COMPTEL limits on 26Al 1.809 MeV line emission from gamma^2 Velorum

TL;DR

This study uses COMPTEL gamma-ray observations to set upper limits on 26Al emission from gamma^2 Vel, refining nucleosynthesis models for Wolf-Rayet stars based on new distance measurements.

Contribution

The paper provides the first gamma-ray flux upper limit for 26Al from gamma^2 Vel using updated distance data, constraining nucleosynthesis yields in Wolf-Rayet stars.

Findings

Upper limit of 1.1 x 10^{-5} ph cm^{-2} s^{-1} for 26Al emission from gamma^2 Vel.

Estimated 26Al yield of (6.3^{+2.1}_{-1.4}) x 10^{-5} solar masses.

Implications for Wolf-Rayet star nucleosynthesis models.

Abstract

The Wolf-Rayet binary system gamma^2 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 gamma^2 Vel. We derive an upper 1.8 MeV flux limit of 1.1 10^{-5} ph cm^{-2} s^{-1} (2 \sigma) for the WR star. With the new distance estimate, COMPTEL measurements place a limit of (6.3^{+2.1}_{-1.4}) 10^{-5} M_\odot the 26Al yield of gamma^2 Vel, thus constrains theories of nucleosynthesis in Wolf-Rayet stars. We discuss the implications in the context of the binary nature of gamma^2 Vel and present a new interpretation of the IRAS Vela shell.