J/A+A/640/A112         TRAPPIST-1 transit timings                (Ducrot+, 2020)

TRAPPIST-1: Global Results of the Spitzer Exploration Science Program Red Worlds. Ducrot E., Gillon M., Delrez L., Agol E., Rimmer P., Turbet M., Guenther M.N., Demory B-O., Triaud A.H.M.J., Bolmont E., Burgasser A., Carey S.J., Ingalls J.G., Jehin E., Leconte J., Lederer S.M., Queloz D., Raymond S.N., Selsis F., Van Grootel V., de Wit J. <Astron. Astrophys. 640, A112 (2020)> =2020A&A...640A.112D 2020A&A...640A.112D (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Exoplanets Keywords: planets and satellites: terrestrial planets - planets and satellites: atmospheres - techniques: photometric Abstract: With more than 1000 hours of observation from Feb 2016 to Oct 2019, the Spitzer Exploration Program Red Worlds (ID: 13067, 13175 and 14223) exclusively targeted TRAPPIST-1, a nearby (12pc) ultracool dwarf star, finding that it is orbited by seven transiting Earth-sized planets. At least three of these planets orbit within the classical habitable zone of the star, and all of them are well-suited for a detailed atmospheric characterization with the upcoming JWST. The main goals of the Spitzer Red Worlds program were (1) to explore the system for new transiting planets, (2) to intensively monitor the planets' transits to yield the strongest possible constraints on their masses, sizes, compositions, and dynamics, and (3) to assess the infrared variability of the host star. In this paper, we present the global results of the project. We analyzed 88 new transits and combined them with 100 previously analyzed transits, for a total of 188 transits observed at 3.6 or 4.5um. For a comprehensive study, we analyzed all light curves both individually and globally. We also analyzed 29 occultations (secondary eclipses) of planet b and eight occultations of planet c observed at 4.5um to constrain the brightness temperatures of their daysides. We identify several orphan transit-like structures in our Spitzer photometry, but all of them are of low significance. We do not confirm any new transiting planets. We do not detect any significant variation of the transit depths of the planets throughout the different campaigns. Comparing our individual and global analyses of the transits, we estimate for TRAPPIST-1 transit depth measurements mean noise floors of ∼35 and 25ppm in channels 1 and 2 of Spitzer/IRAC, respectively. We estimate that most of this noise floor is of instrumental origins and due to the large inter-pixel inhomogeneity of IRAC InSb arrays, and that the much better interpixel homogeneity of JWST instruments should result in noise floors as low as 10ppm, which is low enough to enable the atmospheric characterization of the planets by transit transmission spectroscopy. Our analysis reveals a few outlier transits, but we cannot conclude whether or not they correspond to spot or faculae crossing events. We construct updated broadband transmission spectra for all seven planets which show consistent transit depths between the two Spitzer channels. Although we are limited by instrumental precision, the combined transmission spectrum of planet b to g tells us that their atmospheres seem unlikely to be CH4-dominated. We identify and model five distinct high energy flares in the whole dataset, and discuss our results in the context of habitability. Finally, we fail to detect occultation signals of planets b and c at 4.5um, and can only set 3σ upper limits on their dayside brightness temperatures (611K for b 586K for c). Description: The dataset used in this work includes all time-series observations of TRAPPIST-1 carried out by Spitzer/IRAC since the discovery of its planetary system: 45 h of observations gathered within the DDT program 12126 in Feb and March 2016 (Gillon et al. 2017Natur.542..456G 2017Natur.542..456G, Delrez et al. 2018MNRAS.475.3577D 2018MNRAS.475.3577D, hereafter D2018), and all data (1080h) taken within the Spitzer Exploration Science program Red Worlds (ID 13067) between Feb 2017 and Oct 2019 (see Fig. 1) including data from the DDT program 13175 (PI: L. Delrez) targeting occultations of the two inner planets and data from the DDT program 14223 (PI: E. Agol) taken in Oct 2019 to better constrain the masses of the planets and to tighten the ephemeris forecast for observations with JWST,see Agol et al. (2020, MBRAS, in press.). All these data can be accessed through the online Spitzer Heritage Archive database (http://sha.ipac.caltech.edu). Objects: ---------------------------------------------- RA (2000) DE Designation(s) ---------------------------------------------- 23 06 29.37 -05 02 29.0 TRAPPIST-1 = K2-112 ---------------------------------------------- File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file tablea1.dat 101 159 Baseline for the individual