While the IPA chart lists it as a fully open vowel, the rounded equivalent of [a], Ladefoged[3] characterizes it as near-open, the rounded equivalent of [æ].
It occurs allophonically in Weert Limburgish[5] as well as in some speakers of Danish[6] and Swedish.[7] Certain transcriptions of Danish use ⟨ɶ⟩ to denote an open-mid front rounded vowel [œ].[6]
In Maastrichtian Limburgish, the vowel transcribed with ⟨ɶː⟩ in the Mestreechter Taol dictionary is phonetically near-open central [ɐ̹ː]. It is a phonological open-mid front rounded vowel, the long counterpart of /œ/.[8]
Riad (2014) reports that [ɶː] in Stockholm Swedish is sometimes difficult to distinguish from [ɒː], which is the main realization of the /ɑː/ phoneme, a sign that both vowels are phonetically very close.[7]
Features
Its vowel height is open, also known as low, which means the tongue is positioned far from the roof of the mouth – that is, low in the mouth.
Its vowel backness is front, which means the tongue is positioned forward in the mouth without creating a constriction that would be classified as a consonant. Rounded front vowels are often centralized, which means that often they are in fact near-front.
It is rounded, which means that the lips are rounded rather than spread or relaxed.
Near-open;[9] allophone of /ø/ between /ʁ/ and /v/ as well as an allophone of /œ/ between /ʁ/ and a nasal.[10] Other speakers pronounce it the same as [œ].[6] See Danish phonology
Riad, Tomas (2014), The Phonology of Swedish, Oxford University Press, ISBN978-0-19-954357-1
Traunmüller, Hartmut (1982), "Vokalismus in der westniederösterreichischen Mundart.", Zeitschrift für Dialektologie und Linguistik, 2: 289–333
Wells, J. C. (1975), "The Association's Alphabet", Journal of the International Phonetic Association, 5 (2): 52–58, JSTOR44525810, p. 52: Although it may seldom or never be needed for phonemic transcription, I feel that for completeness' sake, and to fill an awkward gap in our vowel chart, we should recognize this symbol for an open front rounded vowel.