![]() ![]() Offline mode (after the observation, with all data files already stored in the disk) PQL can be operated in both near-real time mode (during the observation) and Option available is to select a set of files and request to shift and align them. Sky subtraction looking for the nearest N frames around the selected one. For example, you will be able to select a file,Ĭompute some statistics values (background, FWHM, min, max, …) or ask for the In addition, PQL allows you to execute manually in an interactive way Sky subtraction (using N-nearest frames or own sky ) The contours are copied, and the image looks like below.Only display the FITS image with no processing.Use always the WCS system and any color you like. A dialog appears where you choose coordinate system, colour and linewidth. Go back to the contours window and click File -> Paste contours. Bring up the contour window again, and click File -> Copy contours. Clock on the frame where the Spitzer image is (You may have to click the menu ( Edit -> Pointer) first. Finally, we copy the contours to the HST image.I got something looking as the second image below. Click ( Analysis -> Contours) and choose the number of contours and spacing. Start by making the contours of the Spitzer image.To make sure that we are showing the same area, click ( Frame -> Math -> Frame -> WCS).You should now have the two images side by side. To see both images, click the " tile" button.Load the second image in this frame in the same way as the first.Make a second frame by clicking on the " frame" button followed by " new".Click on " scale" button and the " zscale" ( or Scale -> zscale in the menues). Change scaling to something more useful, with the buttons in the main DS9 window or the meny items. ![]() Normally, the default image scaling makes it impossible to see the faint structures in these images.To load the images in DS9, they need each to be in separate "frames". We represent the HST image as a pixel image (since it has the highest resolution), and the IRAC image as contours. There are some sources on the web (see the link above or ). In my opinion, the manual is hard to read and does not include all features in the software. SAOimage DS9 is a program that is powerful, but tricky to use. Ok, now we have some data, let's see how we can check how well the two maps correspond. (the strange shape of the observed region is due to the way that Spitzer observes: it observes several "patches" of the area and then stitches them together). I got the ACS image in filter F435 (4350 Angstrom or 0.44 micron) which looks like this: Most data are public so you can download lots of beautiful images. First, I downloaded a Hubble Space Telescope image from HLA ( Hubble Legacy Archive). Most astronomical data are distributed as fits files, and other formats can be inverted into fits.įor this presentation I decided to use two images of the Starburst galaxy M82. FITS-files are astronomical images that have information about the area of the sky that has been observed. To create overlays the data need to be in the FITS format for all these techniques to work. Or to show an optical image of a spiral galaxy and overlay contours of the molecular gas (from observations of CO).Įnough said, lets get started. Examples would be to mark all the stars detected on an optical image on a near-infrared of the same area. Usually I want to compare two or more maps, taken with different telescopes and different resolution. Hi there! Today I'd like to tell you about the techniques that I use to create overlays of astronomical data. ![]()
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