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We measured the mid-infrared extension of the gaseous disk surrounding sevenBe stars in order to constrain the geometry of their circumstellar environmentsand to try to infer physical parameters characterizing these disks. We used theVLTI/MIDI instrument with baselines up to 130 m to obtain an angular resolutionof about 15 mas in the N band and compared our results with previous K bandmeasurements obtained with the VLTI/AMBER instrument and/or the CHARAinterferometer. We obtained one calibrated visibility measurement for each ofthe four stars, p Car, zeta Tau, kappa CMa, and alpha Col, two for delta Cenand beta CMi, and three for alpha Ara. Almost all targets remain unresolvedeven with the largest VLTI baseline of 130m, evidence that their circumstellardisk extension is less than 10 mas. The only exception is alpha Ara, which isclearly resolved and well-fitted by an elliptical envelope with a major axisa=5.8+-0.8mas and an axis ratio a/b=2.4+-1 at 8 microns. This extension issimilar to the size and flattening measured with the VLTI/AMBER instrument inthe K band at 2 microns. The size of the circumstellar envelopes for theseclassical Be stars does not seem to vary strongly on the observed wavelengthbetween 8 and 12microns. Moreover, the size and shape of Alpha Ara's disk isalmost identical at 2, 8, and 12microns.

VLTI/MIDI observations of 7 classical Be stars