How do I download data from Spitzer?

Downloading data: the basics, and generic instructions

The Spitzer Heritage Archive (SHA) is the permanent home for all of the data collected during the Spitzer mission, plus all the documentation you need to understand it all. The SHA will eventually be formally part of IRSA's archive holdings. Right now (as of May 2010), the SHA is still being developed, though it is quite operational now. If you get started using it now, you may be able to influence some of the features that are incorporated! Right now, it contains most of the cryogenic Spitzer data.

The SHA is a web-based interface to the Spitzer archive, and it lives here: http://irsa.ipac.caltech.edu/applications/Spitzer/SHA/ Because it is web-based,

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 Spot and Leopard are both pretty powerful visualization tools, allowing you to do much more than just download Spitzer data (see "questions to think about" below!).  

All of Spitzer's operations (planning, scheduling, processing) are centered around Astronomical Observation Requests (AORs). Observer name, date of observation, object or area of the sky observed, and instrument used (IRAC, MIPS, or IRS) are part of the AOR. Since most observations are made at multiple wavelengths, the observations taken in response to the AOR consists of a "package" of images of a target made at different wavelengths or what Spitzer calls channels. At least at this time, you can only download entire AORs at a time -- there is no way to download just part of an AOR.

1. Start up Leopard. Go grab the software and install it if you need to. (The software package is called "Spitzer Pride", as in "a group of cats" -- Spot the cheetah and Leopard. Spot is used for observation planning, and Leopard is used for downloading data.)

2. Go up to the "query" menu in the upper left of the window and search by position or program id or observer to obtain whatever data you want. For example, if you are part of the IC2118 Research Program, you would want to retrieve data for programs 235 and 266. Since the team was not interested in getting IR spectra, the program has just IRAC and MIPS data available for download. Below is an example of what a Leopard query based on observer name (Tim Spuck) will produce.

3. Find the AOR you want in the list of returned AORs. Select it by clicking the box to the left of the Programs you are interested in and press "OK".

Types of Data you can Download

BCD – or Basic Calibrated Data are data that have gone through some very basic automated processing. These data are individual frames from the observation, and are in FITS format. They have been flux and/or wavelength (if appropriate) calibrated, flat-fielded, and some limited cosmetic restoration (e.g., cosmic-ray removal) has been applied. The spatial 'world' coordinates are derived from telescope pointing information only.

PBCD – or post-Basic Calibrated Data are data that has gone through much more processing. These data are the result of combining all individual BCD frames from a single AOR; the product is an averaged and registered single image suitable for photometric measurements, and with first order removal of seams between the component images. The post-BCD mosaics are calibrated in MJy/ster. The post-BCD products are delivered to the observer in the form of a single FITS image file per AOR. In other words, post-BCD data is the finished product. (Caveat: For some specific situations -- usually found in IRAC observations over a large area -- the specific observing strategy may instead result in many small mosaics rather than one big one.)

(Wondering what is FITS format?)

4. Select the wavelengths you want, and the kind of data you want. Click on the little diskette icon to begin the download. It will launch something called the "Subscriber" to manage the download. Important!: If you just want the mosaics, just choose the Post-BCD data to download. (If you want to reprocess the data from the beginning, or combine data from more than one AOR, you'll need the BCDs, but this is really not for the faint-of-heart.)

5. Wait for the download to finish. The Leopard subscriber is smart enough to pick up where it leaves of if there is a network hiccup mid-transfer.

6. Unzip the files that Leopard puts on your disk. On Windows or Macs, you should be able to simply double-click on the zip file to make it work. On a linux machine (or from a Mac terminal), this will also work: "unzip P00235-_IRAC_map.zip" etc. for the other files you have downloaded.

7. What are all these files? This is the real thing, not sugar-coated for the average John Q. Public -- it's giving you all of the things you might need as a professional astronomer. So, you need to learn a little about how this works in order to decipher what you've downloaded:

• Cheatsheet for just the post-BCD stuff:
  • *maic.fits = the mosaic (MosAIC), e.g., what you are really looking for (probably!)
  • *munc.fits = the errors (UNCertanties) on the fluxes in the mosaic (should be larger on the edges, for example)
  • *mcov.fits = the coverage (COVerage), e.g., how many frames were taken over each part of the sky. That way, you can see where on the edges we have only one frame
  • *maics.fits = for IRAC only, mosaic of just the short exposures (we get a short and a long for each position)
  • *muncs.fits = for IRAC only, the errors (UNCertanties) on the fluxes in the mosaic of just the short exposures
  • *mcovs.fits = for IRAC only, the coverage of just the short; ought to be identical to the long coverage map.
  • *mfilt.fits = for MIPS-70 only, the mosaic of the filtered data (trying to get rid of instrumental artifacts)
  • *mfunc.fits = for MIPS-70 only, the errors (UNCertanties) on the fluxes in the filtered mosaic.
  • *mfcov.fits = for MIPS-70 only, the coverage in the filtered mosaic; ought to be the same as the original (unfiltered) coverage map.

