J/A+A/699/A150 Dark skies of the slightly eccentric WASP-18 b (Deline+, 2025)
Dark skies of the slightly eccentric WASP-18 b from its optical-to-infrared
dayside emission.
Deline A., Cubillos P.E., Carone L., Demory B.-O., Lendl M., Benz W.,
Brandeker A., Guenther M.N., Heitzmann A., Barros S.C.C., Kreidberg L.,
Bruno G., Kitzmann D., Bonfanti A., Farnir M., Persson C.M., Sousa S.G.,
Wilson T.G., Ehrenreich D., Singh V., Iro N., Alibert Y., Alonso R.,
Barczy T., Barrado Navascues D., Baumjohann W., Bergomi M., Billot N.,
Borsato L., Broeg C., Busch M.-D., Collier Cameron A., Correia A.C.M.,
Csizmadia Sz., Davies M.B., Deleuil M., Delrez L., Demangeon O.D.S.,
Derekas A., Edwards B., Erikson A., Fortier A., Fossati L., Fridlund M.,
Gandolfi D., Gazeas K., Gillon M., Guedel M., Hasiba J., Helling C.,
Isaak K.G., Kiss L.L., Korth J., Lam K.W.F., Laskar J.,
Lecavelier des Etangs A., Magrin D., Maxted P.F.L., Merin B., Mordasini C.,
Nascimbeni V., Olofsson G., Ottensamer R., Pagano I., Palle E., Peter G.,
Piazza D., Piotto G., Pollacco D., Queloz D., Ragazzoni R., Rando N.,
Ratti F., Rauer H., Ribas I., Santos N.C., Scandariato G., Segransan D.,
Simon A.E., Smith A.M.S., Stalport M., Sulis S., Szabo Gy.M., Udry S.,
Van Grootel V., Venturini J., Villaver E., Walton N.A., Westerdorff K.
<Astron. Astrophys. 699, A150 (2025)>
=2025A&A...699A.150D 2025A&A...699A.150D (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Exoplanets ; Photometry ; Optical
Keywords: techniques: photometric -
planets and satellites: atmospheres -
planets and satellites: individual: WASP-18 b
Abstract:
Ultra-hot Jupiters are gas giant exoplanets strongly irradiated by
their star, which sets intense molecular dissociation leading to
atmospheric chemistry dominated by ions and atoms. These conditions
inhibit day-to-night heat redistribution resulting in large
temperature contrast. Phase-curve observations over several passbands
offer insights on the thermal structure and properties of these
extreme atmospheres.
We aim to perform a joint analysis of multiple observations of WASP-18
b from the visible to the mid-infrared, using unpublished data from
CHEOPS, TESS and Spitzer. Our purpose is to characterise the planetary
atmosphere with a consistent view over the large wavelength range
covered, including JWST data.
We implement a model for the planetary signal including transits,
occultations, phase signal, ellipsoidal variations, Doppler boosting,
and light-travel time. We fit jointly more than 250 eclipse events and
derive atmospheric properties using General Circulation Models and
retrieval analyses.
We obtain new ephemerides with unprecedented precisions of 1 second
and 1.4 millisecond on the time of inferior conjunction and orbital
period, respectively. We compute a planetary radius of
Rp=1.1926±0.0077RJ with a precision of 0.65%, or 550km. Through
a timing inconsistency with JWST, we discuss and confirm orbital
eccentricity (e=0.00852±0.00091), and constrain the argument of
periastron to ω=261.9-1.4+1.3deg. We show that the large
dayside emission implies the presence of magnetic drag and super-solar
metallicity. We find a steep thermally-inverted gradient in the
planetary atmosphere, which is common for ultra-hot Jupiters. We
detect the presence of strong CO emission lines at 4.5µm from an
excess of dayside brightness in the Spitzer/IRAC/Channel 2 passband.
Using these models to constrain the reflected contribution in the
CHEOPS passband, we derive an extremely low geometric albedo
ACHEOPS=0.027±0.011.
The orbital eccentricity remains a potential challenge for planetary
dynamics that might require further study given the short-period
massive planet and despite the young age of the system. The
characterisation of the atmosphere of WASP-18 b reveals the necessity
to account for magnetic friction and super-solar metallicity to
explain the full picture of the dayside emission. We find the
planetary dayside to be extremely unreflective, but when juxtaposing
TESS and CHEOPS data, we get hints of increased scattering efficiency
in the visible, likely due to Rayleigh scattering.
