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Next: On the Origin of Up: Discussion Previous: Global Properties of Sources

Notes on Individual Sources

Below, comments are given on each of the detections that were reported in Tables 2 through 4 and shown in Figures 3 through 6.

S1 - Figure 3a - One of the more easily discernible stars detected. It is easy to see that the He II emission is coincident with a bright continuum point source.

S2 - Figure 3b - This star is to the West of SSC A. The star is blended with SSC A due to the use of the IRAF magnify command. However, it is the brightest of the WR stellar candidates.

S3 - Figure 3c - A star due North of SSC A whose He II emission is the lowest of the WR candidates. The reason for this low amount of emission might be because the internal reddening around this star is larger than the average intrinsic reddening in NGC 1569.

S4 - Figure 3d - Again, another WR star that is close to SSC A and has a low He II emission compared to the other candidates. The arguments for S3 can be applied here.

S5 - Figure 4a - A WR star that is Northeast of SSC A. The He II emission is coincident with the bright point source underneath.

S6 - Figure 4b - This He II source is close to the star and is probably associated with it given the errors in image shifting and rotating. It is the only WR star close to SSC B. The He II emission is comparable to Galactic and LMC WR stars.

S7 - Figure 4c - The WR star found spectroscopically by Drissen & Roy (1994). It is at the larger, brighter source of continuum light in the F555W image. As was stated in their article, the ring nebula was probably the result of the stellar wind from the WR star and its progenitor. There are other point sources inside the bubble which could be associated with the nebula as well and therefore, helped to contribute to the shell's expansion.

C1 - Figure 5a - A cluster within the large H II region West of SSC A. The cluster has two distinct portions. The Southern part has the associated He II emission, and the Northern portion contains several red stars. It is impossible to know whether they are associated or coincident. Recall that KS97 have spectra showing nebular He II over this region. Therefore, we conclude that C1's He II emission is primarily nebular in origin covering an area of 0.0794 arcsec$^2$, but there could be WR stars lost in KS97's spectra due to continuum dilution. However, if we assume that all the emission is due to WR stars, the number of WNL equivalent stars (using 1.7$\times $ 10$^{36}$ ergs s$^{-1}$ for the He II flux of an average WNL star from Vacca & Conti 1992) is three. This is cluster 10 in [Hunter et al.(2000)] and our M$_{F555W}$ magnitude agrees with theirs given the uncertainties in both measurements.

C2 - Figure 5b - A cluster lying Southwest of SSC A. This also has the separation between red stars and He II emission. The red stars are found at the center of the cluster while the brightest He II is at its Eastern edge. The He II emission is equivalent to four WNLs and has an area of 0.0893 arcsec$^2$. Also, the colors of the system (and C1) are predominantly influenced by red stars. This is cluster 13 in [Hunter et al.(2000)] and our M$_{F555W}$ magnitude agrees with theirs given the uncertainties in both measurements.

C3 - Figure 5c - Another cluster where the strongest continuum source is a ``hole" in the He II image signifying red stars. The peak of He II emission is found to the Northeast of the brightest continuum pixel and has an area of 0.0496 arcsec$^2$. Also, there is a slight rise in the [O III] flux near the peak He II and gives strong evidence for a nebular origin. KS97's spectra also cover this region which they find only nebular emission. However, if one assumes that all the emission is from WR stars and using the same average emission of a WNL star, the number of WNL equivalents is two. This is not classified as a detected cluster in [Hunter et al.(2000)].

C4 - Figure 5d - SSC A. González-Delgado et al. (1997) report the finding of 25-40 WNL equivalent stars in SSC A. However, if one uses our numbers and assumes that all the emission is from WR stars, the number of WNL equivalents is $\sim$50. This number is larger than their estimate and suggests that there is some nebular component (with a maximum area of 0.823 arcsec$^2$) that we cannot separate in this study. However, continuum dilution of the broad $\lambda4686$ emission line might be a problem in the González-Delgado et al. (1997) spectra. Thus, the number must be somewhere between the two numbers, probably nearer their estimate. This is cluster A in [Hunter et al.(2000)] and our M$_{F555W}$ magnitude agrees with theirs given the uncertainties in both measurements.

C5 - Figure 5e - A cluster on the very edge of the starburst and may not be a part of the starburst which created SSC A and its surroundings. Interestingly, this cluster has no red stellar population within or near it. It is the only cluster like this and is far removed from the other four clusters. If one assumes that all the He II emission is from WR stars, the number of WNL equivalent stars is three, similar in number to C1-C3. However, the area of emission is much smaller at 0.0298 arcsec$^2$. This is cluster 39 in [Hunter et al.(2000)] and our M$_{F555W}$ magnitude agrees with theirs given the uncertainties in both measurements.

U1 - Figure 6a - The banana-shaped contour is where the maximum level of emission is. It is on the Southern edge of SSC A and is South of S2. The emission is probably nebular in origin with an area of 0.00992 arcsec$^2$, but the He II emission is similar to the average He II emission of Galactic or LMC WR stars.

U2 - Figure 6b - The cluster to the North (V = 18.1; B-V = 0.63) of U2 has a large population of red stars. Thus, this He II emission might be related to the group of stars just like the situation in the clusters. Therefore, it is possible that one WR star is adjacent to the cluster. However, since no star is seen its nebular origin is more realistic (with an area of 0.0198 arcsec$^2$).

U3 - Figure 6c - The circular point source is surrounded by three bright clusters. No stellar point sources are found between the three. The emission is most probably nebular in origin, but could be a WR star since the He II emission is comparable to the average He II emission of Galactic or LMC WR stars.


next up previous
Next: On the Origin of Up: Discussion Previous: Global Properties of Sources
Patrick Shopbell 2000-09-20