Visualize AOR using Leopard (optional but useful if truly new at this)

The point of this is to see specifically where the telescope will be/was pointed for a given observation. If you have an observation that is a big mosaic, you can see where each individual pointing fell. This helps you understand why you have so many files when you download Spitzer data.

1. From Leopard's main window, select an AOR.
2. Under the Images menu, choose ISSA, and select a 5 degree image in the wavelength of your choice (25, 60, 100, 160 microns).
3. Under the Overlays menu, choose "AORs on image." (5th from the bottom on the Overlays menu.) Depending on your wavelength, each colored box may result in one or two data frames, each of which is a file you get from Leopard, as well as scads of associated files for each of those frames! (Note that there are lots of other overlay options to explore, and we encourage you to do so, but if you want to see where your observations fall on the sky, you need to pick "AORs on image.")

There is more information on visualization in the Spot and Leopard User's Guides.

Downloading Data: How can I find already-reduced Spitzer data?

Including polished mosaics and source lists!

Downloading Data: How can I find any prior observations for an object?

Has a particular target ever been observed with any of Spitzer's instruments? Or, would this target be a good proposal for a new project?

Downloading Data: How can I quickly get a mosaic of my object?

Get me a mosaic, quick! Don't bother me with preambles or complete explanations, I just want a picture. (Also see What is a mosaic and why should I care?)

Downloading Data: I need the image as a FITS file, how can I get this?

OK, I'm ready for a real fits file that doesn't have any losses due to compression.

Downloading Data: What should I do if there is more than one mosaic of the same object?

What to do if there is more than one imaging observation of your favorite target. Includes an example for finding the best possible image of a target, M16. If you have more than one image of a target that you need to combine, this naturally leads into mosaicking. An example is given for the ONC, including a link explaining how to combine (mosaic) the images.

Downloading Data: How can I get a spectrum of my object?

Spitzer is more than just imaging -- IRS and MIPS take spectra as well as images.

Downloading Data: I'm ready to advance to a highly technical and in-depth discussion on downloading Spitzer data.

This tells you how to start from the same place professional astronomers do. You will have to learn how to mosaic frames using the Spitzer tools developed for professional astronomers by the Spitzer Science Center. This needs a lot of disk space, and, well, a little bit of courage! And access to IDL would help a lot.

Questions to think about and things to try with Spot/Leopard

• This item is easiest to do with Leopard. Pick an object to search on, anything you want.
  • Which program(s) (if any) have observations? With which instruments?
  • Who requested the observations? (bonus: What are they investigating?)
  • Has Spitzer observed it yet?
  • When are the data going to be available to download? If they are available, download the post-BCD mosaics.
• Try the questions on this page using Spitzer data for the three color planes.
• This item can be done with Spot or Leopard, perhaps slightly easier with Spot than Leopard. You might find it useful to consult "Using Spot to get data from other wavelengths". For a given object, whether or not you can find Spitzer data, find images of the object from another mission or survey, in another (non-Spitzer) wavelength.
  • What wavelength(s) did you pick?
  • What features are more apparent in the other wavelength compared to Spitzer? Are there other differences?
• This item can be done with Spot or Leopard, perhaps slightly easier with Spot than Leopard. For a given object, on top of one of those images of an object from another mission or survey, pick a catalog (such as IRAS) to overlay on the image. Figure out how to just have it show the brightest or just the faintest things. Warning: if you choose to overlay the 2mass catalog over a large region, you will be waiting for several minutes while the computer renders many 1000s of points.
  • What other catalog(s) at what other wavelength(s) did you pick?
  • Were there a lot of sources in the region you picked, in the catalog you picked? Why? (You may wish to pick another catalog for comparison.)

Come up with your own answers and then discuss downloading data.

Possibly useful resources

• Leopard pocket guide
• Spot pocket guide
• Leopard User's Guide
• Spot User's Guide