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IRSA Frequently Asked Questions

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For Astronomers

What kinds of data are available at IRSA?

IRSA is chartered to curate the calibrated science products from NASA's infrared and sub-millimeter missions. We offer access to digital archives through powerful query engines, including VO-compliant interfaces, and offers unique tools such as the recently modernized IRAS scan processing tool Scanpi. IRSA exploits a re-useable architecture to deploy cost-effective archives for customers, including: the Spitzer Space Telescope; the 2MASS and IRAS all-sky surveys; and multi-mission datasets such as COSMOS. In the near future, IRSA will serve public data from the WISE all-sky survey and the Planck mission

IRSA also offers value-added data sets, for which we are not the primary curator, but for which there is an additional value, such as having the ability to retrieve other IRSA data, and having it in the same, standard format. These data sets include USNO-B, DENIS and SDSS, among others.

For more information, see the Mission Summary page. More detailed information on specific holdings is available are available on IRSA's holdings index (divided by data type): catalogs, images, and spectra.


Which infrared telescopes have looked at my favorite source?

To find data for a specific target in IRSA, use the data discovery service ("RADAR"). RADAR searches all science data products across all IRSA's data sets based on a target name (e.g., M31) or coordinates (e.g., 17h44m34s -27d59m13s).


How do I access data in the Infrared Science Archive?

There are two primary means for retrieving data from the archive:

From IRSA's top navigation bar, select Missions to view a list of all missions that have data served by IRSA. The associated search tools for specific data sets will be pre-populated with mission search parameters.

IRSA has various search services that are applicable to multiple missions:


Catalog Search searches all source catalogs served by IRSA. Basic Catalog Search, which is accessed from a different page, provides quick access to IRSA's popular catalogs with simplified search options.

Finder Chart is a visualization tool that displays an image of a region of the sky at various wavelengths and epochs.

Cutouts: Returns small "cutouts" of a user-specified size of image data sets archived at IRSA. Images are provided in FITS and JPEG formats.

What format are IRSA data files in?

Images are generally provided as FITS files, with W3C-compliant header information, and are compatible with any FITS viewer. Quicklook previews of spectra or images are often also presented as JPEGs, viewable with any picture viewer or Web browser.

IRSA catalogs and spectra are usually served in (ASCII) text files in IPAC table format.

For more information about using and troubleshooting tables with IRSA services, see Why am I having trouble uploading my table? in this FAQ.


How can I get a bigger 2MASS image?

IRSA currently serves 2MASS FITS images with a maximum size (1024 arcseconds square) set by the original observations.

The Montage astronomical image mosaic engine provides the capability to combine 2MASS FITS images to produce an output mosaic. Montage offers an online service that returns mosaics from three large-survey data sets: 2MASS, SDSS and DSS. The mosaics are currently limited in size to 2 square degrees. The Montage code is available for download from the project web page. The code is written in C and runs from the command line on all common Unix platforms, including Linux, Solaris, Mac OS X, and IBM AIX. Montage was funded by the NASA Earth Sciences Technology Office (ESTO) Compute Technologies (CT) program, and the NSF National Virtual Observatory.


Can I download an entire mission dataset in IRSA's holdings?

IRSA does not provide the ability to download entire datasets for all its mission holdings. Some datasets are available for bulk download via ftp. The IRAS catalogs are also available for direct download. Additional mission datasets are in preparation, and will be available soon.

For datasets not prepared for bulk download, some mission data may have small enough volume that it is straight-forward to download using IRSA's program interface. In other cases, however, IRSA's holdings are too large to support bulk download of the entire thing without negatively impacting the bandwidth for other users. In such cases, please contact us directly.


How can I download large portions of a catalog?

To download a large portion of a catalog (for example, the entire sky more than ten degrees from the Galactic plane), use the Polygon search option in IRSA's Catalog Search service. In many cases, such as the example, you will need to define several areas both in order to cover the desired area and to ensure that the output files are under the 1 GB file size limit. If you choose to script such queries (see below), please take care to have no more than four queries running at one time in order to avoid impacting other users.

Some catalogs are available for direct download.

How do I download data from IRSA on the command line?

Many IRSA services can be accessed via an HTTP GET/POST program interface. The request is typically a set of "parameter=value" pairs, and the return is an XML document containing links to the requested data. Specifically, the following individual services support program-friendly interfaces:

Catalog Search (Guide) Search IRSA's catalog holdings
IRSA Image Server Direct download of images and image cutouts
2MASS Image Inventory Service 2MASS image access
Finder Chart Obtain 2MASS, DSS, and SDSS image cutouts
Atlas Image queries for a variety of individual data sets
Cutouts Image cutouts for a variety of individual data sets
Spitzer Heritage Archive Program Interface Access the Spitzer Heritage Archive
Dust Extinction Compute interstellar reddening using IRSA's DUST service
Spitzer Post-BCD products Search Spitzer post-BCD data products
SWAS Spectrum Service Search SWAS spectra
IRAS scan processing tool, SCANPI View, plot, and average IRAS survey scans

Furthermore, many IRSA services will return a command-line script (using the wget implementation of HTTP GET/POST) to repeat the query just performed.


How do I do an HTTP GET/POST command?

A commonly used program for HTTP GET/POST commands is wget, and it may be used with any of IRSA's services. For download instructions, see the IRSA wget help document. For examples of using wget with IRSA's Catalog Search service, see the Gator Program Interface Guide.


How do I acknowledge data obtained from IRSA?

If you use IRSA in your research, please include the following acknowledgement in your paper:

"This research has made use of the NASA/IPAC Infrared Science Archive, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration."

Please include also in your paper acknowledgements requested by individual missions and data providers.


