Lambda Andromedae

Lambda Andromedae (λ And, λ Andromedae) is the Bayer designation for a binary star in the northern constellation of Andromeda. At an estimated distance of approximately 86.1 light-years (26.4 parsecs) from Earth, it has an apparent visual magnitude of +3.8. This is bright enough to be seen with the naked eye.

Lambda Andromedae is a single-lined spectroscopic binary with an orbital period of 20.5212 days. The spectrum of the primary matches a stellar classification of G8 III-IV, suggesting that it is an evolved star that lies part way between the subgiant and giant stages. The mass of this star is similar to the Sun, but it has expanded to around seven times the Sun's radius. It is radiating over 23 times the luminosity of the Sun from its outer envelope at an effective temperature of 4,800 K, giving it the characteristic yellow hue of a G-type star.

This is an RS Canum Venaticorum variable and its brightness varies by 0.225 magnitudes, reaching a maximum of 3.70, with a period of 54.2 days. Such variability is theorized to occur because of tidal friction, which results in chromosphericactivity. However, the orbit of this system is nearly circular, so the cause of this system's variability remains uncertain. The X-ray luminosity of this star, as measured by the ROSAT satellite, is 2.95 × 1030 erg s−1.