J/AJ/157/217 Transit times of five hot Jupiter WASP exoplanets (Bouma+, 2019)
WASP-4b arrived early for the TESS mission.
Bouma L.G., Winn J.N., Baxter C., Bhatti W., Dai F., Daylan T.,
Desert J.-M., Hill M.L., Kane S.R., Stassun K.G., Villasenor J.,
Ricker G.R., Vanderspek R., Latham D.W., Seager S., Jenkins J.M.,
Berta-Thompson Z., Colon K., Fausnaugh M., Glidden A., Guerrero N.,
Rodriguez J.E., Twicken J.D., Wohler B.
<Astron. J., 157, 217-217 (2019)>
=2019AJ....157..217B 2019AJ....157..217B (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Exoplanets
Keywords: binaries: close -
planets and satellites: individual (WASP-4b, WASP-5b, WASP-6b,
WASP-12b, WASP-18b, WASP-46b) - planet-star interactions
Abstract:
The Transiting Exoplanet Survey Satellite (TESS) recently observed
18 transits of the hot Jupiter WASP-4b. The sequence of transits occurred
81.6±11.7 s earlier than had been predicted, based on data stretching
back to 2007. This is unlikely to be the result of a clock error, because
TESS observations of other hot Jupiters (WASP-6b, 18b, and 46b) are
compatible with a constant period, ruling out an 81.6 s offset at the
6.4σ level. The 1.3 day orbital period of WASP-4b appears to be
decreasing at a rate of P=-12.6±1.2 ms per year. The apparent period
change might be caused by tidal orbital decay or apsidal precession,
although both interpretations have shortcomings. The gravitational
influence of a third body is another possibility, though at present
there is minimal evidence for such a body. Further observations are
needed to confirm and understand the timing variation.
Description:
WASP-4 was observed by TESS with Camera 2 from 2018 August 23 to
September 20, within the second "sector" of science operations. The star
is designated as TIC 402026209 in the TESS Input Catalog (Stassun et al.
2018, J/AJ/156/102). The pixel data for an 11x11 array surrounding WASP-4
were averaged into 2 min stacks by the onboard computer. The data were
downlinked via the Deep Space Network (http://deepspace.jpl.nasa.gov/),
and the spacecraft time stamps were calibrated against the ground-station
clocks. The spacecraft clock times were then transformed by the Payload
Operations Center into the Temps Dynamique Barycentrique (TDB) reference
system. The images were then reduced to light curves by the Science
Processing Operations Center (SPOC) at NASA Ames (Jenkins et al.
2016SPIE.9913E..3EJ).
We repeated all the data reduction and analysis steps described in this
paper for other hot Jupiters observed by TESS for which timing data exists
spanning many years. First, we checked which hot Jupiters were observed
over the first three TESS sectors using a combination of tessmaps
(http://github.com/lgbouma/tessmaps) and TEPCat (Southworth
2011MNRAS.417.2166S 2011MNRAS.417.2166S). We recalculated the barycentric corrections using
the Eastman et al. (2010PASP..122..935E 2010PASP..122..935E) code and found values that agreed
with the light-curve headers to within about 1 s. We then selected hot
Jupiters for which there were at least five distinct epochs reported in
the peer-reviewed literature. We required that each observation be of a
single transit, that the midpoint be fit as a free parameter, and that the
time system be clearly documented. Our final hot Jupiter sample included
WASP-4b, 5b, 6b, 18b, and 46b.
