new results from ground-based transit spectroscopy observations jacob bean harvard-smithsonian cfa...
Post on 21-Dec-2015
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New Results from Ground-Based Transit Spectroscopy Observations
Jacob Bean
Harvard-Smithsonian CfA
University of Chicago
A new technique for ground-based transit spectroscopy
Observation strategy:
•Time-series spectroscopy with multi-object spectrographs during transits/occultations
•Simultaneous spectra of target and multiple reference stars during transits – “differential spectroscopy”
•Wide slits of 12” eliminate slit losses
Goals…
•Reveal the bulk composition of the planet.
•Resolve the tension between conflicting results.
submitted to ApJ and available on astroph
New Results for GJ1214b:
• New spectroscopy in J, H, and K simultaneously (Magellan + MMIRS)
• New spectroscopy 0.61 – 0.85 μm (VLT + FORS)
• New narrow-band photometry at 2.09 μm (VLT + HAWKI)
• Re-analysis of previously reported spectroscopy 0.78 – 1.00 μm (VLT + FORS)
submitted to ApJ and available on astroph
New Results for GJ1214b:
NIR Spectroscopy of GJ1214b
107 photons per exposure in K-band
50 ppm on the transit depth
GJ1214
NIR Spectroscopy of GJ1214b
K-band data
NIR Spectroscopy of GJ1214b
Parameter decorrelation
NIR Spectroscopy of GJ1214b
NIR Spectroscopy of GJ1214b
443 ppm per minute
3.4 times the photon noise
NIR Spectroscopy of GJ1214b
652 ppm per minute
6.0 times the photon noise
NIR Spectroscopy of GJ1214b
608 -- 1060 ppm per minute
2.5 times photon noise
Optical Spectroscopy of GJ1214b
504 – 1432 ppm per minute
1.3 times the photon noise
Broadband data for GJ1214b
Broadband data for GJ1214b
Our new measurements
Broadband data for GJ1214b
Re-analyzed previous measurement
Broadband data for GJ1214b
Spitzer data (Desert et al. 2011)
Broadband data for GJ1214b
Croll et al. (2011) measurements
Broadband data for GJ1214b
• No spectral features detected
• Croll et al. (2011) K-band point inconsistent with MMIRS broadband point at 4.1σ
Broadband data for GJ1214b
• No spectral features detected
• Croll et al. (2011) K-band point inconsistent with MMIRS broadband point at 4.1σ
• Solar composition model in chemical equilibrium ruled out at 7.9σ
• Solar composition model with methane removed is ruled out at 5.2σ
K-band spectroscopy for GJ1214b
• No spectral features detected
• Confirm results of Crossfield et al. (2011) at lower resolution
K-band spectroscopy for GJ1214b
• No spectral features detected
• Confirm results of Crossfield et al. (2011) at lower resolution
• Solar composition model in chemical equilibrium ruled out at 4.3σ
• Solar composition model with methane removed is consistent
• No spectral features detected
Optical spectroscopy for GJ1214b
• No spectral features detected
• Solar composition model in chemical equilibrium ruled out at 6.6σ
• Solar composition model with methane removed ruled out at 5.2σ
Optical spectroscopy for GJ1214b
Summary:
GJ1214…
•A remarkably complete ground-based spectrum
•Spectrum is flat, no deeper transit in the K-band
•Atmosphere is either >70% water, or has high-altitude clouds/haze
Results for other planets with the same technique coming soon
Observation schematic
spectrum
12” x 30” slits
Appro
x 5’