# ζ Pup: XMM RGS line-profile analysis

### O VIII at 18.969 A

For this line we use both the RGS1 and RGS2 data, and as with the other lines, we do not allow *shift* to be a free parameter.

First we repeat the non-porous fit shown on the main page.

#### Non-porous: RGS1+2

This fit is quite poor, again, with systematic errors likely dominating. And it looks like there are systematic shifts between the two datasets. We explored this in the previous set of fits. Summarizing those experiments, fitting only the RGS2 data yields a formally acceptable fit, with a somewhat lower *taustar*.

You can compare these results to the same sort of model fit to the *Chandra* spectrum. The results are similar.

Next, we'll fit models with *anisotropic porosity* assuming flattened, radially oriented clumps. We use the "stretch" porosity length distribution, h(r), parameterized by *h*_{inf}. We will fit first with *h*_{inf} a free parameter, and then at fixed values of *h*_{inf} = 0.5, 1, 2, and 5 R_{*}.

We cannot calculate formal confidence limits on the model parameters because the best-fit is not acceptably good.

####
aniso-porous: RGS1+2, *h*_{inf} free

We find a best-fit *h*_{inf} = 0 and so recover the non-porous fit. So we don't bother showing it here.

####
aniso-porous: RGS1+2, *h*_{inf} = 0.5

####
aniso-porous: RGS1+2, *h*_{inf} = 1

####
aniso-porous: RGS1+2, *h*_{inf} = 2

####
aniso-porous: RGS1+2, *h*_{inf} = 5

Now for models with *isotropic* porosity.

####
iso-porous: RGS1+2, *h*_{inf} free

####
iso-porous: RGS1+2, *h*_{inf} = 0.5

####
iso-porous: RGS1+2, *h*_{inf} = 1

**Note**: with *h*_{inf} = 1, *taustar* has increased by 39 percent.

####
iso-porous: RGS1+2, *h*_{inf} = 2

####
iso-porous: RGS1+2, *h*_{inf} = 5

*last modified*: 16 May 2012