Grundahl, F, Clausen, J V, Hardis, S & Frandsen, S 2008, ' A new standard: age and distance for the open cluster NGC 6791 from the eclipsing binary member V20 ', Astronomy & Astrophysics, vol. 492, pp. 171-184 . https://doi.org/10.1051/0004-6361:200810749