Table of Contents

1) CCDs: what they do and how they work
2) Available image processors for astronomy
3) Download ds9
4) Download iris
5) Learning ds9
6) Using ds9 with 2 Chandra activities
7) where to get images
8) Chandra X-ray Observatory
9) Sloan Digital Sky Survey
10) image processing projects for high school or college

• CCDs: what they do and how they work

• Astronomical image processors

            Two good choices (both free) are Iris and DS-9.

            Typical IP Functions

                    1) scaling (linear, log, ...)
                    2) false color palettes
                    3) shift, rotate, flip
                    4) +, -, x, /  counts or images
                    5) zoom, slice (intensity profiling), histogram
                    6) filter: sharpen, blur
                    7) photometry:  integrate counts, convert to magnitude, remove
                        background (sky)
                    8) remove bias and dark count, apply flat field corrections,
                    9) repair image defects (hot/cold pixels; cosmic rays)
                    10) multiple file processing:  batch, animate
                    11) control telescope; operate CCD

•  Download Iris

            A short guide to using Iris

•  Download ds9    (used by the Chandra X-ray Observatory, but also a general

 image processing tool)
 
•  Connecting to the Chandra Analysis software

                1. move the mouse over the Analysis menu in the ds9 window
                2. press the left mouse button to display menu options
                3. move the mouse down to the Virtual Observatories option and release
                4. when the Virtual Observatories dialog box appears, click the mouse in
                    the button to the left of the Chandra Ed option
                5. wait until the button turns green, and then close the dialog box

               Once this connection has been made to the Chandra Education data and
                analysis server, you can load the image of your choice. The analysis tool
                set will load automatically with the image.

Learning ds9 :
       Introduction

       Part 1: First Look: Qualitative Analysis

• Quick List of Basic Techniques
• Loading the Cas-A Image
• Looking at an X-ray image
• Contrast & Bias

contrast (drag right mouse vertically: varies rate of color change with counts)
bias (drag right mouse horizontally: increasing bias increases minimum counts displayed)
view contrast/bias box under Color
• Color
• Counting Photons
• Image Manipulation & Pixel "Value"

more about linear, log, square root scaling
• Closing an Image


Part 2: More Features for Qualitative Analysis (all under Analysis)

• Horizontal and vertical cuts (aka "slice" )
• Pixel value table  (6 pixel x 6 pixel table of counts values centered on cursor pixel)
• Display contours (set contour parameters with "Contours Parameters" menu; then Generate, then Apply)
• Display coordinate grid

 
Part 3: First Look at Quantitative Analysis
• Introduction
• Identifying Interesting Features
• Defining Regions of Interest

left click to create a circle; left click inside & drag to move; drag on handle bars to resize;
delete key to remove region or Delete All under Region
• Spatial Analysis
• Counts in Regions (under Chandra Ed Analysis under Analysis)

provides net counts in region, surface brightness count
• Radial Profile Plot

create annulus region (Region, Shape); double click inside to vary annulus parameters;
RPP provides counts plot inside annuli as a function or radius
• Spectral & Timing Analysis
• Energy Spectrum

provides counts-vs-energy from ACIS (Advanced CCD Imaging Spectrometer) within Region
• Light Curve

provides counts-vs-time from ACIS within Region; use bin = 0

•  Chandra Ed - Cas A

 
• load Cas A (assuming ds9 already open)
• Supernovas & Chandra: contextual narrative
• activity 1: improving the image contrast/bias
• activity 2: distance to and age of Cas A
• activity 3: size of Cas A
• activity 4:  making a light curve
• activity 5: radial intensity profile
• activity 6: making energy spectra

 
• Chandra Ed - 3C273
• activity 2: redshift and distance to a quasar
• load 3C273
• activity 3: luminosity of 3C273
• activity 4: size of 3C273
• activity 5: the gravitational energy and size of the black hole
• activity 6: faster than light?

where to get images

Astronomical images are decentralized in location.  They generally reside at
the web site of the organization or satellite which produced the image, although
there are a few central repositories.  Two such repositories are

Skyview    provides access to 30 sky surveys across the spectrum from radio to gamma ray

(examples include the optical DSS, the gamma-ray COMPTON, the x-ray ROSAT and
HEAO, the infrared IRAS, and the radio 408 MHz)

Aladin       provides access to 2MASS, IPAC (both infrared) in addition to those provided in Skyview

Both Skyview and Aladin provide reasonably friendly interfaces.  Both allow you to view a FITS image interactively with a web browser, without downloading the image to a local drive.  Skyview allows you to download and save FITS images to your local drive.  Aladin only provides that option if you are running the stand-alone Java option.  In general images provided by different satellites or observatories will not have the same image size, so the user should pay close attention to the angular size of the image, which is generally provided in the associated information.

However, there are many more sites with publicly accessible astronomical data that have recently come on-line that are not part of either of the above 2 atlases.  Examples of these are Chandra X-ray Observatory and the Sloan Digital Sky Survey (SDSS).  Instructions for accessing images for these sites are provided below.
Many atlases will retrieve images if given the common name of an object (if it is relatively well known), but all atlases will retrieve images based on the object's coordinates (right ascension and declination).

