|FOR RELEASE:||9:20 AM PDT June 7, 2001|
MCCORMICK OBSERVATORY SEARCH FAILS TO FIND
BARNARDíS STAR PLANET
Philip Ianna and Jennifer Bartlett of the Department of Astronomy at the University of Virginia announced today that photographic plates taken of Barnardís Star at the Leander McCormick Observatory, Charlottesville, Virginia, fail to indicate any planetary companions to this near-by star. Their time-series analysis of photographic observations taken since 1969 reveals no evidence of any periodic perturbations that might be caused by an orbiting planet.
Barnardís Star is a particularly interesting object, not only because of its nearness and noticeably changing position, but also because at least one astronomer claimed to have detected evidence of planetary companions. The late Edward Emerson Barnard, an astronomer at Yerkes Observatory in Williams Bay, Wisconsin, discovered the faint, red dwarf that bears his name in 1916. It is the second-closest stellar system to our own Sun at a distance of 5.95 light-years, according to the McCormick study. The closest star to our Sun, Proxima Alpha Centauri is a little more than four light-years away. The position of Barnardís Star is moving against the background of ďfixedĒ stars faster than any other star.† Ianna and Bartlett measured this proper motion to be 10.3324 arcseconds per year. In comparison, the angular diameters of the Sun and Moon are each about 1,800 arcseconds. In addition to its angular velocity, Barnardís Star is approaching our Solar System at a speed of approximately 69 miles per second. Although it is now a very faint star in the constellation Ophiuchus, it will be the nearest star to our own in 11,800 AD. At that time, it will be found in the constellation Draco and appear twice as bright but will still not be visible to the naked eye.
In 1963, the late Peter van de Kamp, an astronomer at Sproul Observatory in Swarthmore, Pennsylvania, announced the detection of the first planet outside our Solar System. Based upon observations of Barnardís Star made at the Sproul Observatory between 1916 and 1962, he claimed that it had a planetary companion of about 1.6 times the mass of Jupiter that orbited the star every 24 years. Later, Van de Kamp revised his analysis and asserted that Barnardís Star had two smaller planets, with approximately 0.7 and 0.5 times the mass of Jupiter.
Since Van de Kampís first announcement, a number of other searches using a variety of methods have failed to confirm his results.† Ianna and Bartlett conducted an analysis of the substantial collection of photographic material relating to Barnardís Star at the McCormick Observatory. Previous studies of fewer observations at the McCormick Observatory, in which Ianna participated, also failed to detect any planets orbiting Barnardís Star.
In their new study, Ianna and Bartlett calculated the motion of Barnardís Star by comparing its position with that of 12 reference stars in 924 images taken between April 1969 and August 1998 at McCormick Observatory. These photographs were made with the 26.25‑inch Fraunhofer refractor that was manufactured by Alvan Clark and Sons in 1885. Van de Kamp worked at the McCormick Observatory before going to Swarthmore College as director of Sproul Observatory in 1937. Although he once reviewed a small set of McCormick observations of Barnardís Star, those observations were not used in the current analysis because the early plate material is of too poor quality to be useful for this study.
If Barnardís Star had planets, it would appear to wobble. For each observation, Ianna and Bartlett obtained the difference between their predicted position for Barnardís Star and the actual observed position. This analysis yielded no perturbations of the position of Barnardís Star that would correspond with either of Van de Kampís earlier theories.†
†Bartlett said that this failure to replicate Van de Kampís results, while not unexpected, does not completely eliminate the possibility that such planets exist. The Sproul Observatory material available to Van de Kamp is unique. In 1982, his analysis used nearly 20,000 exposures taken between 1938 and 1981 at Sproul Observatory compared with the much smaller number of McCormick observations. However, the McCormick refractor was not subjected to physical changes such as those experienced by the Sproul refractor. In 1949, the aluminum cell holding the Sproul objective lens was replaced with cast iron and the photographic emulsion in use also changed. Nonetheless, this study further reduces the likelihood that any Barnardís Star has any companions as massive as Jupiter.
†Ianna and Bartlett made their announcement in a poster presentation at the 198th Meeting of the American Astronomical Society in Pasadena, California. Their presentation was titled, ďA Barnard's Star Perturbation Search Using McCormick Observatory Photographic Plate Material.Ē
†Dr. Ianna recently retired as a professor in the Department of Astronomy at the University of Virginia. He obtained his bachelorís and masterís degrees at Swarthmore College, where Dr. Van de Kamp was director of Sproul Observatory. He completed his doctorate at Ohio State University. His primary research interest is astrometry, the accurate measurement of stellar positions and motions. He supervised Ms. Bartlettís research on this project in partial completion of the requirements for a masterís degree, which she received in May.† Ms. Bartlett has accepted a position as a visiting assistant professor in the Department of Physics and Astronomy at Hampden-Sydney College near Farmville, Virginia.
†Ianna and Bartlett gratefully acknowledged the support of the National Science Foundation (NSF grant AST 98-20711) and Litton Marine Systems, Incorporated.
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