Planetary Debris Pollutes Surface of Dwarf Stars with Iron

The European Organization for Astronomical Research in the Southern Hemisphere, or ESO as it is otherwise known, has found pollution on the the surface of some types of stars.

Scientists who recently looked at stars that hosted planets found that dwarf stars in many cases had iron enrichment on their surfaces. When looking at giant stars scientists found that they did not contain iron enrichment on their surface.

It is thought that the pollution found on the surface of the dwarf stars is the result of planetary debris landing in the stars top layer. The reason the researchers believe that this pollution does not show up in the surface of giant stars is that when the planetary debris hits the giant star's surface it is diluted and ends up moving into deeper layers of the star.

The head writer of the research results, Luca Pasquini from the ESO said, "It is a little bit like a Tiramisu or a Capuccino. There is cocoa powder only on the top," according to ESO.

The researchers note that a couple of questions arise from the fact that plants seem to be found around stars that are iron enriched. The next challenge will be to find it if the iron occurs on the stars surface as a result of the planets being present of if the iron on the star's surface is was helps planets to form in the vicinity of the star.

At the moment it is only possible for astronomer to investigate the pollution sitting in the outer layer of a star. These means they can guess what the stars inner composition might be made up of, but they cannot be sure of this.

In the attempt to tackle the question of whether iron enriched stars related to the presence of planets scientist investigated different star types. Pasquini said, "We find that evolved stars are not enriched in metals, even when hosting planets. Thus, the anomalies found in planet-hosting stars seem to disappear when they get older and puff up."

So far scientists think that the reason for the difference between planet hosting red giants and younger stars is their structure. The area of the star that is of particular relevance is the convective zone. On a young star like the sun this zone makes up on 2 percent of the star's total mass where as the convective zone of a red giant makes up for 35 percent more mass than a younger star.

When planetary debris falls onto the younger star the thin outer layer makes it appear metallic. However, when the planetary debris falls onto the surface of a red giant its huge convective zone diluted and absorbs the debris, thus making it not visible.

Source

ESO press release about recent discouver
http://www.eso.org/public/outreach/press-rel/pr-2007/pr-29-07.html