There is a thesis ( in Rom. Lang.) on
http://www.iatp.md/dava/vinerean_9/vinerean_9.html
which sustains that the vowels "ã"(&) and "â" (1) in Rom are the
unrounded variants of "o" and "u".
Unfortunately the author does not say anything about some other
posiblities about obtaining this "ã" and "â" he just mention that if one
prounces "o", if this one will un-round the lips one will get an "ã" and
if one say "u" and will un-round the lips one will get this "â".
Letting by side the etymological proof, I am interested ybout how one
see the way to obtain these "â" and "ã" in other way as unrounding the
"o" and "u"; the way how the author explained it o > ã and u > â appears
very credible to me since if one indeed unround the lips , one will get
these results.
Alex