Langer et al. 1978
Langer, W.D., R.W. Wilson, P.S. Henry, and M. Guelin, 1978: Observations of anomalous intensities in the lines of the HCO+ isotopes. Astrophys. J., 225, L139-L142, doi:10.1086/182812.
The J equals 1-0 rotational line of H13CO+ has been detected in the dark clouds L134N and Taurus Molecular Cloud 1 (TMC-1) and found to have, at selected positions, an intensity about twice that of the common isotope. The corresponding HC18O+ observations, however, yield a normal H13CO+/HC18O+ isotope ratio. We suggest that low-excitation foreground material is absorbing the HCO+ emission. The presence of this cold material must also affect the lines of other abundant molecules with large dipole moments, such as HCN, H2CO, and CS; these lines should be used cautiously as probes of the high-density dark clouds, and the less abundant isotopic species should be observed to check for opacity effects.
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Langer, W.D., Wilson, R.W., Henry, P.S., and Guelin, M.: Observations of anomalous intensities in the lines of the HCO+ isotopes, Astrophys. J., 225, L139-L142, doi:10.1086/182812, 1978.
Langer, W.D., R.W. Wilson, P.S. Henry, and M. Guelin (1978), Observations of anomalous intensities in the lines of the HCO+ isotopes, Astrophys. J., 225, L139-L142, doi:10.1086/182812.
Langer, W.D., R.W. Wilson, P.S. Henry, and M. Guelin, 1978: Observations of anomalous intensities in the lines of the HCO+ isotopes. Astrophys. J., 225, L139-L142, doi:10.1086/182812.
Langer, W.D., Wilson, R.W., Henry, P.S., & Guelin, M. 1978, Astrophys. J., 225, L139, doi:10.1086/182812.
Langer WD, Wilson RW, Henry PS, Guelin M. Observations of anomalous intensities in the lines of the HCO+ isotopes, Astrophys J 1978;225:L139-L142. doi:10.1086/182812.
W.D. Langer, R.W. Wilson, P.S. Henry, M. Guelin, Astrophys. J. 225, L139-L142, doi:10.1086/182812 (1978).
