J/ApJ/900/L44 Kepler TTVs for 6 exomoon candidates (Kipping, 2020)
An independent analysis of the six recently claimed exomoon candidates.
Kipping D.
<Astrophys. J., 900, L44 (2020)>
=2020ApJ...900L..44K 2020ApJ...900L..44K
ADC_Keywords: Exoplanets; Photometry
Keywords: Exoplanet dynamics ; Exoplanets ; Natural satellites (Extrasolar)
Abstract:
It has been recently claimed that KOIs-268.01, 303.01, 1888.01,
1925.01, 2728.01, and 3320.01 are exomoon candidates, based on an
analysis of their transit timing. Here, we perform an independent
investigation, which is framed in terms of three questions: (1) Are
there significant transit timing variations (TTVs)? (2) Is there a
significant periodic TTV? (3) Is there evidence for a nonzero moon
mass? We applied rigorous statistical methods to these questions
alongside a reanalysis of the Kepler photometry and find that none of
the Kepler objects of interest (KOIs) satisfy our three tests.
Specifically, KOIs-268.01 and 3220.01 pass none of the tests and
KOIs-303.01, 1888.01, and 1925.01 pass a single test each. Only
KOI-2728.01 satisfies two, but fails the cross-validation test for
predictions. Further, detailed photodynamical modeling reveals that
KOI-2728.01 favors a negative-radius moon (as does KOI-268.01). We
also note that we find a significant photoeccentric effect for
KOI-1925.01 indicating an eccentric orbit of at least e>(0.62±0.06).
For comparison, we applied the same tests to Kepler-1625b, which
reveals that (1) and (3) are passed, but (2) cannot be checked with
the cross- validation method used here, due to the limited number of
available epochs. In conclusion, we find no compelling evidence for
exomoons among the six KOIs. Despite this, we were able to derive
exomoon mass upper limits versus semimajor axis, with KOI-3220.01
leading to particularly impressive constraints of MS/MP<0.4%
[2σ] at a similar semimajor to that of the Earth-Moon.
Description:
We obtained the Simple Aperture Photometry (SAP) and Pre-Data search
Conditioning (PDC) DR25 photometric time series from MAST for each
KOI. Short cadence (SC) data are used with preference over long
cadence (LC), whenever available.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 37 7 Statistical tests for evidence for exomoons,
using gravitational effects only (Section 3)
fig1.dat 57 94 Transit timing variations (TTVs) for the six
claimed exomoon candidate hosts
--------------------------------------------------------------------------------
See also:
J/ApJS/208/16 : Kepler transit timing observations. VIII. (Mazeh+, 2013)
J/ApJS/225/9 : Kepler TTVs. IX. Full long-cadence data set (Holczer+, 2016)
J/ApJS/229/30 : Revised properties of Q1-17 Kepler targets (Mathur+, 2017)
J/AJ/154/5 : Transit timing variations of 145 Kepler planets (Hadden+, 2017)
J/ApJS/234/9 : A spectral approach to transit timing variations (Ofir+, 2018)
J/A+A/615/A79 : KOINet. Study of exoplanet systems via TTVs (von Essen+, 2018)
J/ApJ/887/261 : Compil. of planets around M dwarfs (Martinez-Rodriguez+, 2019)
J/other/RAA/19.41 : TTVs of Kepler exoplanets (Gajdos+, 2019)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 12 A12 --- Name Name of the source
14- 18 F5.1 --- BIC [-32.3/93.9] Bayesian information criterion,
BICP,T
20 A1 --- n_BIC Are there statistically significant TTVs?
(Yes/No)
22- 23 I2 % Good [0/54]? Percentage of Good TTV predictions
25 A1 --- n_Good Is there a statistically significant periodic
TTV? (Yes/No)
27- 30 F4.1 --- logK [-6.9/1.9] logKM:X value (see Figure 2)
32 A1 --- n_logK Do the observations support a statistically
significant nonzero moon mass? (Yes/No)
34- 37 F4.2 % Ms/Mp [0.39/5.9]? Ms to Mp ratio upper limit at 60Rp,
2σ
--------------------------------------------------------------------------------
Byte-by-byte Description of file: fig1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 12 A12 --- Name Source identifier
14- 15 I2 --- Epoch [0/34] Epoch number
17- 26 F10.5 --- tau [-33/1408] Median reference time of
transit minimum (1)
28- 34 F7.5 --- e_tau [0.00077/0.0071] Lower 34.1% uncertainty in tau
36- 42 F7.5 --- E_tau [0.00095/0.007] Upper 34.1% uncertainty in tau
44- 48 F5.1 min TTV [-20/35] Median Transit timing variation (1)
50- 53 F4.1 min e_TTV [1/10] Lower 34.1% uncertainty in TTV
55- 57 F3.1 min E_TTV [1.4/9.7] Upper 34.1% uncertainty in TTV
--------------------------------------------------------------------------------
Note (1): Derived in this work using model T. Transit times are quoted
as BJDUTC-2455000. TTVs are defined against the maximum a-posteriori
ephemeris obtained from model P. TTVs do not propagate the uncertainty
of the ephemeris itself.
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 05-Jan-2022