First results from VLTI near-infrared interferometry on high-mass young stellar objects

Abstract

Due to the recent dramatic technological advances, infrared interferometry can now be applied to new classes of objects, resulting in exciting new science prospects, for instance, in the area of high-mass star formation. Although extensively studied at various wavelengths, the process through which massive stars form is still only poorly understood. For instance, it has been proposed that massive stars might form like low-mass stars by mass accretion through a circumstellar disk/envelope, or otherwise by coalescence in a dense stellar cluster. Therefore, clear observational evidence, such as the detection of disks around high-mass young stellar objects (YSOs), is urgently needed in order to unambiguously identify the formation mode of the most massive stars. After discussing the technological challenges which result from the special properties of these objects, we present first near-infrared interferometric observations, which we obtained on the massive YSO IRAS 13481-6124 using VLTI/AMBER infrared long-baseline interferometry and NTT speckle interferometry. From our extensive data set, we reconstruct a model-independent aperture synthesis image which shows an elongated structure with a size of ~ 13 x 19 AU, consistent with a disk seen under an inclination of - 45°. The measured wavelengthdependent visibilities and closure phases allow us to derive the radial disk temperature gradient and to detect a dust-free region inside of 9.5 AU from the star, revealing qualitative and quantitative similarities with the disks observed in low-mass star formation. In complementary mid-infrared Spitzer and sub-millimeter APEX imaging observations we detect two bow shocks and a molecular outflow, which are oriented perpendicular to the disk plane and indicate the presence of a bipolar outflow emanating from the inner regions of the system.