J/MNRAS/455/357 2MASS J18212815+1414010 field stars (Sahlmann+, 2016)
Parallax of the L4.5 dwarf 2M1821+14 from high-precision astrometry with
OSIRIS at GTC.
Sahlmann J., Lazorenko P.F., Bouy H., Martin E.L., Queloz D., Segransan D.,
Zapatero Osorio M.R.
<Mon. Not. R. Astron. Soc., 455, 357-369 (2016)>
=2016MNRAS.455..357S 2016MNRAS.455..357S (SIMBAD/NED BibCode)
ADC_Keywords: Stars, standard ; Positional data ; Proper motions ;
Parallaxes, trigonometric
Keywords: atmospheric effects - techniques: high angular resolution -
astrometry - parallaxes - brown dwarfs
Abstract:
We used the OSIRIS camera at the 10.4m Gran Telescopio Canarias (GTC)
to monitor the astrometric motion of the L4.5 dwarf 2M1821+14 over 17
months. The astrometric residuals of 11 epochs have an rms dispersion
of 0.4mas, which is larger than the average precision of 0.23mas per
epoch and hints towards an additional signal or excess noise.
Comparison of the point-spread functions in OSIRIS and FORS2/VLT
images reveals no differences critical for high-precision astrometry,
despite the GTC's segmented primary mirror. We attribute the excess
noise to an unknown effect that may be uncovered with additional data.
For 2M1821+14, we measured a relative parallax of 106.15±0.18mas
and determined a correction of 0.50±0.05mas to absolute parallax,
leading to a distance of 9.38±0.03pc. We excluded at 3σ
confidence the presence of a companion to 2M1821+14 down to a mass
ratio of 0.1 (∼5MJupiter) with a period of 50-1000d and a separation
of 0.1-0.7au. The accurate parallax allowed us to estimate the age and
mass of 2M1821+14 of 120-700Myr and 0.049+0.014-0.024M☉,
thus confirming its intermediate age and substellar mass. We
complement our study with a parallax and proper motion catalogue of
587 stars (i'≃15.5-22) close to 2M1821+14, used as astrometric
references. This study demonstrates submas astrometry with the GTC, a
capability applicable for a variety of science cases including the
search for extrasolar planets and relevant for future astrometric
observations with E-ELT and TMT.
Description:
We observed 2M1821+14 with the OSIRIS camera of the GTC in the
broad-band i'-filter with an exposure time of 45s and 1x1 pixel (px)
binning.
Over a timespan of 506d (∼1.4yr) from 2013 May to 2014 October we
obtained 17 epochs.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table5.dat 115 588 Astrometric catalogue
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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- 4 I4 --- N Star sequential number
6- 11 F6.3 mag i'mag i' magnitude
13- 17 F5.3 mag e_i'mag rms uncertainty on i'mag
19- 29 F11.7 deg RAdeg Right ascension (J2000)
31- 35 F5.3 arcsec e_RAdeg rms uncertainty on RAdeg
37- 46 F10.7 deg DEdeg Declination (J2000)
48- 52 F5.3 arcsec e_DEdeg rms uncertainty on DEdeg
54- 59 F6.2 mas/yr pmRA Relative proper motion along RA, pmRA*cosDE
61- 64 F4.2 mas/yr e_pmRA rms uncertainty on pmRA
66- 72 F7.2 mas/yr pmDE Relative proper motion along DE
74- 77 F4.2 mas/yr e_pmDE rms uncertainty on pmDE
79- 84 F6.2 mas rho Angular distance (differential chromatic
refraction (DCR) parameter ρ)
86- 89 F4.2 mas e_rho rms uncertainty on rho
91- 96 F6.2 mas varpi Relative parallax
98-101 F4.2 mas e_varpi rms uncertainty on varpi
103-109 F7.4 yr Ep-2000 Mean epoch of observation (Ep-2000)
111-115 F5.2 --- Qual chi2 value for the epoch residuals that
flags the quality of the fit
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 28-Jul-2016