HD 187123

Extra-Solar Planet System

Light Curve of the star HD187123 Fall 1998.

This star has been observed to exhibit Radial Velocity variations consistent with there being a planet in a 3.097 day orbit around it. See the Extrasolar Planets Encyclopaedia information on HD187123.

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 "Phase" which is just the time. "Phase" is measured from when the planet is between us and the star and is equal to 1.0 when the planet has completed an orbit. We observed this star and its "planet" on 11 nights in 1998 and each night is plotted with a different symbol. You can see that the individual nights agree with each other very well so there are NO big spots on the star and NO large pulsations of the star.

If the planet transits the disk of the star then the brightness of the star will go down to about -2.13 and stay at that brightness for about 3 hours = 0.04 phase = 18 points. So far we have not seen a transit, but we have marked the place with a tiny dot on the light curve.

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 can have since we could be seeing the orbit pole on.
In this plot we show that there are no eclipses of the star HD187123 by its planet. The dots with the error bars are the observations and the line is the prediction of what an eclipse would look like.

To learn more about this star, these observations and a background star which we found to be variable see our publication IBVS 4820
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