Tania Australis (Mu Ursae Majoris)

Tania Australis, Mu Ursae Majoris (μ UMa), is a red giant star in a spectroscopic binary system located 230 light-years away in the constellation Ursa Major (the Great Bear). With an apparent magnitude of 3.06, it is the eighth brightest star in the constellation. It is part of the Three Leaps of the Gazelle, an asterism that corresponds to the Great Bear’s feet.

Star system

Mu Ursae Majoris is a spectroscopic binary star composed of an evolved red giant and a fainter companion star.

Tania Australis (Mu Ursae Majoris A), the primary component, has the spectral class M0 IIIab. It is an aging star on the asymptotic giant branch (AGB), an evolved, cool, luminous star with an inert carbon-oxygen core. It has exhausted the supply of hydrogen in its core and is now fusing helium into carbon in a shell around the core and hydrogen into helium in another shell. Once the helium shell runs out of fuel, the giant will enter the thermally pulsing AGB stage.

Tania Australis has a mass of 6.3 solar masses and has expanded to a size of 75 solar radii as it evolved away from the main sequence. It has an estimated luminosity between 977 and 1,200 times that of the Sun and an effective temperature of 3,899 K. It spins at 7.5 km/s.

The companion, Mu Ursae Majoris B, has a mass of 0.96 solar masses. The two components orbit each other with a period of 230.089 days at a separation of 0.0028 arcseconds, corresponding to an orbital distance of only 0.2 astronomical units (Earth – Sun distances).

Mu Ursae Majoris A and B are too close together to be resolved visually, even in the largest of telescopes. The presence of the companion can only be inferred from its effect on the primary component’s spectrum.

Tania Australis is a suspected variable star. Its brightness has been observed to vary from magnitude 2.99 to 3.33. It is catalogued as AAVSO 1016+42 by the American Association of Variable Star Observers.

Tania Australis (Mu Ursae Majoris), image credit: ESO/Digitized Sky Survey 2 (CC BY 4.0)

Facts

Tania Australis is part of the Three Leaps of the Gazelle, a relatively bright star pattern formed by three pairs of stars that represent the paws of the Great Bear. The old Arabic asterism is formed by Alula Australis (Xi Ursae Majoris) and Alula Borealis (Nu Ursae Majoris), Tania Australis (Mu Ursae Majoris) and Tania Borealis (Lambda Ursae Majoris), and Talitha (Iota Ursae Majoris) and Alkaphrah (Kappa Ursae Majoris).

Alula Australis and Alula Borealis form the first leap (the first spring), Tania Australis and Tania Borealis the second leap, and Talitha and Alkaphrah the third leap.

Three Leaps of the Gazelle, image: Stellarium

In Arabic legend, the Three Leaps asterism represented the leaps of a gazelle that fled across a large pond after being startled by a lion. In Arabic, it was called Kafzah al Thiba’, meaning “the springs of the gazelle.”

Even though they appear close in the sky, Tania Australis and Tania Borealis are not physically related. Tania Borealis lies 138 light-years away and is almost 100 light-years closer to us. The blue-white subgiant is the fainter of the pair, shining at magnitude 3.45.

Tania Australis and Tania Borealis – the Second Leap, image credit: ESO/Digitized Sky Survey 2 (CC BY 4.0)

Name

The name Tania Australis (pronunciation: /ˈteɪniə ɔːˈstreɪlɪs/) is derived from the Arabic phrase Al Fiḳrah al Thānia, meaning “the second spring (of the gazelle)” or “the second leap (of the gazelle).” The word australis is Latin for “southern” or “the south side.” The name refers to the star’s position in the Three Leaps of the Gazelle asterism.

Mu Ursae Majoris was also called Alkafzah al Thaniyah, meaning “the second leap,” and Al Phikra al Thania or Al Fikrah, “the vertebra.”

The International Astronomical Union’s (IAU) Working Group on Star Names (WGSN) approved the name for the primary component of the Mu Ursae Majoris system on July 20, 2016.

