We determine the orbital elements for the K0 IV + white dwarf ( WD ) system IP Eri , which appears to have a surprisingly long period of 1071 d and a significant eccentricity of 0.25 .
Previous spectroscopic analyses of the WD , based on a distance of 101 pc inferred from its Hipparcos parallax , yielded a mass of only 0.43 M _ { \odot } , implying it to be a helium-core WD .
The orbital properties of IP Eri are similar to those of the newly discovered long-period subdwarf B star ( sdB ) binaries , which involve stars with He-burning cores surrounded by extremely thin H envelopes , and are therefore close relatives to He WDs .
We performed a spectroscopic analysis of high-resolution spectra from the HERMES/Mercator spectrograph and concluded that the atmospheric parameters of the K0 component are T _ { eff } = 4960 K , \log { g } = 3.3 , [ Fe/H ] = 0.09 and \xi = 1.5 km s ^ { -1 } .
The detailed abundance analysis focuses on C , N , O abundances , carbon isotopic ratio , light ( Na , Mg , Al , Si , Ca , Ti ) and s -process ( Sr , Y , Zr , Ba , La , Ce , Nd ) elements .
We conclude that IP Eri abundances agree with those of normal field stars of the same metallicity .
The long period and non-null eccentricity indicate that this system can not be the end product of a common-envelope phase ; it calls instead for another less catastrophic binary-evolution channel presented in detail in a companion paper .