Barry, Don C.; Cromwell, Richard H.; Hege, E. Keith, Chromospheric activity and ages of solar-type stars, Astrophysical Journal, Part 1, April 1987, 315: 264–272, Bibcode:1987ApJ...315..264B, doi:10.1086/165131
Barry, Don C.; Cromwell, Richard H.; Hege, E. Keith, Chromospheric activity and ages of solar-type stars, Astrophysical Journal, Part 1, April 1987, 315: 264–272, Bibcode:1987ApJ...315..264B, doi:10.1086/165131