This is the 4824th most frequent Russian word.
известными
Well-known.
The word 'известными' is an instrumental plural form used here to describe the attribute of the musicians.
Известными являются музыканты этого оркестра.
The musicians of this orchestra are well-known.
The word 'известными' serves as a predicate adjective in the instrumental case, indicating the result of becoming famous.
Эти художники стали известными благодаря своим уникальным картинам.
These artists became famous because of their unique paintings.
Here, 'известными' is an instrumental plural adjective describing the alumni and expresses their quality or state.