Editorial: Seeing that which remains hidden: tracer and proxy species in astrochemistry

1 Background and motivation Molecular abundances are crucial for obtaining information about astronomical objects, spanning from molecular clouds to star-forming regions and planetary atmospheres (Herbst and van Dishoeck, 2009; Tielens, 2013). In this context, the importance of tracers and proxy species is unquestionable. For example, the study of species with distinct isotopic composition (also known as isotopologues), enabling the determination of key isotopic ratios such as D/H or 14N/15N,...