Analysis and calibration of absorptive images of Bose-Einstein condensate at nonzero temperatures.

We describe the method allowing quantitative interpretation of absorptive images of mixtures of Bose-Einstein condensate and thermal atoms which reduces possible systematic errors associated with evaluation of the contribution of each fraction and eliminates arbitrariness of most of the previous approaches. By using known temperature dependence of the BEC fraction, the analysis allows precise calibration of the fitting results. The developed method is verified in two different measurements and compares well with theoretical calculations and with measurements performed by another group.