Large Magellanic Cloud loop nebulae and their stellar contents

Does the ellipticity of globular clusters correlate with luminosity?

“…Generally it has been accepted that the main cause of the ellipticity of the globular clusters is rotation, even if other processes as interactions with the Galaxy's tidal field or effects of an anisotropic velocity dispersion tensor have been discussed, too. Also part of the flattening of the globulars may be relics of the initial conditions, and it appears tha.t the study of the shapes of the clusters can tell something about cluster formation.Beginning with Shapley and Sawyer (1927b) and Shapley (1930) a number of determinations of axial ratios of globulars of the Milky Way System, the Magellanic Clouds, and M31 using different techniques have been published (Kholopov 1952, 1953, Lindsay 1956, Dickens and Woolley 1967, Kadla et al 1976, 1977, Frenk and Fall 1982, Geyer et al 1983, Spasova and Staneva 1984, Staneva et al 1985, White and Shawl 1987, Lupton 1989, Davoust and Prugniel 1990, D'Onofrio et al 1994). There are many attempts to correlate the ellipticity with other properties of the globular clusters, e.g.…”

“…NGC 6273 = M19 has been omitted because the flatness of this globular is largely affected by interstellar dust in the galactic foreground as has been stated by van den Bergh (1982. The mean error of the absolute magnitude is of the order 0.3 mag, whereas the mean errors of the ellipticities given by Geyer et al (1983) are shown by the bars. A weak relation between E and MV is indicated.…”

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Using the data by Geyer et al (1983) and by White and Shawl (1987) it has been looked for the dependence of the ellipticity of Galactic globular clusters on luminosity. There is evidence that the moderate bright objects are the roundest, while the most luminous as well as the weaker globulars are more flat,tened, on the average.

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“…Because of the expected random distribution of the axial orientations with respect to the line of sight the tentative dependence will not be a sharp relation, rather the data will be continuously distributed between a maximum ellipticity E,,, and t = 0 at a given luminosity. We mainly concentrate on the data by Geyer et al (1983) as well as by White and Shawl (1987). Although the latter authors have shown a satisfying agreement between the axial ratios of the two samples the differences between the data of individual objects are often very large and surpass the given mean errors several times.…”

“…1 the absolute magnitudes taken from Harris (1996) of the nineteen objects examined by Geyer et al (1983) have been drawn versus the measured ellipticity E = 1 -b / a . Herein a is the observed large and b the small…”