56 Andromedae

Lore & Background

The primary component is an aging giant star of spectral class K0 III, having exhausted hydrogen at its core and evolved off the main sequence. It is a red clump giant that has undergone a helium flash and now generates energy through helium fusion. The star is about 3.1 billion years old, has 1.3 times the Sun's mass, and has expanded to 11 times the Sun's radius. It radiates 56 times the Sun's luminosity from an enlarged photosphere at an effective temperature of 4,765 K. Its rotation rate is negligible, suggesting the rotation axis likely points toward Earth.

The faint secondary component has a magnitude of 11.93. As of 2001, it was located at an angular separation of 18.50″ along a position angle of 77°. This separation has changed little since 1903, when it was measured at 18.4″ along a position angle of 80°. The system is moving further from Earth with a heliocentric radial velocity of +62 km/s and traverses the celestial sphere at a relatively high proper motion of 0.183″ per year. The pair is positioned near the line of sight to the open cluster NGC 752, which lies 1,490 light-years away.

Reader's Guide

56 Andromedae serves as a useful example of a probable binary system containing a red clump giant primary. Its measured parallax of 10.0 mas from the Gaia space observatory provides a reliable distance of 327 light-years, and its high proper motion of 0.183″ per year and radial velocity of +62 km/s indicate significant motion relative to the Sun. The primary's status as a red clump giant—a star that has undergone helium flash and now fuses helium in its core—offers insight into the later evolutionary stages of intermediate-mass stars. The secondary component's nearly unchanged separation and position angle over nearly a century (18.4″ at PA 80° in 1903 versus 18.50″ at PA 77° in 2001) suggests a long-period, gravitationally bound orbit, though the article notes the system is only a 'probable' binary. The system's location near the line of sight of the open cluster NGC 752 (at 1,490 light-years) provides a useful foreground/background contrast for studies of stellar populations and distances.

Did You Know?

• 56 Andromedae has a combined apparent visual magnitude of 5.69, just bright enough to be dimly visible to the naked eye under good seeing conditions.
• The secondary component's angular separation changed only slightly from 18.4″ in 1903 to 18.50″ in 2001.