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Paper: Studying Young Circumstellar Disks with ALMA
Volume: 344, The Cool Universe: Observing Cosmic Dawn
Page: 190
Authors: Menard, F.
Abstract: Accretion disks are pivotal elements in the formation and early evolution of solar-like stars. On top of supplying the raw material for stellar build-up, their internal conditions also regulate the formation of planets. Their study therefore holds the key to solve the mystery of the formation of our Solar System. This article focuses on observational studies of circumstellar disks associated with pre-main sequence solar-like stars and presents a few selected problems where ALMA will contribute in finding answers. At optical and near-infrared wavelengths, the direct measurement of disk parameters poses an obvious challenge: at the distance of typical star forming regions (e.g. ∼140 pc for Taurus), a planetary system like ours (with a diameter of ≈ 50AU out to Pluto, but excluding the Kuiper belt) subtends only 0.″35. Moreover, its surface brightness is low in comparison to the bright central star. Hence, high angular resolution and high contrast imaging techniques are required if one hopes to resolve and measure such protoplanetary disks. Fortunately, potent imaging instruments have been available for about 10 years now. They cover a large part of the electromagnetic spectrum, from the UV/optical with HST, the near-infrared with ground-based adaptive optics systems to the millimeter range with long-baseline radio interferometers. It is therefore not surprising that our knowledge of the structure of disks surrounding low-mass stars has made a gigantic leap forward in the last decade. However, the angular resolution of current millimeter interferometers will remain significantly poorer than the resolution that is available at shorter wavelengths (∼ 0.″1) until ALMA provides the necessary long baselines. At that time, astronomers will have access to data of comparable resolution over a very large wavelength range, with unprecedented sensitivity. As a direct consequence, our understanding of the disk structure and evolution should improve just as much. In the following pages I will attempt to give an overview of the structural and physical parameters of protoplanetary disks that can be estimated today from direct observations.
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