Monika Lendl Austrian Academy of Sciences Space Research Institute Collaborators: VLT observations of giant L. Delrez (Unv. of Liège) exoplanet atmospheres: M. Gillon (Unv. of Liège) reliability and new results 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.)
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Transmission spectra Signature of elements in the plantary atmosphere imprinted on stellar light Amplitude Variations in the observed transit radius ;
Targets
Targets
Targets
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) Huitson+ (2012), Sing+ (2008)
Observed transmission spectra Na K H 2 O Clear atmosphere Atmosphere with cloud layer Rayleigh scattering, high-altitude clouds/hazes
Observed transmission spectra ● 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
Ground based observatories 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 Large ground-based observatories for exoplanet transmission spectra ● improved target sample – fainter stars ● more observing time available ● independend measurements VLT/FORS2 (Bean+ 2010) Magellan (Jordan+ 2013) ● complementary wavelength regions Gemini (Gibson+ 2013)
VLT + FORS2 Our program: WASP-49 with FORS2 at VLT/UT1 4 separate transits (3 observed)
WASP-49b P = 2.78 d R p = 1.12 (5) R J M p = 0.34 (3) M J A hot Saturn with a density of < 0.3 ρ J , predicted to possess an extended ρ p = 0.27 (3) ρ J atmosphere T eq = 1369 (39) K Lendl et al. (2012)
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?
WASP-49 b contamination 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 spectrophotometry Spectrophotometry extract spectra (wide windows) clean outliers (spatial/temporal) binning 10 nm (20 nm for red end) relative photometry 10 nm bins 27 lightcurves per transit using all references 81 lightcurves in total
WASP-49 b spectrophotometry
FORS2 LADC L inear A tmospheric D ispersion C orrector Uneven transparency Temporally variable Rotating structures on images, strongest at meridian crossing Time-variable flatfield component introducing red noise in lightcurves
FORS2 analysis Parametric CNM Mix
FORS2 analysis Parametric CNM Mix
Parametric baseline
WASP-49 b spectrophotometry
FORS2 analysis Parametric CNM Mix
FORS2 analysis Parametric CNM Mix
Common Noise Model
Common Noise Model
Common Noise Model “white“ transit parameters C ommon N oise M odels
Transmission spectrum -- CNM
FORS2 analysis Parametric CNM Mix
FORS2 analysis Parametric CNM Mix
Transmission spectrum -- mix
Transmission spectrum -- mix
FORS2 analysis Parametric CNM Mix
Combined analysis
WASP-49 b transmission spectrum
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.
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