2 Stellar properties

HD 80606 (HIP 45982) and HD 80607 (HIP 45983) are the two components of a visual binary system. They have common proper motions and the fitted systemic velocity for HD 80606 ($\gamma$ = 3.767 $\pm$ 0.010 km s$^{\rm -1}$) is almost equal to the mean radial velocity measured for HD 80607 ( $\langle RV\rangle$ = 3.438 $\pm$ 0.025 km s$^{\rm -1}$). The difference between the two values can be explained by the binary orbital motion. The main stellar characteristics of HD 80606 and HD 80607 are listed in Table 1. The spectral types, apparent magnitudes, colour indexes, parallaxes and proper motions are from the HIPPARCOS Catalogue (ESA 1997). The projected stellar rotational velocity, $v\sin i$, was measured using the mean ELODIE cross-correlation dip width and the calibration by Queloz et al. (1998). The rms of the HIPPARCOS photometric data is large for both stars ( $\sigma_{H_{\rm p}}\simeq40$ mmag) but this measured scatter is classified as "duplicity-induced-variability'' in this catalogue. The angular separation between the two visual components is about 30  $^{\prime\prime}$. This value is not much larger than the satellite detector size so contamination from one component onto the other is probably responsible for the observed scatter. The contamination is also probably responsible for the difference in parallaxes (a factor of two) and for the abnormally large uncertainties on this parameter ( $\sigma_{\pi}\simeq1$ mas is expected with HIPPARCOS for a 9th magnitude star).

We derived the atmospheric parameters (LTE analysis) using HIRES high signal-to-noise spectra with the same method as in Santos et al. (2000a). We used the same line list and oscillator strengths as these authors, except for some lines that could not be used because they were out of the HIRES spectral coverage or fell just between two non-overlapping orders of the echelle spectra. Our line list finally consisted of 18 Fe I lines and only 3 Fe II lines. We estimated the uncertainties on the derived atmospheric parameters in the same way as in Gonzalez & Vanture (1998). The two stars have almost the same iron abundance and are very metal-rich dwarfs (respectively 2.7 and 2.4 times the solar iron abundance). An independent study (Buchhave et al., in prep.) using the same HIRES spectra but a different line list gives consistent results. For the lithium abundance measurement, we summed all our ELODIE spectra in the $\lambda$ 6707.8 Å Li I line region. No trace of lithium was detected giving upper limits (3-$\sigma$ confidence level) on the corresponding equivalent widths for both stars. The abundance upper limits were then derived using the curves of growth by Soderblom et al. (1993). The lithium abundances are scaled with $\log({\rm H})=12$.

  

Table 1: Observed and inferred stellar parameters for HD 80606 and HD 80607.

$$\begin{tabular}{llr@{ $~\pm~$ }lr@{ $~\pm~$ }l} \hline \multi... ...{$<$0.78} & \multicolumn{2}{c}{$<$0.77}\\ \hline \end{tabular}$$