Wednesday 18 April 2012

Looking for HD 97658b.

HD 97658b is a planet with a mass 8.2 times that of the Earth, orbiting a K-type star (HD 97658b) 69 light years from Earth. It was discovered in 2010 by the High Resolution Echelle Spectrometer at the Keck Observatory; its discovery was reported in 2011 by a team of scientists lead by Andrew Howard of the Department of Astronomy and Space Sciences Laboratory at the University of California, Berkeley, and reported in a paper in The Astrophysics Journal. The planet was discovered using the radial-velocity technique: it orbits a star with a mass 85% of that of the Sun every 9.5 days, this causes the star to wobble on its access, enabling astronomers to detect the planet and calculate its mass.

Diagram showing the orbits of HD 97658b (white) and Earth (green) about their respective stars. Planet and star not to scale.

Later in 2011, in a paper on the online arXiv database at Cornell University Library, which was also submitted to The Astrophysics Journal, a team lead by Gregory Henry of Center of Excellence in Information Systems at Tennessee State University described observations of HD97685b transiting its star (passing in front of the star when seen from Earth) by the Automated Photometric Telescopes at Fairborn Observatory, from which they calculated that it has a radius of 2.93 times that of the Earth, which translates to a volume of 105 times the Earth's.

In a new paper published on arXiv on 14 April 2012 and submitted for publication in Astrophysical Journal Letters, a team of astronomers lead by Diana Dragomir of the Department of Physics and Astronomy at the University of British Columbia publish the results of a new study of HD 97658b, using the MOST Space Telescope.

An artist's impression of the MOST Space Telescope. University of British Columbia.

The new study was unable to detect HD 97658b transiting the star, despite using a more sensitive instrument. They calculate that the MOST Space Telescope would have been able to detect such transits if the planet had a radius 1.87 times that of the Earth or greater. They therefore conclude that the Fairborn Observatory study was erroneous; either HD 97658b does not transit its star, or it is too small to have been detected by the instruments at Fairborn.

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