The SDSS Catalog Archive Server (CAS) has images, spectra, and catalog data for every one of the objects SDSS. This tutorial gives instructions for how to use the CAS to find an SDSS image of a specified object if you know the RA and Dec.
Get the image
- Go to the CAS’s Navigate tool. To access the tool from the CAS main page, look under Advanced Tools. (To access the Navigate tool from the public main page, look under Visual Tools).
- Look at the ra and dec input boxes near the top left of the tool. Enter the coordinates of your object. You may enter them either as decimal degrees or as HMS/DMS. If you enter them as HMS/DMS, use the format “hh:mm:ss ±dd:mm:ss”, and be sure to include seconds even if they are 00. (You may have to re-format the results you copied from SIMBAD).
- Click the blue Search button. You will see an interactive image of your object in the center panel.
- Find your object. Click the directional buttons (NWSE) to pan the image, and click on the + or – magnifying glasses to zoom in our out within the image.
- Click on one or more of the Drawing Options checkboxes in the left-hand panel to redraw the image with various features selected.
Here is a list of what each of the drawing options does:
- Draw a N-S, E-W grid through the center
- Draw the name, scale, ra, and dec on image
- Draw a small blue circle around each recognized object
- Draw a small red square around each object with a spectrum
- Draw a small yellow cross-hair around each object targeted for spectroscopy
- Draw the outline (in green) of each object
- Draw the bounding box (in pink) of each object
- Draw the outline of each imaging field (in gray)
- Draw the outline (in orange) of each mask considered to be important
- Draw the outline of each spectral plate (in pink)
- Invert the image (display as black-on-white)
- Click on any object in the image. You will see the object’s data in the right-hand panel. The data displayed are the object’s ra and dec, and the object’s magnitudes in the SDSS’s five filters (u, g, r, i, z). You will also see a close-up image of the object.
- Click Add to Notes to add the selected object to your online notebook. Click Show Notes to show the notebook. From your notebook, you can click Navigate to return to the Navigate tool. You can also Export the notebook to your computer.
Explore the Object
- Click the Explore link in the right panel of the Navigate tool to go to the Explore tool. To access the tool from the astronomers’ main page, look under Advanced Tools. To access the tool from the public main page, look under Visual Tools.
- At the top of the Explore tool window, you will see the object’s identifier, ra and dec, and SDSS long object ID.
- Below the name and position data, you will see a close-up image of the object, with a scale. The object’s photometric data is to the right of the image. The magnitudes (u, g, r, i, z) are in the first row.
You can also use the Explore tool to get the SDSS’s FITS images for your object.
Get FITS Images
To see FITS images of the object, click on the FITS link below the PhotoObj heading in the left-hand menu. Corrected Frames are the final step of processing for SDSS images. There is one image for each filter. Right-click on the label for the filter whose image you want to download.