The Hipparcos Catalogue mission discovered Arcturus to be a binary star system. Arcturus A is an orange colored giant K1.5IIIFe-0.5 star. The spectral type implies an effective temperature of the star is about 4300 K and a mass about 20 times that of the sun.
The Apparent Magnitude and distance indicate a luminosity 110 times that of the sun. The star has about 28 times the diameter of the sun.
The companion Arcturus B is about 3.3 magnitudes dimmer than A. At 0.255 arc sec of separation, the projected distance between the stars is 2.9 AU.
According to Burnham, Arcturus is the fourth brightest star in the sky.