Stellar Spectra
&
Radial Velocity Curves

Spectra of stars of all spectral types. Regular variations over time in a star's spectrum can be plotted as a curve, as shown in the diagrams below. Image credit & copyright KPNO 0.9-m Telescope, AURA, NOAO, NSF.

RV curve for HD 142, a multiple companion system, with data from AAT. Wright JT, Marcy GW, Fischer DA, et al. (2007) "Four new exoplanets, and hints of additional substellar companions to exoplanet host stars." Astrophysical Journal, 657: 533-545.

Planet b has a period of about 349 days and a minimum mass of 1.28 MJUP. Planet c is not fully constrained and has not yet been officially announced or included in the regularly updated Catalog of Nearby Exoplanets. Its period seems to be in excess of nine years.

Measured velocity (filled circles) vs. time for the two proposed planets of HD 108874. Vogt SS, Butler RP, Marcy GW, et al. (2005) "Five new multicomponent planetary systems." Astrophysical Journal, 632: 638-658.

Two planets have been confirmed around the yellow Sun-like star HD 108874. They orbit in a stable 4:1 mean motion resonance, whose regularity is clearly visible in this set of radial velocity curves. The inner planet, which follows a circular orbit in the habitable zone, has a minimum mass of 1.37 MJUP and a period of 13 months. This planet is an excellent candidate to host Earth-like exomoons. The outer planet is the same size as Jupiter, orbiting in a period of about 4.4 years, as compared with a dozen Earth years for Jupiter itself.