Abstract:
We present Hubble Space Telescope Near Infrared Camera and Multi-Object Spectrometer (NICMOS) coronagraphic observations of the environment in the region of the young star-disk system GM Aurigae. Scattered near-infrared light in two spectral bands (F110W = 1.1 μm and F160W = 1.6 μm) trace the morphology of circumstellar dust to a distance of ~700 AU from the star. An ~300 AU radius outwardly flared disk inclined 50°-55° to the plane of the sky surrounded by a tenuous envelope is seen in the NICMOS images, confirming the size and suspected flared nature of the disk suggested by earlier CO and optical observations. The NICMOS images probe the disk region with spatial resolutions of ~0ˮ.1 at radial distances of 0ˮ.35 to ~4ˮ.5-5ˮ.0 from the largely unobscured (A_v < 0.5) central star. The midplane of the disk 1ˮ.3 from GM Aurigae is revealed in silhouette against the previously unseen "lower" portion of the illuminated disk along its minor axis (as projected onto the sky). We comment on surface brightness profiles along the disk major and minor axes, as well as isophotal maps of the disk. From these photometric data we have measured the integrated flux density of the disk, beyond the instrumental inner radius of 0ˮ.35, as 8.0 and 9.3 mJy (± 20%) at F110W and F160W, respectively, corresponding to disk scattering fractions of L_ disk/L_* = 0.025 (±20%) in both bands. By fitting the photometric properties of the disk to a scattered-light model, we estimate the disk mass to be ~0.04 M_ꙩ. Additionally, we find two diffuse red polar lobes along the disk minor axis, likely the result of a bipolar outflow, at distances of ±3ˮ.8 from GM Aurigae (~900 AU with our inferred inclination) with peak H-band surface brightnesses of ~14 μJy arsec^-2. We also note the existence of a broad (~3'' wide) band of blue material within the NICMOS field of view, spatially coincident with and extending at least 12'' from the northeast outer region of the disk major axis.