analysis of each transit tablea2.dat 39 159 Transit Timings and Depths Obtained from Individual Analyses of each transit tablea3.dat 39 29 Transit timings and depths Obtained from Individual Analyses of each blended or partial transit tablea4.dat 36 49 Transit Timings and Depths Obtained from Global Analyses of each transit with ddf variations allowed for 3.6um channel tablea5.dat 36 110 Transit Timings and Depths Obtained from Global Analyses of each transit with ddf variations allowed for 4.5um channel tablea6.dat 39 157 *Transit Timings and transit timing variation tablea7.dat 33 159 *Median values and median absolute deviations of the residuals in and out of transit -------------------------------------------------------------------------------- Note on tablea6.dat: calculated as the difference of the transit timing from the value given by the linear regression calculated with the reference timing, the period of the planet and the epoch of the transit. Note on tablea7.dat: using the residuals from the global analyses planet-by-planet. -------------------------------------------------------------------------------- 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) Byte-by-byte Description of file: tablea1.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 10 A10 --- --- TRAPPIST-1 11 A1 --- Planet [b-h] Planet name 13- 22 A10 "date" Obs.date Date of observations (start) 24- 26 I3 --- Npoints Number of points per light curve 28- 30 I3 --- Epoch Epoch of transit 32- 83 A52 --- Baseline Most appropriate baseline for systematics corrections 85- 88 F4.2 --- Bw White noise scaling factor 90- 93 F4.2 --- Br Red noise scaling factor 95- 98 F4.2 --- CF Correction factor 100-101 A2 --- Channel [c1 c2] Spitzer/IRAC channel (c1 for 3.6mum, c2 for 4.5mum) -------------------------------------------------------------------------------- Byte-by-byte Description of file: tablea2.dat tablea3.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1 A1 --- Planet [b-h] Name of planet 3- 5 I3 --- Epoch Epoch of transit 7- 16 F10.5 d Timing Timing of transit (BJD-50000) 18- 24 F7.5 d e_Timing Error on timing 26- 30 F5.3 % Depth Depth of transit 32- 36 F5.3 % e_Depth Error on depth of transit 38- 39 A2 --- Channel [C1 c2] Spitzer/IRAC channel (c1 for 3.6mum, c2 for 4.5mum) -------------------------------------------------------------------------------- Byte-by-byte Description of file: tablea4.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1 A1 --- Planet [b-h] Name of planet 3- 5 I3 --- Epoch Epoch of transit (1) 7- 16 F10.5 d Timing timing of transit (BJD-50000) 18- 24 F7.5 d e_Timing Error on timing 26- 30 F5.3 % Depth depth of transit (1) 32- 36 F5.3 % e_Depth Error on depth of transit -------------------------------------------------------------------------------- Note (1): only for Spitzer/IRAC channel 1 at 3.6um. -------------------------------------------------------------------------------- Byte-by-byte Description of file: tablea5.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1 A1 --- Planet [b-h] Name of planet 3- 5 I3 --- Epoch Epoch of transit (1) 7- 16 F10.5 d Timing Timing of transit (BJD-50000) 18- 24 F7.5 d e_Timing Error on timing 26- 30 F5.3 % Depth Depth of transit (1) 32- 36 F5.3 % e_Depth Error on depth of transit -------------------------------------------------------------------------------- Note (1): only for Spitzer/IRAC channel 2 at 4.5um. -------------------------------------------------------------------------------- Byte-by-byte Description of file: tablea6.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1 A1 --- Planet [b-h] Name of planet 3- 5 I3 --- Epoch Epoch of transit 7- 16 F10.5 d Timing Timing of transit (BJD-50000) 18- 24 F7.5 d e_Timing Error on timing 26- 32 F7.3 % TTV Transit timing variation associated to this timing 34- 39 F6.3 % e_TTV Error on ttv calculation -------------------------------------------------------------------------------- Byte-by-byte Description of file: tablea7.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1 A1 --- Planet [b-h] Name of planet 3- 5 I3 --- Epoch Epoch of transit 7- 10 I4 ppm Median-in Median of residual in transit 12- 15 I4 ppm sigma-in std of residual in transit 17- 20 I4 ppm Median-out Median of residual out of transit 22- 25 I4 ppm sigma-out std of residual out of transit 27- 30 F4.2 --- Signi Significance 32- 33 A2 --- Channel [c1 c2] Spitzer/IRAC channel (c1 for 3.6mum, c2 for 4.5mum) -------------------------------------------------------------------------------- Acknowledgements: Elsa Ducrot, educrot(at)uliege.be References: Delrez et al., 2018MNRAS.475.3577D 2018MNRAS.475.3577D, Early 2017 observations of TRAPPIST-1 with Spitzer.
(End) Elsa Ducrot [Liege, Belgium], Patricia Vannier [CDS] 25-Jun-2020
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