Description:
Raw, normalised and residual photometric light curves of the WASP-18
planetary system obtained with the space-based instruments CHEOPS,
TESS and Spitzer. Planet-related signal only (transit, occultation and
planetary flux) is also reported after correction of the instrumental
systematic noise. Occultation depths measured as a function of
wavelengths (incl. JWST - Coulombe et al. 2023) and as a function of
time (occultation depth variability) are also provided.
Objects:
--------------------------------------------------
RA (2000) DE Designation(s)
--------------------------------------------------
01 37 25.03 -45 40 40.3 WASP-18 = HD 10069
--------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
cheopsrw.dat 276 13760 CHEOPS raw photometry
tessrw.dat 261 93313 TESS raw photometry
spitzerw.dat 92 8519 Spitzer raw photometry
cheopslc.dat 461 12788 CHEOPS light curves
tesslc.dat 456 67162 TESS light curves
spitzelc.dat 293 8515 Spitzer light curves
occdepwl.dat 74 414 Occultation depths versus wavelength
fmaxvar.dat 80 146 Dayside flux variability with time
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See also:
J/ApJ/707/167 : Transiting planetary system WASP-18 (Southworth+, 2009)
J/A+A/567/A128 : X-ray sources in WASP-18 field (Pillitteri+, 2014)
J/AcA/70/1 : WASP-18 photometric timeseries and timing data
(Maciejewski+, 2020)
Byte-by-byte Description of file: cheopsrw.dat
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Bytes Format Units Label Explanations
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1- 26 A26 "datime" Time UTC time of observation
28- 43 F16.10 d MJD MJD time of observation
45- 62 F18.10 d BJD BJD time of observation
64- 75 E12.6 e- Flux Raw flux
77- 83 F7.2 e- e_Flux Raw flux error
85 I1 --- Status Status flag
87- 92 I6 --- Event Event flag
94-109 F16.10 e- Dark Dark current
111-122 E12.6 e- Bkg Background level
124-135 E12.6 --- ContaLC Contamination estimate
137-148 E12.6 --- e_ContaLC Contamination error
150-165 F16.12 e- SmearLC Smearing estimate
167-169 F3.1 e- e_SmearLC [0] Smearing error
171-178 F8.4 deg RollAngle Spacecraft roll angle
180-182 I3 pix Loc-X Expected PSF X location
184-186 I3 pix Loc-Y Expected PSF Y location
188-194 F7.3 pix Cent-X PSF centroid X location
196-202 F7.3 pix Cent-Y PSF centroid Y location
204-205 I2 --- VisitNo Visit number
207-208 I2 s TExptime Total exposure time
210-225 F16.9 e-/s FluxPerSec Raw flux
227-240 F14.10 e-/s e_FluxPerSec Raw flux error
242-258 F17.15 --- FluxNorm Normalised flux
260-276 F17.15 --- e_FluxNorm Normalised flux error
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Byte-by-byte Description of file: tessrw.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 15 F15.10 d Time Time of observation (BJD-2457000)
17- 24 F8.6 d TimeCorr Time correction
26- 32 I7 --- CadenceNo Cadence number
34- 44 F11.5 e-/s FluxSAP ?=- SAP flux
46- 54 F9.6 e-/s e_FluxSAP ?=- SAP flux error
56- 67 F12.5 e-/s NkgSAP ?=- SAP background level
69- 77 F9.6 e-/s e_NkgSAP ?=- SAP background error
79- 89 F11.5 e-/s FluxPDCSAP ?=- PDCSAP flux
91- 99 F9.6 e-/s e_FluxPDCSAP ?=- PDCSAP flux error
101-105 I5 --- Qual Quality flag
107-109 A3 pix PSFCentr1 [-] PSF center 1
111-113 A3 pix e_PSFCentr1 [-] PSF center 1 error
115-117 A3 pix PSFCentr2 [-] PSF center 2
119-121 A3 pix e_PSFCentr2 [-] PSF center 2 error
123-136 F14.9 pix MOMCentr1 ?=- MOM center 1
138-148 F11.9 pix e_MOMCentr1 ?=- MOM center 1 error
150-163 F14.9 pix MOMCentr2 ?=- MOM center 2
165-175 F11.9 pix e_MOMCentr2 ?=- MOM center 2 error
177-185 F9.6 pix PosCorr1 ?=- Position correction 1
187-195 F9.6 pix PosCorr2 ?=- Position correction 2
197-198 I2 --- Sector TESS sector number
