J/MNRAS/486/5094 NGTS-4b A sub-Neptune transiting in the desert (West+, 2019)
NGTS-4b: A sub-Neptune transiting in the desert.
West R.G., Gillen E., Bayliss D., Burleigh M.R., Delrez L., Gunther M.N.,
Hodgkin S.T., Jackman J.A.G., Jenkins J.S., King G., McCormac J.,
Nielsen L.D., Raynard L., Smith A.M.S., Soto M., Turner O., Wheatley P.J.,
Almleaky Y., Armstrong D.J., Belardi C., Bouchy F., Briegal J.T.,
Burdanov A., Cabrera J., Casewell S.L., Chaushev A., Chazelas B., Chote P.,
Cooke B.F., Csizmadia S., Ducrot E., Eigmuller P., Erikson A., Foxell E.,
Gansicke B.T., Gillon M., Goad M.R., Jehin E., Lambert G., Longstaff E.S.,
Louden T., Moyano M., Murray C., Pollacco D., Queloz D., Rauer H., Sohy S.,
Thompson S.J., Udry S., Walker S.R., Watson C.A.
<Mon. Not. R. Astron. Soc., 486, 5094-5103 (2019)>
=2019MNRAS.486.5094W 2019MNRAS.486.5094W (SIMBAD/NED BibCode)
ADC_Keywords: Exoplanets ; Photometry ; Spectroscopy ; Optical
Keywords: techniques: photometric - planets and satellites: detection -
stars: individual: NGTS-4-planetary systems
Abstract:
We report the discovery of NGTS-4b, a sub-Neptune-sized planet
transiting a 13th magnitude K-dwarf in a 1.34d orbit. NGTS-4b has a
mass M=20.6±3.0M⊕ and radius R=3.18±0.26R⊕, which
places it well within the so-called 'Neptunian Desert'. The mean
density of the planet (3.45±0.95g/cm3) is consistent with a
composition of 100 per cent H2O or a rocky core with a volatile
envelope. NGTS-4b is likely to suffer significant mass loss due to
relatively strong EUV/X-ray irradiation. Its survival in the Neptunian
desert may be due to an unusually high-core mass, or it may have
avoided the most intense X-ray irradiation by migrating after the
initial activity of its host star had subsided. With a transit depth
of 0.13±0.02 per cent, NGTS-4b represents the shallowest transiting
system ever discovered from the ground, and is the smallest planet
discovered in a wide-field ground-based photometric survey.
Description:
NGTS-4 was observed using a single NGTS camera over a 272 night
baseline between 2016 August 06 and 2017 May 05. The survey has
operated at ESO's Paranal observatory since early 2016 and consists of
an array of 12 roboticized 20cm telescopes. The facility is optimized
for detecting small planets around K and early M stars (Chazelas et
al. 2012SPIE.8444E..0EC; Wheatley et al. 2013EPJWC..4713002W 2013EPJWC..4713002W; McCormac
et al. 2017PASP..129b5002M 2017PASP..129b5002M; Wheatley et al. 2018MNRAS.475.4476W 2018MNRAS.475.4476W).
A total of 190696 images were obtained, each with an exposure time of
10s. The data were taken using the custom NGTS filter (550-927nm).
The complete data set was searched for transit-like signals and a ∼0.2
per cent signal was detected at a period of 1.33734d. Confirming such
a shallow transit signal from the ground is challenging, even given
some of the best 1m-class telescopes available for precision
time-series photometry. We therefore undertook a campaign of
photometric follow-up using four different facilities (see Table 2).
Our first follow-up photometry of NGTS-4 was carried out at the South
African Astronomical Observatory (SAAO) on 2017 November 27, with the
1.0m telescope and one of the three frame-transfer CCD Sutherland
High-speed Optical Cameras (SHOC Coppejans et al.
2013PASP..125..976C 2013PASP..125..976C). We monitored transit events of NGTS-4b using the
Las Cumbres Observatory (LCO) 1m global telescope network (Brown et
al. 2013PASP..125.1031B 2013PASP..125.1031B). All observations were taken using the
Sinistro cameras. We also monitored a transit event using the
SPECULOOS-South facility (Burdanov et al. 2018haex.bookE.130B 2018haex.bookE.130B; Delrez
et al. 2018SPIE10700E..1ID) at Paranal Observatory in Chile on the
night of 2018 April 15, taking advantage of the telescope
commissioning period. SPECULOOS-South consists of four robotic 1m
Ritchey-Chretien telescopes, and we were able to utilize two of these
(Europa and Callisto) to observe the transit event. Two transits of
NGTS-4 were observed with Eulercam on the 1.2m Euler Telescope at La
Silla Observatory (Lendl et al. 2012A&A...544A..72L 2012A&A...544A..72L, Cat.
