J/AJ/164/59 GJ1132b planet/stellar radius at 0.7-4.5µm (Libby-Roberts+, 2022)
The Featureless HST/WFC3 Transmission Spectrum of the Rocky Exoplanet GJ 1132b:
No Evidence for a Cloud-free Primordial Atmosphere and Constraints on Starspot
Contamination.
Libby-Roberts J.E., Berta-Thompson Z.K., Diamond-Lowe H.,
Gully-Santiago M.A., Irwin J.M., Kempton E.M.-R., Rackham B.V.,
Charbonneau D., Desert J.-M., Dittmann J.A., Hofmann R., Morley C.V.,
Newton E.R.
<Astron. J., 164, 59 (2022)>
=2022AJ....164...59L 2022AJ....164...59L
ADC_Keywords: Stars, M-type; Exoplanets; Spectra, infrared
Keywords: Exoplanet atmospheres ; Exoplanet atmospheric composition ;
Extrasolar rocky planets ; Exoplanets ; Transmission
spectroscopy ; Starspots
Abstract:
Orbiting an M dwarf 12pc away, the transiting exoplanet GJ1132b is a
prime target for transmission spectroscopy. With a mass of 1.7M⊕
and radius of 1.1R⊕, GJ1132b's bulk density indicates that this
planet is rocky. Yet with an equilibrium temperature of 580K, GJ1132b
may still retain some semblance of an atmosphere. Understanding
whether this atmosphere exists and its composition will be vital for
understanding how the atmospheres of terrestrial planets orbiting M
dwarfs evolve. We observe five transits of GJ1132b with the Wide Field
Camera 3 (WFC3) on the Hubble Space Telescope (HST). We find a
featureless transmission spectrum from 1.1 to 1.7µm, ruling out
cloud-free atmospheres with metallicities <300x solar with >4.8σ
confidence. We combine our WFC3 results with transit depths from TESS
and archival broadband and spectroscopic observations to find a
featureless spectrum across 0.7 to 4.5µm. GJ1132b therefore has a
high mean molecular weight atmosphere, possesses a high-altitude
aerosol layer, or has effectively no atmosphere. Higher-precision
observations are required in order to differentiate between these
possibilities. We explore the impact of hot and cold starspots on the
observed transmission spectrum GJ1132b, quantifying the amplitude of
spot-induced transit depth features. Using a simple Poisson model, we
estimate spot temperature contrasts, spot covering fractions, and spot
sizes for GJ1132. These limits, as well as the modeling framework, may
be useful for future observations of GJ1132b or other planets
transiting similarly inactive M dwarfs.
Description:
We observed five transits of GJ1132b with Wild Field Camera 3
(WFC3/IR) grism spectroscopy (GO14758, PI Berta-Thompson). We used the
G141 grism, providing stellar spectra at a resolution of
R=λ/Δλ=130 covering approximately 1.1-1.7µm.
Objects:
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RA (2000) DE Designation(s)
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10 14 51.78 -47 09 24.2 GJ 1132 = L 320-124
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 107 22 The Rp/Rs for each wavelength bin across each visit
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See also:
J/ApJ/747/35 : HST/WFC3 transit observation of GJ1214b (Berta+, 2012)
J/A+A/546/A14 : Limb-darkening for CoRoT, Kepler, Spitzer (Claret+, 2012)
J/ApJ/761/166 : Terrestrial exoplanet atmospheres. I. (Hu+, 2012)
J/ApJ/821/93 : Rotation & Galactic kinematics of mid M dwarfs (Newton+, 2016)
J/AJ/154/142 : Corrected photometry GJ1132 for all eclipses (Dittmann+, 2017)
J/A+A/601/A106 : Sunspot on 1921-2011 (Mandal+, 2017)
J/AJ/153/191 : Transiting planet GJ 1132 (Southworth+, 2017)
J/A+A/618/A142 : Radial velocity for GJ 1132 (Bonfils+, 2018)
J/AJ/156/140 : 4 new eclipsing mid M-dwarf systems from MEarth (Irwin+, 2018)
J/AJ/156/217 : Stellar properties for Mdwarfs in MEarth-South (Newton+, 2018)
J/AJ/156/178 : NIR transmission spectra of TRAPPIST-1 planets (Zhang+, 2018)
J/A+A/628/A39 : Radial velocities of GJ 357 (Luque+, 2019)
J/AJ/159/239 : Transmission Spectroscopy Metric of exoplanets (Guo+, 2020)
J/AJ/159/57 : HST spectroscopic LCs Kepler 51b & 51d (Libby-Roberts+, 2020)
J/AJ/161/23 : RVel & light curve of low mass star TOI 540 (Ment+, 2021)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 5 F5.3 um WStart [1.15/1.61] Wavelength start
7- 11 F5.3 um WEnd [1.17/1.63] Wavelength end
13- 19 F7.5 --- V1Rp/Rs [0.04/0.06] Visit 1 Planet /Stellar Radius
21- 27 F7.5 --- e_V1Rp/Rs [0.0006/0.002] Uncertainty in V1Rp/Rs
29- 35 F7.5 --- V2Rp/Rs [0.04/0.06] Visit 2 Planet / Stellar Radius
37- 43 F7.5 --- e_V2Rp/Rs [0.0006/0.002] Uncertainty in V2Rp/Rs
45- 51 F7.5 --- V3Rp/Rs [0.04/0.06] Visit 3 Planet / Stellar Radius
53- 59 F7.5 --- e_V3Rp/Rs [0.0005/0.001] Uncertainty in V3Rp/Rs
61- 67 F7.5 --- V4Rp/Rs [0.04/0.06] Visit 4 Planet / Stellar Radius
69- 75 F7.5 --- e_V4Rp/Rs [0.0005/0.001] Uncertainty in V4Rp/Rs
77- 83 F7.5 --- V5Rp/Rs [0.04/0.06] Visit 5 Planet / Stellar Radius
85- 91 F7.5 --- e_V5Rp/Rs [0.0006/0.0009] Uncertainty in V5Rp/Rs
93- 99 F7.5 --- RpRs [0.04/0.05] Weighted average Planet / Stellar
Radius
101-107 F7.5 --- e_RpRs [0.0002/0.0004] Uncertainty in Rp/Rs
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History:
From electronic version of the journal
(End) Prepared by [AAS], Coralie Fix [CDS], 25-Oct-2022