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Multi-epoch observations have revealed the variability of pre-main sequencestars and/or their environment. Moreover, structures in orbital motion aroundthe central star, resulting from planet-disk interaction, are predicted tocause temporal variations in the brightness distributions of protoplanetarydisks. Through repeated observations with the Very Large TelescopeInterferometer (VLTI) over nearly two decades, the ESO Archive has become atreasure chest containing high-resolution multi-epoch near- and mid-infraredobservations of the potential planet-forming regions in protoplanetary disks.We aim to investigate whether the existing multi-epoch observations provideevidence for the variability of the brightness distributions of the innermostfew astronomical units of protoplanetary disks and to quantify any variationsdetected. We present different approaches to search for evidence of temporalvariations based on multi-epoch observations obtained with the VLTI instrumentsPIONIER, AMBER, and MIDI for 68 pre-main sequence stars. For nine objects inour sample, multi-epoch data obtained using equal baselines are available thatallow us to directly detect variations in the visibilities due to temporallyvariable brightness distributions. Significant variations of the near-infraredvisibilities obtained in different epochs with PIONIER and/or AMBER for HD50138, DX Cha, HD 142527, V856 Sco, HD 163296, and R CrA were found. Byestimating the impact of a small variation of the baseline on the measuredsquared visibilities, we are able to compare the data of another 12 pre-mainsequence stars. Thereby, we find evidence for temporal variations of thebrightness distribution of one additional object, AK Sco. Besides the twobinaries DX Cha and AK Sco, HD 50138 and V856 Sco also show signs ofvariability caused by variations of asymmetric structures in the brightnessdistribution.

Interferometric study on the temporal variability of the brightness distributions of protoplanetary disks