Establish whether extreme HCO+ abundances occur in unresolved astrophysical regions

Determine whether HCO+ abundances as high as approximately 10^-4 occur in localized astrophysical environments and remain unresolved in current observations, or whether such predictions instead result from gaps in the chemical understanding of HCO+.

Background

The models predict extreme HCO+ abundances only for specific combinations of high temperature, density, and cosmic-ray ionization rate, particularly in shocked and protostellar gas. Such regions may be short-lived or spatially localized, so their emission could be diluted by larger volumes of gas with ordinary HCO+ abundances when measured over a telescope beam or line of sight.

The authors therefore identify an unresolved observational and chemical question: whether the predicted extreme abundances genuinely occur in astrophysical environments but have not been spatially resolved, or whether they reflect incompleteness or inaccuracies in current HCO+ chemical networks.

References

This raises the question of whether such extreme abundances occur in astrophysical environments but remain observationally unresolved, or whether they instead reflect gaps in the current understanding of the chemistry of \ch{HCO+}.

— The curious case of HCO$^+$: Extreme abundances under extreme conditions  (2608.21138 - Dutkowska et al., 21 Aug 2026) in Section 4, subsection “Chemical uncertainties and observational considerations”

This raises the question of why such enhanced \ch{HCO+} abundances have not yet been reported in environments where the required physical conditions are expected to occur.

— The curious case of HCO$^+$: Extreme abundances under extreme conditions  (2608.21138 - Dutkowska et al., 21 Aug 2026) in Section 4, subsection “Chemical uncertainties and observational considerations”