By Elijah Bernstein-Cooper, August 19, 2015, 0 comments.

## HI Spectra

Yesterday I fixed a bug in the HI spectra which changed the median HI spectra. You can see the difference between the older post and the newer post. This bug affected only the chosen HI range by a few km/s.

We can check whether or not this has a noticable effect on the derived parameters from the $A_V$ vs. N(HI) relationships for each cloud. Before on the left, and after the bug fix on the right. Planck $A_V$ data was used.

Perseus

Taurus

California

#### Figure 1

Planck $A_V$ vs. N(HI) for each cloud, before on the left, and after the bug fix on the right. The fits between the two are within 10% of each other, except for the polynomial median fit in California. This is because there is one median bin skewed by a small number of points.

And below we show a similar comparison of the Lee+12 IRIS $A_V$ data.

Perseus

#### Figure 2

Lee+12 $A_V$ vs. N(HI) for each cloud, before on the left, and after the bug fix on the right. The fits between the two are within 10% of each other, except for the polynomial median fit in California. This is because there is one median bin skewed by a small number of points.

### Removing an HI background

The experiemnt of removing an HI background based on the fitted components of the spectrum will be affected. To recap, I ran the experiement of subtracting the fitted components in the California median spectrum from Figure 5 from the HI cube. I excluded the fitted component used to calculate the HI width, as this is our presumed cloud of interest. I subtracted these components from every line of sight.

#### Figure 3

Planck $A_V$ vs. N(HI) for California. For ease of comparison the results without any background subtraciton are shown at the bottom right. The component subtraction changed the fitted intercept by 1 mag, however did not change much of the structure in the N(HI) / $A_V$ distribution. The intercept in this experiment with the corrected HI spectra.