Science With the Virtual Observatory 2005 Summer School

Exercise #11 Combining Tools

A) Create finding chart images for a list of targets

For example: create DSS2 images with overlayed sources from NOMAD catalog

Use DataScope to download images and catalogs and use Aladin to create the overlayed images.

Or download images and catalogs directly from Aladin.

B) Find AO natural guide stars or tip/tilt reference stars for laser guide stars

In this exercise we will use VO enabled tools to plan an observation session with the Keck II telescope using the laser guide star.  To use the laser guide star, we also need a natural star for tip/tilt corrections. This is necessary because the laser moves in sync with the telescope and any tip/tilt errors can not be measured using the laser guide star alone. A good tip/tilt reference star shall satisfy the following conditions:

• The tip/tilt (TT) reference star must be less than 35 arcsec from the science target. In practice there is a irregular non-vignetted zone in which the tip/tilt star must be located. For simplicity, we will consider this zone a circle.
• The TT star should be bright , ideally between 10 and 19 Rmag, higher values of B-V better.
• The TT star should not be an extended source, ie not a galaxy.

To do

We start with a target list and proceed to find 2 or 3 possible TT reference star candidates for each target. Then we assemble a new list containing the targets and the TT stars. 

Step 1

For each target, perform a cone search using GSC2.2 or USNOB. Make a table with columns: RA, DEC, Rmag, type, distance to target, sorted by distance to target. Extract up to 3 rows where Rmag is between 10 and 19 and type is star. Save those rows.

Step 2

For each target, retrieve a DSS2 50" x 50" image centered at the target's coordinates and verify that the TT star candidates from step 1 are not extended objects. Remove the extended objects from list.

Shui Hung Kwok
NVO Summer School 2006

The NVO Summer School is made possible through the support of the National Science Foundation and the National Aeronautics and Space Administration.