J/A+A/544/A72). The observations took place on the nights beginning
2018 April 15 and 2018 April 19. Both transits were observed using the
same broad NGTS filter that was used to obtain the discovery
photometry.
Finally, we obtained multi-epoch spectroscopy for NGTS-4 with the
HARPS spectrograph (Mayor et al. 2003Msngr.114...20M 2003Msngr.114...20M) on the ESO 3.6m
telescope at La Silla Observatory, Chile, between 2017 December 01 and
2018 April 10 under programme ID 0101.C-0623(A). We used the standard
HARPS data reduction software to measure the radial velocity of NGTS-4
at each epoch.
Objects:
-----------------------------------------------------------
RA (ICRS) DE Designation(s)
-----------------------------------------------------------
05 58 23.75 -30 48 42.3 NGTS-4 = 2MASS J05582375-3048424
-----------------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table4.dat 358 1 Stellar Properties for NGTS-4
table5.dat 329 1 Planetary properties for NGTS-4b for a circular
orbit and eccentric orbit
table1a.dat 34 33339 NGTS photometry of NGTS-4
table1b.dat 34 193 Eulercam photometry of NGTS-4 (2018-04-15)
table1c.dat 34 140 Eulercam photometry of NGTS-4 (2018-04-19)
table1d.dat 34 111 LCO photometry of NGTS-4
table1e.dat 34 473 Speculoos/Callisto photometry of NGTS-4
table1f.dat 34 471 Speculoos/Europa photometry of NGTS-4
table1g.dat 34 360 SAAO photometry of NGTS-4 (2017-11-27)
table1h.dat 34 2160 SAAO photometry of NGTS-4 (2018-04-22)
table2.dat 69 12 A summary of the follow-up photometry of NGTS-4
table3.dat 61 14 HARPS radial velocities for NGTS-4
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See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
VII/233 : The 2MASS Extended sources (IPAC/UMass, 2003-2006)
J/A+A/615/A76 : Spectroscopic parameters of stars (SPECIES). I. (Soto+, 2018)
Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 h RAh Right ascension (J2000) (1)
4- 5 I2 min RAm Right ascension (J2000) (1)
7- 11 F5.2 s RAs Right ascension (J2000) (1)
13 A1 --- DE- Declination sign (J2000) (1)
14- 15 I2 deg DEd Declination (J2000) (1)
17- 18 I2 arcmin DEm Declination (J2000) (1)
20- 24 F5.2 arcsec DEs Declination (J2000) (1)
26- 41 A16 --- 2MASS 2MASS source designation
(HHMMSSSS+DDMMSSS) (1)
43- 61 I19 --- GaiaDR2 Gaia DR2 source designation (2)
63- 69 F7.3 mas/yr pmRA Proper motion in right ascension (2)
71- 75 F5.3 mas/yr e_pmRA Error on pmRA (2)
77- 82 F6.3 mas/yr pmDE Proper motion in declination (2)
84- 88 F5.3 mas/yr e_pmDE Error on pmDE (2)
90- 94 F5.1 km/s RVgaia Radial velocity from Gaia DR2 (2)
96- 98 F3.1 km/s e_RVgaia Error on RVgaia (2)
100-104 F5.3 mas plx Parallax (2)
106-110 F5.3 mas e_plx Error on plx (2)
112-116 F5.1 pc Dist Distance (2)
118-120 F3.1 pc e_Dist Error on Dist (2)
122-126 F5.2 mag Vmag V-band magnitude from APASS (3)
128-131 F4.2 mag e_Vmag Error on Vmag (3)
133-137 F5.2 mag Bmag B-band magnitude from APASS (3)
139-142 F4.2 mag e_Bmag Error on Bmag (3)
144-148 F5.2 mag gmag g-band magnitude from APASS (3)
150-153 F4.2 mag e_gmag Error on gmag (3)
155-159 F5.2 mag rmag r-band magnitude from APASS (3)
161-164 F4.2 mag e_rmag Error on rmag (3)
166-170 F5.2 mag imag i-band magnitude from APASS (3)
172-175 F4.2 mag e_imag Error on imag (3)
