Parker et al 1998

From Tauwiki

[edit] Science Ideas

1. Table 1 of UIT Observations of LMC give a comprehensive list of HII regions(by Davis et al 1976) and OB Associations (by Lucke and Hodge 1970), useful for analysis.

1. B1 (λeff = 1521A,λpeak = 1443A,δλ = 354A)and B5 λeff = 1615A,λpeak = 1518A,δλ = 225A ).

The transmission curve of the B5 filter is similar to that of the B1 filter on the long wavelength side of the peak but does not go to as short wavelengths as the B1 filter, thereby acting as an airglow suppressing filter. The B5 filter was used when observations were made on the dayside of the orbit, and the B1 filter was used for nightside observations.

Objective is to find the O stars, using UV photometry, which discriminates between the temperatures of the hottest stars better than visible photometry but also potentially provides data on hundreds or thousands of stars in the time it takes to get a classification spectrum of a single star.

1. UV photometry of 37,333 stars, table 2.

1. Catalog of Magellanic cloud HII regions compiled by Davis, Elliott, and Meaburn 1976 is called DEM regions.

1. Kennicutt and Hodge 1986 have published H_alpha fluxes for many DEM regions, and Parker et al them with FUV fluxes measured in UIT images over apertures of equal sizes. (section 4).

1. in Figure 16,they present the plot of the H_alpha flux to FUV observations and modeled fluxes for DEM regions. Following paras are their discussions based on that figure.

We calculated the ratio of the total stellar flux to the integrated aperture flux for our FUV images. The median values of the flux ratios are 0.72 and 0.78 for the B1 and B5 filters, respectively, i.e., about one-quarter of the total FUV flux in a region typically comes from diffuse FUV light. However, note that quite a few regions have flux ratios very close to unity within the errors, indicating very little contribution from diffuse FUV light in those instances. Sources for the diffuse FUV flux could be either scattered light or the light from a population of stars fainter than our PSF photometry limit.

If the light is from faint stars, then the fact that some of the DEM regions have stellar-to-integrated flux ratios close to unity would imply that some regions do not have significant populations of such fainter (lower mass) stars. However, there is no obvious correlation in Figure 16 between brightness of the region and the flux ratio, which argues against the diffuse flux's being due to a constant spatial distribution of faint stars. It also means that the brighter (presumably more active and populous) regions do not have proportionately greater or fewer faint, unresolved stars, e.g., there is not a low-mass cutoff or increase in the star formation activity within the detection limits of the diffuse flux. Cornett et al. (1997) found ratios for the stellar to integrated flux in the SMC somewhat lower than we found in these LMC regions and argued that dust-scattered radiation is a major contributor to the diffuse flux.

[edit] Data

1. UIT data for LMC, Mosaic for Various regions in LMC