In traditional Chinese astronomy, Tania Australis was known as 中台二 (Zhōng Tái èr), the Star of Second Middle Step. It formed a Chinese asterism known as Three Steps, which corresponded to the Arabic Three Leaps of the Gazelle. The asterism was part of the Supreme Palace Enclosure, which represented the imperial court.

Location

Tania Australis and Tania Borealis appear almost halfway between the Big Dipper and the Sickle of Leo, the asterism that marks the head of the celestial Lion. The two relatively bright stars stand out in this part of the sky on a clear night. Tania Borealis is the northern of the two stars and Tania Australis is the southern.

At declination +41° 30, Tania Australis never rises for observers south of the latitude 48° S and is best seen from the northern hemisphere.

The location of Tania Australis (Mu Ursae Majoris), image: Stellarium

The stars of the Second Leap of the Gazelle can be used to find the faint constellation Leo Minor (the Smaller Lion), which lies just below the Great Bear’s feet, between the two stars and the Sickle of Leo.

Tania Australis and Tania Borealis can also be used to find the Little Pinwheel Galaxy (NGC 3184, NGC 3180) and the galaxy NGC 3198. The Little Pinwheel Galaxy is an unbarred spiral galaxy located approximately 39.8 million light-years away and NGC 3198 is a barred spiral galaxy 47 million light years away. The galaxies have apparent magnitudes of 10.4 and 10.3.

Tania Australis, Tania Borealis, NGC 3184 and NGC 3198, image credit: ESO/Digitized Sky Survey 2 (CC BY 4.0)

Constellation

Tania Australis is located in the constellation of Ursa Major. Associated with the nymph Callisto, who was turned into a bear in Greek mythology, the Great Bear is one of the ancient constellations catalogued by the Greek astronomer Claudius Ptolemy in the 2nd century CE. It is the largest constellation in the northern celestial hemisphere and the third largest constellation in the sky, after Hydra and Virgo. It stretches across 1,280 square degrees of the far northern sky.

Ursa Major is best-known for the Big Dipper, one of the most recognizable northern asterisms. Formed by seven bright stars, the prominent star pattern makes the Great Bear one of the most familiar constellations in the night sky.

The brightest stars in Ursa Major include the A-type stars Alioth (Epsilon Ursae Majoris), Mizar (Zeta Ursae Majoris), Merak (Beta Ursae Majoris), Phecda (Gamma Ursae Majoris) and Megrez (Delta Ursae Majoris), the K-type giants Dubhe (Alpha Ursae Majoris) and Psi Ursae Majoris, and the hot blue main sequence star Alkaid (Eta Ursae Majoris).

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

Other notable stars in the constellation include the yellow dwarf Chalawan (47 Ursae Majoris) and orange dwarf HIP 57274, each with three orbiting extrasolar planets, the contact binary star W Ursae Majoris, a prototype for its own class of variable stars, and the red dwarf Lalande 21185, the fourth nearest star system to the Sun (after Alpha Centauri, Barnard’s Star and Wolf 359).

The Great Bear constellation hosts many bright and well-known deep sky objects. These include the planetary nebula Messier 97, better known as the Owl Nebula, the Pinwheel Galaxy (Messier 10c1), Bode’s Galaxy (Messier 81), the Cigar Galaxy (Messier 82), and the barred spiral galaxies Messier 108 and Messier 109.

The best time of the year to observe the stars and deep sky objects of Ursa Major is during the month of April, when the constellation appears higher above the horizon in the early evening. The entire constellation is visible from locations between the latitudes 90° N and 30° S.

The 10 brightest stars in Ursa Major are Alioth (Epsilon UMa, mag. 1.77), Dubhe (Alpha UMa, mag. 1.79), Alkaid (Eta UMa, mag. 1.86), Mizar (Zeta UMa, mag. 2.04), Merak (Beta UMa, mag. 2.37), Phecda (Gamma UMa, 2.438), Psi Ursae Majoris (mag. 3.01), Tania Australis (Mu UMa, mag. 3.06), Talitha (Iota UMa, mag. 3.14), and Theta Ursae Majoris (mag. 3.166).

Tania Australis – Mu Ursae Majoris