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Queries and Searches

Query Results
Data Products
Cross Correlation
Database Table Information

Queries and Searches

To find all x-ray observations available for 3c273:

  • Start on the main search page.
  • Enter "3c273" in the "Object Name or Coordinates" box.
  • Check the boxes beside the "Recent X-Ray Missions" and "Past X-Ray Missions" sections to select all the x-ray missions.
  • Click "Start Search".

To find all RXTE observations of sco x-1 during January of 1999:

  • Start on the main search page.
  • Enter "sco x-1" in the "Object Name or Coordinates" box.
  • Enter "1999-01-01 .. 1999-01-31" in the "Observation Dates" box.
  • Check the box beside RXTE.
  • Click "Start Search"

To query a list of objects or coordinates:

  • On any form with a "Object Name or Coordinates" entry box, enter all the coordinates and object names with semicolons (;) separating them.

To search by keyword in abstracts:

  • Start on the main search page.
  • Choose one or more missions or tables.
  • Uncheck all table types except "Proposals, abstracts, and schedules".
  • Click "Detail Mission/Catalog Search".
  • If more than one table is found, a page will be displayed where you will need to choose a table. Choose one that mentions abstracts in the name, unless you already know that a table has abstracts.
  • Click "Specify Additional Parameters".
  • A new page is displayed showing all the available columns for the table.
  • Make sure the checkbox in the leftmost column for the abstract row is on.
  • Change the operator to "=" or "!=", and enter a search term in the left text box. You can use '*' or '%' as a multi-character wildcard. There is an automatic wildcard added to the end so you can just enter a partial keyword.
  • Click "Start Search".

To get all rows of a table:

  • (If you want the table in plain text, pipe-delimited format, you can use the simpler method discussed next.)
  • Start on the main search page.
  • Choose one or more missions or tables.
  • Click "Detail Mission/Catalog Search".
  • If more than one table is found, a page will be displayed where you will need to choose tables.
  • Select tables by clicking the checkboxes before each table.
  • Click "Specify Additional Parameters".
  • A new page will be displayed where you could enter parameter search criteria. If you want to get all the rows, don't change any defaults here.
  • Change the "Limit Results to" menu selection to "No Limit" or as many rows as you would like.
  • Click "Start Search".

Store a query in a local file for later use.

  • Submit a query from any of the Search Interfaces
  • If a "Save Query To File" button appears in the "Search Based on" box on the Results page click it. The encoded query string will be saved to your machine.
  • When you want to re-run the query select the "Query File And Session Uploads" button on the Main Search page.
  • Enter the local file name or click the "Browse" button to locate the file.
  • Click on the "Load Query" button

Plot a source location within Chandra ACIS or HRC Field of View

or
  • Enter a source and select the Chandra mission from the Main Search, Keyword Search or Quick Search form.
  • A "F" will be displayed in the Services column of the results table if observation data are available.
  • Click the "F" to display the plot. Here's an example.

Using the Browse Notification Service

This service allows users to be notified when changes (e.g. an observation is scheduled, completed, or archived) occur for a source in selected mission master tables.

  • Go To The Browse Notification Service home page
  • Enter a username and password to create a new account or to access an existing account
  • Make sure your e-mail address is correct
  • enter a source name or position, click on one or more missions and press Submit
  • Repeat as necessary
You'll be notified!

Query Results

To get the query results in a plain text table:

  • If you are on a page where you are entering query parameters, look for an option labeled "Output Format". Change the format to "Text Table" and submit your query.
  • If you are already viewing your results, you can change the display format to a text table by clicking the "Redisplay" button at the top of the results page.

To choose individual columns to be displayed:

  • Start on the main search page.
  • Choose one or more missions or tables.
  • Click "Detail Mission/Catalog Search".
  • If more than one table is found, a page will be displayed where you will need to choose a table. If you choose more than one, you will lose the ability to select which columns will be displayed.
  • Click "Specify Additional Parameters".
  • A new page is displayed showing all the available columns for the table. The first column is a checkbox that determines if the column will be shown.
  • Check or uncheck columns.
  • Set any query parameters you wish.
  • Click "Start Search".

To see all the columns for a row in the results:

  • If you have not yet submitted your query, look for an option labeled "Show All Parameters" and check that box. Then submit the query. All columns will be displayed for all rows in the results.
  • If you are already looking at the results of a query and want to see all the columns for one row, you can do so by clicking the Display all parameters icon.
  • If you are already looking at the results of a query and want to see all the columns for several rows, you can do so by checking the boxes at the beginning of each row of interest, then click the "Display" button after the table.

To download an entire table:

  • Start on the catalog index page.
  • Find the table you are interested in. Click on the link on the number of table rows to download the table in an ascii file.

To plot results:

