From a combination of deep Hubble Space Telescope V and I images with groundbased images in the same bands, we have obtained color–magnitude diagrams of M10, M22, and M55, extending from just above the hydrogen burning limit to the tip of the red giant branch, down to the white dwarf cooling sequence. We have used the color-magnitude arrays to extract main sequence luminosity functions (LFs) fr...

Some of the accreting black holes exhibit much stronger variability patterns than usual stochastic variations. Radiation pressure instability is one proposed mechanisms which could account for this effect. We aim to model luminosity changes objects with hole mass 10, 10$^5$, and 10$^7$ solar masses, using time-dependent evolution an accretion disk unstable due dominant radiation pressure. use a...