IRCS/Subaru Observations of Water in the Inner Coma of Comet 73P-B/Schwassmann-Wachmann 3: Spatially Resolved Rotational Temperatures and Ortho-Para Ratios

TL;DR

This study used IRCS/Subaru to observe water in comet 73P-B's inner coma, measuring spatially resolved rotational temperatures and ortho-para ratios, revealing temperature gradients but no change in nuclear spin states.

Contribution

First spatially resolved measurements of water rotational temperatures and ortho-para ratios in comet 73P-B's inner coma using IRCS/Subaru.

Findings

Rotational temperature decreases from ~110 K to ~90 K with distance from nucleus.

No significant variation in water production rate during observations.

Ortho-para ratio remains consistent with statistical equilibrium value of 3.0.

Abstract

Comet 73P-B/Schwassmann-Wachmann 3 was observed with IRCS/Subaru at geocentric distance of 0.074 AU on UT 10 May 2006. Multiple H2O emission lines were detected in non-resonant fluorescence near 2.9 microns. No significant variation in total H2O production rate was found during the (3 hour) duration of our observations. H2O rotational temperatures and ortho-to-para abundance ratios were measured for several positions in the coma. The temperatures extracted from two different time intervals show very similar spatial distributions. For both, the rotational temperature decreased from ~110 K to ~90 K as the projected distance from the nucleus increased from ~5 to ~30 km. We see no evidence for OPR change in the coma. The H2O ortho-para ratio is consistent with the statistical equilibrium value (3.0) for all spatially resolved measurements. This implies a nuclear spin temperature higher than ~ 45 K.