Spectroscopic%20Observations%20of%20HD%20209458%20b

1
Spectroscopic Observations of HD 209458 b

• Lewis Kotredes
• Ge/Ay 132 Final

2
Background

• According to http//exoplanets.org, there are 110
  currently known extrasolar planets
• Most extrasolar planets were detected using
  high-precision radial velocity surveys
• Several of these planets are known to undergo
  transits partial occultations of their host
  stars by the planets
• HD 209458 b is the most studied of these

3
HD 209458 b

• HD 209458 is a star of spectral class G0V, with a
  V magnitude of 7.65
• This star has one known planet with a period of
  3.525 days
• In 2000 it was announced that this planet
  undergoes transits with a depth of 1.5

4
Transmission Spectroscopy

• Direct spectroscopy of the planets so far
  discovered is difficult due to the high contrast
  ratio between close companions
• For transiting planets, atmospheres can be probed
  by examining their effects on starlight

5
Transmission Spectroscopy

• Using narrow-band filters specific spectral lines
  in the atmosphere can be observed as changes to
  measured transit depth
• Spectra of the star in and out of transit can be
  compared to see spectral features
• Secondary eclipses can be examined for reflected
  planetary spectra

6
Na

• The first detection of a species in an exoplanet
  atmosphere was accomplished using narrow-band
  filters
• Charbonneau et al used a filter designed to
  observe the Na D lines on STIS and measured a 3s
  change to transit depth

7
Ly a

• Vidal-Madjar et al used a grating spectrometer
  with STIS to examine the transit of HD 209458 b
• The measured depth of the transit in this line
  was 15, much higher than the measured optical
  depth
• This suggests an atmospheric radius larger than
  the Roche limit

8
OI and CII

• Further measurements by Vidal-Madjar et al
  suggest the presence of OI and CII in the
  extended outer atmosphere
• The transit depth for these species is greater
  than that of Na, but not so great as for HI

9
Infrared Spectra

• Many attempts have been made to detect CO lines
  (around 2.2 mm) in the atmosphere of HD 209458 b
• Some of these attempts have used occultation
  spectroscopy of the secondary eclipse, and have
  produced upper limits on this species

10
Conclusions

• Attempts to measure spectra of extrasolar planets
  are still in the nascent stages
• As more transiting planets are discovered, we are
  developing tools to learn about them