J/AJ/159/100 Flux & RVs of the dwarf G9-40 with K2 & HPF (Stefansson+, 2020)
A Sub-Neptune-sized planet transiting the M2.5 dwarf G9-40: validation with the
Habitable-zone Planet Finder.
Stefansson G., Canas C., Wisniewski J., Robertson P., Mahadevan S.,
Maney M., Kanodia S., Beard C., Bender C.F., Brunt P., Clemens J.C.,
Cochran W., Diddams S.A., Endl M., Ford E.B., Fredrick C., Halverson S.,
Hearty F., Hebb L., Huehnerhoff J., Jennings J., Kaplan K., Levi E.,
Lubar E., Metcalf A.J., Monson A., Morris B., Ninan J.P., Nitroy C.,
Ramsey L., Roy A., Schwab C., Sigurdsson S., Terrien R., Wright J.T.
<Astron. J., 159, 100 (2020)>
=2020AJ....159..100S 2020AJ....159..100S
ADC_Keywords: Exoplanets; Stars, dwarfs; Stars, variable; Photometry, infrared;
Optical; Radial velocities; Stars, masses; Stars, ages
Keywords: Exoplanet astronomy ; Exoplanet systems ; Radial velocity ;
Exoplanet detection methods ; Transit photometry ; Low mass stars ;
Mini Neptunes ; Exoplanets
Abstract:
We validate the discovery of a 2-Earth-radii sub-Neptune-sized planet
around the nearby high-proper-motion M2.5 dwarf G9-40 (EPIC212048748),
using high-precision, near-infrared (NIR) radial velocity (RV)
observations with the Habitable-zone Planet Finder (HPF), precision
diffuser-assisted ground-based photometry with a custom narrowband
photometric filter, and adaptive optics imaging. At a distance of
d=27.9pc, G9-40b is the second-closest transiting planet discovered by
K2 to date. The planet's large transit depth (∼3500ppm), combined with
the proximity and brightness of the host star at NIR wavelengths
(J=10, K=9.2), makes G9-40b one of the most favorable
sub-Neptune-sized planets orbiting an M dwarf for transmission
spectroscopy with James Webb Space Telescope, ARIEL, and the upcoming
Extremely Large Telescopes. The star is relatively inactive with a
rotation period of ∼29days determined from the K2 photometry. To
estimate spectroscopic stellar parameters, we describe our
implementation of an empirical spectral-matching algorithm using the
high-resolution NIR HPF spectra. Using this algorithm, we obtain an
effective temperature of Teff=3404±73K and metallicity of
[Fe/H]=-0.08±0.13. Our RVs, when coupled with the orbital
parameters derived from the transit photometry, exclude planet masses
above 11.7M⊕ with 99.7% confidence assuming a circular orbit.
From its radius, we predict a mass of M=5.0-1.9+3.8M⊕ and
an RV semiamplitude of K=4.1-1.6+3.1m/s, making its mass
measurable with current RV facilities. We urge further RV follow-up
observations to precisely measure its mass, to enable precise
transmission spectroscopic measurements in the future.
Description:
G9-40 was observed by the Kepler spacecraft as part of Campaign 16 of
the K2 mission. It was proposed as a K2 Campaign 16 target by the
following programs: GO16005_LC (PI: Crossfield), GO16009_LC (PI:
Charbonneau), GO16052_LC (PI: Stello), and GO16083_LC (PI: Coughlin).
The star was monitored in long cadence mode (30 minute cadence) for 80
days from 2017-December-7 to 2018-February-25.
We obtained four visits of G9-40 with the Habitable-zone Planet Finder
(HPF) Spectrograph with the goal to measure its Radial Velocity (RV)
variation as a function of time. HPF is a high-resolution (R∼55000)
NIR spectrograph recently commissioned on the 10m Hobby-Eberly
Telescope (HET) in Texas covering the information-rich z, Y, and J
bands from 810 to 1280nm.
