J/AJ/153/15 Photometry and spectroscopy of EPIC 201702477 (Bayliss+, 2017)
EPIC 201702477b: a transiting brown dwarf from K2 in a 41 day orbit.
Bayliss D., Hojjatpanah S., Santerne A., Dragomir D., Zhou G., Shporer A.,
Colon K.D., Almenara J., Armstrong D.J., Barrado D., Barros S.C.C.,
Bento J., Boisse I., Bouchy F., Brown D.J.A., Brown T., Cameron A.,
Cochran W.D., Demangeon O., Deleuil M., Diaz R.F., Fulton B., Horne K.,
Hebrard G., Lillo-Box J., Lovis C., Mawet D., Ngo H., Osborn H., Palle E.,
Petigura E., Pollacco D., Santos N., Sefako R., Siverd R., Sousa S.G.,
Tsantaki M.
<Astron. J., 153, 15-15 (2017)>
=2017AJ....153...15B 2017AJ....153...15B (SIMBAD/NED BibCode)
ADC_Keywords: Planets ; Stars, double and multiple ; Stars, dwarfs ;
Photometry, ugriz ; Radial velocities
Keywords: planetary systems - techniques: photometric -
techniques: spectroscopic
Abstract:
We report the discovery of EPIC 201702477b, a transiting brown dwarf
in a long period (40.73691±0.00037day) and eccentric
(e=0.2281±0.0026) orbit. This system was initially reported as a
planetary candidate based on two transit events seen in K2 Campaign 1
photometry and later validated as an exoplanet candidate. We confirm
the transit and refine the ephemeris with two subsequent ground-based
detections of the transit using the Las Cumbres Observatory Global
Telescope 1m telescope network. We rule out any transit timing
variations above the level of ∼30s. Using high precision radial
velocity measurements from HARPS and SOPHIE we identify the transiting
companion as a brown dwarf with a mass, radius, and bulk density of
66.9±1.7MJ, 0.757±0.065RJ, and 191±51g/cm3 respectively.
EPIC 201702477b is the smallest radius brown dwarf yet discovered,
with a mass just below the H-burning limit. It has the highest density
of any planet, substellar mass object, or main-sequence star
discovered so far. We find evidence in the set of known transiting
brown dwarfs for two populations of objects-high mass brown dwarfs and
low mass brown dwarfs. The higher-mass population have radii in very
close agreement to theoretical models, and show a lower-mass limit
around 60MJ. This may be the signature of mass-dependent ejection of
systems during the formation process.
Description:
The Las Cumbres Observatory Global Telescope (LCOGT) is a network of
fully automated telescopes. Currently there are 10 LCOGT 1m telescopes
operating as part of this network, eight of which are in the southern
hemisphere: three at the Cerro Tololo Inter-American Observatory
(CTIO) in Chile, three at the South African Astronomical Observatory
(SAAO) in South Africa, and two at Siding Spring Observatory (SSO) in
Australia. Each telescope is equipped with an imaging camera; either a
"Sinistro" or an SBIG STX-16803. The Sinistro is LCOGT's custom built
imaging camera that features a back-illuminated 4K*4K Fairchild
Imaging CCD with 15µm pixels (CCD486 BI). With a plate scale of
0.387''/pixel, the Sinistro cameras deliver a FOV of 26.6'*26.6',
which is important for monitoring a sufficient number of reference
stars for high-precision differential photometry. The cameras are read
out by four amplifiers with 1*1 binning, with a readout time of ∼45s.
The SBIG STX-16803 cameras are commercial CCD cameras which feature a
frontside-illuminated 4K*4K CCD with 9µm pixels-giving a field of
view of 15.8'*15.8'. These cameras are typically read out in 2*2
binning mode, which results in a read-out time of 12s.
The Transiting Exoplanet CHaracterisation (TECH;
lcogt.net/science/exoplanets/tech-project/) project uses the 1m
telescopes in the LCOGT network to photometrically characterize
transiting planets and transiting planet candidates.
