Delta Hydrae, Latinized from ô Hydrae, is a triple star in the equatorial constellation of Hydra. It is visible to the naked eye with an apparent visual magnitude of 4.146. Based upon an annual parallax shift of 20.34 mas, it is located about 160 light years distant.
This is a hierarchical triple system. ô Hydrae Aa and ô Hydrae Ab form a close binary system with an orbital separation of 0.9 astronomical units, taking about 200 days to complete an orbit. The outer companion, ô Hydrae B, has an angular separation of from the AaâÂÂAb pair, along a position angle of , as of 2003. At the system's distance, this separation translates in a physical projected separation of 147 AU.
The brighter component, ô Hydrae Aa, is an A-type main sequence star with a stellar classification of A1 Vnn. It is spinning rapidly with a projected rotational velocity of 285 km/s. This is giving the star an oblate shape with an equatorial bulge that is 20% larger than the polar radius. It has an estimated 2.43 times the mass of the Sun and 3.1 times the Sun's radius. The star radiates 42.7 times the solar luminosity from its photosphere at an effective temperature of 8,995 K.
Its inner companion, ô Hydrae Ab, is a red dwarf star, with 0.58 times the mass, 0.54 times the Sun's radius, and an effective temperature of 3,973 K. It may form a common envelope system when the primary evolve into a red giant.
The outer companion has a visual magnitude of 11.15. X-ray emissions have been detected from this location in space, which may be coming from a companion star.
In the catalogue of stars in the Calendarium of Al Achsasi Al Mouakket, this star was designated Lisan al Shudja, which was translated into Latin as Lingua Hydri, meaning the snake's tongue. This star, along with õ Hya, ö Hya, ÷ Hya, àHya and àHya (Minchir), were Ulugh Beg's Min al Azýal, "Belonging to the Uninhabited Spot".
According to the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, Min al Azýal or Minazal were the title for five stars: ô Hya as Minazal I, ÷ Hya as Minazal II, õ Hya as Minazal III, àHya as Minazal IV and ö Hya as Minazal V (exclude àHya)
In Chinese, (), meaning Willow (asterism), refers to an asterism consisting of ô Hydrae, àHydrae, ÷ Hydrae, àHydrae, õ Hydrae, ö Hydrae, àHydrae and ø Hydrae Consequently, ô Hydrae itself is known as (, .)
The people of Groote Eylandt called Unwala, "The Crab", for the star cluster including this star, õ Hya (Ashlesha), ö Hya, ÷ Hya, àHya and àHya (Minchir).