1 Introduction

The star was discovered by Merrill & Burwell (1933) who mention its spectrum as "pec''. In the notes they add that "the bright lines are extraordinarily intense and include forbidden lines of ionized iron as in eta Car. The nebular line $\lambda$ 4658 also is bright''. Allen (1973) detected a large infrared excess. No radio flux was measurable by Sistla & Seung (1975); Altenhoff et al. (1976), Woodsworth & Hughes (1977) neither at 10.7 GHz, nor at 5 GHz. Ciatti et al. (1974) and Leibowitz (1977) gave detailed descriptions of the spectrum.

Ciatti et al. (1974) mention strong lines of Balmer and Paschen series, OI 8446 (much stronger than $\lambda$7774 and the Paschen lines), permitted and forbidden lines of Fe II, [O I] 6300, [S II] 4068. Strong emissions of He I of the triplet system ($\lambda\lambda$4026, 4120, 4471, 5876, 7065, 10830) and of the singlet ($\lambda$4387, 6678) and of Ca II (M.2) are also observed, as well as [O II] 7318-30, [Fe III] and [N II] (5755 and faint 6584). They also suggest that the spectrum of a late type companion (type M) might be present.

Leibowitz (1977) analysed low dispersion spectra in the range 3600-8500 and provided a list of line identifications which include besides the elements noted by Ciatti et al. (1974) a number of other elements. He estimates the type of the underlying star as O 9-9.5.

The star was also observed by Andrillat & Swings (1976) in the 7500-12000 region but at rather low dispersion.

An analysis of the H$\alpha$ width by Swings & Andrillat (1981) lead to the following values: H$\alpha$ 240 km$\,$s^-1, wings up to 2000 km$\,$s^-1; [N II] 210 and 300 km$\,$s^-1 respectively.

The star was also observed spectrophotometrically by Swings (1981) who found strong emissions of P7, H$\alpha$, H$\beta$ and H$\gamma$, as well as of Fe II 9277 and [S III] 9069.

Gravina (1982) observed the star at 93 Å/mm at H$\gamma$ and found variations in the different emission features over four nights which can be up to a factor of five. Martel & Gravina (1985a) observed the star again in 1985 and found V= 11.66, B-V =+0.42 and U-B=-0.20. They also analyzed the emission line spectrum the same year (Martel & Gravina 1985b) and found among the emissions present [Fe III] 4658 and [O III] 5007. Strafella et al. (1987) found in the K band a variability of more than one magnitude. Allen & Swings (1976) showed that the star had an important infrared excess.

Finally Thé et al. (1994) classified the star as B[e].