WebChaSeR

If you do not wish to install ChaSeR, data may still be obtained through WebChaSeR, a web version of ChaSeR. While it has the same search capabilities as ChaSeR, it is not possible to select individual files for download. Using this interface, you can only select complete packages of primary and secondary products; see the "Select" step for information on the different packages.

Due to the slightly different functionality, portions of this thread - mainly the Three Steps to Using ChaSeR section - do not apply to users of WebChaSeR. The two applications are similar enough, however, that the thread may serve as a helpful guide.

1. Browse

Chandra Archive data may be browsed using any of the fields in the ChaSeR GUI, such as Instrument, Grating, ObsID, and Category. Since we are interested in an ACIS-I observation of G21.5-0.9, leave only the appropriate Instrument (ACIS-I) and Grating (NONE) options checked and enter the Target Name.

Figure 2 shows the completed form.

Figure 2: The complete form to search for ACIS-I observations of G21.5-0.9

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Figure 2: The complete form to search for ACIS-I observations of G21.5-0.9

Click the "Submit" button to enter the request.

2. Select

The Search Results window brings up all the observations that match our search criteria, as shown in Figure 3.

Figure 3: The Search Results window for ACIS-I observations of G21.5-0.9

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Figure 3: The Search Results window for ACIS-I observations of G21.5-0.9

Search results may be sorted by the "Order By..." menu.

The "Order By..." menu can be used to sort the results; here we have ordered them by "Observation ID."

Click on ObsID 1843 to highlight the row. After doing so one may:

• Use the "Detail" button to display specifics about the observation (Figure 4).

  Figure 4: Details of the observation

  

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  Figure 4: Details of the observation

  Use the "Save" button to write this information to a text file.

• Click on the "Images" button to see preview images; Figure 5.

  Figure 5: Preview images of the observation

  

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  Figure 5: Preview images of the observation

  Cycle through the available images with the "Prev Image" and "Next Image" buttons.

• Write the table information to a file ("Save").

Now the desired data products may be selected for download using the "Select primary products", "Select secondary products", and "Select supporting products" buttons.

The data products are arranged such that the products necessary for most analyses (e.g. the CIAO threads) are in the primary directory. If you are interested in reprocessing your data, you will also need the level 1 files, which are in the secondary directory. Each of the threads also includes a list of the files needed to complete it.

By default, all primary and secondary products are pre-selected. If you are only interested in downloading the specific files need for a thread, but need some help determing what those are, check the Standard Data Distribution Contents webpage. These tables list the file extensions (aka "Type") and the "Content"; the content keyword is how the products are labeled in the ChaSeR interface.

The selections are submitted using the "Add to retrieval list" button. You can then highlight a different observation and add the same (or different) data products to the cart for it. Once you have selected all the data you are interested in, proceed to the next step.

3. Retrieve

Click on "View retrieval list" to view the observations and data products submitted for selection (Figure 6).

Figure 6: The retrieval list

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Figure 6: The retrieval list

Since all the primary and secondary products were selected for retrieval, only the categories are listed. If specific files are chosen, they are listed individually.

One may see the list of data filenames and sizes (Figure 7) by clicking on the "Browse selected products" button.

Figure 7: Browse Results window

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Figure 7: Browse Results window

The total file size of the package is listed at the top of the screen. Use this information to make sure there is sufficient disk space to download and unpack the data.

The "Retrieve selected products" button is used to start the retrieval process. The files are compiled into a tarred package which is placed onto the anonymous FTP server (cda.harvard.edu) by default; the tarfile can also be saved directly to a local disk. When the download is complete, the ChaSeR window will look as shown in Figure 8. Note that the location of the logfile (chaser.log) and the FTP directory in which the tarfile was placed are given at the bottom of the GUI.

Figure 8: Completed download screen

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Figure 8: Completed download screen

When the download has completed, the location of the logfile (chaser.log) and the FTP directory in which the tarfile was placed are displayed at the bottom of the GUI.

The name and location of the tarfile is recorded in chaser.log, along with the ObsID that was downloaded:

unix% cat /export/chaser.log
[09/01/2008 14:55:46:310 EST]  Request retrieval of 1843
[09/01/2008 14:55:46:366 EST]  File(s) package_146_080109145545.tar.* will be available at cda.harvard.edu:/pub/srftp/I6bjzJSZ