GM Aurigae: A Disk Cleared by a Planet?

GM Aurigae is a classical T Tauri star that has been studied at many wavelengths (optical through radio) with a variety of techniques (imaging, photometry, spectroscopy). The system is believed to be between 2 and 10 million years old and is surrounded by a large circumstellar dust disk. The dust disk is detected through the characteristic infrared excess emission in its broad band spectral energy distribution (SED) and has been imaged in scattered light by the Hubble Space Telescope. The disk is also seen in CO molecular line images where its velocity structure is well modeled with Keplerian rotation.

The SED shows a dearth of excess emission at near-IR wavelengths and this has been interpreted as due to a gap in the disk between the star and 4AU. We have recently constructed scattered light, SED, and dynamical models for the GM Aur disk, specifically to investigate whether the 4AU gap could be caused by the interaction of a planet with the disk.

We find that the scattered light images and SED can indeed be explained with a 300AU, 0.05 solar mass disk that is cleared of material out to 4AU from the star. Dynamical models of planets interacting with disks show that such a gap may be formed by a Jupiter mass planet and that the gap will be long-lived. At present we are unable to tightly constrain the mass of the unseen planet, but future mid-IR observations with the Space Infrared Telescope (SIRTF) will enable us to place tighter constraints on the planet mass. We also predict that the orbiting planet will cause the central star to wobble by 0.1 milliarcsec over a period of about four years and this motion should be detectable with high precision interferometry with the Keck telescope and the future Space Interferometry Mission (SIM).

We have published our findings in two papers:

NICMOS Coronagraphic Observations of the GM Aurigae Circumstellar Disk
Schneider, G., Wood, K., Silverstone, M., Hines, D.C., Koerner, D.W., Whitney, B., Bjorkman, J.E., & Lowerance P.J.
2003, AJ, 125, 1467 PDF

Constraints on a Planetary Origin for the Gap in GM Aurigae's Protoplanetary Disk
Rice, W.K.M., Wood, K., Armitage, P.J., Whitney, B., & Bjorkman, J.E.
2003, MNRAS, 342, 79 PDF

Below we show some of the images and models from these papers.

Two-color image of GM Aur taken with HST/NICMOS in coronagraphic mode. The composite combines images taken in the F110W (blue) and F160W (red) filters. The inset shows the data on a logarithmic stretch. The images show the scattered light disk and dark dust lane.

NICMOS images, scattered light models, and residuals (data-model) for the GM Aur disk. Upper panels are F110W and lower panels are F160W. Panels (left to right) show: NICMOS data, scattered light model disk at viewing angle of 50 degress, model at 55 degrees, residuals of 50 degree model, residuals of 55 degree model.
GM Aur's SED (squares) showing the large IR excess emission characteristic of a circumstellar dust disk. Our models show the SED for disks that have been cleared by planets of different masses: 0.085MJup (dot), 1.7MJup (solid), 21MJup (dot-dash), 43MJup (dash).
Zoom-in of the SED showing that SIRTF data in the 3 to 20 micron range will help to constrain the planet mass.

Disk surface density from a dynamical model of the interaction of a Jupiter mass planet with GM Aur's disk.

Two-dimensional surface density map from the dynamical simulation. A movie showing the planet clearing the gap may be seen at Ken Rice's web page.

Disk temperature structure calculated by our Monte Carlo radiative equilibrium code (left panels) and the disk density structure (right panels). The density stretch is (density)^0.1 to show the extent of the disk material that intercepts and reprocesses the stellar radiation far from the disk midplane. Note the hot inner edge and disk surface. The sizescales for the panels are 6AU (top), 20AU (middle) and 300AU (bottom).

Updated: June 2003