Orthogonal polynomials and measures on the unit circle. The Geronimus transformations

12 pages, no figures.-- MSC2000 codes: 42C05, 15A23.-- Published in Special Issue dedicated to William B. Gragg on the occasion of his 70th birthday.In this paper we analyze a perturbation of a nontrivial positive measure supported on the unit circle. This perturbation is the inverse of the Christoffel transformation and is called the Geronimus transformation. We study the corresponding sequences of monic orthogonal polynomials as well as the connection between the associated Hessenberg matrices. Finally, we show an example of this kind of transformation.The work of the first author (L. Garza) has been supported by a grant from the Universidad Autónoma de Tamaulipas. The work of the second author (J. Hernández) has been supported by a grant from the Fundación Universidad Carlos III de Madrid. The research of the third author (F. Marcellán) has been supported by Dirección General de Investigación, Ministerio de Educación y Ciencia of Spain, grant MTM 2006-13000-C03-02.Publicad