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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 (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:
FileName Lrecl Records Explanations
ReadMe 80 . This file table5.dat 115 588 Astrometric catalogue
Byte-by-byte Description of file: table5.dat
Bytes Format Units Label Explanations
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
History: From electronic version of the journal
(End) Patricia Vannier [CDS] 28-Jul-2016
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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