\begin{table}%t2
\caption{\label{observations}{\it Chandra} data used in this work.}
%\centering
\par
\begin{tabular}{cccccc}
\hline
\hline
Region name    & Position (J2000)  & Obs ID & Observation date  & Exposure time & Ref.     \\
\hline
$\rho$~Oph cores B+F & 16$^{\rm h}$27$^{\rm m}$17$^{\rm s}$ $-$24$\degr$34$\arcmin$39$\arcsec$ & 635 & 2000-04-13 & 100~ks & \citet{IMA01a, IMA01b, IMA02} \\ 
$\rho$~Oph core A    & 16$^{\rm h}$26$^{\rm m}$34$^{\rm s}$ $-$24$\degr$23$\arcmin$28$\arcsec$ & 637 & 2000-05-15 & 100~ks &  \citet{DAN00} \\
$\rho$~Oph mosaic    & 16$^{\rm h}$25$^{\rm m}$32$^{\rm s}$ $-$24$\degr$25$\arcmin$03$\arcsec$ & 618 & 2000-06-22 & 5~ks  & {\it This work} \\ 
$\rho$~Oph mosaic   & 16$^{\rm h}$28$^{\rm m}$26$^{\rm s}$ $-$24$\degr$17$\arcmin$33$\arcsec$ & 623 & 2000-02-08 & 5~ks &  {\it This work} \\ 
Cha~I                   & 11$^{\rm h}$10$^{\rm m}$12$^{\rm s}$ $-$76$\degr$34$\arcmin$30$\arcsec$ & 1867 & 2001-07-02 & 70~ks &  {\it This work} \\ 
R CrA                     & 19$^{\rm h}$01$^{\rm m}$50$^{\rm s}$ $-$36$\degr$57$\arcmin$30$\arcsec$ & 19 & 2000-10-07 & 20~ks &  {\it This work} \\ 
IC~348                  & 03$^{\rm h}$44$^{\rm m}$30$^{\rm s}$ $+$32$\degr$08$\arcmin$00$\arcsec$ & 606  & 2000-09-21 & 50~ks & \citet{PZ01,PZ02} \\ 
NGC~1333                 & 03$^{\rm h}$29$^{\rm m}$05$^{\rm s}$ $+$31$\degr$19$\arcmin$19$\arcsec$ & 642 & 2000-07-12 & 50~ks & \citet{GET02} \\ 
Orion                   & 05$^{\rm h}$35$^{\rm m}$15$^{\rm s}$ $-$05$\degr$23$\arcmin$20$\arcsec$ & 18 & 1999-10-12 & 47~ks & \citet{FEI02} \\
Orion                   & 05$^{\rm h}$35$^{\rm m}$15$^{\rm s}$ $-$05$\degr$23$\arcmin$20$\arcsec$ & 1522 & 2000-04-01 & 36~ks & \citet{FEI02} \\
\hline
\end{tabular}
\end{table}