Emission maps from a variety of molecules identify two adjacent, unusual regions in the star-forming Rho Oph cloud. The first is a region of intense DCO(+) emission that arises in a compact (0.26 x 0.10 pc), dense (about 500,000/cu cm), massive (40 solar masses), yet cold (less than 20 K) core. The second is a separate region of rare 2 cm H2CO emission at slightly blueshifted velocities bordering the southwestern tip of the DCO(+) emission region. This second (0.15 x 0.03 pc) region has a density greater than 10 to the 6th/cu cm and a mass of at least 18 solar masses and is warmer than the first region. There is sufficient mass in this core complex to form a massive star, but, unlike other similar, more distant, massive cores, there is no evidence for any embedded massive or high-luminosity stars. The dramatic differences between the spatial distributions of these unusual molecular emission regions suggests that the second region traces a high-density, warmed compression front propagating into the first region, a remnant of the original cloud.
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Loren et al. (1986) studied this question.