200-202 I3 --- Orbit TESS orbit number
204 I1 min ExpTime Exposure time
206-223 F18.10 d BJD BJD time of observation (TDB)
225-232 F8.6 --- FluxSAPNorm ?=- SAP normalised flux
234-242 F9.7 --- e_FluxSAPNorm ?=- SAP normalised flux error
244-251 F8.6 --- FluxPDCSAPNorm ?=- PDCSAP normalised flux
253-261 F9.7 --- e_FluxPDCSAPNorm ?=- PDCSAP norm. flux error
--------------------------------------------------------------------------------
Byte-by-byte Description of file: spitzerw.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 F8.6 --- Phase-Orb Orbital phase (pre-proc)
10- 27 F18.10 d BJD BJD time of observation (TDB)
29- 36 F8.6 --- FluxRawNorm Normalised raw flux
38- 45 F8.6 --- FluxNorm Normalised flux (pre-proc)
47- 55 F9.7 --- e_FluxNorm Normalised flux error (pre-proc)
57- 65 F9.6 --- FluxResInit Residuals (pre-proc)
67- 74 F8.6 --- FluxModInit Full model (pre-proc)
76- 83 F8.6 --- PlanetModelInit Planet model (pre-proc)
85- 87 F3.1 --- eModelInit [0] Model error (pre-proc)
89 I1 --- IRAC [1/4] IRAC channel
91- 92 I2 --- VisitNo Visit number
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Byte-by-byte Description of file: cheopslc.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 26 A26 "datime" Time UTC time of observation
28- 43 F16.10 d MJD MJD time of observation
45- 62 F18.10 d BJD BJD time of observation
64- 75 E12.6 e- Flux Raw flux
77- 83 F7.2 e- e_Flux Raw flux error
85 I1 --- Status Status flag
87 I1 --- Event Event flag
89-104 F16.10 e- Dark Dark current
106-121 F16.9 e- Bkg Background level
123-134 E12.6 --- ContaLC Contamination estimate
136-147 E12.6 --- e_ContaLC Contamination error
149-164 F16.12 e- SmearLC Smearing estimate
166-168 F3.1 e- e_SmearLC [0] Smearing error
170-177 F8.4 deg RollAngle Spacecraft roll angle
179-181 I3 pix Loc-X Expected PSF X location
183-185 I3 pix Loc-Y Expected PSF Y location
187-193 F7.3 pix Cent-X PSF centroid X location
195-201 F7.3 pix Cent-Y PSF centroid Y location
203-204 I2 --- VisitNo Visit number
206-207 I2 s TExpTime Total exposure time
209-224 F16.9 e-/s FluxPerSec Raw flux
226-238 F13.10 e-/s e_FluxPerSec Raw flux error
240-256 F17.15 --- FluxNorm Normalised flux
258-274 F17.15 --- e_FluxNorm Normalised flux error
276-293 F18.15 --- Phase Best fit orbital phase
295-311 F17.15 --- Model Full model
313-324 E12.6 --- e_Model Full model error
326-342 F17.15 --- PlanetModel Best fit planet model
344-355 E12.6 --- e_PlanetModel Best fit planet model error
357-374 F18.15 --- SystModel Best fit systematics model
376-387 E12.6 --- e_SystModel Best fit systematics model error
389-405 F17.15 --- FluxDet Best fit detrended (planet-only) flux
407-423 F17.15 --- e_FluxDet Best fit detrended flux error
425-444 F20.15 --- FluxRes Best fit residuals
446-461 F16.12 --- e_FluxRes Best fit residuals error
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tesslc.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 15 F15.10 d Time Time of observation (BJD-2457000)
17- 24 F8.6 d TimeCorr Time correction
26- 32 I7 --- CadenceNo Cadence number
34- 44 F11.5 e-/s FluxSAP SAP flux
46- 54 F9.6 e-/s e_FluxSAP SAP flux error
56- 65 F10.5 e-/s NkgSAP SAP background level
67- 74 F8.6 e-/s e_NkgSAP SAP background error
76- 86 F11.5 e-/s FluxPDCSAP PDCSAP flux
88- 96 F9.6 e-/s e_FluxPDCSAP PDCSAP flux error
98 I1 --- Qual [0] Quality flag
100-102 A3 pix PSFCentr1 [-] PSF center 1
104-106 A3 pix e_PSFCentr1 [-] PSF center 1 error
108-110 A3 pix PSFCentr2 [-] PSF center 2
112-114 A3 pix e_PSFCentr2 [-] PSF center 2 error
116-129 F14.9 pix MOMCentr1 MOM center 1
131-141 F11.9 pix e_MOMCentr1 MOM center 1 error
143-156 F14.9 pix MOMCentr2 MOM center 2
158-168 F11.9 pix e_MOMCentr2 MOM center 2 error
