Relation between the interstellar gas speed and the component ratios of the interstellar gas number densities at HD 61005 and the Sun (red lines) that give the observed morphology at HD 61005. Used interstellar gas number densities at the Sun are n_{H S} = 0.2 cm^-3, n_{He S} = 0.015 cm^-3, and n_{p S} = 0.032 cm^-3. After division of the density ratios by maximal averaged efficiency factor for the radiation pressure, we obtain the relation independent of the particle properties in our model. The blue line shows the Stark approximation with considered dependence of the drag coefficients on the velocity of the ISM gas. The dashed line shows a function , where C_f is fitted to the measured data.