J/AJ/157/71 Keck/NIRC2 astrometry for GSC 6214-210 b (Pearce+, 2019)
Orbital motion of the wide planetary-mass companion GSC 6214-210 b: no evidence
for dynamical scattering.
Pearce L.A., Kraus A.L., Dupuy T.J., Ireland M.J., Rizzuto A.C.,
Bowler B.P., Birchall E.K., Wallace A.L.
<Astron. J., 157, 71-71 (2019)>
=2019AJ....157...71P 2019AJ....157...71P (SIMBAD/NED BibCode)
ADC_Keywords: Stars, pre-main sequence ; Exoplanets ; Photometry, infrared
Keywords: astrometry - brown dwarfs -
planets and satellites: individual GSC 6214-210 b - stars: imaging -
stars: individual: GSC 6214-210
Abstract:
Direct-imaging exoplanet surveys have discovered a class of 5-20 MJup
substellar companions at separations >100 au from their host stars,
which present a challenge to planet and star formation models. Detailed
analysis of the orbital architecture of these systems can provide
constraints on possible formation mechanisms, including the possibility
that they were dynamically ejected onto a wide orbit. We present astrometry
for the wide planetary-mass companion GSC 6214-210 b (240 au; ∼14 MJup)
obtained using NIRC2 with adaptive optics at the Keck telescope over
10 years. Our measurements achieved astrometric uncertainties of
∼1 mas per epoch. We determined a relative motion of 1.12±0.15 mas/yr
(0.61±0.09 km/s), the first detection of orbital motion for this
companion. We compute the minimum periastron for the companion due to our
measured velocity vector and derive constraints on the orbital parameters
through our modified implementation of the Orbits for the Impatient
rejection sampling algorithm. We find that close periastron orbits, which
could indicate that the companion was dynamically scattered, are present
in our posterior but have low likelihoods. For all orbits in our posterior,
we assess the detectability of close-in companions that could have
scattered GSC 6214-210 b from a closer orbit, and find that most potential
scatterers would have been detected in previous imaging. We conclude that
formation at small orbital separation and subsequent dynamical scattering
through interaction with another potential close-in object is an unlikely
formation pathway for this companion. We also update stellar and substellar
properties for the system using the new parallax from Gaia DR2 (Cat. I/345).
Description:
We used the near-infrared imaging camera NIRC2 coupled with the
adaptive optics system (Wizinowich et al. 2000PASP..112..315W 2000PASP..112..315W) on the
Keck II telescope to obtain high-resolution imaging of the GSC 6214-210
system. We used a total of 77 images in this study. Observations from
2008, 2009, and 2010 were previously reported in Ireland et al.
(2011ApJ...726..113I 2011ApJ...726..113I), and were reanalyzed for this study. All images
used in this study were obtained with the K' filter and the narrow
camera, with adaptive optics in natural guide star mode.
Objects:
--------------------------------------------------------------------
RA (ICRS) DE Designation(s)
--------------------------------------------------------------------
16 21 54.67 -20 43 09.1 GSC 6214-210 = 2MASS J16215466-2043091
--------------------------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table6.dat 117 85 Astrometric measurements by image
fits/* . 77 List of images
--------------------------------------------------------------------------------
See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
J/MNRAS/461/794 : Scorpius-Centaurus K-Type Stars (Pecaut+, 2016)
http://koa.ipac.caltech.edu/cgi-bin/KOA/nph-KOAlogin : Keck Observatory Archive
Byte-by-byte Description of file: table6.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 A11 "date" Date Observation date (1)
13- 22 F10.2 d JD Julian Date
24- 34 A11 --- PI Principal Investigator
36- 57 A22 --- FileName Name of the FITS file in subdirectory fits
59- 60 A2 --- KOA Data set number in Keck Observatory Archive
62- 65 F4.1 s Tint [10/20]? Integration time (2)
67- 68 A2 --- Track Tracking mode (3)
70- 76 F7.2 mas rho [2194.63/2205.79] Separation ρ
78- 81 F4.2 mas e_rho [0.5/4.81] Uncertainty in rho
82 A1 --- n_rho [m] ρ is the mean value for observations
of this Date
84- 90 F7.3 deg PA [175.333/175.639] Position angle
92- 96 F5.3 deg e_PA [0.012/0.134] Uncertainty in PA
97 A1 --- n_PA [m] PA is the mean value for observations
of this Date
99-102 I4 --- S/N1 [499/3719]? Signal-to-noise ratio for the
primary (4)
104-106 I3 --- S/N2 [10/145]? Signal-to-noise ratio for the
companion (4)
108-112 F5.2 mas FWHM [37.64/65.3]? Full-width at half-maximum (5)
114-117 F4.2 mas e_FWHM [0.01/0.11]? Uncertainty in FWHM
--------------------------------------------------------------------------------
Note (1): All images were obtained with the NIRC2 imager on Keck II in the K'
filter with no coronagraph.
Note (2): Integration time is determined as the integration time per coadd times
the number of coadds.
Note (3): Tracking mode as follows:
PA = Position Angle mode;
VA = Vertical Angle mode.
Note (4): S/N is computed as the ratio of the sky-subtracted sum of pixel values
within an aperture centered over the object to the standard deviation of pixel
values in an annulus outside the object's PSF.
Note (5): The FWHM is determined as 2.355x the larger of the two sigmas of the
2D Gaussian fit.
--------------------------------------------------------------------------------
History:
From electronic version for Table 6
FITS images downloaded from:
http://koa.ipac.caltech.edu/cgi-bin/KOA/nph-KOAlogin (August 2019)
Images for 2018 Jul 1 sent by the author
Acknowledgements:
Adam Kraus [University of Texas at Austin]
(End) Tiphaine Pouvreau [CDS] 13-Aug-2019