Engineering topics
Publications and source records attributed to Encrenaz, P. J..
The 1(10)-1(11) transition of ortho-H2D(+) at 372 GHz has been sought in several dark clouds. The transition was not detected; the best upper limits obtained are about 0.3 K (3 sigma). We derive upper limits for the ortho-H2D(+) column density and briefly discuss their meaning in comparison with a simple chemical model we have developed (Pagani et al., 1992).
The 1(10)-1(01) transition of H2(O-18) has been searched for in several sources without positive detection. However, in NGC 2264 and NGC 7538, possible emission features are suspected. Implications of these feataures, if confirmed, are discussed. The best upper limit obtained in Orion (0.9 K) indicates that in that cloud, the water abundance should not be more than 1 percent that of CO.
The first detection of interstellar CCD has been obtained in the N = 3-2, J = 7/2-5/2 line at 216.3732 GHz towards the Kleinman-Low nebula. An abundance ratio CCD/CCH of 0.045 is found, indicating in this molecule a deuterium enhancement similar to that found for HNC, but an order of magnitude higher than for HCN. Negative results towards DR 21(OH), NGC 2264, L 134N, TM Cl, Rho OphB2, and IRC 10216 rule out a stronger D enhancement for CCD than for other deuterated molecules in these sources. Predictions of currently developed ion-molecule reaction schemes are consistent with the CCD line detected and the negative results.
Emission from the J = 1-0 transition of carbon monoxide has been mapped over an area of 40 by 55 arcmin in cloud L134, and visual extinctions over the entire cloud have been obtained by means of star counts. Line intensities of at least 2 K are observable down to an extinction level of about one magnitude. From observations of the J = 1-0 transition of the (C-13)O isotopic species at 18 locations in the cloud, a linear correlation is found between the local thermodynamic equilibrium (LTE) column densities of (C-13)O and magnitudes of visual extinction.
Measurements of the spatial variation of HC-12N-14 and HC-13N-14 line emission from the molecular cloud associated with the Orion Nebula indicate that HC-12N-14 has a high central opacity. This result seems to contradict a recent suggestion that the observed hyperfine structure of the line indicates a low opacity, which in turn would yield a C-13/C-12 abundance significantly different from other determinations. The observed hyperfine structure can be understood in the high-opacity case if radiative trapping in the lines is considered.
Cases of line emission were observed from the molecular clouds associated with the Orion Nebula and the rho Ophiuchi complex. The emission is attributed to a certain rotational transition of CO consisting of the isotopes C-12 and O-17. This observation signifies the first detection of O-17 outside the solar system. It is pointed out that the relative abundance of O-17 is an important astrophysical quantity because of a possible enrichment during the hot CNO cycle.