Estimate of the Total Number of Wolf-Rayet Stars in NGC 1569

It was unlikely that we detected all WR stars within NGC 1569, since many are ``blurred" into SSC A, and this method principally detects WN stars. We derived a total number of detected Wolf-Rayet stars from our data to be 51$\pm$19. This was primarily based on the equivalent number of WNL stars in the C sources. For deriving the minimum number of WR stars in NGC 1569, we assumed that all He II emission in the C sources was nebular unless previously identified as due to WR stars. Then, we took the minimum number of equivalent WNL stars of SSC A (25; González-Delgado et al. 1997) and the individual WR stars found in this paper (7). For the maximum number of WR stars in NGC 1569, we assumed that all He II emission in the C sources was due to WR stars. Because we did not know exactly what type of WR stars produce the He II emission, we determined the equivalent number of WNL stars within each cluster. The total flux of a C source was converted to a luminosity, divided by the average He II luminosity of a WNL star (using 1.7$\times$10$^{36}$ ergs s$^{-1}$ from Vacca & Conti 1992), and the number (truncated to an integer) gave the equivalent number of WNL stars for that C source. This was discussed in Section 4.2, which gave the equivalent number of WNL stars for each C source. Thus, we took the maximum number of equivalent WNL stars of SSC A (50; this paper), the equivalent number of WNL stars in the other C sources (12) and the individual WR stars (7) to arrive at our detected number and range.

If we assume that all the nebular He II is produced from the ionizing continua of massive stars, then we can estimate the total number of WR stars in NGC 1569. Using the values of I(He II 4686)/I(H$\beta$) from KS97 along with the updated Figure 9 from [Schaerer(2000)], we can determine the total number of stars. In the last section, we discussed a probable age of the clusters as 3-4 Myr. Over this age range, the ratio of WNL/Total WR stars is 0.65$\pm$0.35. Dividing the number of detected WR stars by this percentage gives us an indication of the total number of WR stars within NGC 1569. Within roughly a factor of two, the total number of WR stars in NGC 1569 comes out to be 78$\pm$51. The updated figures of [Schaerer & Vacca(1998)] were corrected for an error in the normalization of the fluxes from WR atmosphere models. Using the old Figure 9 of [Schaerer & Vacca(1998)], the ratio of WNL/Total WR stars was 0.3$\pm$0.3 which gave an estimated total WR number of 160$\pm$60. This amount of WR stars is similar to the number of observed WR stars in the LMC. Whereas, the updated model gives a total number closer to the detected amount.