#
CEN1B: *Chandra* grating spectrum

The data shown here are from James MacArthur's first extraction (9 July 2009), using Pat Broos's software, and carefully separating the dispersed spectra of the two components (A + B), using narrower than usual extraction apertures. The exposure time in 149.0 ks.

The Chandra observing proposal has some background information.

**Component B** - whose data are shown here - is the somewhat brighter source to the NE. This is a quick and dirty presentation and analysis of the data, showing the entire MEG and HEG (first order, coadded -1 and +1) spectra, and Gaussian fits to one line and one line complex. There are 3525 MEG counts and 1899 HEG counts in the first order spectra.

Component A is shown here.

## The HETGS spectra

**HEG**

Note that the light, vertical lines are the wavelengths of emission lines seen in the Chandra spectrum of DoAr 21.

I fit a one temperature *bapec***wabs* model to these data. The fit was not good. The best-fit parameters of interest were kT = 10.9 keV; sigma = 859 km/s; N_H = 0.43 X 10^{22} (seems lower than it should be).

### 6.182 Angstroms: Si XIV Ly-alpha

These data were fit with a *wgauss* + *powerlaw* model. The MEG and HEG data were fit simultaneously. The dashed vertical line is the rest wavelength of the line, and the two dotted vertical lines represent Doppler shifts of +/- 3000 km/s (arbitrarily; we don't know the wind properties of this star or stars).

This fit is acceptable. It has a best-fit σ = 1420 km/s. Very broad. I fit the nearby continuum first.

### 6.7 Angstroms: Si XIII helium-like res., int., for.

These data were fit with a *hegauss* + *powerlaw* model. The MEG and HEG data were fit simultaneously.

This fit is statistically good. It has a best-fit R = f/i = 20 (upper boundary for the program - so basically the upper limit is unconstrained - the intercombination line strength is consistent with zero - probably a problem with blending and modeling the continuum; the lower 68% confidence limit is R = 5 and the 95% limit is R = 2). G = (f+i)/r = 0.97, and the line width σ = 1275 km/s.

*last modified*: 10 July 2009