The European Space Agency's Faint Object Camera aboard NASA's Hubble Space Telescope has successfully taken its first engineering test pictures of the heavens. This "first light" picture for the Faint Object Camera (FOC) is the culmination of several weeks of intensive check-out and testing of the camera, following the launch of the Hubble Space Telescope (HST) last April 24.
The FOC is the HST's most acute "eye" on the universe. It makes full use of HST's unprecedented resolution and light-gathering capabilities.
"Almost a month after the launch of the HST, it is a great satisfaction to know that the solar arrays and the FOC are working even better than we anticipated," says ESA HST Project Manager, Robin Laurance.
The target selected for the first FOC engineering test is a group of stars in the open star cluster NGC 188, about four degrees from the North Star, Polaris. The cluster was selected because the positions and magnitudes of the cluster's stars are accurately known, and the cluster is not occluded by Earth as seen from the orbit of the Space Telescope. Approximately 5,000 light-years away, NGC 188 is the oldest known open cluster, having an estimated age of 12 billion years - nearly the age of our galaxy. At the large distance of NGC 188, stars will appear as unresolved point sources - even with the HST.
The FOC images show that the focus of the HST's mirror has been significantly improved by ground controllers since the historic "first light" picture from the HST's other imaging system, the Wide Field and Planetary Camera, which was taken on May 20th.
The accompanying pictures show two stars in the cluster NGC 188 as seen from the ground (left) and by the Faint Object Camera onboard the Hubble Space Telescope (right). The two stars are separated by 2.9 arcseconds in the sky. The dramatic improvement in spatial resolution between the two images is immediately apparent.
"These first images are a tribute to the excellent work of the scientists and engineers working for the past 15 years on the FOC Science Team," stated Dr. F. Duccio Macchetto, the FOC Science Team Leader.
The ESA HST Project Scientist, Peter Jakobsen, was thrilled to see the quality of the first images from the FOC. "After waiting all these years, this is a very exciting time. We are now ready to start our observations with a tool more powerful than ever before." One of the area of concern had been the pointing of the HST given the extremely small field of view of the FOC. "The whole team put in a lot of work in preparing for these observations, and we broke out the champagne when we saw the very stars we had expected to see in the FOC image," enthused Peter Jakobsen.
The ground-based image was obtained with the 2.5 meter Nordic Optical Telescope at the Observatorio del Roque de los Muchachos on the island of La Palma and shows the unavoidable blurring caused by turbulence in the Earth's atmosphere.
From space, with the FOC and a still to be perfectly focused telescope, the images are well separated and look almost like point sources. In reality, about 20 percent of the energy is concentrated in a tight core less than 0.1 arcseconds in diameter, while the remaining light is spread in a surrounding diffuse "halo" of size approximately 0.8 arcseconds in diameter.
During the next several weeks, as the telescope's focus is adjusted, it is expected that the image quality will be further improved with a much larger fraction of the halo light being concentrated in the 0.1 arcsecond core.
The FOC consists of two complete detector systems which fully utilize the spatial resolving power of the HST. A series of optical relays inside the FOC magnify the high-resolution image produced by the telescope's 2.4 meter primary mirror. The incoming starlight is then amplified by an image intensifier tube to produce an electronic image, which is scanned by a sensitive television camera and converted into digital data for transmission to Earth where it is reconstructed into a picture.
Amongst the many observations the FOC will make are quasars. According to estimates, the light we receive from these brilliant beacons may have traveled 13 billion years before reaching us. "The very detailed images from the FOC should confirm the theory according to which quasars are the bright cores of galaxies," says Dr. F. Duccio Macchetto. "I am very much looking forward to the close up look the FOC will give us. I am pretty sure we will see galaxies around all of the quasars we observe."
Space Telescope Science Institute, Baltimore, MD