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Radial-velocity variations of the H-alpha emission measured on the steepwings of the H-alpha line, prewhitened for the long-time changes, varyperiodically with a period of (218.025 +/- 0.022)d, confirming the suspectedbinary nature of the bright Be star Pleione, a member of the Pleiades cluster.The orbit seems to have a high eccentricity over 0.7, but we also brieflydiscuss the possibility that the true orbit is circular and that theeccentricity is spurious owing to the phase-dependent effects of thecircumstellar matter. The projected angular separation of the spectroscopicorbit is large enough to allow the detection of the binary with large opticalinterferometers, provided the magnitude difference primary - secondary is nottoo large. Since our data cover the onset of a new shell phase up todevelopment of a metallic shell spectrum, we also briefly discuss the recentlong-term changes. We confirm the formation of a new envelope, coexisting withthe previous one, at the onset of the new shell phase. We find that the fullwidth at half maximum of the H-alpha profile has been decreasing with time forboth envelopes. In this connection, we briefly discuss Hirata's hypothesis ofprecessing gaseous disk and possible alternative scenarios of the observedlong-term changes.

Properties and nature of Be stars: 27. Orbital and recent long-term variations of the Pleiades Be star Pleione = BU Tauri