k2-231 b: a sub-neptune exoplanet transiting a solar twin in … › data › kepsciconv › ... ·...
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K2-231 b: A sub-Neptune exoplanet transiting a solar twin in Ruprecht 147
The K2 survey of Ruprecht 147 finds a transiting planet Ruprecht 147 is the oldest nearby star cluster
While searching Everest light curves for stellar rotation, we noticed six transits in the light curve for this solar twin.
While looking for rotation, we found a planet
Surveyed with K2 during Campaign 7 (GO 7035, Science PI Curtis), R147 is the oldest (2.7 Gyr) nearby (300 pc) star cluster, making it a critical benchmark for stellar astrophysics: see, Curtis et al. (2013), Curtis (2016), and Torres et al. (2018).
This figure shows clusters with rotation data; those shaded red were surveyed with Kepler/K2. 0 20 40 60 80
Day since start of Campaign 7
0.999
1.000
1.001
1.002
Nor
mal
ized
Flu
x
The chromospheric emission is consistent with its siblings and empirical expectations (Mamajek & Hillenbrand 2008), as is its chemical composition (cluster [Fe/H] = +0.10 ± 0.04 dex).
K2-231 is a typical solar twin
3931 3932 3933 3934 3935 3936Wavelength (Angstroms)
0.00
0.05
0.10
0.15
0.20
0.25
0.30
Rel
ativ
e Fl
ux
ISM
M★ = 1.01 M¤ R★ = 0.95 R¤ Teff = 5695 K [Fe/H] = +0.14 dex log R’HK = −4.8 dex
Jason L. Curtis,1 Andrew Vanderbug,2 Guillermo Torres,3 Adam L. Kraus,2 Daniel Huber,4 Andrew W. Mann,5 Aaron C. Rizzuto,2 Howard Isaacson,6 Andrew W. Howard,7 Christopher E. Henze,8 Benjamin J. Fulton,7 Jason T. Wright9
(1) Columbia University (2) University of Texas, Austin (3) Harvard–Smithsonian Center for Astrophysics (4) University of Hawaii (5) University of North Carolina, Chapel Hill (6) University of California, Berkeley (7) California Institute of Technology (8) NASA Ames Research Center (9) Pennsylvania State University
Published in the Astronomical Journal (2018, 155, 173. arXiv 1803.07430)
Most binary scenarios are ruled out by combining precise RVs from HARPS, with high-resolution imaging from Keck/NIRC2 (NRM, AO), and isochrone modeling of the broadband photometry. Very-low-mass stars (VLM) and sub-stellar objects would negligibly dilute the transits.
Validation and Properties K2-231 is likely single
15 10 5 0 -5 -10 -15∆ Right Ascension (arcseconds)
-15
-10
-5
0
5
10
15
∆ D
eclin
atio
n (a
rcse
cond
s)
0 200 400 600 800 1000Projected Separation, ρ (mas)
10
8
6
4
2
0
Con
trast
, ∆ K
(mag
)
Hydrogen Burning Limit
VLM stars
RV ?
10
8
6
4
2
0
0 200 400 600 800 1000
0 100 200 300Projected Separation (AU)
0.07
0.120.200.300.400.500.600.700.85
Seco
ndar
y M
ass
(sol
ar)NRM Photometric Modeling
AO
Mitigating background blends
UKIRT/WFCAM image of K2-231 (big red circle), and neighboring stars blended in the K2 aperture (black circle). Transits are visible with the same depths in a smaller aperture (dashed black line), leaving one blend that could host the transits. Keck/HIRES RVs show it is not an EB.
Transit analysis and statistical validation
We re-extracted the light curve with a circular moving aperture to reject most background stars, corrected for K2 systematics (Vanderburg & Johnson et al 2014), then fit the transits with EXOFAST (Eastman et al. 2013).
We applied the BLENDER statistical validation technique (Torres et al. 2004, 2011, 2015) to calculate the false positive likelihood caused by unseen stars, constrained by high-resolution spectroscopy, AO imaging, precision RVs, and color information, and found a 99.86% probability that K2-231 b is a planet.
J.L.C. is funded by the National Science Foundation Astronomy and Astrophysics Postdoctoral Fellowship under award AST-1602662 and the National Aeronautics and Space Administration under grant NNX16AE64G issued through the K2 Guest Observer Program.
K2-231 b is a typical exoplanet
We estimated the planet mass with the probabilistic mass–radius relation Forecaster (Chen & Kipping 2017), and found Mp = 7 +5 −3 ME At V = 12.7, this may be measurable with existing precision radial velocity facilities.
The mass of K2-231 b
Comparison with planets located in the Kepler field
K2-231 b is found near a relative maximum in the distribution of planet size and orbital period, after accounting for the shorter duration of the K2 campaign (i.e., sensitive to Porb < 40 d).
