Are Falling Planets “Polluting” Stars With Metals?

Are Falling Planets “Polluting” Stars With Metals?

After finding evidence that giant planets fall into stars at higher rates than expected, I now have found evidence suggesting that the inward migration of giant planets disrupts smaller planets into the star. At least, that was the hypothesis I used to guide me to find a correlation between the planet's orbital eccentricity and the star's iron fraction, expressed as “Fe/H”. My hypothesis was that perhaps the planets with the highest eccentricities have more recently begun their migration to towards the star, and so may have more recently scattered other planets into the star. The planets that are already “hot Jupiters”, that is, planets that have already migrated into the short period orbits that have been largely circularized, have already had more time pass since disrupting any planets into the star. The star has had more time to mix the pollution from these planets deeper into the star, so since I have found that the stars with the highest eccentricity planets have higher Fe/H, my explanation is this high Fe/H is in a surface layer having been deposited by recent planet infall.

I expected that the pattern would be different for planets in longer orbits that would not have disrupted planets into the star, and I find that over 200 days, this is the case: the correlation breaks down. It also expect that low mass planets may not be as effective in disrupting planets into the star, so I make a cut of 0.1 Jupiter masses. The data for low mass planets is not as good, so I will either work on more careful analysis or wait for better data before saying whether this is the case.

My two recent papers on this are here:

http://arxiv.org/abs/1211.1984

http://arxiv.org/abs/1301.4229

Could whole-planet pollution be a significant contributor to measurements of stellar Fe/H? This is an important question for which I am looking at whether the numbers of planets is high enough. I am intrigued by a paper by Zhungmu Li (astro-ph 1302.0099.) in which he shows how the tracks of Fe/H in clusters don't follow a one-population track like you would expect from a single population in a cluster. Perhaps when stars are young and in clusters, these stars' metallicities are also affected by the infall of whole planets.