Objects:
---------------------------------------------------------------
RA (ICRS) DE Designation(s)
---------------------------------------------------------------
23 34 15.09 -42 03 41.0 WASP-4 = 2MASS J23341508-4203411
23 57 23.76 -41 16 37.7 WASP-5 = 2MASS J23572375-4116377
23 12 37.74 -22 40 26.3 WASP-6 = 2MASS J23123773-2240261
01 37 25.03 -45 40 40.4 WASP-18 = 2MASS J01372503-4540404
21 14 56.86 -55 52 18.5 WASP-46 = 2MASS J21145687-5552184
---------------------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 90 59 WASP-4b transit times, uncertainties,
and references
table5.dat 90 39 WASP-5b transit times, uncertainties,
and references
table6.dat 90 18 WASP-6b transit times, uncertainties,
and references
table7.dat 90 58 WASP-18b transit times, uncertainties,
and references
table8.dat 90 62 WASP-46b transit times, uncertainties,
and references
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See also:
J/A+A/501/785 : Discovery and characterization of WASP-6b (Gillon+, 2009)
J/AJ/137/3826 : Two transits of the giant planet WASP-4b (Winn+, 2009)
J/ApJ/707/167 : Transiting planetary system WASP-18 (Southworth+, 2009)
J/MNRAS/396/1023 : Transiting planetary system WASP-5 (Southworth+, 2009)
J/MNRAS/399/287 : Transiting planetary system WASP-4 (Southworth+, 2009)
J/ApJ/733/127 : Four transits of WASP-4b (Sanchis-Ojeda+, 2011)
J/A+A/539/A159 : WASP-4b transit griz light curves (Nikolov+, 2012)
J/MNRAS/422/1988 : Three short-period, transiting exoplanets (Anderson+, 2012)
J/ApJ/809/77 : Transiting Exoplanet Survey Satellite (TESS)
(Sullivan+, 2015)
J/MNRAS/450/1760 : Transiting planet WASP-6b (Tregloan-Reed+, 2015)
J/AJ/156/102 : The TESS Input Catalog and Candidate Target List
(Stassun+, 2018)
Byte-by-byte Description of file: table[25678].dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 13 F13.5 d Ttra Measured transit midtime (BJDTDB) (1)
15- 21 F7.5 d e_Ttra [5e-05/0.00184] 1σ uncertainty in Ttra (2)
23- 27 I5 --- Epoch [-4037/1925] Epoch
29 I1 --- H13 [0/1]? The midtime value was taken from
Hoyer et al. (2013MNRAS.434...46H 2013MNRAS.434...46H) (=1) or
from Ref (=0) (only in Table 2)
31- 55 A25 --- Ref Reference describing the original observations
(3)
57- 75 A19 --- Bibcode Bibcode of the reference
77- 90 A14 --- Com Comment on Ref
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Note (1): In Table 5: all of the literature times except for the two
Moyano et al. (2017MNRAS.471..650M 2017MNRAS.471..650M) times are from the homogeneous
Hoyer et al. (2012ApJ...748...22H 2012ApJ...748...22H) analysis.
In Table 7: all of the literature times are from the homogeneous
Wilkins et al. (2017ApJ...836L..24W 2017ApJ...836L..24W) analysis.
In Table 8: all of the literature times are from the homogeneous
Petrucci et al. (2018MNRAS.473.5126P 2018MNRAS.473.5126P) analysis. Fourteen of the light curves
were acquired by ETD observers (see Petrucci et al. 2018MNRAS.473.5126P 2018MNRAS.473.5126P).
Note (2): σTtra was evaluated from the sampled posteriors by taking the
maximum of the difference between the 84th percentile minus the median, and
the median minus the 16th percentile. The resulting error variances then
appeared to have been overestimated, so we lowered the uncertainties as
described in Section 2.2.
Note (3): In Table 2, The Hoyer et al. (2013MNRAS.434...46H 2013MNRAS.434...46H) BJDTT times are
equal to BJDTDB for our purposes (Urban & Seidelmann 2012, Explanatory
Supplement to the Astronomical Almanac (Mill Valley, CA: Univ. Science
Books)). We omitted the timing measurements from Southworth et al. (2009,
J/MNRAS/396/1023) because there were technical problems with the computer
clock at the time of observation (Nikolov et al. 2012, J/A+A/539/A159). The
two C. Baxter et al. (2019, in preparation) times were obtained from
Spitzer/IRAC transit light curves in the 3.6 and 4.5 µm channels.
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History:
From electronic version of the journal
(End) Tiphaine Pouvreau [CDS] 05-Sep-2019