Development of Iodine Cells for the Subaru HDS and the Okayama HIDES: II. New Software for Precise Radial Velocity Measurements

We have developed a computer code for precise measurements of stellar radial velocity variations with iodine ($\mathrm{I}_2$) cells attached to the High Dispersion Spectrograph (HDS) on Subaru Telescope and the HIgh Dispersion Echelle Spectrograph (HIDES) on Okayama 188 cm reflector. Our modeling technique for $\mathrm{I}_2$ data is similar to those described by Butler et al. (1996, AAA 65.036.447) and Valenti et al. (1995, AAA 64.036.209) concerning the point that the stellar spectrum taken through the $\mathrm{I}_2$ cell (star$+ \mathrm{I}_2$ spectrum) is modeled as the product of high-resolution stellar and $\mathrm{I}_2$ template spectra convolved with the modeled instrumental profile (IP) of the spectrograph. In order to generate a template stellar spectrum, we have devised a new method to extract an intrinsic stellar spectrum from observed star$+ \mathrm{I}_2$ spectra. This enables us to obtain a well-established template stellar spectrum even in cases when the IP and the wavelength scale are apt to vary with time and the observational conditions, and the existing method which reconstructs the IP from a B-star$+ \mathrm{I}_2$ spectrum (Butler et al. 1996; Endl et al. 2000, A&A, 362, 585) fails. We here report on the results of our Doppler measurements of three solar-type stars, 16 Cyg B, $\tau$ Cet, and $\upsilon$ And, based on data collected with HDS and HIDES for about one year. These results show that we have achieved a precision of about $5 \hbox{--} 6 \,\mathrm{m} \,\mathrm{s}^{-1}$ over a time span of one year with our current analysis package with both spectrographs.