Iodine-Cell Spectroscopy at Okayama Astrophysical Observatory: First Results

Abstract

Toward the aims of spectroscopically searching for planetary systems around stars, or detecting oscillations of solar-type stars for stellar seismology, we have started an experimental project of very precise determinations of stellar radial velocity variations based on the iodine-cell ($\mathrm{I}_{2}$ cell) technique at Okayama Astrophysical Observatory. We here report on the first preliminary results of test observations for two planet-harboring stars ($\upsilon $ And and $\tau $ Boo) based on data obtained by using the newly developed $\mathrm{I}_{2}$ cell and processed with a practical and quick analysis method. We confirmed that the internal statistical error can be as small as $5 \hbox{--} 6 \,\mathrm{m} \,\mathrm{s}^{-1}$ at best. Then, the resulting radial velocity solutions turned out to be in reasonable agreement with the well-established predicted variations over a time span of 4–5 days; the $O-C$ deviations indicate that a short-time-scale precision of $\sim 15\,\mathrm{m} \,\mathrm{s}^{-1}$ has been accomplished in a practical sense.

Iodine-Cell Spectroscopy Applied to Investigating the Solar Differential Rotation

“…Cadež (2005), Snodgrass andUlrich (1990), andSivaraman, Gupta, andHoward (1993). We can see that our results are in good agreement with those derived spectroscopically in the 1970s and 1980s mainly based on the photoelectrical Doppler compensator method, in contrast to the other comparatively more recent (but seemingly less reliable) studies (Wittmann, 1996;Jejčič andČadež, 2005) where radial-velocity measurements were done by using telluric lines for wavelength calibration on a CCD detector. This fact encouragingly substantiates the reliability and practicability of the spectroscopic method with an iodine cell for investigating the differential rotation of the Sun, which may become widely exploited for the purpose of studying the nature of solar rotation.…”

“…In this way, they could achieve a very high precision of a few m s −1 in detecting the (relative) variation of stellar radial velocity, which eventually lead to their successful discovery of a number of extrasolar planets. Basically following their concept, Takeda et al (2002) also worked out a similar approximate (less accurate but easier) way of analysis, and confirmed an accomplishment of sufficiently high precision. Thus, it would be interesting to apply this technique to the solar case, which does not seem to have been tried so far to our knowledge.…”

“…Regarding the determination of radial velocities 3 from the spectra described in Section 2, we followed the procedure explained in Takeda et al (2002; cf. Section 4.2 therein), which determines δṽ (differential radial velocity) based on three spectra [i) P (λ) ("pure Sun" template spectrum), ii) Q(λ) ("lamp+I 2 " spectrum), and iii) F (λ) ("Sun+I 2 " spectrum)] (cf.…”

“…We can see that the typical value of is ≈ 20 -30 m s −1 . Considering that Takeda et al (2002) accomplished a precision of ≈ 5 -6 km s −1 by using the full spectrum range of ≈ 1000 Å (i.e., ≈ 5000 -6000 Å, where I 2 lines are mainly observed; cf. Figure 1), we can reasonably understand the reason why the precision is degraded by a factor of ≈ 5 -6 this time, since the (E -W configuration) corresponding to the mid-position of the slit], plotted against the radial distance from the disk center.…”

Detection of Gravitational Redshift on the Solar Disk by Using Iodine-Cell Technique

“…Regarding T λ , we adopt the spectrum (S/N ≈ 1000 with the resolving power of R ≈ 400000) recorded for the I 2 cell at Lick Observatory in the 5000-6300Å region by using the Fourier Transform Spectrometer at the McMath telescope of the National Solar Observatories at Kitt Peak (Marcy and Butler, 1992), which was kindly provided by Dr. G. W. Marcy (see also Takeda et al, 2002).…”