BURR RIDGE, Ill. — In his day job, Kersey H. Antia is a psychologist who specializes in panic disorders. In his private life, Mr. Antia dons a long white robe, slips a veil over his face and goes to work as a Zoroastrian priest, performing rituals passed down through a patrilineal chain of priests stretching back to ancient Persia.

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Sally Ryan for The New York Times

Zoroastrians gathered for an annual fire ceremony last month in Burr Ridge, Ill. A portrait of the Prophet Zarathustra is in the background.

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