Yes. Astronomer Westphal, during Cycle 1, did a study of circumstellar matter around nearby stars, and in Cycle 4, Astronomer Barbieri searched for low-mass companions to nearby astrometric binaries. The above Hubble Space Telescope image of AB Auriga's complex circumstellar disk comes with the following caption:
Normally, a young star's bright light prevents astronomers from seeing material closer to it. That's why astronomers used a coronograph in these two images of AB Aurigae to block most of the light from the star. The rest of the disk material is illuminated by light reflected from the gas and dust surrounding the star. The image on the left represents the best ground-based coronographic observation of AB Aurigae. Paul Kalas of the Space Telescope Science Institute took the image with the University of Hawaii's 2.2-meter telescope. The telescope's coronograph eclipsed a 33.5-billion-mile (53.6-billion-kilometer) area centered on the star. This area is nine times larger than our solar system. The picture shows that the star resides in a region of dust clouds - the semicircular-shaped material to the left of the star. The Hubble telescope image on the right shows a windowpane-shaped occulting bar -- the dark bands running vertically through the middle of the image and horizontally across the upper part of it. The occulting bar covers the innermost part of the disk and star, about 7.1 billion miles (11.5 billion kilometers) or 1.4 times our solar system's diameter. The diagonal lines are the remnants of the diffraction spikes produced in Hubble telescope images of bright stars. The disk is extremely wide: its diameter is roughly 1,300 times Earth's distance from the Sun. The disk material seen in this image is at a distance equivalent to well beyond Pluto's orbit. One faint background star is visible at 5 o'clock. The star's disk shows a wealth of structure, with bright spiral-shaped bands from 9 o'clock to 6 o'clock and closer to the star from 12 o'clock to 3 o'clock. The outermost of these bands are seen in the ground-based image. The imaging spectrograph data show that these bands are themselves composed of numerous smaller bands. The smallest features include some bright knots of material to the left of the star. These knots are close in size to the resolution limit of the Hubble telescope and have diameters 1.3 to 3 billion miles (2 to 5 billion kilometers) wide or 14 to 32 times Earth's distance from the Sun. The brightest knot is at 9 o'clock. The image was taken Jan. 23 and 24, 1999. False colors were used to bring out details in AB Aurigae's disk. The wavelength range is 2,000 to 10,100 Angstroms.
Credit: C.A. Grady (National Optical Astronomy Observatories, NASA Goddard Space Flight Center), B. Woodgate (NASA Goddard Space Flight Center), F. Bruhweiler and A. Boggess (Catholic University of America), P. Plait and D. Lindler (ACC, Inc., Goddard Space Flight Center), M. Clampin (Space Telescope Science Institute), and NASA.
Another dramatic object is the star Beta Pictoris which has a disk of material in orbit around it which is several times the size of our solar system, and whose inner regions seem to have been swept clean of material. The interpretation is that planets have formed in the inner part of this disk, removing asteroidal material, which is now only present in the detectable outer regions of this disk. Spectroscopic studies by the Hubble Space Telescope have also detected complex patterns of motion in the gaseous component of this disk which may have something to do with planet formation.
It is sometimes the case that it is not the star itself that is intriguing or mysterious but the content of its immediate surroundings. With the advent of infrared astronomy in the late '60's, a whole new window onto the circumstellar environment was quickly opened. Within a few short years, astronomers in England, France and the United States discovered that the sky was filled with star-like objects visible only weakly through their optical emissions, but acting as powerful infrared beacons announcing their existence. Subsequent studies showed that the emission came from microscopic dust grains often associated with the atmospheres of red giant or supergiant stars. In the outer layers of these distended, cool stars, dust grains composed of carbon or silicon could condense like rain drops from out of the hot gases there. They are eventually expelled by radiation pressure to form enormous cocoons around these stars, preventing the star's direct optical observation. For many years it was believed that copious infrared emission from a star was only a signpost of extreme age, or in some cases the presence of very hot gases. In 1983 this general opinion began to change.
The Infra Red Astronomical Satellite's survey of nearly the entire sky made a remarkable series of discoveries once the data was analyzed by astronomers. When the radiation from the bright star Vega was examined, a star that has long served as a standard measure of brightness for stellar magnitude scales, it was found that its infrared emission was greater than expected for a star of its temperature and visual brightness. The excess infrared emission could only be explained if Vega were embedded in a cloud of particles heated by Vega itself so that the particles emit infrared radiation. Following a systematic study of all the nearby stars, astronomers were astonished to discover such clouds of circumstellar matter around 30 percent of them. A most spectacular example of this circumstellar material is found in the case of the star Beta Pictoris.
By blotting out the bright disk of Beta Pictoris, astronomers were able to detect the faint infrared emissions from a circumstellar disk of material in orbit around it. The disk has a thickness of 50 AU and a radius of at least 320 AU. For comparison, Pluto orbits the Sun at a distance of 29 AU. Is this material in the form of comets, asteroids or even planets? We don't yet know but there must be quite a lot of whatever it is. By comparison, all the 'rubble' orbiting our own Sun would not be nearly as bright as that seen around Beta Pictoris if seen from the same distance.
There is also new, and of course exciting, evidence that in the famous Great Nebula in Orion ( M-42), many of the young stars can be seen with the Hubble Space Telescope and have protoplanetary disks. Clearly, if you want to build planets, you had better start out with a disk of suitable material out of which you can accrete planets. Evidently, this is not a rare process at all for stars similar in mass to our Sun.
As for stars such as Alpha Centauri, a recent Hubble Space telescope study in 1998 did not detect any objects larger than Jupiter orbiting that star.
Copyright 1997 Dr. Sten Odenwald
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