Search for CO isotopes in cores of massive molecular clouds

Using the newly installed SIS receiving system of the 13.7 m telescope of P MO, the CO isotope line pair, (CO)-C-13 and (CO)-O-18 J = 1 - 0, were obser ved in a search for dense cores in 64 IRAS sources with high color indices or H2O masers. Maps were obtained for some of the sources. The line pair wa s detected in all the target sources. The emission of (CO)-C-13 J = 1 - 0 i s strong showing that the emission regions are dense. The pair lines of the CO isotopes were measured for the first time in at least 60 sources. Anten na temperatures, center velocities and line widths are obtained with Gaussi an fitting. Preliminary analyses were made for the emission intensities and line profiles.