2004BaltA..13..419T

Several nearby star-forming regions (SFRs) have been uniformly searched for dense condensations of C¹⁸O with the NANTEN radio telescope. After that, the C¹⁸O cores in the Taurus, Ophiuchus North, Lupus and Chamaeleon star-forming regions have been observed in H¹³CO⁺, which traces much denser parts of the condensations - up to n(H₂) > 10⁵ cm^–3. The H¹³CO⁺ cores have been found not only in the active SFRs, but also in the regions of low activity, such as the Oph North region. The detection rates of these cores are similar in both regions. However, the H¹³CO⁺ cores in Oph North are of smaller mass and density, and they seem to be immature to form stars. It is suggested that their time-scale in the starless phase is ∼10⁶ yr, i.e., significantly longer than the free-fall time.