The first transit event for EPIC201702477b monitored by the TECH
project was on 2015 March 15 from CTIO. We observed the target from
01:00 UT to 08:13 UT using a Sinistro in the r-band. The exposure
times were 240s, the observing conditions were photometric, and the
airmass ranged from 2.3 to 1.2. We detected a full transit of EPIC
201702477b with a depth and duration consistent with that seen in the
K2 data. The next transit event occurred 41 days later on 2015 April
28, and was observable from SAAO. EPIC201702477 was monitored between
17:00 UT and 22:50 UT using an SBIG camera, again in the r-band. The
exposure times were 180s, the observing conditions were again
photometric, and the airmass ranged from 1.8 to 1.2.
The photometric data are provided in Table1.
We performed radial velocity follow-up observations of EPIC 201702477
with the SOPHIE and High-Accuracy Radial velocity Planetary Searcher
(HARPS) spectrographs. Both instruments are high-resolution (R∼40000
and 110000 for SOPHIE and HARPS, respectively), fiber-fed, and
environmentally controlled echelle spectrographs covering visible
wavelengths. We obtained three spectra with SOPHIE (OHP programme
ID:15B.PNP.HEBR) from 2015 June 12 to 2016 February 17 with exposure
times of 1800 and 3600s, reaching an S/N between 8 and 22 per pixel at
5500Å. We obtained 10 other spectra with HARPS (ESO programme
ID:096.C-0657) from 2016 January 10 to February 15 with exposure times
between 900 and 3600s, corresponding to an S/N between 3 and 17 per
pixel at 5500Å.
The derived radial velocities are reported in Table3.
Objects:
-------------------------------------------------------------------------------
RA (ICRS) DE Designation(s) (Period)
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11 40 57.79 +03 40 53.7 EPIC 201702477b = NAME EPIC 201702477b (P=40.73691)
-------------------------------------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 50 192 r-band differential photometry for EPIC 201702477
from LCOGT 1m
table3.dat 66 13 SOPHIE and HARPS radial velocities of EPIC 201702477
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See also:
J/A+A/594/A100 : K2 new planetary and EB candidates (Barros+, 2016)
J/AJ/146/113 : Differential griz photometry of HATS-3 (Bayliss+, 2013)
J/A+A/523/A88 : A Jupiter-mass companion around HD 109246 (Boisse+, 2010)
J/A+A/505/853 : HD16760 radial velocity curve (Bouchy+, 2009)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 16 F16.10 d BJD Barycentric Julian Date (BJD-2400000)
18- 29 F12.10 --- Flux [0.985/1.007] Relative flux in the r band
31- 36 F6.4 --- e_Flux [0.0014/0.0035] Uncertainty in Flux
38- 50 A13 --- Inst Instrument used to get Flux (CTIO/Sinistro, or
SAAO/SBIG) (1)
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Note (1): Instruments used are defined as follows:
CTIO/Sinistro = Cerro Tololo Inter-American Observatory (CTIO) using a
Sinistro camera;
SAAO/SBIG = South African Astronomical Observatory using a SBIG camera.
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 F11.5 d BJD Barycentric Julian Date (BJD-2400000)
13- 18 F6.3 km/s RV [29.6/38.2] Radial velocity
20- 24 F5.3 km/s e_RV [0.007/0.06] 1σ error in RV (σRV)
26- 31 F6.3 km/s BS [-0.12/0.13] Bisector span (Vspan)
33- 37 F5.3 km/s e_BS [0.01/0.1] 1σ error in Vspan (σvspan)
39- 43 F5.3 km/s FWHM [6.3/9.7] Full Width at Half Maximum
45- 49 F5.3 km/s e_FWHM [0.013/0.12] 1σ error in FWHM (σFWHM)
51- 54 I4 s Texp [900/3600] Exposure time
56- 59 F4.1 --- S/N [2.9/21.7] Signal-to-Noise ratio (given per pixel
at 550nm)
61- 66 A6 --- Inst Instrument used (SOPHIE or HARPS) (1)
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Note (1): The instruments are defined as follows:
SOPHIE = Spectrographe pour Observation des Phenomenes des Interieurs
stellaires et des Exoplantes (literally meaning "Spectrograph for
the observation of the phenomena of the stellar interiors and of
the exoplanets");
HARPS = High-Accuracy Radial velocity Planetary Searcher.
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History:
From electronic version of the journal
(End) Prepared by [AAS]; Sylvain Guehenneux [CDS] 15-Jun-2017