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    {\small\rm\thepage\hfill
    \quad\quad ACTA ASTRONOMICA SINICA \hfill
    \hspace{2mm} Vol.44\vspace{2mm}}}} %%%%%%%
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    {\small\rm  suppl.\hfill J. Esimbek et al.: A Survey of CO Emission
    in Water Maser Sources %%（作者：题目名称）
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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 A Survey of CO Emission
    in Water Maser Sources \\[2mm] Associated
with Low Color Index IRAS Sources    %%（文题）
%\\[1ex]
%$\!\!^*$
}

\vs\vs{\normalsize Jarken Esimbek\up{1,2},\hs\hs Yuefang Wu\up{1}
\hs\&\hs Hongbo Zhang\up{2}}  %%（本文作者）

\vs
({\footnotesize 1~{\it Astronomy Dept, CAS-PKU Joint Beijing Astrophysics Center}~
100871}) \\%%（本文作者单位）
({\footnotesize 2~{\it Urumqi Astronomical
Observatory,NAO,CAS,Urumqi}~ 830011}) \vs\vs \ec

\normalsize
\begin{quotation}

 \no{\bf A{\scriptsize\bf BSTRACT }}~~~\small
Using the 13.7\,m radio telescope of the Qinghai station of Purple
Mountain Observatory at Delingha, we searched for CO J=1-0 line in
98 water masers in December 2001. The results show that 66 sources
are associated with molecular gas. 13 sources have been identified
to be molecular outflow candidates. Their properties are discussed
briefly in connection with low color index IRAS sources associated
with water masers.

 \vn
 \no{\bf Key words}~~  pulsar-mode  change-spectrum
\end{quotation}

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

\vs\vs   The masers spots and large-scale outflows tend to be
associated with the deeply embedded and probably young stellar
objects(YSOs). The relation between water masers and molecular gas
is very important for understanding the evolution of YSOs and the
interaction between sources and their parent clouds. Fig.1 shows
distributions of IRAS sources associated with water masers in the
IRAS color-color diagram(Jarken et al 2003). The upper-right
region or high red color index region of the diagram satisfies
Woot and Churchwell(WC)
 criterion which is related with high
mass star formation (Wood and Cheuchwell 1989). The criterion of Emerson (Emerson 1987),
is given to select low mass cloud cores. The
lower-left region or high blue color index region satisfied the criterion of
Wu (Wu Y et al.
1996), which is about the candidates of OH/IR sources. Lowwer red and blue
color index objects which do not
satisfy any criterio locate in the center
region. This region contains 98 sources with
-0.5${<}$log($F_{25}$/$F_{12}$)${<}$0.5 and
-0.5${<}$log($F_{60}$/$F_{12}$)${<}$1.  Are these masers still in gas and dust
regions? Is there any high velocity gas near them? With these questions we
observed the 98 objects in
the CO (J=1-0) lines.

\para{\large\bf{2}~~Observations}

\vs\vs Our observations were carried out by the 2.6-mm system of
the 13.7\,m radio telescope at Qinghai station of Purple Mountain
Observatory, in CO J=1-0 transition of 115271.201\,MHz. We used a
cooled frequency mixer receiver with a typical temperature 250\,K
(single band). The 1024-channel AOS spectrometer has a total
bandwith of 170\,MHz and equivalent velocity resolution of
0.43\,km$\,s^{-1}$. The flux was corrected for atmospheric
absorption. The antenna at the working wavelength had a half-power
beamwidth of 54'', the pointing and tracking accuracies were
better than 10''. The antenna efficiency is 0.50 during the
observation period. All spectra are taken in the position
switching mode.

\newpage
\vspace*{1mm}
\para{\large\bf{3}~~Results and Discussions}

\vs\vs Among 98 water maser sources 66 were detected with CO J=1-0
emission, that is, 37 of 45 interstellar sources and 29 of 53
stellar sources are associated with molecular clouds. The results
suggest that the detection rate (82$\%$)of CO emission in
interstellar water maser sources is higher than that(55$\%$) in
stellar maser sources for these low IRAS color index objects. The
reasons for the difference may be concerned with density,
distribution of the associated gas and the size of the gas region.

\begin{figure}[tbhp]
\center {\includegraphics [bb=87 207 379 447,scale=0.9]{fig1.eps}}
\center {\includegraphics [bb=0 168 408
458,scale=0.75]{table1.eps}}
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     % Fig.\,1~~ }
\end{figure}

 Thirty-four of the 66 maser sources have multiple components, which may be
 involving clustering
structure. Of the remaining detected sources,  13 have
high-velocity gas, including 4 interstellar sources and 9 stellar
sources. The high-velocity gas may be caused by the mass ejection
of the center sources. Mapping observations are necessary to
identify outflows in theses sources.

The 13 new outflow candidates are associated with MSX sources.
This means that these low color index IRAS sources still have mid
infrared radiation.




\vs\vn{\bf ACKNOWLEDGEMENTS}~~ We are grateful for the staff at
Qinghai Station for their assistance for the observations. This
project is supported by the NSFC Grant 10203003, 10128306 and
10133020 and the G1999075405 NKBRSF.

\bc {\bf References} \ec

\vspace{-4mm} \no \fns

\nref Jarken E., Wu Y., Wang J., 2003, in preparation
 \nref Wood D.O.S., Churchwell E.,  ApJ, 1989, 340, 265
  \nref Emerson J.P., Star Forming Regions,  Peimbert M.,  Jugaku J., eds.,
  Proc. Of the Symp,
Tokyo, Japan, Nov. 11-15, 1985. Reidel publishing Co.,
 1987, 115, P.19
\nref Wu Y., Mao R., Sun j., et al.,  in 3$^{rd}$ EAMA
Ground-Based Astronomy in ASIA. N. Kaifu(ed.), NAO press, 1996,
167-169

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