Laboratories and Webpage designed by Andrew Nicholson 2004

Introduction:

Have you ever wondered if there are other solar systems like ours in the universe?  In 1994 the Hubble Space Telescope (HST) looked deep into the Orion Nebula (M42) and found newly forming stars with clouds of dust ang gas (including ionized hydrogen) surrounding them.  If these stars have protoplanetary disks, disks that may one day evolve into planets, then they are proplyds.  In the picture to the left you can see four potential proplyds.  In this lab we will study some HST images of proplyds using the Sky Image Processor (SIP), a free JAVA based image processor, and measure the size of the proplyds.

Now let us go over how to measure the size of a proplyd.  When the Hubble Space Telescope takes a picture of a region in space each pixel in the picture has an angular size () as shown in the diagram below.

where is the angular size of each pixel and d is the distance from the Hubble Space Telescope to the region in space being observed. Now if we look at just one pixel:

where is the angular size of the pixel, is half of , d is the distance from the Hubble Space Telescope tot he pixel and y is the length of the pixel. After doing some trigonometry to find the length of the pixel:

So if we know the angular size of a pixel and the distance from the Hubble Space Telescope to the region being observed we can find the size of the region.  Luckily we know both of these values.  The angular size of a pixel is 4.85x10^-7 radians or 0.1 arc seconds and the distance from the Hubble Space Telescope to the proplyds we are studying is 1500 light years or 103131500 AU (Astronomical Units). Thus each pixel on the Hubble Space Telescope has a length of:

y d* = (4.85x10^-7 radians)(10313500 AU) = 50 AU

or 50 times bigger than Earth`s orbit around the Sun!

Procedure:

1. Please go to http://www.phys.vt.edu/~jhs/SIP/. If a Java Security Warning window appears click on Grant This Session.
2. Now click on Start SIP.
3. Under File click on Open Image File From The Internet.
4. When asked for the URL type http://campus.pari.edu/tw/SGRA/U3J1030HR.fits
5. Another way to open the file is SIP is to type http://campus.pari.edu/tw/SGRA/U3J1030HR.fits in Internet Explorer and click on Save.  Then, in SIP, under File click on Open Image File From User’s Machine and tell SIP where you saved the image file.
6. If the picture is very dark click on Automatic Contrast Ajustment under View.
7. Under View click on Change Image Display Parameters.
8. Change the Zoom Factor to x4.  If you get a blue screen, close your web browser completely and open a new window.
9. Click and drag a box around the proplyd. Notice the gray bar at the right side of the window, after drawing the box it should give you the box limits. Choose either x or y direction and calculate how many pixels are in either direction. See the example below:

10. Now calculate the length of the proplyd by taking the number of pixels in either the x or y direction and multiplying that by 50 AU.

Challenge Question: How does this compare with the size of our solar system?