Stellar Classification & Planet Detection

• Within 12.5 light years, there are 33 stars. Most of them are Red dwarfs.The ultimate goal: To find Earth-like planets, if they exist, and to search for evidence of life.

Exoplanet detection methods:

Indirect:

• Radial velocity (Doppler method)

• Transits

• Gravitational microlensing

• Pulsar planets

• Astrometric

Direct

• Optical imaging

• Infrared interferometry

Exoplanet types:

• Neptune

• Gas giants

• Super Earth

• Terrestrial

• More than 5000 Exoplanet have been confirmed by NASA

Gravitational microlensing:

• Planets can also be detected by gravitational microlensing. This method takes advantage of the fact that, according to general relativity, light rays are bent by a gravitational field. Or equivalently, space-time is distorted and light travels along straight paths in the distorted reference frame)

• When the lensing star passes in front of the source star, the light from the source star is amplified by a factor of as much as 10-20.

• The typical duration of a microlensing event is minutes to hours

• If the lensing star has planets, then the light curve can be distorted (i.e., you get spikes)

The planets must be near the Einstein ring radius to be detected. Typically, the ring radius is outside of the habitable zone, so this technique is not that useful for finding habitable planets

• The majority of all detected planets have masses below that of Saturn, though the survey sensitivity is much lower for those planets. Low-mass planets are thus found to be much more common than giant planets.