The planet was detected around the binary CM Draconis located approximately 45 light years from Earth. The binary system consists of two red dwarf stars in a close orbit around each other. This binary star was chosen as a target for planetary searches because its orbital plane is seen exactly edge-on and the component stars are small, having diameters equal to 25% of the the Sun's. The binary was observed using the Four College Consortium 0.8m Automatic Photometric Telescope (APT), located in southern Arizona, which conducted photometry from 1995-1997. By measuring the amount of light received from the binary, periodic eclipses can be observed as each star passes in front of the other every 30.2 hours. On the morning of June 1, 1996, an unexpected decrease of 7% in the amount of light from the system was detected during a 3.5 hour interval. This light loss can be accounted for by the motion of a Jupiter-size object in front of one of the stars.
Through computer modeling of the light drop, the physical proporties of the planet were determined. Analysis of the data reveals that the planet is located approximately 1.3 astronomical units from the binary system, or 30% more than the distance of the earth from the sun, and its orbital period is between 1.8 and 2.6 years. A planet with a diameter 90% that of Jupiter's accounts for the observed light loss. Since an earlier transit possibly took place on May 27, 1994, as reported by Dr.s Eduardo Martin and Hans-Jorg Deeg of the Instituto de Astrofisica de Canarias, the orbital period may be 2.01 years or 735 days. If this is the case the next transit will occur during early June of 1998. However it is not certain whether the previous transit was the same planet.
If this result is verified by further observations, it would be the first evidence of an eclipse of a star by a planet outside our solar system. Planetary transit events do occur in our solar system when Mercury and Venus move across the face of the Sun, but while these transits are visible they produce no perceptible dimming of the Sun since relative sizes of these planets are very small in comparison to the Sun. These transits are also very rare. Venus' next transits occur on June 8, 2004 and June 6, 2012. Given the rarity in our own solar system, "photometric observations of an eclipse around another star are particularly exciting because they yield a direct measure of a planet's size, unlike other planetary search methods," comments Astronomy Professor Ed Guinan of Villanova University.
This work was supported by National Science Foundation grants to Villanova University and the Four College Consortium.
For More Information Contact
Dr. Edward F. Guinan (610) 519-4820,
guinan@ucis.vill.edu.