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Exoplanets - Professional Detection

Professional Astronomers use very large telescopes and highly sensitive spectrometers to look of changes in a stars characteristics. Such methods include:
  • Photometric changes in stellar brightness
  • Radial velocity measure of a stars "wobble"

Additional methods include:

  • Astrometry - precise measurements of a star path along the celestial sphere
  • Microlensing - the act of altering a path of light by the result of an unseen massive object (like a planet)
  • Optical and Infrared Interferometry - by combing the light from two or more telescopes, resolution is greatly increased

The rule of professional detection is increased spectrometer sensitivity and improved resolution. For spectrometer sensitivity:

An Echelle type spectrometer - like the image above - is the preferred style. There are five methods used to increase a spectrometers sensitivity:

  • Increase the number of grooves cut into a diffraction grating
  • Improved fiber optic quality
  • Extending the focal length of the light inside the spectrometer
  • Improved resolution of the CCD camera
  • Introduce Iodine gas through which light must pass prior to entering the slit of the spectrometer

The last method has been used the pioneering gurus of exoplanet detection Geoff Marcy and Paul Butler. By introducing iodine gas, the overall spectrum is enhanced and provides an iodine line on the spectra to act as a ruler for helping to increase accuracy in measurements.

The improved spectrometer is designed to increase sensitivity of detecting the "wobble" of a star:

and also to determine of an atmosphere is present on the unseen planet (a spectra of a star is known, so any added spectra will be assumed to be a part of the planets atmosphere).

This wobbling will affect the stars path along the sky. By using precise Astrometric measurements, the net effect can be determined by comparing the predicted path of the star with the actual path.

Microlensing if fairly new, but light from the star should be affected by a transiting planet:

Interferometry is the method of determining phase changes in an electro-magnetic signal. These changes are overlapped to cancel out any ambient noise so only the desired signal is enhanced. Radio Interferometry has been used for some time, and essentially is used to create a much larger, virtual disk that can detect larger wavelengths. Optical Interferometry is much more challenging since the wavelengths are much smaller. Unlike radio Interferometry where the distortions of the atmosphere result in phased distortion, more precise measure of small wavelengths are possible - but the sources of these short wavelengths are often very dim so optical interferometer components must include very large telescopes.

Take a look at the Additional Resource section to get up to date information direct from the pioneers in the field.

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