J/AJ/156/178 NIR transmission spectra of TRAPPIST-1 planets (Zhang+, 2018)
The near-infrared transmission spectra of TRAPPIST-1 planets b, c, d, e, f,
and g and stellar contamination in multi-epoch transit spectra.
Zhang Z., Zhou Y., Rackham B.V., Apai D.
<Astron. J., 156, 178-178 (2018)>
=2018AJ....156..178Z 2018AJ....156..178Z (SIMBAD/NED BibCode)
ADC_Keywords: Exoplanets ; Effective temperatures ; Spectra, infrared ;
Stars, double and multiple
Keywords: planets and satellites: atmospheres -
planets and satellites: individual TRAPPIST-1 -
planets and satellites: terrestrial planets - stars: late-type -
techniques: spectroscopic
Abstract:
The seven approximately Earth-sized transiting planets in the TRAPPIST-1
system provide a unique opportunity to explore habitable- and
nonhabitable-zone small planets within the same system. Its habitable-zone
exoplanets - due to their favorable transit depths - are also worlds for
which atmospheric transmission spectroscopy is within reach with the
Hubble Space Telescope (HST) and James Webb Space Telescope (JWST). We
present here an independent reduction and analysis of two HST Wide Field
Camera 3 (WFC3) near-infrared transit spectroscopy data sets for six
planets (b through g). Utilizing our physically motivated detector
charge-trap correction and a custom cosmic-ray correction routine, we
confirm the general shape of the transmission spectra presented by
de Wit et al. (2016Natur.537...69D 2016Natur.537...69D). Our data reduction approach leads
to a 25% increase in the usable data and reduces the risk of confusing
astrophysical brightness variations (e.g., flares) with instrumental
systematics. No prominent absorption features are detected in any
individual planet's transmission spectra; by contrast, the combined
spectrum of the planets shows a suggestive decrease around 1.4 µm
similar to an inverted water absorption feature. Including transit depths
from K2, the SPECULOOS-South Observatory, and Spitzer, we find that
the complete transmission spectrum is fully consistent with stellar
contamination owing to the transit light source effect. These spectra
demonstrate how stellar contamination can overwhelm planetary absorption
features in low-resolution exoplanet transit spectra obtained by HST
and JWST and also highlight the challenges in combining multi-epoch
observations for planets around rapidly rotating spotted stars.
Description:
The data presented in this study were obtained in two HST Wide Field
Camera 3 (WFC3) programs (GO-14500 and GO-14873, PI: de Wit) targeting
the TRAPPIST-1 system. In the following, we refer to the two programs
as Program 1 and Program 2, respectively. Program 1 consists of one visit,
executed on 2016 May 4, and covers the overlapping transits of planets
TRAPPIST-1 b and c. The results were initially published in de Wit et al.
(2016Natur.537...69D 2016Natur.537...69D). Program 2 consists of four visits, executed between
2016 December and 2017 January, and covers the transits of planets
TRAPPIST-1 d, e, f, and g (de Wit et al. 2018NatAs...2..214D 2018NatAs...2..214D). In the two
programs, the six inner planets (TRAPPIST-1 b-g) have been observed
at least once during transit. In addition, the observations include two
overlapping transits of the planet pairs b and c and e and g. For
convenience, we label the seven transits in chronological order as
Transit 1, 2, 3, 4, 5, 6, and 7.
Objects:
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RA (ICRS) DE Designation(s)
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23 06 29.37 -05 02 29.0 TRAPPIST-1 = EPIC 246199087
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File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table5.dat 36 6 Parameters used as input in transit profile
fitting from Gillon et al. (2016Natur.533..221G 2016Natur.533..221G,
2017Natur.542..456G 2017Natur.542..456G)
table8.dat 70 7 Planetary parameters for water absorption
calculations
table13.dat 33 84 Transmission spectra
table14.dat 33 77 Transmission spectra in the interpolated bins
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See also:
J/A+A/549/A10 : Transits of GJ 1214 (Harpsoe+, 2013)
J/A+A/563/A21 : GJ 1214 Trappist and Spitzer light curves (Gillon+, 2014)
J/ApJ/799/180 : Radii of 430 KOI Earth- to Neptune-sized planets
(Silburt+, 2015)
Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1 A1 --- Pl [bcdefg] TRAPPIST-1 planet
3- 8 F6.3 deg Incl [89.65/89.86] Inclination (1)
10- 14 F5.3 deg E_Incl [0.025/0.22] Upper limit uncertainty in Incl
16- 20 F5.3 deg e_Incl [0.025/0.27] Lower limit uncertainty in Incl
22- 30 F9.6 d T [1.5109/12.35294] Orbital period (2)
32- 36 F5.2 --- a [20.5/83.2] Semimajor axis, expressed in units
of stellar radius
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Note (1): Gaussian-distributed priors.
Note (2): Fixed parameters.
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Byte-by-byte Description of file: table8.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1 A1 --- Pl [bcdefg] TRAPPIST-1 planet
3- 7 F5.3 Mgeo Mass [0.24/1.63] Planet mass
9- 14 F6.4 Mgeo E_Mass [0.0038/0.63] Uperr limit uncertainty in Mass
16- 21 F6.4 Mgeo e_Mass [0.0038/0.63] Lower limit uncertainty in Mass
23- 27 F5.1 K Teff [198.6/400.1] Effective temperature
29- 31 F3.1 K e_Teff [3.8/7.7] Uncertainty in Teff
33- 36 I4 ppm Deltad [-413/77] Transit depth Δd
38- 40 I3 ppm e_Deltad [113/266] Uncertainty in Deltad
42- 46 F5.3 Rgeo Rad [0.772/1.127] Planet radius
48- 52 F5.3 Rgeo e_Rad [0.03/0.041] Uncertainty in Rad
54- 58 F5.1 --- AH [-11.1/2.5] Water absorption amplitude AH
(see Equation (5))
60- 63 F4.1 --- e_AH [1/13.6] Uncertainty in AH
65- 68 F4.1 --- E_AH [3.2/29.7] 3σ upper bound of AH
70 I1 --- Trans [1/7] Transit number
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Byte-by-byte Description of file: table13.dat table14.dat
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Bytes Format Units Label Explanations
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1 I1 --- Trans [1/7] Transit number
3 A1 --- Pl [bcdefg] TRAPPIST-1 planet
5- 9 I5 0.1nm Wave [11377/16613]? Wavelength (Å) (only in
Table 13) (1)
11- 17 F7.5 --- Depth [0.00356/0.00824] Transit depth
19- 25 F7.5 --- E_Depth [9e-05/0.00037] Upper limit uncertainty in Depth
27- 33 F7.5 --- e_Depth [9e-05/0.00038] Lower limit uncertainty in Depth
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Note (1): In Table 14, the central wavelengths of the 11 bins are an arithmetic
series from 11500 to 16500 Å.
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History:
From electronic version of the journal
(End) Tiphaine Pouvreau [CDS] 21-Mar-2019