Global Exoplanet Red Dwarf Survey (GERDS): Washington, Part 3
The basis of this survey began after the discovery of exoplanets around two Red Dwarfs: GJ 436 and GJ 876. Commander Paul Shankland and colleagues published a paper on the orbital dynamics of the three exoplanets surrounding GJ 876, and one of the conclusions was that astronomers are more likely to detect exoplanets around red dwarfs because of the physical characteristics of the star. A red dwarf, also called an M-dwarf or K-dwarf because of their spectral class, is a small cool star with between 0.33 and 0.08 solar masses and 0.33 times the diameter of our own sun. Because the protostellar disk on these small stars is also small, the planets accreted around these stars will likely be closer in mass to terrestrial planets than Jovian planets. Of the terrestrial planets discovered around other stars thus far, most are significantly bigger than Earth, some 50 times the mass of the Earth. If one derives the orbital dynamics of a 20 Earth-mass planet around an M-dwarf between the masses of 0.3 and 0.08 Earth-masses, it becomes apparent that both the astrometric and photometric detection techniques would be easier with these smaller stars and smaller planets than with bigger stars and bigger planets. The reason is that the ratio of planet mass and size to the star mass and size are greater with the smaller star smaller planet system than with the bigger star bigger planet system. Thus, the 'wiggle' of the star's motion through the sky will be greater, and in the event of a planetary transit, the dip in the amount of light coming from the star will be greater. If exoplanets around M-dwarfs are easier to detect, the USNO site in urban Washington can actually provide decent data.
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