Effects of Earth atmosphere on groundbased transit spectroscopy

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Effects of Earth atmosphere on ground-based
transit spectroscopy

• Claire Moutou (LAM)

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In-transit observations 3 hours Out-of-transit
typ lt 3 hr on the same night another sequence
another night
Fin
Fout
Fout
sum(Fin)?
Fout
T
sum(Fout)?
Additional observation of a telluric std (hot
rotating ) before and after the transit Double
differential calibration 8m teltexpfew min3 hr
transit2A bandpass10-3 det
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• Brown 2001  transmission spectra as diagnostics
  of extrasolar giant planet atmospheres 

Expected from HIRES Photon-noise limited SNR1250
/pix R20,000 Core of NaI lines detected
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many attempts

• 1 transit on Keck/HIRES (2 hrs)
• 5 transits on the VLT/UVES (18 hrs)
• 1 transit on SUBARU/HDS (5hrs)
• 1 transit on WHT/UES (5 hrs)
• 1 transit on CFHT/ESPaDOnS (5 hrs)
• 1 transit on VLT/ISAAC (8.5 hrs)
• 3 transits on Keck/NIRSPEC (14.5 hrs)
• 11 transits on HET/HRS (27 hrs)
• 1 transit on SUBARU/HDS (5hrs)

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Keck HD 209458 51 Peg
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• During commissioning of UVES
• Partial transit
• Detection limit0.5-1

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• Rauer et al (2000, 2004)
• WHT/UES
• 1 sigma1/140 continuum in 5min exp
• Photon statistics only (in 5min)
• 4 nights on WHT necessary
• (but never performed)

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• 5 transits of HD 209458 with VLT/UVES
• spectral rossiter stellar line profile is the
  reference
• NaI line not detected at a level 7-5 10-4

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• Search for HeI at 1083nm
• VLT/ISAAC 1 transit
• Limit0.5

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• Expected signature 10-3
• Non detection x3 larger than needed to test theory

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Another 0.1-1 detection limit
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• lt0.1 in 5A bin

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What limits detection?

• Instrumental short-term fluctuation
• Telluric lines
• Airmass variations
• Seeing (photons in slit)
• Out of transit reference (gtgttransit)

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Deming et al 05 NIRSPEC data in K from Brown 02
Telluric CO lines
telluric H2O lines
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Successful detections!

• More photons (HET)
• A cleaner way to use the telluric standard
• A cleaner way of correcting for instrumental
  defects
• wave calib, blaze, non-linearity effects

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• Blueshift? planet motion high speed wind from
  hot dayside
• 3x signature of NaI in HD 209458
• Against the presence of high altitude clouds

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• Consistent with HST/STIS results
• Variation in the apparent NaI radius is the same
  for both planets (750 km)
• Symmetrical line

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• Empirical correction of HDS data for
  non-linearity effects (line depth corr w count
  level)
• 0.056 (0.007) 5sig det
• Residual noise10-30 higher than Poisson stats

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How to decrease the threshold?

• Data acquisition
• Several transits averaging of systematics
• Systematic use of a telluric standard
• Out-of-transit spectra during the transit night
  (long baseline)
• Data reduction
• Special care for instrumental defects telluric
  removals
• Origins of systematics continuum normalization,
  ?-calibration, removal of stellar IS lines from
  standard, differential limb-darkening
  calculation, stellar activity, RM effect,
  seeing/resolving power variations (slit spectrog)

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Perspectives (1)

• More visible echelle spectra of other bright
  transiting planets
• HD 189733
• HD 209458
• HD 17156
• HD 149026
• HAT-P-2b
• Extend GB detections in the near-IR
• CRIRES obs of HD 189733 on Sept 17th

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Perspectives (2)

• Get back to all previous observations and beat
  systematics! (see HDS 3rd try)
• Search for more components than  easy  NaI!
• Ionised species from more extended exosphere
• How does it complete the space obs?
• Resolving power
• Multiple visits over years
• Larger spectral coverage
• HST/STIS (7hr) HDS/HDS (5hr) for NaI HD209458
• Will theoricians ever believe in ground-based
  detections??