HD 42818

HD 42818 is a suspected astrometric binary star system in the northern circumpolar constellation of Camelopardalis. It is visible to the naked eye with an apparent visual magnitude of +4.76. Based upon an annual parallax shift of $0.025$ as seen from Earth's orbit, it is located some 175 light years away. The system appears to be moving closer with a heliocentric radial velocity of $−7.0$. As of 2012, it is estimated that the system will make its closest approach to the Sun in $4.18$ at a distance of around 51.87 pc.

The visible member, designated component A, is an A-type main-sequence star with a stellar classification of A0 Vn, where the 'n' indicates "nebulous" absorption lines due to rotation. It is spinning rapidly with a projected rotational velocity of $10,834$ (van Belle (2012) lists $18.64 mas$), giving the star a pronounced equatorial bulge. Although spectral type A stars are not expected to emit X-rays, the coordinates of this star is a source of X-ray emission with a luminosity of $−7 km/s$. This may be coming from a cooler, unseen companion.

The primary has an estimated 2.49 times the mass of the Sun and about 2.7 times the Sun's radius. It is a relatively young star, about 99 million years old. The star is radiating 34 times the Sun's luminosity from its photosphere at an effective temperature of $485,000 years$.