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On the spectra of unbounded subnormal operators. (English) Zbl 0647.47036

A well-known theorem of Putnam [Trans. Am. Math. Soc. 119, 509-523 (1965; Zbl 0138.079)] asserts that the spectrum of the real part of a bounded Hilbert space hyponormal operator is precisely the projection of the spectrum of the operator onto the real line.
In the first part of the present paper the authors give an elementary proof of this theorem for bounded subnormal operators. Then they show that the result can be extended to the class of unbounded subnormal operators with bounded real parts.
Reviewer: Mircea Martin

MSC:

47B20 Subnormal operators, hyponormal operators, etc.

Citations:

Zbl 0138.079
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