Tracing dust at the edge of destruction: NIR observations of YSO transitional disks and nearby AGN with the Keck interferometer

After a short introduction to modern infrared long baseline interferometry, I will present the results of two actual projects of mine, dealing with dust around stars and AGN. Based on observations with the Keck interferometer, we could show that the infrared-excess in transitional YSO class II disks typically derives from circumstellar disk material, and not from a close companion star. Disk dissipation induced by planet formation now appears to be the most likely interpretation of the found structures. In the second part of the talk, I summarize recent progress on NIR interferometry of Seyfert nuclei, which successfully resolves the innermost dust at the edge of sublimation in the AGN radiation field. The data confirms that the NIR excess of Seyfert SED derives from circumnuclear dust emission at a few tens-to-hundreds of mpc, and not from direct AGN emission.