HD 209458

Extra-Solar Planet System

Light Curve of the star HD209458 Fall 1999.

This star has been observed to exhibit Radial Velocity variations consistent with there being a planet in a 3.5 day orbit around it. See the Extrasolar Planets Encyclopaedia information on HD209458.

Using our automated 0.5 meter telescope. we take pictures of this star and the nearby stars. We measure the brightness of the 9 brightest stars and compare them one to each other. If it becomes cloudy then all the stars will become fainter by the same amount and their relative brightness will not change.

In the graph below the brightness is plotted along the left side in magnitudes. Along the bottom of the graph is plotted the Universal Time which is just the time in London.

If the planet transits the disk of the star then the brightness of the star will go down by about 0.016 and stay at that brightness for about 3 hours. So far we have not seen a whole transit, but we will keep trying.

The first few points of this eclipse were made while the sun was not fully down so they are not right on the line. So we will have to try again to get a full eclipse.
The importance of detecting transits of the planet is that if we see the transit then we know that the planet's orbital plane is in the line of sight and the mass of the planet can then be calculated. The radius of the planet can be found from the duration of the eclipse, assuming a radius of the star and then the density of the planet can be found. If we do not see the transit then we just have the minimum mass that the planet could have.

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