Mass segregation of different populations inside the cluster NGC 6101

We have used ESO telescopes at La Silla and the Hubble Space Telescope (HST ) in order to obtain accurate B, V, I CCD photometry for the stars located within 200" (similar or equal to2 half-mass radii, r(h) = 1.71') from the c enter of the cluster NGC 6101. Color-Magnitude Diagrams (CMDs) extending fr om the red-giant tip to about 5 magnitudes below the main-sequence turnoff MSTO (V = 20.05 +/- 0.05) have been constructed. The following results have been obtained from the analysis of the CMDs: a) The overall morphology of the main branches confirms previous results from the literature, in particu lar the existence of a sizeable population of 73 "blue stragglers" (BSS), w hich had been already partly detected (27). They are considerably more conc entrated than either the subgiant branch (SGB) or the main sequence (MS) st ars, and have the same spatial distribution as the horizontal branch (HB) s tars (84% probability from K-S test). An hypothesis on the possible BSS pro geny is also presented. b) The HB is narrow and the bulk of stars is blue, as expected for a typical metal-poor globular cluster. c) The derived magni tudes for the HB and the MSTO, V-ZAHB = 16.59 +/- 0.10, V-TO = 20.05 +/- 0. 05, coupled with the values E(B - V) = 0.1, [Fe/H] = -1.80, Y = 0.23 yield a distance modulus (m - M)(v) = 16.23 and an age similar to other "old" met al-poor globular clusters. In particular, from the comparison with theoreti cal isochrones, we derive for this cluster an age of 13 Gyrs. d) By using t he large statistical sample of Red Giant Branch (RGB) stars, we detected wi th high accuracy the position of the bump in the RGB luminosity function. T his observational feature has been compared with theoretical prescriptions, yielding a good agreement within the current theoretical and observational uncertainties.