What are data tags and how do I use them?

Data tags are strings of specific single object search queries that can be used as citations in scientific papers, journal articles, and other publications. Readers may use the tag to run the same query and view the results. Data tags are automatically returned by most queries to IRSA services.

To run a search query using a data tag, go to the Data Tag service home page, enter the search string into the Input Data Tag field, and click Submit.

To create a data tag for your own paper or article, run your query on an IRSA data retrieval service (such as Catalog Search), then look for the data tag string on the results page, usually preceded with any of the following text:

Please note that data tags are not available for queries using the table-upload/Multi-Object Search option.

IRSA services that provide data tags include:

Additional documentation can be found in the instructions for using data tags


Where do I find the documentation for a catalog?

Catalog documentation can be found on the column descriptions page for each catalog. Detailed documentation for the data set will be linked from that page. To access the column descriptions page, click on any column name on the Gator query page for that catalog, or on a search results page click on any column name other than clon, clat, dist, angle, or columns from your table upload search (ending in _u on the search results page). Documentation for IRSA-created output columns such as clon, clat, dist, and angle is provided here.


How do I cross-correlate two catalogs?

Currently, this process is performed manually by following these steps:

  1. Find and download the smaller of the two catalogs, using a service such as Catalog Search.
  2. Using the Table Upload/Multi-Object Search option, upload the catalog you just downloaded back into Catalog Search for the second catalog. Do not change the table format, which should be in IPAC Table format format with RA and Dec in the header row.
  3. Choose a search radius consistent with the kind of data being searched, based on the estimated spatial resolution and pointing uncertainty of the two data sets.
    Note: Large search radii tend to result in multiple matches.
  4. Run your query on the second catalog.

IMPORTANT: Data sets can have varying spatial resolutions, resulting in multiple cross-matches. Also, depending on the catalog size, the job could take several minutes (or more) to process.


Where can I find images for my presentation?

Depending on your specific needs, there are a few places you can view and download presentation-quality images.

The Featured Images Gallery is a gallery of all images featured on IRSA's home page.

Several 2MASS images are available in the following online galleries:

Lastly, the Cool Cosmos educational site has a nice collection of images from various missions:


Why am I having trouble uploading my table?

The table upload option, or "Multi-Object Search", allow the user to search for multiple targets in a single query. However, in order for IRSA's services to work, the table must be properly formatted. All IRSA services with the table-upload option will accept IPAC Table Format, with position specified using decimal degrees in J2000.

In general, IRSA services will accept some or all of the following formats:

Not all IRSA services accept all formats, however. In particular, the Catalog Search service accepts only the standard IPAC Table with J2000 decimal degrees, and requires that the filename and column names comply with the DBMS constraints.

Here are a few resources for validating and troubleshooting tables:

The Table Upload Help page is a general document describing which table formats work with IRSA's services, best practices for successful table upload, and troubleshooting tips.

The Table Check Service will tell you whether your table will be interpreted correctly by an IRSA service. It will also reformat and validate the table to ensure it complies with specific formatting rules. The reformatted table can then be downloaded as an ASCII or VO-table file and uploaded to the specific IRSA service.

The Table Converter Service converts a table from IPAC ASCII table format to a table with user-specified delimiter (such as a comma or tab). Users can download converted tables and use them in conjunction with other software.


How can a project contribute data to the archive?

IRSA is interested in expanding the archive with user-contributed data sets. If you have data that would benefit the infrared and sub-millimeter astronomical community, please contact IRSA through the Helpdesk form, and a member of the science staff will contact you.

To learn more about IRSA's quality standards for its ingested data, as well as links to data formatting and validation tools, please read the Data Quality Assurance page.


What is the observation date for a particular IRAS image?

Due to the nature of the IRAS detectors and observing strategy, the concept of "observation date" isn't at all simple like it would be for most other telescopes (space or ground based). IRAS observed each point on the sky multiple times, and the scans were later combined and used to generate the 2D images served by IRSA. Since the individual scans were taken over a span of months, there isn't a sensible "observation date" that applies to the image products, short of simply using the year (1983). This is all explained in detail in the IRAS Explanatory Supplement, particularly chapters IIIC and VG.


For Teachers

Where can I find teaching resources for my high school or college course?

IRSA is part of a larger consortium of projects called the Infrared Processing and Analysis Center, or IPAC. The IPAC Web site contains several online educational resources for teachers and students, particularly the Cool Cosmos site.

Additionally, IRSA is a co-sponsor of the NASA-IPAC Teacher Archive Research Program (NITARP). NITARP provides a unique opportunity for groups of (primarily) high school teachers and students, with the help of a mentor astronomer, to have an authentic astronomy research experience via working with professional astronomical data and tools. The research team completes the data analysis, and presents their findings to others throughout the scientific community. The teachers are also expected to give presentations at relevant teachers' conferences. The program accepts applications annually in the Fall.

For more information, please see the program's overview site.

The working wiki for the program also provides some insight into the teams' activities, and collects some of the materials developed as part of the program: http://coolwiki.ipac.caltech.edu.


Pictures

Where can I find pictures?

There are several places to look at pictures in IRSA. The first place to look is our Featured Images page. The WISE and Spitzer archives display image previews as you browse the data. Just put in your favorite object name, such as M31 or Crab Nebula, for example. Tutorials on using the WISE Image Archive and Spitzer Heritage Archive (video) are available.

If you're interested in a larger selection of pictures without the need to search by object name, coordinates, etc., the Featured Images are drawn from press releases, many more of which can be found at the following locations:
Infrared Legacy Gallery
IPAC Missions Gallery
WISE Image Gallery