BD−07 436, also known as WASP-77 since 2012, is a binary star system about 344 light-years away. The BD−07 436 system's concentration of heavy elements is similar to the Sun. Its stars display moderate chromospheric activity, including x-ray flares. The primary is a G-type main-sequence star, BD−07 436A (WASP-77A). The star is rotating rapidly, being spun up by the tides raised by the giant planet WASP-77Ab on its close orbit. The secondary is a K-type main-sequence star BD−07 436B orbiting at a distance of 461+200−140 AU. When calculated using spin rates, the two components appear to have different ages, with the secondary one billion years old, while the primary's age is 0.4 billion years. When calculated from X-ray luminosity, the ages are radically different and even more inconsistent at 4.5 and >8.9 billion years respectively. These ages may be unreliable, with the spin rates and X-ray luminosities affected by binary evolution, and ages inferred from the stars' positions in the H-R diagram are 7.99 and 7.3 billion years respectively.
Planetary system In 2012 a transiting hot Jupiter planet b was detected on a very tight, circular orbit. The planet may have an extended gaseous envelope and is losing mass. Its equilibrium temperature is 1715+26−25 K, the nightside temperature is 1786±84 K, and dayside planetary temperature is 1842+34−33 K. Water vapour was detected on the planetary dayside of WASP-77Ab, indicating C/O ratio similar to solar or even lower.
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