Compare the High-Resolution HETG Spectra of Three Sources

Searching the Database

The X-Atlas Search Page offers the capability to search the atlas on a variety of observation and target parameters, such as:

Target Name
Spectral Type
Object Type
Science Category
Right Ascension and Declination (cone search)
Observation ID (ObsID)
Sequence Number
Observer
Project Title
Observation Date
Public Date

Results may be sorted by:

Spectral Type
Target Name
Observation Date
ObsID
RA
Declination
Observer
Program Title

For the purposes of this thread, let us suppose we want to compare the HETG observations of three OB supergiants in the Orion constellation: Delta Ori, Zeta Ori, and Epsilon Ori. Use the drop-down "Science Category" box on the search page to select "Normal Stars and WD." In the "Target Name" text box, input "Ori." Finally, select "HETG" from the "Gratings" drop-down box and click "Search." This will query the database and return all observations that match the search terms. Alternatively, you may click "Search" with no search terms specified and select the desired observations from the entire catalog.

Selecting Observations

The search from the previous section will return a list of at least 30 stars. The query results are linked to additional data regarding the observation and targets within the observation that have been extracted for X-Atlas. Clicking on the ObsID brings up data on the instrumental configuration of Chandra for the observation. Similarly, the observer name links to any publications associated with the ObsID. The spectral type displays plots and data of the X-ray hardness and quantiles of the observation. Finally, the object name brings up additional target and observation information about and analyses of the object, including previews plots of the HETG spectra, a preview of the zeroth-order image, hardness ratios, quantiles, and other spectral metrics, spectral fits of the zeroth-order spectrum and the predicted low-resolution ACIS-S and ACIS-I spectra, light curves, and a variability analysis.

For this example, we will select all observations of Delta Ori (ObsID 639), Zeta Ori (ObsIDs 610 and 1524), and Epsilon Ori (ObsID 3753) for comparison. Click the checkboxes in the far left column of the search result table and click "Select Observation(s) for Plotting."

The Plotting Interface

The observations selected from the previous page will appear along with an interface for plotting the spectra from each observation.

1. Select Targets

First, we will select the targets we wish to plot. From the drop-down box to the right of "Target 1," we select "639 - Delta Ori." For "Target 2" and "Target 3" we select "610 - Zeta Ori" and "3753 - Epsilon Ori," respectively. In the option boxes for "Grating Arm" and "Order," we can choose the coadded 1^st, 2^nd, or 3^rd order HEG or MEG spectra. For this example, we will select the 1^st order MEG spectra for each target.

2. Select Datasets

We now proceed to the options listed below "Option B: Customize the output plots." Leave all fields under options "A" or "C" blank or set to the default value. For now, we will only plot the high-resolution HETG spectra for the targets we have selected (this should be selected as the default). The other available datasets include the predicted ACIS-S, ACIS-I, and HETG/ACIS-S zeroth-order spectra and the extracted zeroth-order spectrum.

3. Select Plot Units

Next, we can select the plot units of the output spectral plots. For this demo, we will leave the units in counts/s/Å vs. Å, but we can also choose to view plots of the counts spectra in their original binning, in units of energy. The adaptively-smoothed flux spectra are also available for plotting.

4. Specify Plot Range and Resolution

Finally, we can set the output plot range and resolution. If we want to simply bring up a pre-produced plot of each target, we can choose a plot range from the appropriate drop-down box. If we simply click "Generate Plots," we will use the default plot range (30 Å or the maximum wavelength range, whichever is smaller). However, if we want to examine a specific spectral region, then we input the appropriate wavelengths (in Å) in the "Low Bound" and "High Bound" text boxes. We can also set the resolution of the output plots, in pixels. When customizing the output plots, make sure that all fields under plotting options "A" and "B" are left blank or set to the default.

Output Plots and Data Products

1. Plots

The customized output plots automatically include identifications of key X-ray emission lines. The plots are available for download in GIF and postscript formats.

2. Spectral Data

The high-resolution HETG spectra for each observation are made available in FITS and text format. Included in each file for an observation are the high-resolution HEG and MEG spectra, the extracted zeroth-order spectrum, and the predicted ACIS-S, ACIS-I, and zeroth-order spectra. The entire spectral range is offered for each dataset, regardless of whether only a subset of the spectrum was selected for plotting.

The HEG and MEG spectra are also offered in Pulse Height Amplitude (PHA) format, along with the appropriate gARFs.