5.2 Isophotal Parameters

At the $\mu = 21.85 {^{\rm m} /{\rm arcsec}^{2}}$ isophote in Gunn r we determined the ellipticity, ${\varepsilon_{21.85}}$. JF94 found that ${\varepsilon_{21.85}}$ was better determined than ${\varepsilon_{\rm e}}$ for their data and therefore used ${\varepsilon_{21.85}}$ in their analysis. They also found that ${\varepsilon_{21.85}}$ was close to the maximum ellipticity for disky galaxies for their Coma sample. For disky galaxies, the ellipticity varies substantially with radius, see e.g. the $\varepsilon(r)$ profile for R266 on p. . In Fig.  we compare ${\varepsilon_{21.85}}$ with ${\varepsilon_{\rm e}}$ for the 64 HydraI galaxies in our sample. It is seen that the two ellipticities in most cases agree well, although there is significant intrinsic scatter in the relation. For the analysis of our HydraI data, it will not be important whether we use ${\varepsilon_{\rm e}}$ or ${\varepsilon_{21.85}}$ as measure of the ellipticity. The two very deviating galaxies at ${\varepsilon_{\rm e}}\approx 0.1$ and ${\varepsilon_{21.85}}\approx 0.35$ are R225 and R327, both SB0 galaxies with an ellipticity that varies rapidly with radius. This can be seen from the $\varepsilon(r)$ profiles on p.  and p.  - the two galaxies both have $\log {r_{\rm e}}\approx 1.0$ and $\log r_{21.85} \approx 0.8$ (with r in arcsec).