\leftline{ \underline{\bf Probing Gravitational Potential at the Galactic Center }}

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Session 54 -- MW, Galactic Structure
Oral presentation, Wednesday, 10:30-12:00, Dwinelle 155 Room

[54.01] \leftline{ \underline{\bf Probing Gravitational Potential at the Galactic Center }}

L. Ozernoy$^1$, L. Blitz$^2$, A. Fridman, O. Khoruzhii, V. Lyakhovich$^3~~~~~~~$ ( $^1$GMU \& USRA/NASA/GSFC, $^2$U. of Maryland, $^3$Inst. of Astronomy, Moscow, Russia)

\def\ul#1{$\underline{\smash{\vphantom{y} \hbox{#1}}}$} \def\lax {\ifmmode{_<\atop^{\sim}} \else{${_<\atop^{\sim}}$} \fi} \def\gax {\ifmmode{_>\atop^{\sim}} \else{${_>\atop^{\sim}}$} \fi} \def\kms {\ifmmode{{\rm ~km~s}^{-1}} \else{~km~s$^{-1}$} \fi} \def\mo {~${\rm M}_{\odot}$} \def\moyr {\hbox{~${\rm M}_{\odot} \,{\rm yr}^{-1}$}} \def\etal {{\sl et~al.~}} \def\eg{e.\thinspace g.} \def\ie{i.\thinspace e.}

We explore the dynamics of the gaseous rotating disk in the innermost, central parsec of the Galaxy. Provided that the so called `mini-spiral' observed is a density wave generated by a hydrodynamical instability, the spiral morphology can put interesting constraints to the shape of the gravitational potential assumed to be due to a central point mass plus an extended stellar nucleus. The perturbation theory is developed to describe the dynamics of the spiral wave; the motion of the gas is considered to be isentropic. We have used both analytical techniques and numerical simulations to describe the morphology of the spiral and to constrain the parameters of the potential. The main results of these simulations can be summarized as follows: Although a dominating central point mass of $\sim 10^6$\mo~ is able to generate a one-arm spiral as it was proposed by Lacy \etal (ApJ 380, L 71, 1991), it turns out that it is impossible to reproduce the proposed characteristics of the ``northern arm" for any combinations of the input parameters of the model.$~~$ (A generated spiral that would coincide in the central part, $r<0.5$ pc, with the proposed one differs significantly from the latter at the periphery, $r\gax 1$ pc; on the other hand, agreement with the proposed spiral shape at the periphery is only possible at the expence of rejecting the proposed linear, $r\propto \theta$, spiral shape in the central part). If the observed pattern is either the two-arm or three-arm spiral, its comparatively weak tangling suggests that there is no strong (as high as $10^6$\mo) central point mass concentration. An estimate of $\vert dr/d\theta\vert>0.2$ pc/rad within $r\sim 1$ pc results in the enclosed mass within $r<0.2$ pc not exceeding $10^5$\mo.

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