Epsilon Hydrae

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Epsilon Hydrae is a nearby, multi-star system in the Hydra constellation. It shines as a bright point in the sky with an apparent magnitude of about 3.38 and lies roughly 129 light-years from the Sun.

The system’s main pair, Epsilon Hydrae A and Epsilon Hydrae B, form a close binary. They orbit each other every about 15 years, separated by only about 0.25 arcseconds as seen from Earth. Epsilon Hydrae A is the brighter, larger star: a yellowish giant with about 2 solar masses, roughly 8 solar radii, and about 44 times the Sun’s luminosity, with an surface temperature around 5080 K. It rotates relatively quickly and has a bright companion, Epsilon Hydrae B, which has about 1.66 solar masses.

There is a third component, Epsilon Hydrae C, which is itself a spectroscopic binary detected through its spectral lines. C orbits the AB pair with a very long period of about 870 years and sits a few arcseconds away from AB (about 3 arcseconds).

A possible fourth member, Epsilon Hydrae D, is farther out—about 19 arcseconds from AB—with an estimated orbital period of around 10,000 years.

In naming, Epsilon Hydrae A has the official name Ashlesha, assigned by the IAU in 2018. The system also carries historic names in various cultures, such as its association with the Willow asterism in Chinese astronomy and with Hindu astronomy’s Ashlesha. The AB pair dominates the system’s light, while C is much fainter.