We derive absolute dimensions for two early-type main sequence detached eclipsing binaries in the young open cluster h Persei ( NGC 869 ) .
V615 Persei has a spectral type of B7 V and a period of 13.7 days .
V618 Persei is A2 V and has a period of 6.4 days .
New ephemerides are calculated for both systems .
The masses of the component stars have been derived using high-resolution spectroscopy and are 4.08 \pm 0.06 { M } _ { \odot } and 3.18 \pm 0.05 { M } _ { \odot } for V615 Per and 2.33 \pm 0.03 { M } _ { \odot } and 1.56 \pm 0.02 { M } _ { \odot } for V618 Per .
The radii have been measured by fitting the available light curves using ebop and are 2.29 \pm 0.14 { R } _ { \odot } and 1.90 \pm 0.09 { R } _ { \odot } for V615 Per and 1.64 \pm 0.07 { R } _ { \odot } and 1.32 \pm 0.07 { R } _ { \odot } for V618 Per .
By comparing the observed spectra of V615 Per to synthetic spectra from model atmospheres we find that the effective temperatures of the two stars are 15000 \pm 500 K and 11000 \pm 500 K. The equatorial rotational velocities of the primary and secondary components of V615 Per are 28 \pm 5 km s ^ { -1 } and 8 \pm 5 km s ^ { -1 } , respectively .
Both components of V618 Per rotate at 10 \pm 5 km s ^ { -1 } .
The equatorial rotational velocities for synchronous rotation are about 10 km s ^ { -1 } for all four stars .
The timescales for orbital circularisation for both systems , and the timescale for rotational synchronisation of V615 Per , are much greater than the age of h Per .
Their negligible eccentricities and equatorial rotational velocities therefore support the hypothesis that they were formed by ‘ delayed breakup ’ ( Tohline 2002 ) .
We have compared the radii of these stars to models by the Granada and the Padova groups for stars of the same masses but different compositions .
We conclude that the metallicity of the stars is Z \approx 0.01 .
This appears to be the first estimate of the bulk metallicity of h Per .
Recent photometric studies have assumed a solar metallicity so their results should be reviewed .