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Fig. 3


Top: regions of non-zero HCO+ (blue) and DCO+ (red) abundance, overlaid with contours indicating the hydrogen density (solid gray lines) and temperature (dashed gray lines). The 19 and 21 K contours are shown with a thick dark gray line. The region containing HCO+ is bounded on the upper and lower sides by CO photodissociation and by freezeout at 19 K, respectively. The DCO+ region is bounded by the temperature range 19–21 K. Bottom: the column density of HCO+ and its isotopologues (colored lines), with the 19 K CO snowline indicated by the thick dark gray dashed line. The broad plateau of the DCO+ column density from ~110–150 AU explains the ring morphology seen in line emission. The 3σ line sensitivities (from Sect. 3.2) are shown with the horizontal gray lines.

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