SLIDE 1 Monika Lendl
Austrian Academy of Sciences Space Research Institute Collaborators:
- L. Delrez (Unv. of Liège)
- M. Gillon (Unv. of Liège)
- E. Jehin (Unv. of Liège)
B-O. Demory (Cavendish) Didier Queloz (Cavendish)
- N. Madhusudhan (Univ. of Cambridge)
- C. Hellier (Keele Univ.)
D.R. Anderson (Keele Univ.)
VLT observations of giant exoplanet atmospheres: reliability and new results
SLIDE 2
Good morning!
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SLIDE 4 Transmission spectra
Signature of elements in the plantary atmosphere imprinted on stellar light Variations in the observed transit radius
Amplitude
;
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Targets
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Targets
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Targets
SLIDE 8 Huitson+ (2012), Sing+ (2008)
Observed transmission spectra
Diversity is seen in transmission spectra!
- Cloudy/Hazy (e.g. HD189733b): features (largely) obscured
- Clear (or less cloudy...): features visible (e.g. HD209458b)
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Clear atmosphere Atmosphere with cloud layer Rayleigh scattering, high-altitude clouds/hazes Na K H2O
Observed transmission spectra
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- HST: a reasonable number of transmission spectra with STIS, ACS,
WFC3 (e.g. Charbonneau+ (2002), Vidal-Madjar+ (2003) Pont+ (2007), Deming+ (2013)) BUT strong limits on available time, target magnitude
- High resolution spectrographs (e.g. Redfield+ (2008), Wyttenbach (2015) )
BUT small spectral area covered
Observed transmission spectra
SLIDE 11 Large ground-based observatories for exoplanet transmission spectra
- improved target sample – fainter stars
- more observing time available
- independend measurements
- complementary wavelength regions
Ground based observatories
SLIDE 12 Large ground-based observatories for exoplanet transmission spectra
- improved target sample – fainter stars
- more observing time available
- independend measurements
- complementary wavelength regions
VLT/FORS2 (Bean+ 2010) Magellan (Jordan+ 2013) Gemini (Gibson+ 2013)
Ground based observatories
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Our program:
WASP-49 with FORS2 at VLT/UT1 4 separate transits (3 observed)
VLT + FORS2
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WASP-49b
A hot Saturn with a density of < 0.3 ρJ, predicted to possess an extended atmosphere Lendl et al. (2012) P = 2.78 d Rp = 1.12 (5) RJ Mp = 0.34 (3) MJ ρp = 0.27 (3) ρJ Teq = 1369 (39) K
SLIDE 15 WASP-49 b program
Observations
- VLT/FORS2
- Three full transits
- Multi-object spectroscopy
- 0.7 – 1.02 μm
- Relative spectrophotometry
disperse
- Absorption features?
- Instrument stability?
SLIDE 16 Contamination
- faint star 2.5 arcsec from WASP-49 identified
in the pre-imaging run
- contamination 1-3%
- wide spectral extraction window
- contamination included in the modeling
WASP-49 b contamination
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WASP-49 b spectrophotometry
10 nm bins 27 lightcurves per transit 81 lightcurves in total
Spectrophotometry
extract spectra (wide windows) clean outliers (spatial/temporal) binning 10 nm (20 nm for red end) relative photometry using all references
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WASP-49 b spectrophotometry
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FORS2 LADC
Linear Atmospheric Dispersion Corrector
Uneven transparency Temporally variable Rotating structures on images, strongest at meridian crossing Time-variable flatfield component introducing red noise in lightcurves
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FORS2 analysis
Parametric CNM Mix
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FORS2 analysis
Parametric CNM Mix
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Parametric baseline
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WASP-49 b spectrophotometry
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FORS2 analysis
Parametric CNM Mix
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FORS2 analysis
Parametric CNM Mix
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Common Noise Model
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Common Noise Model
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Common Noise Model
“white“ transit parameters Common Noise Models
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Transmission spectrum -- CNM
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FORS2 analysis
Parametric CNM Mix
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FORS2 analysis
Parametric CNM Mix
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Transmission spectrum -- mix
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Transmission spectrum -- mix
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FORS2 analysis
Parametric CNM Mix
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Combined analysis
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WASP-49 b transmission spectrum
SLIDE 37 FORS2 lessons learned
- Even data affected with the LADC problem can produce
reliable results, but systematics need to be taken care of properly.
- WASP-49b: no Na detected, flat spectrum is an
appropriate fit.
- With the newly-coated LADC, FORS2 becomes
compeditive for transmission spectroscopy.
