Exoplanets Lecture 16 Post Midterm No copyright infringement is intended by the creation or use of these notes Detection Techniques o Direct Imaging Taking pictures using telescope Resolution and Contrast requirements pose a challenge Works only for planets close to Earth Star is much brighter than reflection from planet so you have to take high contrast images and try to block the light from the central star High albedo brightness high reflection not absorbing as much light colder easier to see The farther away the sun and planet is the harder it is to distinguish between the two You need high resolution optics Angular resolution clarity of image Angular resolution lambda wavelength of light divided by distance of telescope size The smaller the angular resolution larger telescope size the clearer the image o Astrometry Measure a massive and close planet s effect on a star s wobble Requires lots of time and high quality data planet must be big close and wobble must be large o Doppler Technique Radial Velocity Measurement Measure the red and blue shift of a star as it orbits its shared center of mass with the surrounding planets Mass and distance determine gravitational pull so large and close planets will affect the stars orbit We look at star s Doppler shift to find a planet s mass Limitation If you look perpendicular to the star you can not see its shifts thus it appears to be stable Not very old technique so biased toward planets with short orbits Ambiguity inclination if the orbital plane is not seen directly you do not get the full Doppler effect Could be huge planet affecting star at an angle or small planet affecting it directly Ex 51 Pegasus Easiest to detect b c they are large and close to the star First discovered planet around a sun like star Exhibits periodic Doppler shift o Transit Eclipse Technique Observing a stars luminosity over time If planet transits across the disk of the star it dims it slightly giving us its size no inclination ambiguity Limitation decreases Must be in line of sight to see transit Must make sure it isn t from sun spots or other variables When planet transits in front of the star observed luminosity When planet transits behind the star observed luminosity increases b c the planet is reflecting light from the star o Doppler and Transit together can find planet density Learned from Exoplanets o Kepler Built to detect earth sized planets Conclusion o Types of Planets Hot Jupiters We have billions of Earth sized planets in the Habitable Zone Ever star has at lease one planet There are multi planet systems out there Many are extremely close to Really big planets that are very hot close to star Heat from sun excites atoms so planet must be large to keep them from escaping atmosphere Presence of Hot Jupiters are a result of migration o They most likely formed beyond frost line gas giant o High eccentricities require gravitational encounters or resonances o These two are features of planet formation model Super Neptunes 5 10x Earth Fairly big and relatively close to stars Super Earths 1 5x Earth Same size or a bit bigger than earth Rocky body low density Most common type of planet found and billions found in a stars habitability zone o Method to find life Habitability Zone Spectroscopy The dispersion of light and measurement of its intensity at different wavelengths o Spectrum single measurement o Spectra multiple measurement o Can be refracted bent by prisms o Or diffracted interfered by gratings Used to find the composition of astronomical objects Absorption or emission of specific wavelengths give electrons of atoms more or less energy o Since this is different in every atom we can use spectroscopy to figure out atoms Absorption spectrum o Light could be reflect on planetary surface and go through a cloud of gas planet s atmosphere o Intense light peaks reflection o Dips absorbed Spectral Sequence o Base on hydrogen and helium lines seen in spectra o OBAFGKM determine heat and brightness Oh Be A Fine Girl Kiss Me More blue light hotter More red light cooler O and B Lifetime to short to assemble planets A and F lots of UV light could be harmful Life could survive in ground oceans ice or ozone layer could protect Age may not allow complex life to arise G habitable our sun for ex K and M very long lifetimes small HZ 90 of stars are K and M o Stellar Life Cycle look for life Most stars are on the main M of OBAFGKM sequence where we Stars spend a majority of their time fusing H and He When core H and He runs out they become giant or super giant Most massive stars die in explosion supernova Other low mass stars leave white dwarf behind stable