# ζ Pup: XMM RGS line-profile analysis

## Ne X Lyman-α at 12.134 A

We fit only the RGS2 data (there is very little RGS1 data, due to a camera failure -- the effects of including that additional data are shown in our archive of previous fits).

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

#### Non-porous: RGS2

This fit is formally pretty good (chi-sq = 24 for 15 d.o.f).

Compare these results to the analogous model fit to the same line in the Chandra spectrum. There is quite good agreement (*taustar* values disagree by only about 10%, well within the formal confidence limit range). The same is true for R_{o}, while the normalizations disagree by about 2-sigma.

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_{*}.

####
aniso-porous: RGS2, *h*_{inf} free

Note that despite the fact that the terminal porosity length's best-fit value is found to be zero (1e-7 or so, actually), the best-fit model parameters are not identical to the non-porous fit. They are very close, of course, but the small differences are probably due to the numerical integration that's required in the aniso case. Note that the 68% upper confidence limit on *h*_{inf} is 0.28, and that enables larger values of *taustar*, and smaller values of *R*_{o}, apparently.

Now, a sequence of fits with fixed *h*_{inf} values of 0.5, 1, 2, and 5.

####
aniso-porous: RGS2, *h*_{inf} = 0.5

####
aniso-porous: RGS2, *h*_{inf} = 1

####
aniso-porous: RGS2, *h*_{inf} = 2

####
aniso-porous: RGS2, *h*_{inf} = 5

#### Summarizing

The effect of porosity and the tradeoff between porosity length and optical depth can be summarized by looking at the joint parameter confidence limits. We show the 68%, 95%, and 99% limits below. The best-fit model is the filled circle.

Now, we'll look at models with *isotropic* porosity.

####
iso-porous: RGS2, *h*_{inf} free

Note poorly constrained *h*_{inf} and *taustar*.

Now, a sequence of fits with fixed *h*_{inf} values of 0.5, 1, 2, and 5.

####
iso-porous: RGS2, *h*_{inf} = 0.5

####
iso-porous: RGS2, *h*_{inf} = 1

**Note**: with *h*_{inf} = 1, *taustar* has increased by 33 percent.

####
iso-porous: RGS2, *h*_{inf} = 2

####
iso-porous: RGS2, *h*_{inf} = 5

#### Summarizing

We show the 68%, 95%, and 99% limits below. The best-fit model is the filled circle.

And here is an extensive log of all these xspec fits.

*last modified*: 10 May 2012