Subaru HDS Transmission Spectroscopy of the Transiting Extrasolar Planet HD 209458b

1
Subaru HDS Transmission Spectroscopy of the
Transiting Extrasolar Planet HD 209458b
Ref. Narita et al. 2005 (PASJ 57, 471) Winn et
al. 2004 (PASJ 56, 655)

• The University of Tokyo
• Norio Narita

collaborators Yasushi Suto, Joshua N. Winn, Edwin
L. Turner, Wako Aoki, Christopher J. Leigh,
Bunei Sato, Motohide Tamura, Toru Yamada
2
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

3
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.
4
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.
5
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.
6
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
7
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 lt 3
• Moutou et al. (2001) VLT /UVES 1

8
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
41006800Å Spectral Resolution 55000 Typical SNR
/ pix 350 Exposure time 500 sec
The phase of observations
Narita et al. 2005
9
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.
10
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.
11
Comparison of Two Spectra
Red and Blue two spectra taken 2.5 hours apart
Green ratio spectra (Blue / Red)
10
Winn et al. 2004
12
Correction Method
In order to correct the instrumental profiles, we
have established an empirical correction method.
13
Correction Result
We could limit instrumental variations almost
within the Poisson noise level.
Winn et al. 2004
14
Difference Spectra
time
planetary orbital phase
We integrate residual over this region.
template
telluric
Narita et al. 2005
15
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).
16
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.
17
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.
18
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).