1995A&A...303..211P

We have investigated the association of the massive, evolved WO star Sand 4 (WR 102) with the peculiar diffuse nebula G2.4+1.4 in which it is embedded. Long slit spectra at four different positions were used to study many regions of the nebula and to derive their physical parameters. From the Hα/Hβ ratio a mean E_B–V=1.25 is derived, with regions of enhanced reddening around Sand 4, and, possibly, at the NE knot of the nebula. We find that the electron density varies from less than 100 to 900cm^–2. The ionization largely changes from one region to another, reaching a maximum at the bright arc north of Sand 4. Regions of strong He II λ468.6 emission are found to the east and 4" west of Sand 4. Some of the knots of which the nebula is composed appear overabundant in He, with He/H up to >0.2. Two regions of the nebula present a marked nitrogen anomaly. We suggest that some regions of the nebula, to the NE and to the west might be the shock front which should have been generated by enhanced mass loss during a previous LBV phase of the star, which is presently forming a partially hidden ring-like structure. The variable helium and nitrogen enrichment of the nebula is tentatively linked with the evolutionary history of Sand 4, in the framework of the present-day evolutionary models of very high mass stars. We also suggest that the successive mass loss phases of the central star are associated with an evolutionary path in the He/H, N⁺/S⁺ diagram. The final fate of Sand 4 should be a type Ib supernova, embedded in a ring-like nebular structure, such as that observed in the Kepler SNR.