CO: dust in the rho Ophiuchi complex

Maps in the J = 1 → 0 lines of 12C 16O and 13C 16O have been obtained in the rho Ophiuchi cloud complex, from the Millimeter Wave Observatory. A region approximately 30' x 30' has been fully covered with a half power beam width of 2.3' and a velocity resolution of .65 and .67 km/s respectively. A comparison with a map of visual extinction obtained by the technique of star count has been made, particularly at the boundaries of the clouds (Encrenaz et al, 1975). Observations of the 12C 18O line show that 13C 16O is not saturated in these parts of the cloud. The integrated CO column density was plotted as a function of visual extinction. The curve obtained is very similar to the H2/Av relation predicted by Hollenbach et al, 1973. For Av greater than 2 mag, CO/Av = 1.6 x 107 cm-2/mag, while for 1 less than Av less than 2 mag the CO column density is much smaller. The agreement with the Copernicus data on zetaOph (Av = 1 mag) is excellent