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

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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 [FORMULA]4057 Å and N V [FORMULA][FORMULA]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 [FORMULA] 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, [FORMULA](4430 Å)[FORMULA]2.5 E(B-V) and [FORMULA](6284 Å)[FORMULA]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.

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© European Southern Observatory (ESO) 1998

Online publication: September 17, 1998