Interferometric-Doppler imaging of stellar surface structure

In this paper we discuss the combination of two basic approaches which shou ld potentially generate images of spatially unresolved stars: differential interferometry and classical spectroscopy. Doppler Imaging provides indirec t observational information on stellar surface structures by modeling the r otational modulation of the observed flux distribution across spectral line s. Similarly, differential interferometry makes it possible to measure the disturbances of photocentroid location of an unresolved star as a function of wavelength and to deduce the corresponding stellar map. We present the g eneral formalism to reconstruct images from spectroscopy and differential i nterferometry data for sources with spatially unresolved structures, and we discuss how their combination improves the image reconstructions. This tec hnique, that we call Interferometric-Doppler Imaging (IDI), leads to signif icant progress in solving some long-standing problems of Doppler Imaging, s uch as latitude smearing and bias as well as the non-uniqueness of the solu tion in the special case of an equator-on star. We treat explicitly the mos t delicate case of non-radial stellar pulsations, for which the cancellatio n of opposite sign temperature or velocity fields introduces additional dif ficulties. The performance of the method is demonstrated, using the indirec t imaging code built on the basis of the developed approach to reconstruct an input image from a series of generated noisy spectra. The problem of ima ge reconstruction from two-aperture interferometry data has been particular ly addressed since it represents the case of most presently operating inter ferometers.