Page 60

Figure 9.

Using

bHROS spectrum of the known extrasolar planet host star HD 82943 near the lithium doublet at 6707.8 Å. The spectrum (black points) is best fit with a model that indicates there is no appreciable 6 Li present in the atmosphere of the star. The result helps rule out the role of external pollution from any extrasolar planet on the spectrum of the host star.

bHROS,

high-resolution

(R=150,000),

high

signal-to-noise (S/N = 700-1100) spectra were obtained for five stars that host extrasolar planets. Detailed profile-fitting of the Li I resonance doublet at 670.78 nm revealed no detectable 6Li in any of the sample stars. In Figure 9 we show the bHROS spectrum of target HD82943 as well as model profiles calculated for different 6Li/7Li isotopic ratios. The derived upper limits to the 6Li fraction in these stars are quite small, being typically 6Li/7Li < 0.02-0.03. These upper limits can be translated into limits on the amount of accreted material and show that less than 0.25 to 0.70 Jupiter masses of metal-rich material has been accreted by these particular stars with planets. Jean-René Roy is deputy director and head of science at As this material is depleted in H and He, the star’s

Gemini Observatory. He can be reached at: jrroy@gemini.edu

metallicity (at least at its surface) would be enhanced. The possibility that a planet-hosting star has accreted

R. Scott Fisher is the Gemini Observatory outreach scientist. He

significant amounts of metal-rich material can be

can be reached at: sfisher@gemini.edu

tested using the two stable isotopes of lithium. Both isotopes are destroyed at relatively low temperatures (2,000,000K for 6Li and 2,500,000K for 7Li) inside stars. During the early stages of the evolution of solar-type stars, deep convection destroys most or all of the primordial lithium, with 6Li being destroyed much more efficiently than 7Li. The fraction of Li destroyed is a strong function of the stellar mass, with 6Li being completely destroyed, even in stars where significant amounts of 7Li is preserved. The ultimate point of the scenario is that one should not expect to find any 6Li in solar-type stars. Any positive detection of 6Li could be a strong indication of external pollution.

60

GeminiFocus

Issue 38 - June 2009  

GeminiFocus

Advertisement