J/A+A/596/A47 FORS2 transmission spectroscopy of WASP-17b (Sedaghati+, 2016)
Potassium detection in the clear atmosphere of a hot-Jupiter:
FORS2 transmission spectroscopy of WASP-17b.
Sedaghati E., Boffin H.M.J., Jerabkova T., Garcia Munoz A., Grenfell J.L.,
Smette A., Ivanov V.D., Csizmadia Sz., Cabrera J., Kabath P., Rocchetto M.,
Rauer H.
<Astron. Astrophys. 596, A47 (2016)>
=2016A&A...596A..47S 2016A&A...596A..47S (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Planets ; Occultations ; Spectroscopy
Keywords: planets and satellites: atmospheres -
planets and satellites: individual: WASP-17b -
techniques: spectroscopic - instrumentation: spectrographs -
stars: individual: WASP-17 - methods: data analysis
Abstract:
We present FORS2 (attached to ESO's Very Large Telescope) observations
of the exoplanet WASP-17b during its primary transit, for the purpose
of differential spectrophotometry analysis. We use the instrument in
its Mask eXchange Unit (MXU) mode to simultaneously obtain low
resolution spectra of the planet hosting star, as well as several
reference stars in the field of view. The integration of these spectra
within broadband and smaller 100Å bins provides us with 'white' and
spectrophotometric light curves, from 5700 to 8000Å. Through
modelling the white light curve, we obtain refined bulk and transit
parameters of the planet, as well as wavelength-dependent variations
of the planetary radius from smaller spectral bins through which the
transmission spectrum is obtained. The inference of transit
parameters, as well as the noise statistics, is performed using a
Gaussian Process model. We achieve a typical precision in the transit
depth of a few hundred parts per million from various transit light
curves. From the transmission spectra we rule out a flat spectrum at
>3σ and detect marginal presence of the pressure-broadened
sodium wings. Furthermore, we detect the wing of the potassium
absorption line in the upper atmosphere of the planet with 3-σ
confidence, both facts pointing to a relatively shallow temperature
gradient in the atmosphere. These conclusions are mostly consistent
with previous studies of this exo-atmosphere, although previous
potassium measurements have been inconclusive.
Description:
In producing the transmission spectrum, we model spectrophotometric
light curves, produced with small integration bins throughout
wavelength domain. The data for all the light curves presented in
Figure 7 are given. These are normalised light curves that are also
corrected for the common mode systematics. From modelling these light
curves using Gaussian processes, we detect signature of Potassium in
the atmosphere this exoplanet, WASP-17b.
Objects:
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RA (2000) DE Designation(s)
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15 59 50.95 -28 03 42.3 WASP-17b = WASP-17b
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
lcdata.dat 693 477 *Normalised light curve fluxes
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Note on lcdata.dat : These are the data for the transit light curves corrected
for the common mode systematics, as plotted in the Fig. 7 of the paper.
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See also:
J/ApJ/709/159 : Relative Ic photometry of WASP-17 (Anderson+, 2010)
J/MNRAS/426/1338 : Transiting planetary system WASP-17 (Southworth+, 2012)
Byte-by-byte Description of file: lcdata.dat
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Bytes Format Units Label Explanations
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1- 18 F18.15 d Time Time stamps of each observation, JD-2457192.5
20- 33 F14.12 --- F5750 Normalized flux at bin centre 5750Å
35- 48 F14.12 --- F5800 Normalized flux at bin centre 5800Å
50- 63 F14.12 --- F5850 Normalized flux at bin centre 5850Å
65- 78 F14.12 --- F5900 Normalized flux at bin centre 5900Å
80- 93 F14.12 --- F5950 Normalized flux at bin centre 5950Å
95-108 F14.12 --- F6000 Normalized flux at bin centre 6000Å
110-123 F14.12 --- F6050 Normalized flux at bin centre 6050Å
125-138 F14.12 --- F6100 Normalized flux at bin centre 6100Å
140-153 F14.12 --- F6150 Normalized flux at bin centre 6150Å
155-168 F14.12 --- F6200 Normalized flux at bin centre 6200Å
170-183 F14.12 --- F6250 Normalized flux at bin centre 6250Å
185-198 F14.12 --- F6300 Normalized flux at bin centre 6300Å
200-213 F14.12 --- F6350 Normalized flux at bin centre 6350Å
215-228 F14.12 --- F6400 Normalized flux at bin centre 6400Å
230-243 F14.12 --- F6450 Normalized flux at bin centre 6450Å
245-258 F14.12 --- F6500 Normalized flux at bin centre 6500Å
260-273 F14.12 --- F6550 Normalized flux at bin centre 6550Å
275-288 F14.12 --- F6600 Normalized flux at bin centre 6600Å
290-303 F14.12 --- F6650 Normalized flux at bin centre 6650Å
305-318 F14.12 --- F6700 Normalized flux at bin centre 6700Å
320-333 F14.12 --- F6750 Normalized flux at bin centre 6750Å
335-348 F14.12 --- F6800 Normalized flux at bin centre 6800Å
350-363 F14.12 --- F6850 Normalized flux at bin centre 6850Å
365-378 F14.12 --- F6900 Normalized flux at bin centre 6900Å
380-393 F14.12 --- F6950 Normalized flux at bin centre 6950Å
395-408 F14.12 --- F7000 Normalized flux at bin centre 7000Å
410-423 F14.12 --- F7050 Normalized flux at bin centre 7050Å
425-438 F14.12 --- F7100 Normalized flux at bin centre 7100Å
440-453 F14.12 --- F7150 Normalized flux at bin centre 7150Å
455-468 F14.12 --- F7200 Normalized flux at bin centre 7200Å
470-483 F14.12 --- F7250 Normalized flux at bin centre 7250Å
485-498 F14.12 --- F7300 Normalized flux at bin centre 7300Å
500-513 F14.12 --- F7350 Normalized flux at bin centre 7350Å
515-528 F14.12 --- F7400 Normalized flux at bin centre 7400Å
530-543 F14.12 --- F7450 Normalized flux at bin centre 7450Å
545-558 F14.12 --- F7500 Normalized flux at bin centre 7500Å
560-573 F14.12 --- F7550 Normalized flux at bin centre 7550Å
575-588 F14.12 --- F7600 Normalized flux at bin centre 7600Å
590-603 F14.12 --- F7650 Normalized flux at bin centre 7650Å
605-618 F14.12 --- F7700 Normalized flux at bin centre 7700Å
620-633 F14.12 --- F7750 Normalized flux at bin centre 7750Å
635-648 F14.12 --- F7800 Normalized flux at bin centre 7800Å
650-663 F14.12 --- F7850 Normalized flux at bin centre 7850Å
665-678 F14.12 --- F7900 Normalized flux at bin centre 7900Å
680-693 F14.12 --- F7950 Normalized flux at bin centre 7950Å
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Acknowledgements:
Elyar Sedaghati, esedagha(at)eso.org
(End) Elyar Sedaghati [DLR, Berlin], Patricia Vannier [CDS] 12-Oct-2016