J/AJ/155/159 RVs of the late-T dwarf GL 758 B host star (Bowler+, 2018)
Orbit and dynamical mass of the late-T dwarf GL 758 B.
Bowler B.P., Dupuy T.J., Endl M., Cochran W.D., MacQueen P.J., Fulton B.J.,
Petigura E.A., Howard A.W., Hirsch L., Kratter K.M., Crepp J.R.,
Biller B.A., Johnson M.C., Wittenmyer R.A.
<Astron. J., 155, 159 (2018)>
=2018AJ....155..159B 2018AJ....155..159B (SIMBAD/NED BibCode)
ADC_Keywords: Stars, brown dwarf ; Stars, late-type ; Stars, T-type ;
Stars, double and multiple ; Radial velocities
Keywords: brown dwarfs - stars: individual (Gl 758)
Abstract:
Gl 758 B is a late-T dwarf orbiting a metal-rich Sun-like star at a
projected separation of ρ∼1.6" (25 au). We present four epochs of
astrometry of this system with NIRC2 at Keck Observatory spanning 2010
to 2017 together with 630 radial velocities (RVs) of the host star
acquired over the past two decades from McDonald Observatory, Keck
Observatory, and the Automated Planet Finder at Lick Observatory. The
RVs reveal that Gl 758 is accelerating with an evolving rate that varies
between 2 and 5 m/s/yr, consistent with the expected influence of the
imaged companion Gl 758 B. A joint fit of the RVs and astrometry yields
a dynamical mass of 42-7+19 MJup for the companion with a robust
lower limit of 30.5 MJup at the 4-σ level. Gl 758 B is on an
eccentric orbit (e=0.26-0.67 at 95% confidence) with a semimajor axis
of a=21.1-1.3+2.7 au and an orbital period of P=96-9+21 yr,
which takes it within ∼9 au from its host star at periastron passage.
Substellar evolutionary models generally underpredict the mass of Gl 758 B
for nominal ages of 1-6 Gyr that have previously been adopted for the host
star. This discrepancy can be reconciled if the system is older - which is
consistent with activity indicators and recent isochrone fitting of the
host star - or alternatively if the models are systematically overluminous
by ∼0.1-0.2 dex. Gl 758 B is currently the lowest-mass directly imaged
companion inducing a measured acceleration on its host star. In the
future, bridging RVs and high-contrast imaging with the next generation
of extremely large telescopes and space-based facilities will open the
door to the first dynamical mass measurements of imaged exoplanets.
Description:
In this work, we present a dynamical mass measurement of the late-T dwarf
Gl 758 B based on new high-contrast imaging observations from Keck/NIRC2
together with 630 RVs of the host star from McDonald Observatory, Keck
Observatory, and the Automated Planet Finder (APF) gathered over the
past 20 years.
Gl 758 was included in the target sample of the long-duration RV planet
search at McDonald Observatory (e.g., Cochran et al. 1997ApJ...483..457C 1997ApJ...483..457C;
Endl et al. 2016, J/ApJ/818/34). The Tull Coude spectrograph (Tull et al.
1995PASP..107..251T 1995PASP..107..251T) was used at the Harlan J. Smith 2.7 m telescope
in combination with an I2 cell in the light path to obtain precise
differential RVs. We commenced observations of Gl 758 on 1998 November 4,
and have accumulated 118 precise RV measurements over the past 19 years.
Gl 758 has been continuously monitored with the High Resolution Echelle
Spectrometer (HIRES; Vogt et al. 1994SPIE.2198..362V 1994SPIE.2198..362V) at the Keck I
telescope since 2006. Altogether 262 spectra were gathered following the
standard setup, observing strategy, and procedure for measuring relative
RVs implemented by the California Planet Search program (Howard et al.
2010ApJ...721.1467H 2010ApJ...721.1467H).
Observations of Gl 758 have been carried out autonomously at the 2.4 m
APF telescope at Lick Observatory since 2013. A total of 250 echelle
spectra were gathered as part of APF's automated Doppler search for rocky
planets (Fulton et al. 2015, J/ApJ/805/175) with the Levy Spectrograph,
which employs an iodine cell to measure precise relative RVs (Vogt et al.
2014PASP..126..359V 2014PASP..126..359V).
Objects:
------------------------------------------------
RA (ICRS) DE Designation(s)
------------------------------------------------
19 23 34.01 +33 13 19.1 GL 758 = HD 182488
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 30 630 Relative radial velocities
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See also:
J/A+A/552/A78 : Solar like stars radial velocities (Zechmeister+, 2013)
J/ApJ/805/175 : Keck and APF radial velocities of HD7924 (Fulton+, 2015)
J/ApJ/818/34 : Radial velocity monitoring of 5 FGK stars (Endl+, 2016)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 13 F13.5 d BJD Barycentric Julian Date (TDB)
15- 20 F6.2 m/s RV [-25.98/29.88] Radial velocity
22- 25 F4.2 m/s e_RV [0.86/5.98] The 1σ uncertainty in RV
27- 30 A4 --- Obs Observatory code (1)
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Note (1): Observatory code as follows:
McD = Harlan J. Smith 2.7 m telescope with the Tull Coude spectrograph
at McDonald Observatory;
Keck = 10m Keck I telescope with the High Resolution Echelle Spectrometer;
APF = 2.4-m Automated Planet Finder telescope with the Levy Spectrograph at
Lick Observatory.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 15-Nov-2018