The approaches mentioned in the section title belong to one family which is called in Newton's book [ 56 ] the short waves or high energy approximation (HEA). It means the scattering by soft particles (or potentials) in the case of the wavelengths short in comparison with the particle size (or correspondingly the case of scattering of high energy particles by the potentials). ...

... We explore the structures immediately surrounding the intermediate-mass young stellar object R Mon with bispec- trum speckle interferometry, conventional near-infrared imaging and by analyzing optical HST archive data. Our near-infrared speckle images with unprecedented diffraction-limited resolution of 55 mas (44 AU; H -band) and 76 mas (61 AU; K -band) represent the highest resolution R Mon images obtained so far and exhibit previously unseen complex structures. ... The features 1­5 are marked. ...