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STEREO/SECCHI L4/L5 campaign

During 2009, the STEREO spacecraft will periodically be making 180-degree rolls so that the heliospheric imager ("HI") instrument can observe the L4 and L5 Lagrange points. The hope is that we may be able to discover objects in the HI images that are clustering at these gravitationally stable points in space. You can read more about this campaign in press releases here and here.

animation of asteroids     The animation here (click for a larger version) illustrates how these asteroids might cluster at the L4/L5 points. It is actually showing the motions of Hilda and Trojan asteroids corotating with Jupiter. These asteroids cluster around Jupiter's L4 and L5 Lagrange points, entirely analagous to what we would predict at the Earth's L4 and L5.

This animation was created by Prof. Aldo Vitagliano using his free N-Body simulation software, SOLEX.

Getting the Data

As with all of our data, the images we take during this campaign will be freely distributed online as soon as we have processed them. The only difference will be that we will not be producing "pretty" versions of them. You will need to download the "FITS" images and play with them yourselves. You can get the files at the STEREO Science Center where you will follow the link to "Instrument Data Archived at SSC" and locate the "img" data for "secchi" (spacecraft "a" or "b"). Alternatively, for convenience, the appropriate data sets are available below as ZIP files:
Each of these zip files contains the FITS data files for the period during which the spacecraft were rolled to point the HI instruments at L4/L5. As future spacecraft rolls occur, the sets will be zipped and added to the above list. Note that as of late August 2009, the STEREO spacecraft have actually entered the L4 and L5 Lagrange points and so will no longer be performing 180-degree rolls to observe these regions.

There are several techniques for playing with the FITS files to make them "prettier", but often a simple median filter and rescaling will enhance the images significantly. You could also try subtracting a simple 'background model' made by taking the minimum value of a stack of all the images. A previous news article on this site discussed processing of SOHO/LASCO files. The procedure is similar for SECCHI. Note that it does require limited skills with some kind of image manipulation software (e.g. GIMP, ImageJ, ImageMagick, etc.) For just viewing the 'raw' FITS image, the "DS9" image viewer.

Identifying Objects

If you think you have found an unknown object in one of the L4/L5 campaign images, the process for reporting it is no different to that of any new STEREO/SECCHI object, and is described on the "STEREO Comets" reporting page. We do ask that you first try to verify that the object you are seeing is not a planet (which tend to be very bright), or a star (which all move at the same speed). A typical asteroid will be very small, and will move at a slightly slower or faster rate than background stars, and possibly in a different direction.

So how do you tell if the object you are seeing is a "known" asteroid? Well to help out, the following lists give the name and x,y pixel location of many of the known asteroids that are in the images at that time. Please note the following regarding these lists:
  • Not all potentially visible asteroids are recorded in these lists. Also, not all asteroids in these lists are bright enough to be visible in the images! (We're working on this...) This point is particularly crucial in HI-2 images, which have an enormous field of view but the stars make it very hard to locate faint images. Also, the HI-2B images are slightly 'fuzzy', so you are best to start working with HI-2A first.
  • The x,y coordinates given assume a "(0,0) coordinate origin" in the lower-left corner of the image. If your software has (0,0) in the upper-left corner, you will need to subtract your y-coordinate from 1024.
  • The coordinates listed in HI-A should be accurate to +/- 2 pixels. The coordinates listed in HI-B should be accurate to +/- 7 pixels
  • Coordinates are only given for objects in one of the images taken during the sequence. This image name is located at the top of the file. So the object will have moved location from the positions stated in these lists if you are not using the exact image listed at the top of the file. (They will not have moved very far, however.)

    • Here are the lists: * The positions listed in these files may be a little less accurate than stated. This is because it takes us a little extra time to get perfect image calibrations. The files will be updated in the future to make any necessary minor modifications.

    Further Informations and Resources

    For more information about the SECCHI instrument fields of view, try the SECCHI Instrument Overview page. You can also click here for an image that shows the fields of view of the SECCHI instruments. (Note that the HI instruments will be pointing in a different direction during the L4/L5 Campaign rolls.) Other resource you might find useful are the Heliospheric Imager home page, the STEREO Science Center or the STEREO Home page. The latter has many links to further resources.

    You are welcome to contact the webmaster if you have questions.