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Visibility distribution of the protostar L1527 IRS in 220 GHz continuum

Image Credit: Yusuke Aso

Visibility distribution of the protostar L1527 IRS observed with ALMA in 220 GHz continuum. Visibility distributions are the Fourier transform of images. The amplitude distribution of this protostar is narrower in the north-south direction (red) than in the east-west direction (blue), revealing 2D structures even in the Fourier domain.

Interferometers do not directly observe intensity distributions but its Fourier transform, visibility distributions. Visibility distributions have often been discussed only along the radial direction by averaging in the azimuthal direction because of sparse sampling in the UV plane and low sensitivity. In contrast, our observations demonstrate that 2D structures around a protostar can be investigated even in the Fourier domain: a profile in the north-south direction (red points) are clearly narrower than one in the east-west direction (blue points). These results help us distinguish a compact protostellar disk and a surrounding protostellar envelope from a structural point of view (Aso et al. 2017, ApJ, 849, 56).