The discrepant mean density of mu Eridani

The star μ Eri = HR 1520 = HD 30211 (B5 IV, V= 4.00 mag) is an SB1 and EA system with an SPB primary. Using the available radial-velocity and photometric time-series observations, I revise the spectroscopic orbital elements and solve the eclipsing light curve. From the orbital solution, I derive the primary's mean density. This mean density is smaller than the value obtained from the star's position in the HR diagram. The discrepancy amounts to about 3σ. I show that the discrepancy can be removed by adding a ``third light'' to the system. However, the ``third light'' would have to be so bright that it is difficult to understand why it has not been detected long ago.