Angular dimensions of accreting young stars

Abstract

ALTHOUGH every star passes through a pre-main sequence stage during its formation, only a few astronomical objects have been considered as likely candidates for the early protostellar evolutionary stage¹. The bulk of the energy observed as radiation emitted by a compact source in the near IR, from 2 to 10 µm, is attributed to thermal emission from a dust shell, where the opacity is a rapidly varying function of the wavelength. To study radiative transfer models, the knowledge of the spatial intensity distribution on the object surface in the near IR is crucial. We have developed a method of IR speckle inter-ferometry² which allows the spatial spectrum of an object in a given direction in the modulus sense to be determined up to the frequency cut-off of the telescope. As usual in speckle interferometry techniques the phase is lost unless sophisticated phase-restoration techniques are used. We applied this method to several protostellar candidates: the BN object, W3IRS5, R MonIRS3, CRL2591 and S140IR at wavelengths 4.8 and 3.5 µm. We present here the results of dealing with BN and W3IRS5, and a more detailed interpretation of the whole set will be given elsewhere.