What are partially voiced stops (as in Danish)?

Question

In researching the Danish language, I've read about a series of stops [b̥ d̥ ɡ̊]. What are those? Apparently they are different from the commonplace voiced stops [b d ɡ] and the voiceless stops [p t k] because analysts have gone to the effort of using a voiced letter with a voiceless diacritic. What phenomenon does this represent; some sort of partial voicing?

Danish also has a contrasting series of stops, which at least one source analyzes as [b̥ʰ ɡ̊ʰ] (I'm leaving out the third member because it's different and out of the scope of this question). What are those? How can a partially voiced stop be aspirated? I thought only voiceless stops could be aspirated.

Note: This is not a question about the behavior of Danish stop phonemes. This question is from a purely phonetic standpoint. I'm trying to figure out what sounds these symbols represent, in general and/or specifically in Danish: [b̥ d̥ ɡ̊ b̥ʰ ɡ̊ʰ]

Answer 1

Danish has no voiced plosives but two series of voiceless plosives, aspirated and unaspirated. These are typically transcribed with <p, t, k; b, d, ɡ> rather than the more phonetically representative <pʰ, tʰ, kʰ; p, t, k>, and even when phonetic precision is called for, with <pʰ, tˢ, kʰ; b̥, d̥, ɡ̊> or <b̥ʰ, d̥ˢ, ɡ̊ʰ; b̥, d̥, ɡ̊>.

This is purely conventional; the ring diacritic means they are voiceless, not partially voiceless. I don't know if some realizations of these phonemes may in fact be partially voiceless, but even if so, that's not what is symbolized by the diacritic.

This is because pretty much all modern linguistic description of Danish is influenced, directly or indirectly, by the work of Otto Jespersen (1860–1943), who put forth a transcription scheme called Dania, first presented in 1890, which preserved greater correspondence with Danish orthography than with the IPA, which was still in early development.

Dania-influenced IPA transcriptions, like the one used in Den Danske Ordbog, also differ from impressionistic (language-independent) IPA in vowel symbols, with <e> representing a sound more like [ɪ], <æ> representing a sound more like [ɛ], and so on.

Comparisons of Dania, its derivations, and IPA transcriptions with various degrees of narrowness can be found in Hans Basbøll's The Phonology of Danish (2005, OUP), Appendix 1, and on Wikipedia.