------------------------------------------------------------------------
From: Lorant Sjouwerman  sjouwerman@jive.nfra.nl 
To: gcnews@aoc.nrao.edu
Subject: submit siopropm.tex Astronomy and Astrophysics, in press

% http://www.nfra.nl/jive/jive/preprints/pre_pub.html
% Title: Stellar positions from SiO masers in the Galactic center
%
% Manuscript number 7482
% 
% 1st author: LO Sjouwerman, JIVE, P.O. Box 2, 7990 AA  Dwingeloo, Netherlands
% 
% submitted for Astronomy \& Astrophysics
% section 11: Celestial mechanics and astrometry
% or sect. 4: Galactic structure \& dynamics
% 
% -----
\documentstyle{l-aa}
%\documentstyle[referee]{l-aa}\def\baselinestretch{2}
% added my own defenitions
\def\kms{${\rm km\,s^{\rm -1}}$}
\def\ap{\ $\approx$\,}
\def\sgra{Sgr~A*}
\def\hho{{\rm H$_{\rm 2}$O}}
%
\input{psfig}
\begin{document}
\title{Stellar positions from SiO masers in the Galactic center}
\author{Lor\'ant O.\ Sjouwerman\inst{1,2,3} \and Huib Jan van
  Langevelde\inst{3}\and Philip J.\ Diamond\inst{4}}
\offprints{ L.\ O.\ Sjouwerman (at JIVE in Dwingeloo); Email:
  sjouwerm@jive.nfra.nl}
\institute{Onsala Rymdobservatorium, S - 439 92 Onsala, Sweden
  \and Sterrewacht Leiden, P.O.\ Box 9513, 2300 RA Leiden, The
  Netherlands
  \and Joint Institute for VLBI in Europe, %Radiosterrenwacht Dwingeloo,
  P.O.\ Box 2, 7990 AA Dwingeloo, The Netherlands
  \and N.R.A.O.\ Array Operations Center, P.O.\ Box 0, Socorro NM
  87801, U.S.A.}
\thesaurus{02.13.3; 03.13.5; 05.01.1; 08.16.4; 10.03.1; 10.11.1}
\date{Received 6 February 1998; accepted 11 September 1998} 
\maketitle

\begin{abstract}
  We report on the possibility of determining milli-arcsecond accurate
  positions (relative to \sgra) for 43 GHz SiO masers located at the
  Galactic center. The SiO masers were found in OH/IR stars in a
  previous Very Large Array survey. We used the Very Long Baseline
  Array and the phased Very Large Array in a phase-referencing scheme
  with a cycle time of 40 seconds. The continuum source \sgra\ is used
  as phase-reference source. Because of the atmospheric phase
  instability at 43 GHz and sensitivity considerations, only 2 sources
  (from 10) were detected.  However, we show that reliable positions
  can be obtained with calculable errors, which allows one to measure
  the proper motion of these stars accurate to \ap\ 30 \kms\ in 5
  years.
  
  \keywords{Masers -- Methods: observational -- Astrometry -- Stars:
    AGB and post-AGB -- Galaxy: center -- Galaxy: kinematics and
    dynamics}
\end{abstract}