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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).