SIMBAD references

We present the results of a search for the negative ion C₄H^– in various dark clouds, low mass star-forming regions and photon-dominated regions (PDRs). We have also searched for C₆H^–, C₂H^– and CN^– in some of the sources. The millimeter-wave observations were carried out with the IRAM-30m telescope. We detect C₄H^–, through the J=9-8 and J=10-9 rotational transitions, in the low mass star-forming region L1527. We thus confirm the tentative detection of the J=9-8 line recently reported toward this source. The [C₄H^–]/[C₄H] ratio found is 0.011%, which is slightly lower than the value observed in IRC +10216, 0.024%, but above the 3σ upper limit we derive in TMC-1, <0.0052%. We have also derived an upper limit for the [C₆H^–]/[C₆H] ratio in the Horsehead Nebula, and for various anion-to-neutral ratios in the observed sources. These results are compared with recent chemical models.