COMPTEL limits on 26Al 1.809 MeV line emission from gamma² Velorum

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The Wolf-Rayet binary system gamma² Vel (WR 11 is the closest known Wolf-Rayet (WR) star. Recently, its distance has been redetermined by parallax measurements with the HIPPARCOS astrometric satellite yielding 258⁺⁴¹₋₃₁ pc, significantly lower than previous estimates (300 -- 450 pc). Wolf-Rayet stars have been proposed as a major source of the Galactic 26Al observed at 1.809 MeV. The gamma-ray telescope COMPTEL has previously reported 1.8 MeV emission from the Vela region, yet located closer to the Galactic plane than the position of gamma² Vel. We derive an upper 1.8 MeV flux limit of 1.1 10⁻⁵ ph cm⁻² s⁻¹ (2 σ) for the WR star. With the new distance estimate, COMPTEL measurements place a limit of (6.3⁺².¹₋₁.₄) 10⁻⁵ M the 26Al yield of gamma² Vel, thus constrains theories of nucleosynthesis in Wolf-Rayet stars. We discuss the implications in the context of the binary nature of gamma² Vel and present a new interpretation of the IRAS Vela shell.