Objects:
-------------------------------------------------
RA (ICRS) DE Designation(s)
-------------------------------------------------
08 58 52.33 +21 04 34.2 G9-40 = EPIC 212048748
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File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table6.dat 43 8 Radial velocities of G 9-40 from Habitable-zone
Planet Finder (HPF)
fig7.dat 73 530 K2 and ground-based diffuser-assisted photometry
of G 9-40
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See also:
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
I/289 : UCAC2 Catalogue (Zacharias+ 2004)
I/298 : LSPM-North Catalog (Lepine+ 2005)
II/328 : AllWISE Data Release (Cutri+ 2013)
IV/34 : K2 Ecliptic Plane Input Catalog (EPIC) (Huber+, 2017)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
J/AJ/128/463 : A preliminary 20pc census from the NLTT cat. (Reid+,2004)
J/AJ/135/907 : Variables in Praesepe identified with KELT (Pepper+,2008)
J/ApJS/200/15 : HARPS-TERRA project. I. (Anglada-Escude+, 2012)
J/AJ/143/93 : Rotational velocities in early-M stars (Reiners+, 2012)
J/ApJ/757/161 : Spectroscopy of 56 exoplanet host stars (Torres+, 2012)
J/ApJ/775/L11 : Stellar rotation periods for KOIs (McQuillan+, 2013)
J/ApJS/224/2 : K2 EPIC stellar properties, 138600 targets (Huber+, 2016)
J/ApJ/825/19 : Mass-radius relation for planets Rp<4 (Wolfgang+, 2016)
J/ApJ/834/17 : Mass & radius planets, moons, low mass stars (Chen+,2017)
J/AJ/154/207 : K2 planetary syst. orbit. low-mass stars (Dressing+,2017)
J/AJ/154/109 : CKS. III. Planet radii (Fulton+, 2017)
J/AJ/153/71 : Kepler follow-up obs. program. I. Imaging (Furlan+, 2017)
J/ApJ/836/77 : Library of high-S/N opt. spectra FGKM stars (Yee+, 2017)
J/A+A/612/A49 : 324 CARMENES M dwarfs velocities (Reiners+, 2018)
J/other/Nat/563.365 : Barnard's star radial velocity curve (Ribas+, 2018)
J/AJ/156/22 : Planetary candidates from K2 Campaign 16 (Yu+, 2018)
J/A+A/629/A111 : L 98-59 (TOI 175) HARPS observations (Cloutier+, 2019)
J/AJ/158/87 : 86 cool dwarfs obs. during K2 Campaigns (Dressing+, 2019)
Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 18 F18.10 d BJD [2458543/2458591] Barycentric Julian date of HPF
observation, in TDB (1)
20- 25 F6.2 m/s RVel [-10.9/11.3] Habitable zone Planet Finder Radial
Velocity
27- 31 F5.2 m/s e_RVel [5.96/10.5] Total RVel uncertainty, including
RVel-d in quadrature
33- 36 F4.2 m/s RVel-d [0.02/0.31] estimated RVel drift error
38- 43 F6.2 --- SNR [103/149] Spectrum signal-to-noise
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Note (1): The date is the observation flux-weighted midpoint; all
exposures are 945s in length.
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Byte-by-byte Description of file: fig7.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 18 F18.10 d BJD [2458497/2458498] Barycentric Julian date of
diffuser observation, in TDB
20- 27 F8.6 --- fluxn [0.99/1.01] Normalized flux, not detrended
29- 36 F8.6 --- fluxd [0.99/1.01] Detrended flux; same as flux after
taking out a line
38- 45 F8.6 --- e_fluxd [0.001/0.002] Error in flux, includes
scintillation error estimate
47- 55 F9.6 --- res [-0.004/0.005] Residual, detrended-model
(flux-d - flux-m)
57- 64 F8.6 --- fluxm [0.99/1] Best fit model flux
66- 73 F8.6 --- airmass [1.04/1.56] Airmass of the observation
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History:
From electronic version of the journal
(End) Prepared by [AAS], Coralie Fix [CDS], 22-Sep-2020