CHAOS. VI. Direct abundances in NGC 2403

Using the Multi-Object Double Spectrograph on the Large Binocular Telescope, we observe two fields with HII regions that cover an Rg/Re range of 0.18-2.31. Thirty-two HII regions contain at least one auroral line detection, and we detect a total of 122 temperature-sensitive auroral lines.

Here, for the first time, we use the intrinsic scatter in the Te-Te diagrams, added in quadrature to the uncertainty on the measured temperature, to determine the uncertainty on an electron temperature inferred for one ionization zone from a measurement in a different ionization zone. We then use all available temperature data within a HII region to obtain a weighted-average temperature within each ionization zone. We rederive the oxygen abundances of all CHAOS galaxies using this new temperature prioritization method, and we find that the gradients are consistent with the results of a recent study of Berg+ (2020, J/ApJ/893/96).