Epsilon Equulei (ε Equulei, ε Equ) is a star system of apparent magnitude +5.23 in the constellation of Equuleus . It is located 176 light years away from the Solar System .
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Components A and B
These two stars make up the brighter part of the Equulei Epsilon star system. They are called Epsilon Equulei A and B and are subgiants of spectral type of F7IV and F5IV respectively. Epsilon Equulei A has a surface temperature of about 6500 K and its luminosity is 11.1 times that of the Sun. The star measures 2.6 solar radii in radius and has a mass 60% greater than the Sun. Meanwhile, Epsilon Equulei B has a temperature of 6300 K and is 7.8 times more luminous than the Sun Its radius is 2.3 times larger than the Sun, and may have a mass of about 1.55 solar masses.
The orbital period of this binary is 101.5 years. Although the average separation between the two stars is 35 AU, the orbit is remarkably eccentric so that the separation between the two varies between 10 and 60 AU. The last periastron was in 1920 and the next will be in 2121.
Finally, it is thought that Epsilon Equulei A may be, in turn, a spectroscopic binary. The orbital period of the latter would be 2.03 days.
Components C and D
Approximately 10 seconds of arc A,B torque can see a star, though this star makes the second star system called Epsilon Equulei C (HIP 103571 / BD +03 4473C), of magnitude 7.3. Type is a star G0V whose binary separation is equal to or greater than 665 AU, implying an orbital period of over 7500 years.
A fourth star, Epsilon Equulei D (BD +03 4473D), completes the star system. 12.4 magnitude, its separation from the bright AB pair is over 4300 AU.
The system Equulei Epsilon has an approximate age of 2200 million years.