Compare Line Profiles from 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
Observation ID
RA
Declination
Observer
Program Title

For the purposes of this thread, let us suppose we want to compare the Fe XVII emission lines for three T Tauri stars observed with HETG: SU Aur, Speedy Mic, and TV Crt. On the search page input "T Tauri" as the "Object Class" and "Normal Stars and WD" as the "Science Category." Clicking on "Search" will query the database and return all observations that match these criteria. Alternatively, you may simply click "Search" with all fields left blank and select the desired observations from the entire catalog.

Selecting Observations

The search from the previous section will return a listing of over ten observations of T Tauri stars, ordered by spectral type. These query results are linked to additional data regarding the observation and targets. Clicking on the Observation ID brings up data on the instrumental configuration of Chandra for the observation. Similarly, the observer name links to a publication by the PI (or to the proposal abstract if no publications are available). The spectral type displays plots and data of the X-ray hardness and quantiles of the observation. Finally, the target 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 SU Aur (ObsID 3755), Speedy Mic (ObsIDs 2536 and 3491), and TV Crt (ObsID 3728) 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 "3755 - SU AUR." For "Target 2" and "Target 3" we select "2536 - SPEEDY MIC" and "3728 - TV CRT," respectively. In the option boxes for "Grating Arm" and "Order," we can choose any one of 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 for each target.

2. Select Spectral Lines

When creating spectral line comparisons, leave all fields under "Option B" blank and proceed to "Option C." Only the HETG (or LETG) spectra can be used to create line profile comparison plots; to examine specific lines in the predicted low-resolution ACIS data, use "Option B" to select the dataset and desired plot range around the line of interest.

Under "Option C," using any five of the six drop-down boxes provided, we select the Fe XVII lines at 15.01, 15.26, 16.78, 17.05, and 17.10 Å.

3. Select Plot Units

We can create line profile comparison plots in units of:

counts s^-1 Å^-1 vs. Å
counts s^-1 Å^-1 vs. Å
counts s^-1 bin^-1 vs. Å
counts s^-1 keV^-1 vs. keV
counts s^-1 Å^-1 vs. Doppler velocity (km s^-1)

For this demo, we will leave the units in counts/s/Å vs. Å.

4. Specify Plot Range and Resolution

We can set the output plot range by specifying the distance from line center we wish to view. The default is 0.5 Å, but we will set it to 0.25 Å.

We can also set the resolution of the output plots, in pixels, but the plotting routine will calculate appropriate dimensions if these fields are left blank.

After all the desired parameters have been set, click "Generate Plots" to produce the specified plots.

Output Plots and Data Products

1. Plots

The line profile comparison 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.