Three Faint Companions of Bright Stars Discovered with New Infrared Camera Developed at Penn State
Three small, faint stars, apparently locked in the gravitational embrace of much larger and brighter companions, have been discovered in the first light from a new infrared camera with innovative optics on the 100-inch telescope at the Mount Wilson Observatory in Pasadena, California.
"This is the first time the historic Mount Wilson telescope has looked at the universe through this new infrared eye, and already it is making new discoveries," says Jian Ge, assistant professor of astronomy and astrophysics at Penn State and leader of the research team, which also developed the infrared camera. The discoveries of the faint stars, to be published in the June issue of Astrophysical Journal Letters and the July issue of the Astronomical Journal, "mark the beginning of a new era in the use of the 100-inch telescope for discovering very interesting faint objects in orbit around brighter stars, such as brown dwarfs, which are neither stars nor planets," says Robert Jastrow, director of the Mount Wilson Institute.
A Gaussian pupil mask designed for deep contrast imaging for faint companions around bright stars. This is the new generation coronagraph technique being supported by NASA for further technology development for the Terrestrial Planet Finder.
One innovative technique that Ge and his team designed into the new infrared camera is a specially shaped mask they installed over the "pupil" of the camera's eye to allow fainter companions to be seen around bright objects. The shaped pupil mask that Ge's team used is an improvement over the circular masks that astronomers have been using to block the light from a bright star in an attempt to see a near-by fainter object, much like the appearance of the corona during a total eclipse of the Sun. The shaped pupil mask is a solid light-blocking circle into which Ge and his team have cut a dozen strategically placed eye-shaped openings. "The image resulting from the first use of the device revealed areas of greater contrast that allowed us to find one of the faint dwarf stars," Ge says. "The technique potentially improves contrast in images by more than tenfold compared to current techniques."
This new technique was proposed in 2001 by David Spergel at Princeton University, who comments, "This is an exciting and beautiful result. Jian and his team have done a remarkable job in taking a theoretical concept and using it to obtain an exciting scientific result. This type of coronagraph likely will be the principal instrument on the successor to the Hubble Space Telescope--an instrument capable of imaging Earth-like planets around nearby stars. Jian's work at Mount Wilson is a pathfinder for the Terrestrial Planet Finder being planned by NASA."
The dwarf stars Ge and his team discovered are less than one-tenth the mass of the Sun and give off a dark-red glow that is dimmer than our hotter Sun's yellow light. One of the stars is about 50 light years from Earth, another is about 27 light years away, and the third is at a distance of about 200 light years. Astronomers consider these stars to be nearby in our solar system's corner of the galaxy. "Our initial conservative estimate is that these are little very-dark-red dwarf stars," says Abhijit Chakraborty, a postdoctoral scholar on Ge's team. "Their mass is only about 80 to 100 times that of Jupiter, which itself is a thousand times smaller than our Sun. They have barely enough mass to burn the hydrogen in their cores, and are close to the size and luminosity of less-massive brown-dwarf objects, which don't have enough mass to ignite into stars at all."
Astronomers are in need of new techniques for imaging a dim object such as an Earth-like planet near a bright star like our Sun because, with current techniques, the star's brightness hides its dimmer near-by companions. "This discovery demonstrates that our new techniques can help reveal dim companions of larger, brighter stars," says John H. Debes, a graduate student in Ge's lab. "These three first-light discoveries demonstrate the potential to use the Mount Wilson and similar telescopes to obtain much better images in high-contrast situations."
Telescopes at the Mount Wilson Observatory have been used since 1908 to make important discoveries about the expansion of the universe, the location of galaxies, and the size of stars, paving the way for the era of modern astronomy. In the mid 1990s, the observatory was upgraded with advanced "adaptive optics" technology, which compensates for image distortions caused by the turbulence in the Earth's atmosphere. "Adaptive optics takes away the twinkling that you see when you look up at the stars in the night sky" Jastrow explains. "Adding adaptive optics made the image quality of the Mount Wilson telescope ten times sharper--as good as if the telescope were in orbit above the Earth's atmosphere."
But light pollution from nearby Los Angeles limited the telescope's capabilities in visible light, so Ge decided to build a camera that would capture infrared light coming from objects in space. One advantage of using infrared light is that it cuts right through optical light pollution. Another advantage is that a comparatively cool object like a brown dwarf glows most brightly in infrared wavelengths. "We developed the Penn State IR Imager and Spectrograph (PIRIS) to be a test bed for new infrared technology to image faint objects, including planets, for the Terrestrial Planet Finder (TPF) mission," explains Ge, who recently joined TPF teams at Princeton University and Ball Aerospace & Technologies Inc. that are studying coronagraph technology.
Ge also has invented and developed other instrument technologies that he and his colleagues at Penn State are in the process of developing further as part of his lab's $2-million instrumentation program for the discovery of extra-solar planets--including Earth-like planets--and galaxies in the early stages of their formation. "We are using our PIRIS camera and the 100-inch Mount Wilson telescope to test a suite of components that we are developing for getting better images and better spectroscopy from infrared instruments," Ge says. The researchers also are working to improve the compactness and reduce the cost of these instruments so they can be used on space telescopes, where size and weight are at the highest premium, as well as on other large ground-based telescopes.
"We hope these observing techniques will help us find and study many fainter dwarf stars and massive planets in binary systems so we can learn how planets form within such systems," Ge says. A tested theory of planet formation would help to point astronomers toward stars that are most likely to have Earth-like planets orbiting them. "None of the planets discovered elsewhere in the universe up to now have been very much like our Earth," Ge comments. "The challenge now is to find Earth-like planets around other stars."
This research was supported by the National Aeronautics and Space Administration and the Penn State Eberly College of Science.
CONTACTS AT PENN STATE:
Jian Ge: jian@astro.psu.edu or +1-814-863-9553
Barbara Kennedy (PIO): science@psu.edu or +1-814-863-4682
CONTACTS AT THE MOUNT WILSON OBSERVATORY:
Robert Jastrow: 310-441-9136, or by e-mail through Kate Barlow: mtwilsoninst3@earthlink.net
Bob Eklund (PIO): BEklund@sprynet.com or +1-310-333-3478
ABOUT THE MOUNT WILSON OBSERVATORY:
PHOTOS :
High-resolution images are available to reporters for publication. Contact Barbara K. Kennedy at science@psu.edu or (+)1-814-863-4682.
The star mu Her and its faint companion
Near-Infrared image of the star mu Her and its companion, which are located 27 light years away from Earth. The image was taken with the Gaussian shaped pupil mask, the new generation coronagraph technique for the TPF mission being planned by NASA. This is the first time this new technique, proposed by Dr. David Spergel at Princeton University, was tested with star light, showing its promise for high-contrast imaging, which could eventually be used to detect Earth-like planets.
The star HD190067 and its faint companion
Near-IR image of HD190067 and its faint companion, which are 50 light years away from Earth. The image was taken with adaptive optics only.
The star HIP 13855 and its faint companion
Near-IR image of HIP 13855 and its faint companion, which are 200 light years away from Earth. The image was taken with adaptive optics only.
PIRIS
Mounted on the historic Mt. Wilson 100-inch telescope in October 2001.