronomy, Tabit was known as 參旗六 (Zhāng Qí Liù), the Sixth Star of Banner of Three Stars. It formed the Banner of Three Stars asterism with Omicron¹ Orionis, Omicron² Orionis, 6 Orionis, Pi¹ Orionis, Pi² Orionis, Pi⁴ Orionis, Pi⁵ Orionis, and Pi⁶ Orionis. The asterism was part of the larger Net mansion, which represented the body of the White Tiger.

Location

Tabit is very easy to find because it is part of Orion’s Shield, a relatively bright star pattern that lies west of the main constellation figure of the Hunter. Tabit is the brightest and westernmost of the Shield stars. It appears roughly two-thirds of the way from Rigel in Orion to Aldebaran in Taurus.

The location of Tabit (Pi³ Orionis), image: Stellarium

Constellation

Tabit is located in the constellation Orion. The celestial Hunter is one of the brightest and best-known constellations in the night sky. It is the 26th largest of the 88 constellations, stretching across 594 square degrees of the sky on the celestial equator. Like all equatorial constellations, it is easily visible from both the northern and southern hemisphere.

Orion is one of the 48 ancient constellations catalogued by the Greco-Roman astronomer Claudius Ptolemy of Alexandria in his Almagest in the 2nd century CE. The constellation is associated with the giant huntsman Orion in Greek mythology. The mythical hunter was known for his exceptional strength and skill.

Orion is best-known for being home to the supergiants Rigel and Betelgeuse, the seventh and 10th brightest stars in the sky, and for containing the Orion Nebula (Messier 42), the nearest massive stellar nursery to the solar system. The constellation also hosts Orion’s Belt, one of the most recognizable asterisms in the sky.

Orion constellation map by IAU and Sky&Telescope magazine (Roger Sinnott & Rick Fienberg) (CC BY 3.0)

Other notable stars in Orion include the hot blue star Bellatrix, the blue giants Meissa and Hatysa, the blue supergiants Saiph, Alnilam and Alnitak, and the bright giant Mintaka.

The best-known deep sky objects in the constellation include the Orion Nebula (Messier 42) with the Trapezium Cluster, De Mairan’s Nebula (Messier 43), the emission nebulae NGC 2024 (the Flame Nebula), NGC 2174 (the Monkey Head Nebula), and Barnard’s Loop, the dark Horsehead Nebula (Barnard 33), the reflection nebulae Messier 78 and the Running Man Nebula (NGC 1977), and the open cluster NGC 2169 (the 37 Cluster).

The best time of the year to see the stars and deep sky objects in Orion is during the month of January, when the constellation climbs higher in the sky in the early evening. The entire constellation can be seen from locations between the latitudes 85° N and 75° S.

The 10 brightest stars in Orion are Rigel (Beta Ori, mag. 0.05 – 0.18), Betelgeuse (Alpha Ori, mag. 0.0 – 1.3), Bellatrix (Gamma Ori, mag. 1.59 to 1.64), Alnilam (Epsilon Ori, mag. 1.64 – 1.74), Alnitak A (Zeta Ori A, mag. 2.00), Saiph (Kappa Ori, mag. 2.09), Mintaka AB (Delta Ori AB, mag. 2.23), Hatysa (Iota Ori, mag. 2.77), Tabit (Pi³ Ori, mag. 3.16), and Eta Orionis (mag. 3.31 – 3.6).

Tabit – Pi³ Orionis