170-178 F9.6 pix PosCorr1 Position correction 1
180-188 F9.6 pix PosCorr2 Position correction 2
190-191 I2 --- Sector TESS sector number
193-195 I3 --- Orbit TESS orbit number
197 I1 min ExpTime Exposure time
199-216 F18.10 d BJD BJD time of observation (TDB)
218-225 F8.6 --- FluxSAPNorm SAP normalised flux
227-235 F9.7 --- e_FluxSAPNorm SAP normalised flux error
237-244 F8.6 --- FluxPDCSAPNorm PDCSAP normalised flux
246-254 F9.7 --- e_FluxPDCSAPNorm PDCSAP normalised error
256-263 F8.6 --- FluxNorm Selected normalised flux
265-273 F9.7 --- e_FluxNorm Selected normalised error
275 I1 --- NoTrends No-trend flag
277 I1 --- Outlier Outlier flag
279-287 F9.6 --- Phase Orbital phase
289-305 F17.15 --- Model Full model
307-318 E12.6 --- e_Model Full model error
320-336 F17.15 --- PlanetModel Best fit planet model
338-349 E12.6 --- e_PlanetModel Best fit planet model error
351-368 F18.15 --- SystModel Best fit systematics model
370-381 E12.6 --- e_SystModel Best fit systematics model error
383-399 F17.15 --- FluxDet Best fit detrended flux
401-417 F17.15 --- e_FluxDet Best fit detrended flux error
419-439 F21.15 --- FluxRes Best fit residuals
441-456 F16.12 --- e_FluxRes Best fit residuals error
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Byte-by-byte Description of file: spitzelc.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 F8.6 --- Phase-Orb Orbital phase (pre-proc)
10- 27 F18.10 d BJD BJD time of observation (TDB)
29- 36 F8.6 --- FluxRawNorm Normalised raw flux
38- 45 F8.6 --- FluxNorm Normalised flux (pre-proc)
47- 55 F9.7 --- e_FluxNorm Normalised flux error (pre-proc)
57- 65 F9.6 --- FluxResInit Residuals (pre-proc)
67- 74 F8.6 --- FluxModInit Full model (pre-proc)
76- 83 F8.6 --- PlanetModelInit Planet model (pre-proc)
85- 87 F3.1 --- eModelInit [0] Model error (pre-proc)
89 I1 --- IRAC [1/4] IRAC channel
91- 92 I2 --- VisitNo Visit number
94 I1 --- Outlier [0] Outlier flag
96-112 F17.15 --- Phase Best fit orbital phase (final)
114-130 F17.15 --- Model Best fit full model (final)
132-148 F17.15 --- e_Model Best fit full model error (final)
150-166 F17.15 --- PlanetModel Best fit planet model (final)
168-184 F17.15 --- e_PlanetModel Best fit planet model error (final)
186-203 F18.15 --- SystModel Best fit systematics model (final)
205-216 E12.6 --- e_SystModel Best fit systematics model error (final)
218-234 F17.15 --- FluxDet Best fit detrended flux (final)
236-252 F17.15 --- e_FluxDet Best fit detrended flux error (final)
254-275 F22.15 --- FluxRes Best fit residuals (final)
277-293 F17.12 --- e_FluxRes Best fit residuals error (final)
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Byte-by-byte Description of file: occdepwl.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 F10.8 um lambda Passband center
12- 21 F10.8 um e_lambda Passband range
23- 39 F17.12 10-6 OccDepth Occultation depth (in ppm unit)
41- 57 F17.13 10-6 e_OccDepth Occultation depth error (in ppm unit)
59- 74 A16 --- Inst Instrument
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Byte-by-byte Description of file: fmaxvar.dat
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Bytes Format Units Label Explanations
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1- 18 F18.10 s BJD BJD time of observation (TDB)
20- 24 I5 --- Epoch Epoch
26- 37 E12.6 --- Fmax Dayside flux
39- 50 E12.6 --- e_Fmax Dayside flux lower error
52- 63 E12.6 --- E_Fmax Dayside flux upper error
65- 80 A16 --- Inst Instrument
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Acknowledgements:
Adrien Deline, adrien.deline(at)unige.ch
References:
Coulombe et al., 2023Natur.620..292C 2023Natur.620..292C
(End) Patricia Vannier [CDS] 07-May-2025