(Figure adapted from Fulton et al. 2017)
The 23 published planets in open clusters (so far)
Planet Name
Pleiades (125 Myr):...
Praesepe (670 Myr):Pr0201 bPr0211 bPr0211 cK2-95 bK2-100 bK2-101 b K2-102 b K2-103 b K2-104 b EPIC 211901114 b
Hyades (727 Myr):eps Tau b HD 285507 bK2-25 b K2-136-A bK2-136-A cK2-136-A dHD 283869 b
NGC 2423 (740 Myr):TYC 5409-2156-1 b
NGC 6811 (1 Gyr):Kepler-66 bKepler-67 b
Ruprecht 147 (2.7 Gyr):K2-231 b
M67 (4 Gyr):YBP 401 b YBP 1194 bYBP 1514 bSAND 364 bSAND 978 b
NGC 6791 (8 Gyr):Several candidates from Montet et al.
References: (1) Barros et al. (2016); (2) Brucalassi et al. (2014); (3) Brucalassi et al. (2017); (4) Ciardi et al. (2017); (5) David et al. (2016); (6) Gaidos et al. (2017); (7) Libralato et al. (2016); (8) Lovis & Mayor (2007); (9) Malavolta et al. (2016); (10) Mann et al. (2016); (11) Mann et al. (2017a); (12) Mann et al. (2017b); (13) Meibom et al. (2013); (14) Obermeier et al. (2016); (15) Pepper et al. (2017); (16) Pope et al. (2016);(17) Quinn et al. (2012); (18) Quinn et al. (2014); (19) Sato et al. (2007); (20) Vanderburg et al. (2018).
KIC/EPICID
C4
211998346211936827211936827211916756211990866211913977211970147211822797211969807211901114
210754593210495452210490365247589423247589423247589423248045685
...
98361499532052
219800881
...211411531211416296211403356
...
DiscoveryMethod
...
RVRVRVTrTrTrTrTrTrTr
RVRVTrTrTrTrTr
RV
TrTr
Tr
RVRVRVRVRV
Tr
V(mag)
...
10.5212.1512.1517.2710.3712.5512.7614.6615.7716.49
3.5310.4715.8811.2011.2011.2010.6
9.45
15.316.4
12.71
13.7014.6814.779.809.71
Period(days)
...
4.432.15
>350010.141.6714.689.9221.171.971.65
594.96.093.4857.9817.3125.58~106
714.3
17.8215.73
13.84
4.0876.9605.118121151
Radius /M sin i
...
0.54 MJ1.844 MJ7.9 MJ3.7 RE3.5 RE2.0 RE1.3 RE2.2 RE1.9 RE9.6 RE
7.6 MJ0.917 MJ3.43 RE0.99 RE2.91 RE1.45 RE1.96 RE
10.6 MJ
2.80 RE2.94 RE
2.5 RE
0.42 MJ0.33 MJ0.40 MJ1.57 MJ2.18 MJ
HostInfo.
...
Late-FLate-GLate-G
0.43 M¤
1.18 M¤
0.80 M¤
0.77 M¤
0.61 M¤
0.51 M¤
0.46 M¤
2.7 M¤ GiantK4.5M4.5K5.5K5.5K5.5K5
Giant
1.04 M¤
0.87 M¤
Solar twin
F9VG5VG5VK3IIIK4III
Notes
None found
HJ, “two b’s”HJ, “two b’s”
Eccentric, 1st multi………………
Candidate
1st everEccentric HJ
…Stellar binaryStellar binaryStellar binary
Candidate (1 transit)
…
……
…
HJHJHJ…
Candidate
Kepler superstamp
References
6
17179
7, 11, 14, 151, 7, 11, 161, 7, 11, 16
1111
7, 1111
1918
5, 104, 124, 124, 1220
8
1313
This work
2, 32, 32, 32, 32, 3
-6 -4 -2 0 2 4 6Hours since mid-transit
0.99920.99940.99960.99981.00001.00021.0004
Normalize
dFlux
We estimated the number of planets that are detectable in K2 for the 126 RV-vetted members. Using the Fressin et al. (2013) occurrence rates for stars with at least one planet <29 d, we expect to find ~1 exoplanet bigger than Earth We apparently found it.
Expected Yield for R147
solarspectra
Ca II K spectrum
“K2 Survey of R147” results at this meeting:T.Bea6y:over-luminousbrowndwarf(poster77)G.Torres:eclipsingbinary(poster95)J.CurHs:gyrochronology(talk,Thurs9am)
10 100 1000 10000Distance (pc)
0.1
1.0
10.0
Age
(Gyr
)
Pleiades M35M34
M37Hyades
Praesepe NGC 6811NGC 752
NGC 6819Ruprecht 147M67
DayofObservaHon
Normalize
dFlux Porb = 13.84 d
Rp = 2.5 RE