J/MNRAS/446/2428 WASP-31b:HST/Spitzer transmission spectral survey (Sing+, 2015)
HST hot-Jupiter transmission spectral survey: detection of potassium in WASP-31b
along with a cloud deck and Rayleigh scattering.
Sing D.K., Wakeford H.R., Showman A.P., Nikolov N., Fortney J.J.,
Burrows A.S., Ballester G.E., Deming D., Aigrain S., Desert J.-M.,
Gibson N.P., Henry G.W., Knutson H., Lecavelier des Etangs A., Pont F.,
Vidal-Madjar A., Williamson M.W., Wilson P.A.
<Mon. Not. R. Astron. Soc., 446, 2428-2443 (2015)>
=2015MNRAS.446.2428S 2015MNRAS.446.2428S (SIMBAD/NED BibCode)
ADC_Keywords: Models, atmosphere ; Stars, double and multiple ; Planets ;
Spectroscopy
Keywords: techniques: spectroscopic - planets and satellites: atmospheres -
planets and satellites: individual: WASP-31b -
stars: individual: WASP-31 - planetary systems
Abstract:
We present Hubble Space Telescope optical and near-IR transmission
spectra of the transiting hot-Jupiter WASP-31b. The spectrum covers
0.3-1.7 µm at a resolution R∼70, which we combine with Spitzer
photometry to cover the full-optical to IR. The spectrum is dominated
by a cloud deck with a flat transmission spectrum which is apparent at
wavelengths >0.52µm. The cloud deck is present at high altitudes
and low pressures, as it covers the majority of the expected optical
Na line and near-IR H2O features. While Na I absorption is not clearly
identified, the resulting spectrum does show a very strong potassium
feature detected at the 4.2σ confidence level. Broadened alkali
wings are not detected, indicating pressures below ∼10 mbar. The lack
of Na and strong K is the first indication of a sub-solar Na/K
abundance ratio in a planetary atmosphere (ln[Na/K]=-3.3±2.8), which
could potentially be explained by Na condensation on the planet's
night side, or primordial abundance variations. A strong Rayleigh
scattering signature is detected at short wavelengths, with a 4σ
significant slope. Two distinct aerosol size populations can explain
the spectra, with a smaller sub-micron size grain population reaching
high altitudes producing a blue Rayleigh scattering signature on top
of a larger, lower lying population responsible for the flat cloud
deck at longer wavelengths. We estimate that the atmospheric
circulation is sufficiently strong to mix micron size particles
upwards to the required 1-10 mbar pressures, necessary to explain the
cloud deck. These results further confirm the importance of clouds in
hot Jupiters, which can potentially dominate the overall spectra and
may alter the abundances of key gaseous species.
Description:
We observed two transits of WASP-31b with the HST STIS G430L grating
during 2012 June 13 and 26, as well as one transit with the STIS G750L
during 2012 July 10. In addition to the STIS data, observations of
WASP-31b were also conducted in the infrared with WFC3 on the HST.
Observations began on 2012 May 13 at 12:53 using the IR G141 grism in
forward spatial scan mode over five HST orbits. We analyse two transit
observations obtained using the Infrared Array Camera (IRAC) instrument
(Programme 90092 with P.I. Desert) on the Spitzer space telescope in
the 3.6 µm and 4.5 µm channels in subarray mode (32x32 pixel, or
39 centred on the planets host). The 3.6 µm observation was performed
on UT 2013 March 9 (between 06:59 and 11:37) and the 4.5 observation
was performed on UT 2013 March 19 (between 12:19 and 16:58).
Objects:
--------------------------------------------------
RA (ICRS) DE Designation(s)
--------------------------------------------------
11 17 45.36 -19 03 17.2 WASP-31b = WASP-31b
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 58 63 WASP-31b broad-band transmission spectral
results and non-linear limb-darkening
coefficients for the STIS G430L, G750L,
WFC3 G141, and Spitzer IRAC.
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See also:
J/A+A/428/1001 : Non-linear limb-darkening law for LTE models. III.
(Claret, 2004)
J/A+A/531/A60 : WASP-31b photometry and radial velocities (Anderson+, 2011)
J/A+A/552/A16 : Limb-darkening for CoRoT, Kepler, Spitzer. II.
(Claret+, 2013)
J/MNRAS/456/1294 : Limb-darkening coefficients (Reeve+, 2016)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 5 I5 0.1nm Lambda1 Lower value of wavelength interval (Å)
7- 11 I5 0.1nm Lambda2 ? Upper value of wavelength interval (Å)
13- 19 F7.5 --- Rp/R* Planet-to-star radius ratio
21- 27 F7.5 --- r_Rp/R* Uncertainty in Rp/R*
29- 34 F6.4 --- c1 Non-linear limb-darkening coefficient for
the HST STIS G430L
36- 42 F7.4 --- c2 Non-linear limb-darkening coefficient for
the HST STIS G750L
44- 50 F7.4 --- c3 Non-linear limb-darkening coefficient for
the HST WFC3 G141
52- 58 F7.4 --- c4 Non-linear limb-darkening coefficient for
the Spitzer IRAC
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History:
From electronic version of the journal
(End) Tiphaine Pouvreau [CDS] 02-Nov-2017