177-181 F5.2 mag Gmag Gaia DR2 G-band magnitude (2)
183-187 F5.2 mag RPmag Gaia DR2 BP-band magnitude (2)
189-193 F5.2 mag BPmag Gaia DR2 RP-band magnitude (2)
195-199 F5.2 mag NGTSmag NGTS magnitude
201-204 F4.2 mag e_NGTSmag Error on NGTSmag
206-210 F5.2 mag Jmag J-band magnitude from 2MASS (1)
212-215 F4.2 mag e_Jmag Error on Jmag (1)
217-221 F5.2 mag Hmag H-band magnitude from 2MASS (1)
223-226 F4.2 mag e_Hmag Error on Hmag (1)
228-232 F5.2 mag Kmag K-band magnitude from 2MASS (1)
234-237 F4.2 mag e_Kmag Error on Kmag (1)
239-243 F5.2 mag W1mag WISE W1 (3.4um) magnitude (4)
245-248 F4.2 mag e_W1mag Error on W1mag (4)
250-254 F5.2 mag W2mag WISE W2 (4.6um) magnitude (4)
256-259 F4.2 mag e_W2mag Error on W2mag (4)
261-265 F5.2 mag W3mag WISE W3 (12um) magnitude (4)
267-270 F4.2 mag e_W3mag Error on W3mag (4)
272-275 I4 K Teff Effective temperature (5)
277-279 I3 K e_Teff Error on Teff (5)
281-285 F5.2 [-] [M/H] Metallicity (5)
287-290 F4.2 [-] e_[M/H] Error on [M/H] (5)
292-295 F4.2 km/s vsini Rotational velocity (5)
297-300 F4.2 km/s e_vsini Error on vsini (5)
302-306 F5.1 km/s RVmod Radial velocity from global modelling
308-310 F3.1 km/s e_RVmod Error on RVmod
312-314 F3.1 [cm/s2] logg Surface gravity (5)
316-318 F3.1 [cm/s2] e_logg Error on logg (5)
320-323 F4.2 Msun Mstar Star mass (5)
325-328 F4.2 Msun e_Mstar Error on Mstar (5)
330-333 F4.2 Rsun Rstar Star radius (5)
335-338 F4.2 Rsun e_Rstar Error on Rstar (5)
340-343 F4.2 g/cm3 rhoStar Star density (5)
345-348 F4.2 g/cm3 e_rhoStar Error on rhoStar (5)
350-353 F4.2 km/s vmac Macroturbulent velocity (5)
355-358 F4.2 km/s e_vmac Error on vmac (5)
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Note (1): Values taken from 2MASS (Skrutskie et al. 2006AJ....131.1163S 2006AJ....131.1163S,
Cat. VII/233)
Note (2): Values taken from Gaia DR2 (Gaia Collaboration 2018A&A...616A...1G 2018A&A...616A...1G,
Cat. I/345)
Note (3): Magnitudes taken from APASS (Henden & Munari 2014CoSka..43..518H 2014CoSka..43..518H)
Note (4): Magnitudes taken from WISE (Wright et al. 2010AJ....140.1868W 2010AJ....140.1868W)
Note (5): Stellar parameters measured by SPECIES (Soto & Jenkins
2018A&A...615A..76S 2018A&A...615A..76S, Cat. J/A+A/615/A76)
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 9 F9.7 d Pc Rotation period for a circular orbit
11- 18 F8.6 d e_Pc Error on Pc
20- 28 F9.7 d Pe Rotation period for an eccentric orbit
30- 37 F8.6 d e_Pe Error on Pe
39- 50 F12.4 d TCc Transit center time (HJD) for a circular orbit
52- 57 F6.4 d e_TCc Error on TCc
59- 70 F12.4 d TCe Transit center time (HJD) for an eccentric orbit
72- 77 F6.4 d e_TCe Error on TCe
79- 82 F4.2 h T14c Duration of transit for a circular orbit
84- 87 F4.2 h e_T14c Error on T14c
89- 92 F4.2 h T14e Duration of transit for an eccentric orbit
94- 97 F4.2 h e_T14e Error on T14e
99-102 F4.2 --- a/Rc Semi-major axis to star radius ratio for a
circular orbit
104-107 F4.2 --- e_a/Rc Error on a/Rc
109-112 F4.2 --- a/Re Semi-major axis to star radius ratio for an
eccentric orbit
114-117 F4.2 --- e_a/Re Error on a/Re
119-122 F4.1 m/s Kc Planet radial velocity semi-amplitude for a
circular orbit
124-126 F3.1 m/s e_Kc Error on Kc
128-131 F4.1 m/s Ke Planet radial velocity semi-amplitude for an
eccentric orbit
