Spectroscopic analyses of the parent stars of extrasolar planetary system candidates
Received 9 September 1997 / Accepted 9 February 1998
The stars Cnc, CrB, 16 Cyg B, 51 Peg, 47 UMa, 70 Vir, and HD 114762 have recently been proposed to harbor planetary mass companions based on small amplitude radial velocity variations. From spectroscopic analyses we derive the following values of [Fe/H] for these stars: 0.29, -0.29, 0.06, 0.21, 0.01, -0.03, and -0.60 (all with an uncertainty of 0.06 dex), respectively; the [Fe/H] value for 16 Cyg A is 0.11. The four 51 Peg-like systems, And, Boo, Cnc, and 51 Peg, have a mean [Fe/H] value of 0.25. Otherwise, the abundance patterns, expressed as [X/Fe], are approximately solar.
We used Fourier analysis, supplemented by line profile synthesis, to derive the following values: , 1.4 0.3, 1.7 0.4, 0.5, and 1.5 km s-1 for Cnc, 51 Peg, 47 UMa, 70 Vir, and HD 114762, respectively. A similar analysis of the spectrum of CrB (with a lower resolving power) yields a value of 1.5 km s-1. Combining these data with published estimates of and rotation periods and assuming that the radial velocity variations are due to the presence of planets, we derive the following masses for the companions: , , , , , and for Cnc, CrB, 51 Peg, 47 UMa, 70 Vir, and HD 114762, respectively; the mass of 16 Cyg B b, calculated using a published estimate for , is . The masses of the companions to And and Boo, which were analyzed in a previous paper, are and , respectively.
We confirm previous claims that Cnc appears to be a subgiant. However, the theoretical isochrone-derived age is much greater than the age of the universe. At this time we have insufficient data to determine the true nature of Cnc, but we suggest that it may be an unresolved stellar binary viewed nearly pole-on. A search for line profile variations might help to resolve this mystery.
Our findings are consistent with a 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, and the material between the 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.
Key words: stars: abundances planetary systems
© European Southern Observatory (ESO) 1998
Online publication: May 12, 1998