Astronomy and Astrophysics – Astrophysics
Scientific paper
1996-09-20
Astronomy and Astrophysics
Astrophysics
34 pages Tex file + 2 page long table + 4 ps figures
Scientific paper
The stars 55 Cnc, 51 Peg, 47 UMa, 70 Vir, and HD 114762 have recently been proposed to harbor planetary mass companions. Using spectrospic methods we find that 55 Cnc and 51 Peg are super metal- rich, 47 UMa and 70 Vir have roughly solar metallicities, and HD 114762 is metal-poor. Otherwise, the abundance patterns, expressed as [X/Fe], are approximately solar. The ages of 47 UMa and 51 Peg are similar to that of the Sun; 70 Vir is slightly older, and 55 Cnc and HD 114762 are at least 10 Gyr old. Our estimates of vsini for the parent stars are 1.4, 1.8, 2.0, < 1, and < 1.5 km/s for 55 Cnc, 51 Peg, 47 UMa, 70 Vir, and HD 114762, respectively. Using these data and estimates for the rotation periods and radii, the corresponding masses of the companions are: > 0.6, 0.51, 4.6, > 20, and > 8.5 MJ. The systems appear to fall into three groups: roughly Jupiter mass companions with small circular orbits with metal-rich parent stars (55 Cnc and 51 Peg), larger companions with larger circular orbits (47 UMa), and much more massive companions with large eccentric orbits around moderately metal- poor parent stars (70 Vir and HD 114762). Our findings are consistent with the recently proposed mechanism whereby a gas giant migrates to within a few hundredths of an AU of its parent star during the formative epoch of the planetary system. During this process the material between the giant planet and the star is accreted onto the latter. If the accreted material is depleted in H and He, then the photospheric composition of the parent star might be altered significantly.
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