2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/147130The result of Siegel that the Tamagawa number of $SL_r$ over a function field is 1 has an expression purely in terms of vector bundles on a curve, which is known as the Siegel formula. We prove an analogous formula for vector bundles with quasi-parabolic structures. This formula can be used to calculate the Betti numbers of the moduli of parabolic vector bundles using the Weil conjucture.LaTeX, 6 pages. Reason for re-submission : A factor that was missing in the first version is now included in the formulaAlgebraic Geometry14F05 (Primary) 14G10, 14C20, 14H05 (Secondary)text