Here is an example of how to find images of the same object at multiple wavelengths using the supernova remnant Cas A:

a) select the RASS3 (RoSat) option (this was a low-resolution x-ray imaging
    satellite) and then download the FITS image to a local drive; note that this
    image is centered on 23 23 25.40, + 58 48 37.96 (2000) and is 3.75 degrees
    square

b) select the IRAS (InfraRed All Sky survey) and download the FITS image;
    note that the image is centered on 23 23 25.40, + 58 48 37.96 (2000) and is
    7.5 degrees square

c) select the DSS
    this image is also centered on 23 23 25.40, + 58 48 37.96  and is 0.15 degrees
    square

• Chandra X-Ray Observatory was launched 3 years ago and has two detectros: the High Resolution Camera (HRC) can record accurate positions as well as the photon arrival time; the Advanced CCD Imaging Spectrometer records accurate position and energy information for the photons.

 

 

To load a Chandra x-ray image

a) first you'll need to retrieve an ObsId (Observation Identification) number for your object; again, we will use Cas A as an example: to do this, go to the Chandra Data Archive Retrieval Interfaceand then select Sort by RA & Dec
(this may take awhile)

b) then locate an ObsId that matches the RA and Dec of your object; in this case, many ObsId numbers fall close to the RA and Dec given above; note that they also happen to be labeled Cas A

c) click on the ObsId link (in the left column) and new screen comes up with the ObsId centered in Select ObsId box;  under Select Data Product Category, check the first box, "fully processed science products (level=2) "  and then click the "Browse Archive and Retrieve Data Products"

d) another screen opens which lists the relevant files and allows you to select the files you want retrieved; the file you want will end with evt2.fits; highlight the name of the file you want in the white box and then click on "RETRIEVE from Archive"

e) a new screen opens, which gives you two options (ftp and a more direct "click to download") to obtain the zipped FITS file (generally a .tar file)

f) after the .tar file is downloaded, it must be unzipped (with WINZIP, for example) before being readable by a FITS viewer

g) what's the scale of this image?  in general, the Chandra ACIS instrument produces images that have a scale of 0.5" (arcseconds)/pixel
(you can verify this by scanning across the image and noticing both the change in pixels and the change in declination)

• Sloan Digital Sky Survey


(The SDSS survey will map in detail one-quarter of the entire sky, determining the positions and absolute brightnesses of more than 100 million celestial objects. It will also measure the distances to more than a million galaxies (all galaxies with g magnitude < 17.8)  and quasars.
 

• provides
• FITS images
• FITS spectra
• photometry information [magnitudes in 5 bands:

u(354.3 nm); g (477.0 nm); r (623.1 nm); i (762.5 nm); z (913.4 nm)]
• spectroscopic information (including line identification, spectral class,

redshift)
• projects for students/teachers
• step-by-step Hubble diagram

(and what its supposed to look like when you're done)
• a sample of data available
            (for most data, mouse over of lower right corner allow image resize)
 
• Get Fields  provides access to individual images (JPG format)

 
• Get Plates allows you to select a plate and then lists all galaxies, stars,

    late-type stars, QSOs, high-redshift QSOs; each object has redshift
    listed; click on object returns GIF spectrum
 
• Get Spectra provides access to individual spectra (GIF format)

green lines are identified lines in object's spectrum; knowledge of rest
    wavelengths will allow doppler shift calculation;
    "official" redshift also provided
violet lines are night sky (atmospheric) emission lines @
    560 nm, 590 nm, 630 nm, 725 nm)
 
• Object Explorer

then click on the Click to Explore link to open the ObjectExplorer
(in some ways the most useful tool, but also the most hidden)

First go to Get Plates to find objects with spectra (and their plate no,
fiber no, object type, and redshift)
Then type in plate and fiber no in ObjectExplorer dialog box

Provides access to FITS images and spectra (although FITS spectra
are only 2 rows wide)

• Useful tools include:
• "Save in Notes" to save Object type, 5-color magnitudes, RA/Dec, and ObjId
• "Show Notes" allows the data then to be saved as HTML or Excel;  
    HTML preserves option to go back to Object Exlorer

find the mass of jupiter or saturn from time-lapse motions of their satellites

• use this saturn image archive at HOU
            (use the big square images done on the yerkes 24; images exist
            from 01/12/02 - 02/28/02)

      saturn satellite viewer shows where saturn's named moons are at a
            give time and date so that you can figure out which satellite is which
            in an image

•  use this jupiter image archive at HOU

    (there is a nice set of images from 01/18/02 - 01/19/02 on the yrt10)
 

    jupiter satellite viewer shows where jupiter's named moons are at
    a give time and date
 

• finding the distance to an asteroid using parallax

 
• a cluster H-R diagram

 
• H-R diagram of globular cluster Pal 5 using SDSS data
• H-R diagram of the Pleiades using Hipparcos data

 
• find the rotation period of the sun with FITS images from UCLA