Panchromatic Imaging of a Transitional Disk: The Disk of GM Aur in Optical and FUV Scattered Light

Hornbeck, J. B. and Swearingen, J. R. and Grady, C. A. and Williger, Gerard and Brown, A. and Sitko, M. L. and Wisniewski, J. P. and Perrin, M. D. and Lauroesch, J. T. and Schneider, G. and Apai, D. and Brittain, S. and Brown, J. M. and Champney, E. H. and Hamaguchi, K. and Henning, T. h. and Lynch, D. K. and Petre, R. and Russell, R. W. and Walter, F. M. and Woodgate, B. (2016) Panchromatic Imaging of a Transitional Disk: The Disk of GM Aur in Optical and FUV Scattered Light. ASTROPHYSICAL JOURNAL, 829 (2). ISSN 1538-4357

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Abstract

We have imaged GM Aurigae with the Hubble Space Telescope (HST), detected its disk in scattered light at 1400 Å and 1650 Å, and compared these with observations at 3300 Å, 5550 Å, 1.1μm, and 1.6μm. The scattered light increases at shorter wavelengths. The radial surface brightness profile at 3300 Å shows no evidence of the 24 AU radius cavity that has been previously observed in sub-mm observations. Comparison with dust grain opacity models indicates the surface of the entire disk is populated with sub- μm grains. We have compiled an SED from 0.1 μm to 1 mm, and used it to constrain a model of the star + disk system that includes the sub-mm cavity using the Monte Carlo Radiative Transfer (MCRT) code by Barbara Whitney. The best-fit model image indicates that the cavity should be detectable in the F330W bandpass if the cavity has been cleared of both large and small dust grains, but we do not detect it. The lack of an observed cavity can be explained by the presence of sub-μm grains interior to the sub-mm cavity wall. We suggest one explanation for this which could be due to a planet of mass < 9 MJ interior to 24 AU. A unique cylindrical structure is detected in the FUV data from the Advanced Camera for Surveys/Solar Blind Channel (ACS/SBC). It is aligned along the system semi-minor axis, but does not resemble an accretion-driven jet. The structure is limb-brightened and extends 190 AU ± 35 AU above the disk midplane. The inner radius of the limb-brightening is 40 ± 10 AU, just beyond the sub-millimeter cavity wall.

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