On the number of comets around other single stars
Citations Over Time
Abstract
It is shown how to obtain interesting limits on the number of comets in orbit around other single stars in clouds similar to the one present in our own solar system. The number of comets around white dwarf stars is constrained directly, and this in turn constrains the presence of comets around main-sequence stars. If a white dwarf possesses a cloud of comets similar to the Oort cloud, it will occassionally accrete a comet. The accretion of a comet may add enough heavy elements to the atmosphere of the white dwarf to produce a recognizable spectral signature; it is suggested that the calcium reported in the white dwarf G 74-7 is due to recent comet accretion. This signature will persist until sedimentation has removed the heavy elements from the atmosphere; the mean time between accretion events is comparable to the sedimentation time for cool DA stars, so this signature should be frequently observed if cometary systems are common. The possibility that cometary systems greater than or approximately equal to 3 times more massive than the Oort cloud are present around most white dwarf stars are excluded and how this limit can be improved is indicated. It is shown that a star keeps most of its comets during the vigorous mass loss phase prior to the appearance of the white dwarf star. Thus, the constraints obtained here may be applied to the main-sequence progenitors of the white dwarfs.