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:
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RA (2000) DE Designation(s)
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23 06 29.37 -05 02 29.0 TRAPPIST-1 = K2-112
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File Summary:
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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
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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.
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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)
Byte-by-byte Description of file: tablea1.dat
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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)
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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)
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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
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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
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Byte-by-byte Description of file: tablea7.dat
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Bytes Format Units Label Explanations
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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