Transcript Document
Subaru HDS Transmission Spectroscopy of the Transiting Extrasolar Planet HD 209458b The University of Tokyo Norio Narita collaborators Yasushi Suto, Josh Winn, Ed Turner, Wako Aoki, Chris Leigh, Bun’ei Sato, Motohide Tamura, Toru Yamada Contents • Introduction – Extrasolar Planets – Transmission Spectroscopy – Past Researches • Subaru Observations • Data Reduction and Results – Correction of Instrumental Profiles – Calculation of Difference Light Curves – Resultant Upper limits • Conclusions and Implications Extrasolar Planetary Science Extrasolar Planets are planets orbiting around main sequence stars other than the Sun. The first extrasolar planet, 51 Peg. b, was discovered by Michel Mayor et al. in 1995. Motivation for Researches So far 137 exoplanetary systems have been identified. We already know that extrasolar planets do exist in the universe, but we do not have enough observational information. What are there in extrasolar planets? Transmission Spectroscopy A method to search for atmospheric components of extrasolar planets. provided by Chris Leigh At least in principle, one can detect atmospheric components as excess absorption in the in-transit spectra. Our Target HD 209458 It is the first extrasolar planetary system in which planetary transits by the companion have been found. Basic data HD209458 G0V (Sun-like star) V = 7.64 HD209458b Orbital Period 3.524738 ± 0.000015 days inclination 86.1 ± 0.1 deg Mass 0.69 ± 0.05 MJ Radius 1.43 ± 0.04 RJ from Extra-solar Planet Catalog ｂｙ Jean Schneider Past Researches From Hubble Space Telescope 2002 An excess absorption of 0.02% in Na D lines was reported. Charbonneau et al. 2002 2003 A strong additional Ly alpha absorption of 15% was found. Vidal-Madjar et al. 2003 2004 Oxygen and Carbon were detected as well. Vidal-Madjar et al. 2004 From ground-based telescopes For the cores of atomic absorption lines (0.3Å) • Bundy & Marcy (2000) Keck I /HIRES < 3 % • Moutou et al. (2001) VLT /UVES ~1% Subaru Observations One night observation covering an entire planetary transit was Orbital Period 3.5 days conducted in Oct. 2002. We obtained total 30 spectra: in 12 out 12 half 6 Observing Parameters Wavelength 4100~6800Å Spectral Resolution 45000 SNR / pix ～ 350 The phase of observations Exposure time ～ 500 Data Reduction Scheme Create a template spectrum from all of the raw spectra. Calibrate the template spectrum in total flux and wavelength shift matched to each spectrum. Calculate residual spectrum and integrate the residual at specific atomic lines. Comparison of Two Spectra Red and Blue ： two spectra taken 2.5 hours apart Green ： ratio spectra (Blue / Red) １０％ Correction Method In order to correct the instrumental profiles, we have established an empirical correction method. S1 and S2 denote each spectrum, while R = S1/S2, then (flux calibration) (wavelength calibration) Correction Result We could limit instrumental variations almost within the Poisson noise. Difference Spectra We integrate residual over this region. time template telluric Difference Light Curves For example: a difference light curve of Hα line. There is no transit-related excess absorption (blue region). Upper Limits Comparison with previous results (Bundy and Marcy 2000) Our upper limits are the most stringent so far from ground-based optical observations. Conclusion and Implication • We performed the first transmission spectroscopy of transiting extrasolar planet using Subaru HDS. • However, we could not detect any transit-related signature. • Our results may imply a limit of photometric accuracy from ground-based observations. • Next we intend to investigate spectroscopic changes caused by planetary transits (i.e. the Rossiter effect).