Author:

Keywords:

circumstellar matter, stars, evolution, stars, latetype, stars, statistics, infrared, stars, kuiper belt, stars, emission, Science & Technology, Physical Sciences, Astronomy & Astrophysics, KUIPER BELT, STARS, EMISSION, 0201 Astronomical and Space Sciences, 5101 Astronomical sciences, 5107 Particle and high energy physics, 5109 Space sciences

Abstract:

We have correlated optical and infrared catalogs in order to extract a large sample of luminosity class III stars with known infrared flux densities. For a non-negligible fraction of G and K giants, a far-infrared excess emission was found, starting beyond 25 mu m. An explanation in terms of present-day mass loss thus becomes unlikely, since the dust should then be warmer and the excess emission less far in the infrared. We believe that the far-infrared excesses of these objects, most likely first-ascent giants, are related to the Vega phenomenon. The dusty disks around these stars, gradually cooled down during their main-sequence phase, could be reheated once the star leaves the main sequence and enters the luminous post-main-sequence phase. The fairly large sample we constructed enables us to derive an estimation for the occurrence of excesses. This fraction of G or K giants with far-infrared excess appears to be distinctly smaller than among main-sequence stars. Since the higher radiation field of giants could lead to a larger evaporation rate of the circumstellar debris, this fact does not conflict with our hypothesis.