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Ref. Narita et al. 2005 (PASJ 57, 471) Winn et al. 2004 (PASJ 56, 655) Subaru HDS Transmission Spectroscopy of the Transiting Extrasolar Planet HD 209458b The University of Tokyo Norio Narita collaborators Yasushi Suto, Joshua N. Winn, Edwin L. Turner, Wako Aoki, Christopher J. 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 M. Mayor and D. Queloz in 1995. The radial velocity curve of 51 Peg. by California & Carnegie Planet Search Team.
Motivation for Researches So far 138 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 of transiting extrasolar planets is one of the best clues to study nature of extrasolar planets.
Transmission Spectroscopy A method to search for atmospheric components of extrasolar planets. 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 = 7.65 HD209458b Orbital Period 3.52474541 ± 0.00000025 days inclination 86.1 ± 0.1 deg Mass 0.69 ± 0.05 MJ Radius 1.32 ± 0.05 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. 2003 A strong additional Ly alpha absorption of 15% was found. 2004 Oxygen and Carbon were detected as well. Charbonneau et al. 2002 Vidal-Madjar et al. 2003 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 conducted in Oct. 2002. Orbital Period 3.5 days We obtained total 30 spectra: in 12 out 12 half 6 Observing Parameters Wavelength 4100~6800Å Spectral Resolution 55000 Typical SNR / pix ～ 350 Exposure time ～ 500 sec The phase of observations Narita et al. 2005
Our Advantage and Uniqueness Our observing strategy We observed before, during and after the transit in a single night and cover a larger range of wavelength (the entire optical band). It is indeed unique and the first attempt for transmission spectroscopy. This strategy enable us to effectively monitor, interpolate and remove large instrumental variations as detailed later.
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 Redand Blue ： two spectra taken 2.5 hours apart Green ： ratio spectra (Blue / Red) １０％ Winn et al. 2004
S1 and S2 denote each spectrum, while R = S1/S2, then (flux calibration) (wavelength calibration) Correction Method In order to correct the instrumental profiles, we have established an empirical correction method.
Correction Result We could limit instrumental variations almost within the Poisson noise level. Winn et al. 2004
Difference Spectra time planetary orbital phase We integrate residual over this region. template telluric Narita et al. 2005
time Difference Light Curves For example: difference light curves of Na D lines. Narita et al. 2005 There is no transit-related excess absorption (blue region).
Upper Limits Comparison with previous results for 0.3 angstrom bandwidth (Bundy and Marcy 2000) Narita et al. 2005 Our upper limits are the most stringent so far from ground-based optical observations.
Check of the Results We injected an artificial signal of 0.03% and 0.2% absorption into several spectra. Narita et al. 2005 We verified that our reduction and analysis procedure do not remove or dilute real signals.
Conclusion and Implication • We performed the first study of transmission spectroscopy in a transiting extrasolar planet using Subaru Telescope. • Our observing strategy had some advantage compared with previous investigators. • However, we could not detect any transit-related signatures. • 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).