A visual binary star system has been observed for 40 years. During that time interval, the two stars have completed exactly one orbit about their common center of mass. The stars are far enough apart that they can be resolved, and observations indicate that the stars are in circular orbits; over the 40-year period, the stars have remained a constant 3.0 arcsec apart. The fainter of the two stars is a G2V star and so is identical to the Sun, with a mass of 1M . The distance to the stars can be determined from the apparent magnitude of the G2V star, and it is determined that the stars are 20 pc away. Assuming that the orbital plane is in the plane of the sky, what is the mass of the brighter companion star, in units M