Bonatto, C.; Bica, E.; Santos, J. F. C., Jr. (abril de 2005). «Spatial dependence of 2MASS luminosity and mass functions in the old open cluster NGC 188». Astronomy and Astrophysics433 (3): 917-929. Bibcode:2005A&A...433..917B. doi:10.1051/0004-6361:20041113.
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Bonatto, C.; Bica, E.; Santos, J. F. C., Jr. (abril de 2005). «Spatial dependence of 2MASS luminosity and mass functions in the old open cluster NGC 188». Astronomy and Astrophysics433 (3): 917-929. Bibcode:2005A&A...433..917B. doi:10.1051/0004-6361:20041113.