J/AJ/156/218 Transit light curves of TRAPPIST-1 planets (Ducrot+, 2018)
The 0.8-4.5 µm broadband transmission spectra of TRAPPIST-1 planets.
Ducrot E., Sestovic M., Morris B.M., Gillon M., Triaud A.H.M.J., De Wit J.,
Thimmarayappa D., Agol E., Almleaky Y., Burdanov A., Burgasser A.J.,
Delrez L., Demory B.-O., Jehin E., Leconte J., McCormac J., Murray C.,
Queloz D., Selsis F., Thompson S., Van Grootel V.
<Astron. J., 156, 218-218 (2018)>
=2018AJ....156..218D 2018AJ....156..218D (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Exoplanets ; Photometry ;
Spectroscopy ; Optical
Keywords: binaries: eclipsing - planetary systems - techniques: photometric -
techniques: spectroscopic
Abstract:
The TRAPPIST-1 planetary system provides an exceptional opportunity for
the atmospheric characterization of temperate terrestrial exoplanets
with the upcoming James Webb Space Telescope (JWST). Assessing the
potential impact of stellar contamination on the planets' transit
transmission spectra is an essential precursor to this characterization.
Planetary transits themselves can be used to scan the stellar photosphere
and to constrain its heterogeneity through transit depth variations in
time and wavelength. In this context, we present our analysis of 169
transits observed in the optical from space with K2 and from the ground
with the SPECULOOS and Liverpool telescopes. Combining our measured
transit depths with literature results gathered in the mid-/near-IR
with Spitzer/IRAC and HST/WFC3, we construct the broadband transmission
spectra of the TRAPPIST-1 planets over the 0.8-4.5 µm spectral range.
While planet b, d, and f spectra show some structures at the 200-300 ppm
level, the four others are globally flat. Even if we cannot discard their
instrumental origins, two scenarios seem to be favored by the data:
a stellar photosphere dominated by a few high-latitude giant (cold) spots,
or, alternatively, by a few small and hot (3500-4000 K) faculae. In both
cases, the stellar contamination of the transit transmission spectra
is expected to be less dramatic than predicted in recent papers.
Nevertheless, based on our results, stellar contamination can still be
of comparable or greater order than planetary atmospheric signals at
certain wavelengths. Understanding and correcting the effects of stellar
heterogeneity therefore appears essential for preparing for the exploration
of TRAPPIST-1 with JWST.
Description:
We observed 37 different transits with 1 or 2 telescopes of the
SPECULOOS-South Observatory (SSO, Burdanov et al. 2018haex.bookE.130B 2018haex.bookE.130B;
Gillon 2018NatAs...2..344G 2018NatAs...2..344G) at Cerro Paranal, Chile, in the context of
the commissioning of the facility. This represents 52 transits in total,
as some were observed with two SSO telescopes simultaneously. Each SSO
robotic telescope has a primary aperture of 1 m and a focal length of 8 m,
and is equipped with a 2kx2k deep-depletion CCD camera whose 13.5 µm
pixel size corresponds to 0.35" on the sky (field of view = 12'x12').
These observations were carried out in an I+z filter for which we
computed an effective wavelength of ∼0.9 µm for a M8-type star like
TRAPPIST-1, taking into account the spectral response curve of the
telescope+atmosphere. Exposure times of 23 s were used for all
observations.
We obtained 13 transits of the TRAPPIST-1 planets with the use of the
2 m Liverpool Telescope (LT, Steele et al. 2004SPIE.5489..679S 2004SPIE.5489..679S) installed
on the island of La Palma at the Roque de los Muchachos observatory. For
our observations, we used the IO:O optical wide field camera which has
4kx4k deep-depletion CCD with 15 µm sized pixels and 10x10 arcmin2
field of view. We used 2x2 binning that resulted in a 0.3 arcsec/pixel
image scale. All the observations were performed in the Sloan z' band with
20 s exposures.
