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G C N E W S
* Newsflash *
- The Newsletter for Galactic Center Research -
gcnews@aoc.nrao.edu http://www.aoc.nrao.edu/~gcnews
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Vol. 20, No. 3 Feb 4, 2005
Recently submitted papers:
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1) Weighing the cusp at the Galactic Centre (Mouawad et al., Astron Nachr)
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Email : nelly@ph1.uni-koeln.de
Title : Weighing the cusp at the Galactic Centre
Author(s): N. Mouawad(1) and A. Eckart(1) and S. Pfalzner(1) and R.
Schoedel(1) and J. Moultaka(1) and R. Spurzem(2)
Institute: (1) I. Physikalisches Institut, Universitaet zu Koeln,
Zuelpicher Str.77, 50937 Koeln, Germany and
(2) Astronomisches Recheninstitut, Moenchhofstr. 12-14,
69120 Heidelberg, Germany
Paper : Astron Nach, accepted for pub
EPrint : astro-ph/0402338
Web : http://hera.ph1.uni-koeln.de/~nelly/Mouawad-CuspGC.ps
Abstract:
As stars close to the galactic centre have short orbital periods it has
been possible to trace large fractions of their orbits in the recent
years. Previously the data of the orbit of the star S2 have been fitted
with Keplerian orbits corresponding to a massive black hole (MBH) with
a mass of M_BH=3-4*10^6M_o implying an insignificant cusp mass.
However, it has also been shown that the central black hole resides in
a 1'' diameter stellar cluster of a priori unknown mass. In a spherical
potential which is neither Keplerian nor harmonic, orbits will precess
resulting in inclined rosetta shaped trajectories on the sky. In this
case, the assumption of non-Keplerian orbits is a more physical
approach. It is also the only approach through which cusp mass
information can be obtained via stellar dynamics of the cusp members.
This paper presents the first exemplary modelling efforts in this
direction. Using positional and radial data of star S2, we find that
there could exist an unobserved extended mass component of several
10^5M_o forming a so-called 'cusp' centered on the black hole position.
Considering only the fraction of the cusp mass M_S2_apo within the
apo-center of the S2 orbit we find as an upper limit that
M_S2_apo/(M_BH + M_S2_apo) <= 0.05. A large extended cusp mass, if
present, is unlikely to be composed of sub-solar mass constituents, but
could be explained rather well by a cluster of high M/L stellar
remnants, which we find to form a stable configuration.
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