J/ApJ/795/166 Extrasolar planet HD 189733b whitelight curve (Crouzet+, 2014)
Water vapor in the spectrum of the extrasolar planet HD 189733b.
II. The eclipse.
Crouzet N., McCullough P.R., Deming D., Madhusudhan N.
<Astrophys. J., 795, 166 (2014)>
=2014ApJ...795..166C 2014ApJ...795..166C (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Planets
Keywords: methods: observational - planets and satellites: atmospheres -
planets and satellites: individual: HD 189733b -
techniques: spectroscopic
Abstract:
Spectroscopic observations of exoplanets are crucial to infer the
composition and properties of their atmospheres. HD 189733b is one of
the most extensively studied exoplanets and is a cornerstone for hot
Jupiter models. In this paper, we report the dayside emission spectrum
of HD 189733b in the wavelength range 1.1-1.7 µm obtained with the
Hubble Space Telescope Wide Field Camera 3 (WFC3) in spatial scan
mode. The quality of the data is such that even a straightforward
analysis yields a high-precision Poisson noise-limited spectrum: the
median 1σ uncertainty is 57 ppm per 0.02 µm bin. We also
build a white-light curve correcting for systematic effects and derive
an absolute eclipse depth of 96±39 ppm. The resulting spectrum shows
marginal evidence for water vapor absorption, but can also be well
explained by a blackbody spectrum. However, the combination of these
WFC3 data with previous Spitzer photometric observations is best
explained by a dayside atmosphere of HD 189733b with no thermal
inversion and a nearly solar or subsolar H2O abundance in a
cloud-free atmosphere. Alternatively, this apparent subsolar abundance
may be the result of clouds or hazes that future studies need to
investigate.
Description:
We used HST WFC3 with the newly implemented spatial scanning mode,
developed in part to enable observations such as these
(McCullough & MacKenty, 2012wfc..rept....8M). In this mode, a controlled
scan is applied to the telescope during the exposure in a direction
perpendicular to the wavelength dispersion direction (Figure 1). This
technique is particularly efficient for bright stars such as HD 189733
(see McCullough et al. 2014ApJ...791...55M 2014ApJ...791...55M, for more details).
One eclipse of HD 189733b was observed on 2013 June 24. The
observations are divided into five HST orbits, the planetary eclipse
occurring during the fourth orbit. In total, 159 exposures of 5.97 s
each were acquired, corresponding to 32 exposures per orbit (except
for the first orbit in which the first image is a direct image).
Objects:
----------------------------------------------------------
RA (ICRS) DE Designation(s)
----------------------------------------------------------
20 00 43.71 +22 42 39.1 HD 189733b = HD 189733b
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 48 159 Whitelight curve
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See also:
J/ApJ/767/64 : Benchmark light curves for exoplanet eclipses (Rogers+, 2013)
J/ApJ/791/55 : HD 189733b in transit light curve (McCullough+, 2014)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 12 F12.6 d MJD Modified Julian Date of exposure start
14- 25 F12.6 d HJD Heliocentric Julian Date of exposure start
27 I1 --- Orbit [1/5] HST orbit in the visit
29- 30 I2 --- Scan Scan direction (1)
32- 40 I9 --- Ph-e Total number of photoelectrons
42- 48 F7.5 --- NFlux Normalized flux before detrending
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Note (1): Direction as follows:
1 = Forward;
-1 = Reverse.
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History:
From electronic version of the journal
References:
McCullough et al., Paper I, 2014ApJ...791...55M 2014ApJ...791...55M, J/ApJ/791/55
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 29-May-2017