A team of astronomers, using the University of Florida mid-IR camera/spectrometer OSCIR on the CTIO 4m Blanco telescope, has discovered a disk around a nearby star that may be forming -- or may have already formed -- planets. The discovery was made by a team comprised of Ray Jayawardhana, Lee Hartmann, Giovanni Fazio (Harvard-Smithsonian Center for Astrophysics) Scott Fisher, Charles Telesco, and Robert Pina (Florida). The dust disk was also discovered independently and simultaneously by a second group using the Keck II 10-m telescope.
The newly-discovered disk surrounds HR4796A in Centaurus. The disk is roughly 250 AU across and is seen nearly edge-on in 20 µm images. It is much younger than the Beta Pictoris disk -- 10 million vs 200 million years old -- and is the right age for planet formation. The binary companion HR4796B is 500 AU from the primary. The composite nature of this system suggests that the presence of a companion star does not necessarily disrupt a disk before it has had enough time to form planets.
Caption: An image of the disk around the star HR 4796A. Star A and its companion B are indicated by crosses. The disk is seen at the wavelength of 19.2 µm. The emission arises from small dust particles heated by star A's visible and ultraviolet light. The elongated shape of the emission indicates that the disk is seen nearly edge-on. In addition, the disk appears to lie in the orbital plane of the binary system. A false-color image is available at: http://www.astro.ufl.edu/news/.
From previous work by Michael Jura at UCLA and colleagues, it was known that the primary star was surrounded by a dust cloud with a central hole. The OSCIR images show that the cloud is indeed a disk. The hole may be due to gravitational clearing by inner planets. The disk truncation at 125 AU radius may represent a similar effect due to the companion. A definitive test of this possibility requires an improved determination of the binary orbit.
The disk is fainter at 10 µm than at 20 µm, but is undetectable at 2 µm the longest working wavelength of many near-IR cameras. OSCIR's 128 × 128 Si:As Rockwell array represents a major advance in mid-IR detector technology which, together with the superb imaging qualities of the Blanco telescope, made this discovery possible. OSCIR was built by Telesco and colleagues at the University of Florida. It is available as a facility instrument at CTIO through a collaborative agreement, with technical support provided by the Florida group. "This discovery is a particularly exciting example of the science enabled by the NSF through the National Astronomy Centers," says Hugh Van Horn, Director of NSF's Division of Astronomical Sciences. "In this case, the cooperation between the University of Florida and CTIO is making this innovative instrument available to all U.S. astronomers." The research of both discovery teams was supported in large part by the NASA Origins Program, with additional support to the CfA/Florida team from NSF, NOAO, and the Smithsonian Institution.