**5. Nebula**

The presence of forbidden lines [N II] 6548, 6584; [O III] 4959, 5007; [Fe III] 4658, 4701, 5270 and [Ar III] 7136 in the spectrum of GR 290 indicates that it has a nebula, but it is not resolved in direct imaging because of the large distance to M33. In 2005, Fabrika et al. [5] first attempted to detect the nebula and study its spatial structure using the panoramic (3D) spectroscopic data acquired on Russian 6-m telescope, and reported the discovery of an extended structure in the velocity field of H*β* line, with an angular extent of ∼ 9 (∼ 30 pc) in the NE-SW direction. An excess corresponding to the dust circumstellar envelope around the object has not been detected in the infrared (IR) emission [9].

Maryeva et al. [22] performed a modeling of circumstellar nebula using using CLOUDY photoionisation code [55,56] and the spectrum acquired on GTC/OSIRIS in order to reproduce the observed nebular emission lines that are clearly seen in the spectrum. GR 290 was found to be surrounded by an unresolved compact H II region with a most probable outer radius R = 0.8 pc and a hydrogen density *nH* = 160 cm<sup>−</sup>3, and having chemical abundances that are consistent with those derived from the stellar wind lines. Hence, this compact H II region appears to be largely composed of material ejected from the star.

In addition, the recent analysis of the 2D spectra obtained with GTC/OSIRIS in September 2018 perpendicular to the dispersion at H*α* line indicates that the nebula has extended and asymmetric structure [23]. Its size is about 25–30 pc, similar to typical H II regions around O-stars. Based on the similarity of sizes and evolutionary status of GR 290, we speculate that this extended nebula consists of material ejected during O-supergiant phase.