TRAPPIST-1 was observed with the K2 telescope in an overall bandpass
ranging from 420 to 900 nm over a period of 79 days in Campaign 12,
which represents a total of 104 transits. The short cadence Target
Pixel File (TPF), with a cadence rate of 1 per minute, was downloaded
from the Mikulski Archive for Space Telescopes (MAST).
Objects:
------------------------------------------------------------------
RA (ICRS) DE Designation(s)
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23 06 29.37 -05 02 29.0 TRAPPIST-1 = 2MASS J23062928-0502285
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File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 20 7 Number of transits observed by K2,
SPECULOOS-South Observatory (SSO), and Liverpool
Telescope (LT) analyzed in this work for each
TRAPPIST-1 planet
table3.dat 69 103 Description of the transit light curves measured
for TRAPPIST-1 planets by K2
table4.dat 69 52 Description of the transit light curves measured
for TRAPPIST-1 planets by SPECULOOS-South
table5.dat 69 13 Description of the transit light curves measured
for TRAPPIST-1 planets by Liverpool Telescope
table6.dat 36 52 Transit timings and depths obtained from the
individual analyses of SPECULOOS light curves
table7.dat 36 103 Transit timings and depths obtained from the
individual analyses of K2 light curves
table8.dat 36 13 Transit timings and depths obtained from the
individual analyses of LT light curves
table10.dat 36 52 Median values and 1σ limits of the
posterior probability distribution functions
(PDFs) deduced for the timings and depths from
their global analyses for SPECULOOS observations
table11.dat 36 95 Median values and 1σ limits of the
posterior PDFs deduced for the timings and
depths from their global analyses for K2
observations
table12.dat 36 13 Median values and 1σ limits of the
posterior PDFs deduced for the timings and
depths from their global analyses for Liverpool
Telescope observations
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See also:
J/AJ/156/178 : NIR transmission spectra of TRAPPIST-1 planets (Zhang+, 2018)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 12 A12 --- Pl Planet
14- 15 I2 --- NK2 [1/42] Number of transits observed by K2
17- 18 I2 --- NSSO [2/20] Number of transits observed by the
SPECULOOS-South observatory
20 I1 --- NLT [1/5]? Number of transits observed by the Liverpool
Telescope
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Byte-by-byte Description of file: table3.dat table4.dat table5.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1 A1 --- Pl [bcdefgh] TRAPPIST-1 planet
3- 13 A11 "date" Date Date of acquisition
15- 20 A6 --- Inst Instrument used (only in Table 4)
22- 24 I3 --- NPts [139/741] Number of data points
26- 28 I3 --- Epoch [5/511] Epoch based on the transit ephemeris
presented in Delrez et al. (2018MNRAS.475.3577D 2018MNRAS.475.3577D)
30- 54 A25 --- Base Baseline function (1)
56- 59 F4.2 --- betaw [0.79/1.95] White noise βw
61- 64 F4.2 --- betar [1/2.14] Red noise βr
66- 69 F4.2 --- CF [0.79/2.18] Correction factor
(CF=βr*βw)
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Note (1): For the baseline function, p(εN) denotes, respectively,
an N-order polynomial function of time (ε=t), the full width at half
maximum (ε=fwhm), x and y positions (ε=xy), the background
(ε=b), the airmass (ε=a), and a scalar (ε=s).
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Byte-by-byte Description of file: table[678].dat table1[012].dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1 A1 --- Pl [bcdefgh] TRAPPIST-1 planet
3- 5 I3 --- Epoch [5/511] Epoch of the transit
7- 16 F10.5 d Time [7738.99/8096.54] Mid-transit timing
(BJDTDB-2450000)
18- 24 F7.5 d e_Time [0.00012/0.01] Uncertainty in Time
26- 30 F5.3 % Depth [0.257/0.988] Transit depth
32- 36 F5.3 % e_Depth [0.027/0.4] Uncertainty in Depth
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History:
From electronic version of the journal
(End) Tiphaine Pouvreau [CDS] 03-Apr-2019