An Improvement of the Radial Velocity Measurement Method for Subaru/HDS

Details An Improvement of the Radial Velocity Measurement Method for Subaru/HDS An Improvement of the Radial Velocity Measurement Method for Subaru/HDS

Sep 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011ess.....2.4405h&link_type=abstract

American Astronomical Society, ESS meeting #2, #44.05

Astronomy and Astrophysics

Astronomy

Scientific paper

Now extra solar planet surveys have been transitioning to the next stage: to clarify the correlation between planet parameters and stellar parameters such as stellar metallicity, mass and age, or occurrence frequency of the habitable Super-Earths with high accuracy RV observations. In such a trend, an improvement of the RV measurement accuracy is crucial for the detection of exoplanets.
It requires that a high dispersion spectrograph and excellent wavelength scaling for stellar templates to measure radial velocities (RV) precisely. And such a good wavelength scale is provided by I2 spectrum for the HDS at the Subaru telescope.
Previously, we obtained stellar templates by deconvolution of IP from the observed star+I2 spectra described in Sato et al. (2002). However, for HDS, it have been reported that the long-term precision of RV measurements was higher than 10ms-1.
En route to improvement trials, we found that the method of obtaining the intrinsic stellar spectrum (a stellar template) can be one of the main sources of uncertainty. Compared with the intrinsic stellar spectrum, because of its low resolution, the deconvolved spectra tend to be noisy.
In order to avoid the calculation of deconvolution, we took the target star’s spectrum of extremely high resolution of R=160,000 without the I2 spectrum as the stellar template. Those templates would not be affected by IP, and its wavelength scale is approximately collected. By using our new stellar template, we have achieved the long-term precision of about 3ms-1 for over four years.
The precision we have achieved indicates that the Subaru/HDS have been extended detection levels into the range of planets with masses about 6 MEarth around 7 days orbit to M-dwarfs with the mass of 0.5MSUN. Suppressing internal errors of RVs would be our near future work.

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