Sigma Hydrae


Sigma Hydrae, also named Minchir, is a solitary star in the equatorial constellation of Hydra. It is visible to the naked eye with an apparent visual magnitude of 4.48. The estimated distance to this star from the Sun, based upon an annual parallax shift of 8.75 mas, is around 370 light-years. At that distance, the visual magnitude of the star is diminished by an interstellar extinction factor of 0.16, due to intervening dust.

Nomenclature

σ Hydrae is the system's Bayer designation.
It bore the traditional name Minchir, appearing as Minchir es-schudscha in Bode's large star atlas, Uranographia. The name which derived from the Arabic appelationمنخر الشجاع minkhar ash-shujāʽ "the nostril brave one" for this star. The name is erroneously spelt as Al Minliar al Shuja in the Yale Bright Star Catalogue.. In 2016, the IAU organized a Working Group on Star Names to catalog and standardize proper names for stars. The WGSN approved the name Minchir for this star on 5 September 2017 and it is now so included in the List of IAU-approved Star Names.
This star, along with Delta Hydrae, Epsilon Hydrae, Zeta Hydrae, Eta Hydrae and Rho Hydrae, were Ulug Beg's Min al Azʽal, "Belonging to the Uninhabited Spot".
In Chinese, 柳宿, meaning Willow , refers to an asterism consisting of Sigma Hydrae, Delta Hydrae, Eta Hydrae, Rho Hydrae, Epsilon Hydrae, Zeta Hydrae, Omega Hydrae and Theta Hydrae. Consequently, Sigma Hydrae itself is known as 柳宿二.
The people of Groote Eylandt, used the name Unwala for the star cluster including this star, Delta Hydrae, Epsilon Hydrae, Zeta Hydrae, Eta Hydrae and Rho Hydrae.

Properties

This is an evolved K-type giant star with a stellar classification of K2 III. The measured angular diameter of this star, after correction for limb darkening, is. At its estimated distance, this yields a physical size of about 27.6 times the radius of the Sun. It has about three times the mass of the Sun and radiates 295 times the solar luminosity from its outer atmosphere at an effective temperature of 4,491 K. Sigma Hydrae is around 430 million years old.