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D. B. Paulson (Astronomy Department, University of Texas)
Planet forming regions are influenced by various factors including chemical composition, initial disk mass, and perhaps stellar mass. In order to characterize the factors influencing planet formation and evolution, we must be careful to separate the effects of each variable. The use of an open cluster removes 2 variables (age and initial chemical composition) while the distances between stars is great enough to not cause a significant number of interactions which might disrupt the planet forming process itself. With the removal of extra variables, we are able to explore the influence of stellar mass on the formation of planets. In addition, using an initially chemically homogeneous cluster enables us to explore the possibility of photospheric stellar enrichment by H depleted disk debris and/or planet infall.
Thus, there are 3 aspects to this project. We are conducting a radial velocity search for planets in the Hyades. We have done analyses of both long- and short-term stellar activity to verify that the radial velocity variations we see are indeed due to orbital motion. For the case of long-period cycles, we do not see correlation between chromospheric activity, as measured by the Ca II K line, and the velocities measured. For 4 of the stars surveyed, we obtained several near-simultaneous velocity and photometric observations and conclude that the rotation of starspots and plage regions across the stellar surface do produce similar radial velocity curves as would short-period planets. And, finally, we have performed a differential abundance analysis of Fe I and II, Si I, Ti I, Na I, Ca I, Mg I and Ba II in order to look for star-to-star variations as evidence of stellar enrichment. Fe, Ti and Si give the most conclusive results that the level of stellar enrichment is not significant.
This research is supported by NASA grants NAG5-4384 and NAG5-9227 and NSF grant AST-9808980.
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.