EDP Sciences
Free access
Issue
A&A
Volume 473, Number 3, October III 2007
Page(s) 707 - 710
Section Astrophysical processes
DOI http://dx.doi.org/10.1051/0004-6361:20078009


A&A 473, 707-710 (2007)
DOI: 10.1051/0004-6361:20078009

On the orientation of the Sagittarius A* system

L. Meyer1, R. Schödel1, A. Eckart1, 2, W. J. Duschl3, 4, V. Karas5, and M. Dovciak5

1  I.Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
    e-mail: leo@ph1.uni-koeln.de
2  Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
3  Institut für Theoretische Physik und Astrophysik, Universität zu Kiel, 24098 Kiel, Germany
4  Steward Observatory, The University of Arizona, 933 N. Cherry Ave. Tucson, AZ 85721, USA
5  Astronomical Institute, Academy of Sciences, Bocní II, 14131 Prague, Czech Republic

(Received 4 June 2007 / Accepted 15 August 2007)

Abstract
Context.The near-infrared emission from the black hole at the Galactic center (Sgr A*) has unique properties. The most striking feature is a suggestive periodic sub-structure that has been observed in a couple of flares so far.
Aims.Using near-infrared polarimetric observations and modelling the quasi-periodicity in terms of an orbiting blob, we try to constrain the three dimensional orientation of the Sgr A* system.
Methods.We report on so far unpublished polarimetric data from 2003. They support the observations of a roughly constant mean polarization angle of ~$60\degr$ $\pm$ $20\degr$ from 2004-2006. Prior investigations of the 2006 data are deepened. In particular, the blob model fits are evaluated such that constraints on the position angle of Sgr A* can be derived.
Results.Confidence contours in the position - inclination angle plane are derived. On a $3\sigma$ level the position angle of the equatorial plane normal is in the range ~ $60\degr{-}108\degr$ (east of north) in combination with a large inclination angle. This agrees well with recent independent work in which radio spectral/morphological properties of Sgr A* and X-ray observations, respectively, have been used. However, the quality of the presently available data and the uncertainties in our model bring some ambiguity to our conclusions.


Key words: black hole physics -- infrared: general -- accretion, accretion disks -- Galaxy: center



© ESO 2007