OBSERVATIONAL SIGNATURES OF PLANETS IN PROTOPLANETARY DISKS. I. GAPS OPENED BY SINGLE AND MULTIPLE YOUNG PLANETS IN DISKS

Abstract

It has been suggested that the gaps and cavities recently discovered in\ntransitional disks are opened by planets. To explore this scenario, we combine\ntwo-dimensional two fluid (gas + particle) hydrodynamical calculations with\nthree-dimensional Monte Carlo Radiative Transfer simulations, and study the\nobservational signatures of gaps opened by one or several planets, making\nqualitative comparisons with observations. We find that a single planet as\nsmall as 0.2 MJ can produce a deep gap at millimeter (mm) wavelengths and\nalmost no features at near-infrared (NIR) wavelengths, while multiple planets\ncan open up a few *10 AU wide common gap at both wavelengths. Both the contrast\nratio of the gaps and the wavelength dependence of the gap sizes are broadly\nconsistent with data. We also confirm previous results that NIR gap sizes may\nbe smaller than mm gap sizes due to dust-gas coupling and radiative transfer\neffects. When viewed at a moderate inclination angle, a physically circular\non-centered gap could appear to be off-centered from the star due to shadowing.\nPlanet-induced spiral arms are more apparent at NIR than at mm wavelengths.\nOverall, our results suggest that the planet-opening-gap scenario is a\npromising way to explain the origin of the transitional disks. Finally,\ninspired by the recent ALMA release of the image of the HL Tau disk, we show\nthat multiple narrow gaps, well separated by bright rings, can be opened by 0.2\nMJ planets soon after their formation in a relatively massive disk.\n