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    {\small\rm\zihao{6}\songti\thepage\hfill
    \quad\quad ACTA ASTRONOMICA SINICA \hfill
    \hspace{2mm} Vol.44\vspace{2mm}}}} %%%%%%%
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    {\small\rm \zihao{6}\songti suppl.\hfill Y. Wei \& Y. Wu: Configuration and Distribution of High Velocity Molecular
Outflows  %%�����ߣ���Ŀ���ƣ�
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\zihao{5}\songti

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    \zihao{6}\songti
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    Vol.44~ Suppl.
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    \small ACTA ASTRONOMICA SINICA
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      Feb.,~2003 \\[-1.5 true mm] %%January
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\vs\vs\vs \bc {\Large\bf Configuration and Distribution of \\[2mm]High
Velocity Molecular
Outflows    %%�����⣩
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}

\vs\vs{\normalsize Yue Wei\hs\&\hs Yuefang Wu }  %%���������ߣ�

\vs
(\footnotesize \pka)\\
 ({\footnotesize 1~{\it  CAS-PKU Joint Beijing Astrophysics Center,
 Beijing}~100871})
\vs\vs \ec

\normalsize
\begin{quotation}

 \no{\bf A{\scriptsize\bf BSTRACT }}~~~\small
We calculate collimation factors of bipolar outflows and present
statistical relationships between the collimation factors and
masses of high-velocity molecular outflows in star formation
regions as well as the luminosity of infrared source and angular
diameters. The collimation histogram shows that low mass outflows
have better collimation. The distribution of outflows in the
Galaxy is also presented.
 %\vn
% \no{\bf Key words}~~  pulsar-mode  change-spectrum
\end{quotation}

\para{\large\bf{1}~~ Introduction}

\vs\vs So far more than 350 molecular outflows related to star
formation have been reported and mapped in CO ($J=2-1$ or $1-0$)
lines. Collimation factor is a morphologic parameter, probably
referring to activity of the proto star and its interaction with
surrounded molecular clouds.

  Our statistics cover more than 200 references with
mapped molecular outflows in star formation regions. The final
sample includes 298 bipolar outflows, 41 monopolar ones (17 with
only blue lobes and 24 only red lobes discovered) and 4 multipolar
ones.

 In this paper, we calculate of collimation factors from the contour maps,
  then discuss the collimation factors statistically. The
distribution of outflows in the Galaxy is presented as well.


\para{\large\bf{2}~~Collimation Factor}

\vs\vs We derived the collimation factor in the following way:
take existing survey maps of
 outflow region; measure its major axis,$D_{\max}$;
assuming that the region is an ellipse, derive minor axis of the
ellipse,$D_{\min}$ from the map. In order to take out the mapping
uncertainty of the telescope beams, we let
$2R_{\max}=\sqrt{D_{\max}^{2}-\theta^2_{\rm FWHM}}$, so as to
$R_{\min}$, where $\theta _{\rm FWHM}$ is telescope beam width;
then the collimation factor is finally defined by
$R_{\max}/R_{\min}$ (Bally \& Lada, 1983) .

\para{\large\bf{3}~~Statistical Results}

\vs\vs The distribution of collimation factor is showed in Figure
1. According to this histogram, low mass outflows appear in the
region 2.0-2.5, while high mass outflows in the region 1-1.5. So
the high mass outflows have worse collimation in general, i.e. they look
rounder than low mass outflows.

\begin{figure}[h]
\center {\includegraphics [bb=64 195 543
588,scale=0.4]{histo.eps}}

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   %{\hspace{3.5cm}
   {%\center
   \footnotesize
Fig.\,1~~ Distribution of collimation factors. Low mass outflows
($L_{bol}<1000L_{\odot}$) are in black, high mass
($L_{bol}>1000L_{\odot}$)in pale grey and the total in white.}

    \end{figure}

 Collimation factor bears no relation with luminosity of
outflow source according to our statistical calculation. It is
comprehensible that high mass flows generally have smaller angular
radii, which indicates they are further.

\para{\large\bf{4}~~Distribution of Outflows in the Galaxy}

\vs\vs With the origin in the sun and the X-axis pointing to the
centre of the Galaxy (GC is at (8,0)), outflow sources are plotted
face on (Fig. 2). We can see that low mass outflows are closer to
the Sun and high mass flows scatter approximately from several
hundred pc to ten thousand pc.

\vspace{-4mm}\begin{figure}[h] \center {\includegraphics [bb=0 0
281 240,scale=0.75]{xy.eps}}
\parbox[tb]{8cm}
   %{\hspace{3.5cm}
   {%\center
   \footnotesize
Fig.\,2~~ Outflows distribution in the Galaxy. The sun is at (0,0)
      and GC at (8,0) Low mass outflows
are plotted in dot and high mass in cross.}

    \end{figure}


\vs\vn{\bf ACKNOWLEDGEMENTS}~~This project is supported, in part by
the grant G1999075405 NKBRSF, 10128306 and 10133020 of NSFC.

\bc {\bf References} \ec

\vspace{-4mm} \no \fns

 \no Bally J., Lada C.J.,  ApJ, 1983, 265, 824\\

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