The 55 UMa Wide Quadruple System
This map show the positions and proper motion vectors for the 55 UMa triple system and star HD 98423.
The distances (calculated via the revised Hipparcos parallaxes) and proper motions for these stars are almost identical (from van Leeuwen 2007). 55 UMa has a revised Hipparcos parallax of 17.00+-0.34 mas (d = 58.8+-1.2 pc) and HD 98423 has a parallax of 17.05+-0.59 mas (d = 58.7+-2.0 pc). As shown, the proper motions agree to within 0.21+-0.71 mas/yr, and their tangential velocities agree to 0.06+-0.20 km/s. The 55 UMa triple system (Aa+Ab+B) has a systemic radial velocity of -3.1+-8 km/s (Liu et al. 1997) and HD 98423 has a radial velocity of -3.1+-1 km/s (Gontcharov 2006).
The 55 UMa triple and HD 98423 are co-distant, and share common proper motion and radial velocity. Hence, HD 98423 should probably be considered "55 UMa C", and the 55 UMa system would appear to be at least quadruple. The 55 UMa system has a very wide AC separation of 500".06, translating to a projected physical separation ~29,400 AU at d = 58.8+-1.0 pc (from weighted mean parallax).
Liu et al. (1997) and Tokovinin (1997) have both mentioned HD 98423 as a common proper motion companion. Tokovinin catalogued the quadruple as IDS 11137+3844, and estimated the total system mass of the quadruple to be 7.64 Msun.
De Rosa et al. (2014) estimate the age of 55 UMa to be 500 Myr, although it is unclear if this isochronal age took into account the unresolved multiplicity of the system. Casagrande et al. (2011) estimated isochronal ages for HD 98423 in the range of 0.9 to 1.0 Gyr.