  • When you are viewing the results of a query, you can plot any numerical column against any other numerical column by clicking on the "Plot" button at the bottom of the table of results. (For this to work, the user needs a Java 1.2 (or higher version) capable browser). Notice that all rows displayed by the user's query are included in the plot - checking or unchecking the checkboxes in a row has no effect.
  • A new page will display with a plot form once the Java applet is loaded.
  • The default mode in this plot form is a scatter plot of ra vs dec; other options include (i) scatter or line plots of all parameters listed in the pull-down x and y parameter menus in either linear or logarithmic scales, (ii) histogram and cumulative histogram plots of the selected x-parameter in either linear or logarithmic scales, and (iii) an Aitoff Projection in Galactic coordinates of the rows. The scatter and line plots and Aitoff Projection options can be used on selected samples of the rows by checking the `Sample data by parameter' checkbox, and selecting a parameter and the desired range of values and/or intervals, e.g., `2 , 4 .. 10' would plot only rows for which the selected parameter had a value of either 2 or in the range from 4 to 10 (notice that the points for the various selection criteria will be plotted in different colors). While non-numerical parameters cannot, of course, be plotted in scatter plots, they can be used as criteria for sample selection, e.g., picking the parameter `status' and entering `Public' in the intervals/value box, would result in a plot not of all the rows but only of that sample of the rows which have a public status.
  • Click "Plot" to plot the selected criteria. To make a hard copy, click the print icon to the right of the plot. Click on "Plot Options Panel" and "Plot Panel" to switch between the plot form and the plot.
  • Plot values can be displayed and downloaded to a local file by clicking the Display/Save Plot Values button.
  • For more sophisticated plotting and/or fitting options than the Browse plotting package can provide, the users should, when making a query, use the `Output Format' option on the `Parameter Search' page to select an appropriate output format for the query results, e.g., choose the `FITS' output format if you intend to use the ftools fv interface, `Excel-compatible' if you plan to use Microsoft Excel, `Pure text' if you plan to use QDP/PLT (this last option will require some text editing of the query results), `VOtable' if you plan to use software that recognizes the Virtual Observatory table format, etc., etc. These output formats can also be selected on the query results page.

Data Products

To get data products:

  • When you are viewing the results of a query, if data products are available they are listed after each results table.
  • Click the checkbox beside each row in the results for which you want data products.
  • Click the "Preview and Retrieve" button to see a list of all the data products available for the selected results rows.
  • A new page will display showing all the available data products.
  • To preview or download individual data products, click on the link to the product's name.
  • To download many or all of the data products, select the products you want by checking the boxes to the left of each one, then click "TAR selected products".
  • A new page will display with a link to your tarfile.
  • If you wish to skip the preview page, you can click the "Retrieve" or "Create Download Script" button on the results page. The "Retrieve" option creates a tar file of all data products for the selected rows. The "Create Download Script" option displays commands that can be used to download individual files.

Generate a script of commands to retrieve data products:

  • Submit a query from any of the Search Interfaces
  • When you are viewing the results of a query, if data products are available they are listed after each results table.
  • Click the checkbox beside each row in the results for which you want data products.
  • Click the "Create Download Script" button to display instructions and commands to download data products.
  • Also displayed is a button to click to create a file of the commands on your local machine.

Cross Correlation

To cross-correlate two tables:

  • Start on the Cross-Correlation page.
  • Choose the primary table.
  • Choose the secondary table.
  • Choose whether to correlate on radius, time, or both, and choose values for radius and time deltas (or leave the default).
  • Click "Begin Search".

To cross-correlate results against another table:

  • When you are viewing the results of a query, you can cross-correlate them with another table by clicking the "Cross-Correlate" button at the bottom of the table of results. All displayed rows are included in the cross-correlation - clicking the checkboxes by each row has no effect.
  • A new page will display - choose the table to correlate with.
  • Choose whether to correlate on radius, time, or both, and choose values for radius and time deltas (or leave the default).
  • Click "Begin Search".

To set up a table cross-correlation:

  • For technical reasons, you should always choose the table with the smaller number of entries in the first table selection box.
    Example, if you want to cross-correlate the Bright Star Catalog (BSC5P) (9110 entries) against the NVSS Source Catalog (1,773,484 entries), you should pick BSC5P as the first table and NVSS as the second table.

  • To estimate a reasonable matching radius, you should study the positional uncertainties (and source sizes if the objects are extended) of entries in both tables using their help documentation,
    e.g., the NVSS documentation can be found at http://heasarc.gsfc.nasa.gov/W3Browse/all/nvss.html.

    In the above example, you would find that typical errors of BSC5P entries are small (<=1" ), whereas the NVSS positions can have errors from several arcseconds to as much as 20" = 0.33', with the majority having errors less than 15" = 0.25'. Thus, a matching radius value of 0.25' would be a reasonable choice for most purposes.

To estimate the number of random matches in a cross-correlation:

  • To estimate the number of random coincidences expected when cross-correlating two tables, you need to know the numbers of entries in both tables, as well as their spatial distribution on the sky. The latter, in many cases, could be roughly assumed to be uniform, but this is not always the case, and you should study the table documentation for any information on this.

  • Using the Bright Star Catalog (BSC5P) and NVSS Source Catalog as an example we find that while the BSC5P entries are spread over the entire 4 pi steradians of the sky (= 41,252.961 square degrees = 1.485107 x 10^8 square arcminutes), the NVSS only covers the 82.1% of the sky North of -40 declination which is easily visible to the VLA. A separate Browse query of the BSC5P table reveals that only 7240 of the 9110 BSC5P entries are in this part of the sky. Thus, when you cross-correlate the BSC5P table against the NVSS table with a 0.25' cross-correlation radius, you are actually searching an area of the sky = 7240 x pi x (0.25)^2 = 1,421.57 square arcminutes. The surface density of NVSS entries is 1,773,484/(0.821 x 1.485107 x 10^8) sources per square arcminute, and thus multiplying the area searched by the latter catalog's surface density, you get 20.7 random matches expected.

    Assuming Poissonian uncertainties, the uncertainty in this estimate is 20.7^0.5 = 4.5, i.e., there are likely 16.2 - 25.2 random matches.

    If you actually perform this particular cross-correlation, you will find that 43 of the BSC5P entries have matches within the cross-correlation radius with 41 NVSS entries, which is a significantly larger number than the expected number of random matches.


Page maintainer: Browse Software Development Team
Last updated: Thursday, 05-Jun-2008 12:15:23 EDT.


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Last modified: Thursday, 05-Jun-2008 12:15:23 EDT

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