Mr Titterton is chairman of the Omega Ensemble but has been the group’s official page turner for the past four years. His job is to sit beside the pianist and turn the pages of the score so the musician doesn’t have to break the flow of sound by doing it themselves. He said he became just as nervous as those playing instruments on stage.

上面一段摘自2021年新高考英语全国卷I的阅读理解B。请问文中的 chairman 前加可以加定冠词吗？我知道，chairman 前面的定冠词通常省略，但这里在 chairman 后面有 of 短语修饰啊，应该是特指吧？这样的定冠词也可以省略吗？