Lecture 14: Searching for planets orbiting other stars III: Using Spectra 1.The Spectra of Stars and Planets 2.The Doppler Effect and its uses 3.Using spectroscopy to measure orbits and masses of exoplanets

NASA Messenger space probe enters into orbit around Mercury

NASA Messenger around Mercury: First Image

Using Spectra for Remote Sensing Measuring spectral lines in the spectrum

Using Spectra for Remote Sensing Forming spectral lines in the spectrum

Venus in Front of the Sun

The Sun in One Spectral Line

Using Spectra for Remote Sensing Forming spectral lines in the spectrum

Direct Detection of Planets The best case to-date of a planet-like system detected in infrared light:

Indirect methods of planet detection Newton’s law of universal gravitation

The Astrometric method Binary stars - Sirius A & B.

The Astrometric method Not successful in planet discovery yet.

The Doppler shift method Doppler shift is measured from the spectral lines of two stars in a binary system:

Using Spectra for Remote Sensing Measuring spectral lines in the spectrum

The Doppler shift What is a Doppler shift ? - true for all waves.

The Doppler shift Doppler shift is measured from the spectral lines:

Mass: Radial velocities seen in star HD the variation is due to a planet that is less massive than Jupiter. (Mazeh et al. 1999; Marcy et al. 2000)

Mass: For HD b: M p sin(i) = M s v s P / 2  a p = const. x ( M s / 1.1M Sun ) M jup Transit light curve helps derive the orbit inclination: i = 86 o Both M p and R p determined to better than 5%!

Mass: Radial velocities seen in star HD they are due to 2 planets, each larger than our Jupiter. (Marcy & Butler 2002; Mayor et al. 2002)

The Spectra of Planets Mars

Main points to take home: 1) Visible light: form of electromagnetic energy (radiation) to which our eyes are sensitive. 2) Spectrum: the amount of light of any given wavelength, emitted or reflected by an object. 3) Thermal spectrum: a simple spectrum that depends only on the object’s temperature. 4) Spectral lines: in emission or absorption; every atom and molecule has a specific set.