Properties and spectroscopic implications of thermal instability in X-ray binary and AGN accretion flows

We address apparent discrepancies between the discrete soft X-ray spectra of some low-mass X-ray binaries and Seyfert galaxies and the predictions of photoionization codes, via an examination of the thermal Stability properties of model accretion flows. We investigate the possibility of eliminating the thermal instability which coincides with the abundance peaks of the lowest few iron-L ions by varying conditions in the model plasmas. We probe in detail the mechanism which controls the onset of instability. We find that the existence of thermal instability al the temperatures where the line-emitting iron-L ions peak in abundance is robust to changes in the Shape of the ionizing spectrum. We test the sensitivity of the thermal instability to changes in elemental abundances. Finally, we discuss the implications of thermal instability for the interpretation of spectra from dynamic accretion flows In low-mass X-ray binaries, Seyfert galaxies, and ''warm absorber'' systems.