Exocomet

A Falling Evaporating Body describes in astronomy a random and variable component in the absorption lines in debris disks around young stars with an age of a few million years. The absorption lines, mostly of ionized calcium are often red-shifted and caused temporarily by gas that is released into the line of sight between the star and the observer. The Falling Evaporating Bodies as are the evaporation of small icy celestial bodies in the vicinity of the star interpreted. Popular Scientifically the Falling Evaporating Bodies are also referred to as Exokometen.

The Falling Evaporating Bodies have been found so far only around young stars with spectral type A, which is often for Herbig. This is the result of a selection effect. These stars evolve quickly enough to have distributed the circumstellar gas from the protostar phase on the radiation pressure, are numerous near the sun as opposed to the B and O stars and their radiation has the necessary luminosity to vaporize small bodies in the space of a few stellar radii. The young A- stars show stellar winds with mass loss rates up to 10-7 solar masses per year. Must be released in order to separate the signal from the Falling Evaporating bodies of the absorption lines of the star wind a correspondingly large amount of gas. The diameter of the detectable Exokometen is therefore estimated at up to 100 kilometers, while the comets in the solar system have a maximum diameter of 20 kilometers. For older stars, the comet activity is reduced so that an accidental discovery is unlikely.

Examples

Falling Evaporating Bodies were detected in the debris disks of the following stars:

• Beta Pictoris
• HD 21620
• HD 42111
• HD 110411
• HD 172555
• 2 Andromedae
• 49 Ceti
• 5 Vulpeculae