Cavities in Inner Circumstellar Disks: The GM Aurigae Case

International audience; Recent modeling based on unresolved infrared observations of the spectral energy distribution (SED) of GM Aurigae suggests that the inner disk of this single TTauri star is truncated at an inner radius of 25 AU. Using the IRAM array, we obtained high angular resolution (about 1.5") observations with a high S/N per channel of the 13CO J=2-1 and C18O J=2-1 and of the 13CO J=1-0 lines. A standard parametric disk model is used to fit the line data in the Fourier-plane and to derive the CO disk properties. Our measurement is based on a detailed analysis of the spectroscopic profile from the CO disk rotating in Keplerian velocity. The millimeter continuum, tracing the dust, is also analyzed. We detect an inner cavity of radius 19 +/-4 AU at the 4.5 sigma level. Its origin remains unclear, but can be linked to planet formation or to a low mass stellar companion orbiting close to the central star (around 5-15 AU). The frequent finding of inner cavities suggests that either binarity is the most common scenario of star formation in Taurus or that giant planet formation starts early.