J/ApJ/791/55 HD 189733b in transit light curve (McCullough+, 2014)
Water vapor in the spectrum of the extrasolar planet HD 189733b.
I. The transit.
McCullough P.R., Crouzet N., Deming D., Madhusudhan N.
<Astrophys. J., 791, 55 (2014)>
=2014ApJ...791...55M 2014ApJ...791...55M (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Planets ; Spectroscopy ;
Infrared sources
Keywords: planetary systems - planets and satellites: atmospheres -
stars: individual: HD 189733 - techniques: spectroscopic
Abstract:
We report near-infrared spectroscopy of the gas giant planet
HD 189733b in transit. We used the Hubble Space Telescope Wide Field
Camera 3 (HST WFC3) with its G141 grism covering 1.1 µm to 1.7 µm
and spatially scanned the image across the detector at 2''/s. When
smoothed to 75 nm bins, the local maxima of the transit depths in the
1.15 µm and 1.4 µm water vapor features are, respectively,
83±53 ppm and 200±47 ppm greater than the local minimum at 1.3 µm.
We compare the WFC3 spectrum with the composite transit spectrum of HD
189733b assembled by Pont et al., extending from 0.3 µm to 24 µm.
Although the water vapor features in the WFC3 spectrum are compatible
with the model of non-absorbing, Rayleigh-scattering dust in the
planetary atmosphere, we also re-interpret the available data with a
clear planetary atmosphere. In the latter interpretation, the slope of
increasing transit depth with shorter wavelengths from the near
infrared, through the visible, and into the ultraviolet is caused by
unocculted star spots, with a smaller contribution of Rayleigh
scattering by molecular hydrogen in the planet's atmosphere. At
relevant pressures along the terminator, our model planetary
atmosphere's temperature is ∼700 K, which is below the condensation
temperatures of sodium- and potassium-bearing molecules, causing the
broad wings of the spectral lines of Na I and K I at 0.589 µm and
0.769 µm to be weak.
Description:
HST program 12881 (McCullough, P. I.) was allocated five HST orbits to
observe the transit of HD 189733b and five orbits to observe its
eclipse. The eclipse observations are reported by Crouzet et al.
(2014ApJ...795..166C 2014ApJ...795..166C). In both cases, the event (transit or eclipse)
occurs in the fourth of the five HST orbits. We observed HD 189733b in
transit with HST WFC3 on 2013 June 5 (Table 1). We used the G141 grism
to obtain slitless spectroscopy with spectral coverage from 1.1um
to 1.7um at a resolution of R = λ/δλ = 130 and
a dispersion of 4.7 nm/pixel (Dressel 2014, Wide Field Camera 3, HST
Instrument Handbook, Ver. 6.0 (Baltimore, MD: STScI)). In each HST
orbit of the visit, we obtained a set of thirty-two 5.97 s exposures,
each with the RAPID sample sequence of seven samples, each with a
512 pixel by 512 pixel subarray. As noted in the Introduction, the
spectra were obtained in spatial scanning mode. We interleaved
scanning first forward and then reversing direction, obtaining 16
forward-reverse pairs of exposures in each orbit. We had intended to
locate the target on the detector such that its first-order spectrum
would be entirely within a region read from a single amplifier;
however, we miscalculated and the first-order spectrum crosses an
amplifier boundary (at physical column 512) corresponding to
λ = 1.55um.
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
table2.dat 55 715 Light curve
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See also:
J/A+A/548/A90 : Looking for the rainbow on exoplanets (Karalidi+, 2012)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 14 F14.6 d JD Modified Julian Date of exposure start
16- 29 F14.6 d HJD Heliocentric Julian Date of exposure start
31 I1 --- Orb [1/5] HST orbit in the visit
33- 34 I2 --- Scan Scan direction (1)
36 I1 --- Samp [1/7] MULTIACCUM sample number
38 I1 --- Flag [0-1] Data-analysis flag
40- 47 I8 ct Cts Total number of photoelectrons
49- 55 F7.5 --- Flux Normalized flux after detrending (2)
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Note (1): Scan direction as follows :
1 = forward;
-1 = reverse.
Note (2): Orbit 1 was not detrended and was ignored.
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History:
From electronic version of the journal
References:
Crouzet et al., Paper II, 2014ApJ...795..166C 2014ApJ...795..166C
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 27-Mar-2017