We use photometric and spectroscopic observations of the eclipsing binary V69-47 Tuc to derive the masses , radii , and luminosities of the component stars .
Based on measured systemic velocity , distance , and proper motion , the system is a member of the globular cluster 47 Tuc .
The system has an orbital period of 29.5 ~ { } d and the orbit is slightly eccentric with e = 0.056 .
We obtain M _ { p } = 0.8762 \pm 0.0048 M _ { \odot } , R _ { p } = 1.3148 \pm 0.0051 R _ { \odot } , L _ { p } = 1.94 \pm 0.21 L _ { \odot } for the primary and M _ { s } = 0.8588 \pm 0.0060 M _ { \odot } , R _ { s } = 1.1616 \pm 0.0062 R _ { \odot } , L _ { s } = 1.53 \pm 0.17 L _ { \odot } for the secondary .
These components of V69 are the first Population II stars with masses and radii derived directly and with an accuracy of better than 1 % .
We measure an apparent distance modulus of ( m - M ) _ { V } = 13.35 \pm 0.08 to V69 .
We compare the absolute parameters of V69 with five sets of stellar evolution models and estimate the age of V69 using mass-luminosity-age , mass-radius-age , and turnoff mass - age relations .
The masses , radii , and luminosities of the component stars are determined well enough that the measurement of ages is dominated by systematic differences between the evolutionary models , in particular , the adopted helium abundance .
By comparing the observations to Dartmouth model isochrones we estimate the age of V69 to be 11.25 \pm 0.21 ( random ) \pm 0.85 ( systematic ) Gyr assuming [ Fe/H ] = -0.70 , [ \alpha /Fe ] = 0.4 , and Y = 0.255 .
The determination of the distance to V69 , and hence to 47 Tuc , can be further improved when infrared eclipse photometry is obtained for the variable .