J/A+A/658/A133 TRAPPIST-1 h NIR spectrum (Gressier+, 2022)
Near-infrared transmission spectrum of TRAPPIST-1 h using Hubble WFC3 G141
observations.
Gressier A., Mori M., Changeat Q., Edwards B., Beaulieu J.P., Marcq E.,
Charnay B.
<Astron. Astrophys. 658, A133 (2022)>
=2022A&A...658A.133G 2022A&A...658A.133G (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Exoplanets
Keywords: planets and satellites: atmospheres - techniques: photometric -
techniques: spectroscopic
Abstract:
The TRAPPIST-1 planetary system is favorable for transmission
spectroscopy and offers the unique opportunity to study rocky-planets
with possibly non-primary envelopes. We present here the transmission
spectrum of the seventh planet of the TRAPPIST-1 system, TRAPPIST-1 h
(RP=0.752R⊕, Teq=173K) using Hubble Space Telescope (HST), Wide
Field Camera 3 Grism 141 (WFC3/G141) data.
Our purpose is to reduce the HST observations of the seventh planet of
TRAPPIST-1 system and by testing simple atmospheric hypothesis put new
constraint on the composition and the nature of the planet.
First we extracted and corrected the raw data to obtain a transmission
spectrum in the Near-IR band (1.1-1.7um). TRAPPIST-1 is a cold
M-dwarf and its activity could affect the transmission spectrum. We
correct for stellar modulations using three different stellar
contamination models, while some fit better the data, they are
statistically not significant and the conclusion remains unchanged
concerning the presence or not of an atmosphere. Finally, using a
Bayesian atmospheric retrieval code we put new constraints on the
atmosphere composition of TRAPPIST-1h.
According to the retrieval analysis, there is no evidence of molecular
absorption in the Near-InfraRed (NIR) spectrum. This suggests the
presence of a high cloud deck or a layer of photochemical hazes in a
primary atmosphere or a secondary atmosphere dominated by heavy
species like nitrogen. This result could even be the consequence of
the lack of an atmosphere as the spectrum is better fitted using a
flat-line. Variations of transit depth around 1.3um are likely due to
remaining scattering noise and results are not improved while changing
the spectral resolution. TRAPPIST-1 h has probably lost its atmosphere
or possesses a layer of clouds and hazes blocking the NIR signal. We
can not distinguish yet between a primary cloudy or a secondary clear
envelope using HST/WFC3 data but we can reject, in most cases with
more than 3σ confidence, the hypothesis of a clear atmosphere
dominated by hydrogen and helium. By testing forced secondary
atmospheric scenario, we find that a CO-rich atmosphere (i.e with a
volume mixing ratio of 0.2) is one of the best fit to the spectrum
with a Bayes Factor of 1.01 corresponding to a 2.1σ detection.
Description:
We provide the ligthcurves for the three observations of Trappist-1h
using the Hubble Space Telescope Wide Field Camera 3 Grism 141. The
raw and the detrended light curves have been extracted and fitted
using the python package iraclis.
Objects:
----------------------------------------------------
RA (2000) DE Designation(s)
----------------------------------------------------
23 06 29.37 -05 02 29.0 TRAPPIST-1h = K2-112h
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File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
lc1.dat 96 42 Lightcurves of observations 1 taken in July 2017
lc2.dat 96 49 Lightcurves of observations 2 taken in
September 2019
lc3.dat 96 43 Lightcurves of observations 3 taken in July 2020
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See also:
J/AJ/156/178 : NIR transmission spectra of TRAPPIST-1 planets (Zhang+, 2018)
J/AJ/156/218 : Transit light curves of TRAPPIST-1 planets (Ducrot+, 2018)
J/A+A/640/A112 : TRAPPIST-1 transit timings (Ducrot+, 2020)
Byte-by-byte Description of file: lc1.dat lc2.dat lc3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 F10.2 d Time Time of exposure, BJD (TBD)
12- 36 E25.18 --- Phase Phase of transit
38- 45 I8 e- FluxRaw Raw flux (total count)
47- 70 E24.18 --- FluxNorm Normalised corrected flux (detrended)
72- 96 E25.18 --- Res Normalised residuals between detrended
and model (residuals)
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History:
From Amelie Gressier, amg.gressier(at)gmail.com
Acknowledgements:
This study makes use of observations with the NASA/ESA Hubble Space
Telescope, obtained at the Space Telescope Science Institute (STScI)
operated by the Association of Universities for Research in Astronomy.
The publicly available HST observations presented here were taken as
part of proposal 15304, led by Julien de Wit. These were obtained from
the Hubble Archive which is part of the Mikulski Archive for Space
Telescopes.
References:
Tsiaras et al., 2016ApJ...820...99T 2016ApJ...820...99T
(End) Patricia Vannier [CDS] 07-Dec-2021