133-135 F3.1 m/s e_Ke Error on Ke
137-139 F3.1 --- ec Eccentricity for a circular orbit (fixed to 0)
141-144 F4.2 --- ee Eccentricity of the eccentric orbit
146-149 F4.2 --- E_ee Upper error on ee
151-154 F4.2 --- e_ee Lower error on ee
156-158 F3.1 deg wc Argument of periastron for a circular orbit
(fixed to 0)
160-161 I2 deg we Argument of periastron for an eccentric orbit
163-164 I2 deg E_we Upper error on we
166-167 I2 deg e_we Lower error on we
169-172 F4.1 Mgeo Mplc Planet mass for a circular orbit
174-176 F3.1 Mgeo e_Mplc Error on Mplc
178-181 F4.1 Mgeo Mple Planet mass for an eccentric orbit
183-185 F3.1 Mgeo e_Mple Error on Mple
187-190 F4.2 Rgeo Rplc Radius of the planet for a circular orbit
192-195 F4.2 Rgeo e_Rplc Error on Rplc
197-200 F4.2 Rgeo Rple Radius of the planet for an eccentric orbit
202-205 F4.2 Rgeo e_Rple Error on Rple
207-211 F5.3 --- Rp/Rc Planet radius to star radius ratio for a
circular orbit
213-217 F5.3 --- e_Rp/Rc Error on Rp/Rc
219-223 F5.3 --- Rp/Re Planet radius to star radius ratio for an
eccentric orbit
225-229 F5.3 --- e_Rp/Re Error on Rp/Re
231-234 F4.2 g/cm3 rhopc Planet density for a circular orbit
236-239 F4.2 g/cm3 e_rhopc Error on rhopc
241-244 F4.2 g/cm3 rhope Planet density for an eccentric orbit
246-249 F4.2 g/cm3 e_rhope Error on rhope
251-254 F4.2 g/cm3 rhoc Star density for a circular orbit
256-259 F4.2 g/cm3 e_rhoc Error on rhoc
261-264 F4.2 g/cm3 rhoe Star density for an eccentric orbit
266-269 F4.2 g/cm3 e_rhoe Error on rhoe
271-275 F5.3 AU ac Semi-major axis for a circular orbit
277-281 F5.3 AU e_ac Error on ac
283-287 F5.3 AU ae Semi-major axis for an eccentric orbit
289-293 F5.3 AU e_ae Error on ae
295-298 I4 K Teqc Planet equilibrium temperature for a circular
orbit
300-302 I3 K e_Teqc Error on Teqc
304-307 I4 K Teqe Planet equilibrium temperature for an eccentric
orbit
309-311 I3 K e_Teqe Error on Teqe
313-316 F4.1 deg ic Inclination of the orbit for a circular orbit
318-320 F3.1 deg e_ic Error on ic
322-325 F4.1 deg ie Inclination of the orbit for an eccentric orbit
327-329 F3.1 deg e_ie Error on ie
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Byte-by-byte Description of file: table1*
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Bytes Format Units Label Explanations
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1- 16 F16.8 d BJD Barycentric Julian Date (TDB)
18- 25 F8.6 --- Flux Relative flux
27- 34 F8.6 --- e_Flux Error on Flux
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 10 I10 "Y:M:D" Night Observation date
12- 19 A8 --- Site Observation site
21- 38 A18 --- Inst Instrument used for the observation
40- 43 I4 --- Nimg Number of images used
45- 47 I3 s Exptime Exposure time
49- 51 A3 --- Binning Binning (1x1 or 4x4)
53- 56 A4 --- Filter Filter used for the observation
58- 69 A12 --- Comment Comment on the observation
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 14 F14.6 d BJD Barycentric Julian Date (TDB)
16- 24 F9.5 km/s RV Radial velocity
26- 32 F7.5 km/s e_RV Error on RV
34- 40 F7.5 km/s FWHM Full width at half-maximum
42- 47 F6.3 --- Contrast Contrast
49- 56 F8.5 km/s BIS Bisector span
58- 61 I4 s Exptime Exposure time
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(End) Ana Fiallos [CDS] 02-Nov-2022