Phonologically, the syllable is /aum/, which is regularly monophthongised
https://en.wikipedia.org/wiki/Monophthong to [õː] in Sanskrit
https://en.wikipedia.org/wiki/Sanskrit_phonology. It is sometimes also written
with pluti https://en.wikipedia.org/wiki/Pluti, as o3m (ओ३म्), notably by Arya
Samaj https://en.wikipedia.org/wiki/Arya_Samaj. When occurring within a
Sanskrit utterance, the syllable is subject to the normal rules of sandhi
https://en.wikipedia.org/wiki/Sandhi in Sanskrit grammar
https://en.wikipedia.org/wiki/Sanskrit_grammar, however with the additional
peculiarity that after preceding a or ā, the au of aum does not form vriddhi
https://en.wikipedia.org/wiki/Vriddhi (au) but guna
https://en.wikipedia.org/wiki/Guna (o) per Pāṇini
https://en.wikipedia.org/wiki/P%C4%81%E1%B9%87ini 6.1.95 (i.e. 'om').
