55 Cancri - System Components

System Components

The primary star 55 Cancri A is a yellow dwarf star of main sequence spectral type G8V. It is smaller in radius and slightly less massive than our Sun, and so is cooler and less luminous. The star has only low emission from its chromosphere, and is not variable in the visible spectrum; but it is variable in X-rays.

55 Cancri A is more enriched than our sun in elements heavier than helium, with 186% the solar abundance of iron; it is therefore classified as a rare "super metal-rich" (SMR) star. This abundance of metal makes estimating the star's age and mass difficult, as evolutionary models are less well defined for such stars. One estimate based on chromospheric activity suggests an age of around 5.5 billion years. Other studies yield age estimates of 7.4 and 8.7 billion years.

A hypothesis for the high metal content in SMR dwarf stars is that material enriched in heavy elements fell into the atmosphere from a protoplanetary disk. This would pollute the star's external layers, resulting in a higher than normal metallicity. The lack of a deep convection zone would mean that the outer layers would retain higher abundance ratios of these heavy elements.

Observations of 55 Cancri A in the submillimeter region of the spectrum have thus far failed to detect any associated dust. The upper limit on emissions within 100 AU of this star is about 850 mJy, at a wavelength of 850 μm. This limits the total mass of fine dust around the star to less than 0.01% of the Earth's mass. However, this does not exclude the presence of an asteroid belt or a Kuiper belt equivalent.

55 Cancri B is a red dwarf star located at an estimated distance of 1065 AU from the primary star, and is much less massive and luminous than our Sun. Despite their wide separation, the two stars appear to be gravitationally bound, as they share a common proper motion. There are indications that component B may itself be a double star, though this is uncertain.