Question

ɑ English spa, father, palm, car, heart. Many North-American dialects of English use this pronounciation where other dialects use [ɒ]: lot, hot, bother, not (knwon as the FATHER-BOTHER merger). Some dialects of English use this vowel where other dialects use [æ] (known as the TRAP-BATH split): southern English English /æ/ (and in parts of New England) inconsistently becomes /ɑː/ before /s/, /f/, /θ/ and /n/ or /m/ followed by another consonant: Hence Received Pronunciation (British standard pronunciation) has pass, glass, grass, class with [ɑː] but mass, crass with [æ]. All six words have [æ] and thus rhyme in most American English, Scottish English and northern English English.

Accepted Answer

Open Back Unrounded http://en.wikipedia.org/wiki/Open_back_unrounded_vowel

Symbol	ɑ
Name	Open Back Unrounded
Notes	English spa, father, palm, car, heart. Many North-American dialects of English use this pronounciation where other dialects use [ɒ]: lot, hot, bother, not (knwon as the FATHER-BOTHER merger). Some dialects of English use this vowel where other dialects use [æ] (known as the TRAP-BATH split): southern English English /æ/ (and in parts of New England) inconsistently becomes /ɑː/ before /s/, /f/, /θ/ and /n/ or /m/ followed by another consonant: Hence Received Pronunciation (British standard pronunciation) has pass, glass, grass, class with [ɑː] but mass, crass with [æ]. All six words have [æ] and thus rhyme in most American English, Scottish English and northern English English.
Ref	http://en.wikipedia.org/wiki/Open_back_unrounded_vowel

English Dialects O Ss Ther P H T