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The Subaru Seminar is
usually held in Room 104 of the Hilo Base Facility, adjacent
to the main lobby. Everyone is welcome to attend. If you are
interested in giving a seminar, please contact Subaru seminar organizers
(Tomonori Usuda, Kumiko S. Usuda, Masayuki Akiyama)
by email : sseminar_at_subaru.naoj.org (please change"_at" to @).
July 23, Monday at 11:00 am
" Micro-arcsecond relative astrometry with single aperture ground based observations "
Tristan Roell
(Friedrich Schiller University of Jena)
We observe the double star system HD19994 with the adaptive optics (AO) system NACO at the 8m UT4/VLT to determine the astrometric signal of the radial velocity planet candidate HD19994Ab as a periodic change in the binary separation of HD19994A and B.
By using AO assisted observations in a narrow band filter, centred in the near infrared K band, we compensate for atmospheric turbulences and suppress differential chromatic refraction.
We expect a minimal astrometric signal for HD19994Ab (M*sini = 1.68 Mj) of 131 micro-arcsec for an elliptical orbit (e=0.3) and at least a signal of 1 milli-arcsec for a 13 Mj object.
To police the stability of the plate scale we use the globular cluster 47 Tuc as a nearly intrinsically stable reference system.
Using a Monte Carlo Simulation with a uniformly distributed velocity dispersion of 631 mas/year (McLaughlin et al., 2006) we derived a relative intrinsic stability of 0.02% per pixel and year.
Thus, with 47Tuc we can detect variations in the NACO plate scale down to 0.3 micro-arcsec per pixel and year.
Hence we reach a final precision in the separation of our science binary of ~100 micro-arcsec over a period of one year, sufficient to check whether the companion is below 13 Mj.