Astron. Astrophys. 338, L91-L94 (1998)

3. The spectra

Table 2 shows the observed line fluxes and the equivalent widths of the identified lines. The spectra of SPH 2 show the main nitrogen lines characterizing a WN star. We can observe the presence of N IV 4057 Å and N V 4603,4610 Å lines used for WN classification, as well as the strong C IV at 5808 Å line characteristic of WC spectra. As opposed to what is expected for a WN star, the N III at 4640 Å line is absent. Smith et al. (1996) propose a three-dimensional classification for WN stars using the He II 5411/He I 5875 ratio as a primary indicator of ionization. In general, the presence of hydrogen is indicated by an oscillating Pickering decrement. Based on this criteria, SPH 2, is classified as a WN4 with no hydrogen.

Table 2. Observed emission line fluxes relative to and equivalent widths.

In Schwartz et al., 1990, is mentioned that the area of Canis Majoris some stars are close to a dark cloud in Puppis, and also SPH 2. The fact that we see the diffuse absorption bands at 4430 Å and 6284 Å is an indication that this star suffers from strong interstellar extinction. The flux distribution, as given in Figs. 1 and 2, shows that SPH 2 is heavily dust reddened. In order to estimate the magnitude of the extinction we used the statistical relations between equivalent widths and color excess for the absorptions at 4430 Å and 6284 Å, (4430 Å)2.5 E(B-V) and (6284 Å)1.4 E(B-V) (Schmidt-Kaler, 1982). From the equivalent widths of these two lines, given in Table 1, we obtained an E(B-V), respectively, of 1.2 and 2.1.

Other absorption features also observed in our spectra are the interstellar lines of Ca II H and K at 3889 Å and 3933 Å and Na I around 5900 Å. The spectrum between 5000 Å and 7500 Å presents the telluric absorption band of O₂ at 6870 Å.

© European Southern Observatory (ESO) 1998

Online publication: September 17, 1998
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