Bloomington musician David Wierhake plays music he composed for "Our Dad is in Atlantis," currently at the Phoenix Theatre. (Provided by Phoenix Theatre)

He lives with an actress in Bloomington, but David Wierhake says his "main squeeze" at the moment is a diamond-studded accordion called Monterrey.

Decked out in his western shirt and white cowboy hat, the gray-bearded musician seems inseparable from his squeezebox in "Our Dad is in Atlantis," a coming-of-age immigration play at the Phoenix Theatre.

Wierhake is not only an accordionist, but a composer who wrote the incidental music that he performs in "Our Dad," Javier Malpica's 75-minute drama about two Mexican brothers who are essentially dumped with various relatives. The boys wonder what happened to their father, who has crossed into the United States, presumably to find work. Eventually, they consider following him.

The 56-year-old Wierhake has been on a long journey of his own, a musical venture that began with playing tuba in his high school band in a small town in Missouri. Through the years, he developed varying degrees of proficiency on drums, keyboards, guitar and accordion. His family moved to Southern Indiana when his father got a job there, and Wierhake ended up on recordings with John Mellencamp and Carrie Newcomer.

In 2005, Wierhake also began performing in the theater. He has been in three plays at Indiana Repertory Theatre, and recently won overlapping roles at the Phoenix and Stage One, Louisville's professional theater for young audiences.

While the Phoenix was preparing to open "Our Dad," he was also performing at Stage One. Through mid-May, he played Israel Hands, "a bad pirate who gets shot and killed" in "Treasure Island: The Adventures of Jim Hawkins."

For "Our Dad," which is performed either in English or Spanish, Wierhake's music serves several purposes. He takes center stage during some scene changes. He sets moods ranging from uneventful to dangerous. At one point, the accordion even plays a character, an obnoxious cousin, who hollers in a dentist's office.

Wierhake said his research for "Our Dad is in Atlantis" involved listening to lots of "Tex-Mex" music. Based on what he heard, he chose to use his new Monterrey, distributed by the Italo-American Accordion Co. of Illinois.

Wierhake performs his compositions live as he conceived them, but he also improvises.

"It's pretty organic. I've come up with tunes that are loosely written, but never really written down. They're in my head. There won't be anything left after the show is over."

Our Dad is in Atlantis

When: Through June 8.

Location: Phoenix Theatre, 749 N. Park Ave.

Tickets: $15-$25.

Info: (317) 635-7529, www.phoenixtheatre.org