ACS transients, SN candidates scenario
---------------------------------------

start aladin

Select V89-preview in the data list, and press the "Load image" button
to load this preview inthe image stack. This provides a base showing
the full CDFS field.

We now wish to inspect the locations of the recently discovered 
transients in the ACS GOODS data. The ACS observing campaign for
the GOODS survey is designed to be done over several epochs 
separated by approximately 40 days. This interval is optimized 
for the discovery and light curve followup of high redshift
supernovae. Supernovae, stars that explode at the end of their 
life, are useful distance indicators when observed at high redshift.
Finding these "transient" objects is possible by comparing images
taken at different epochs. So far the GOODS team have released
the first two epochs of ACS data, and already they have found
a number of Supernovae candidates.

These have been published in IAU circulars and on the GOODS ACS
web page. We've got the coordinates accessible in a loacal
file which we will now load via the "Local" load button at the
bottom left of the Server Selector window.

We have access to a normal file system here, starting in the
AVO prototype working directory. The relevant file is
located here and is called "transients.tsv".

Select this file, and it automatically loads as a plane in the
stack with a label showing the file name. We can change this
name by pressing the "prop" (properties) button in the
main prorotype window.

(a01.jpg)

The positions of the SN candidates is shown overlaid on the image.

We can see which ACS fields they came from by overlaying the full
set of ACS field outlines.

To do this (for both epochs at the same time) we return to the server 
selector window and press the GOODS button to get to the GOODS
data tree list.

Select the top level of GOODS-HST-ACS, then press the "Show all images
fields for this level". This brings up the full ACS fields, for every
epoch and every band (hence the multicolor effect). 

To inspect the details of the SN candidates ( info held in the local
file that we loaded), we can open a drag box around all the points
by clicking and dragging within the image window.

This selects all the sources within the box and shows their details
in the "measurements panel" below the image. Moving the cursor over 
the data shows the column headings as contained in the transients.tsv file.

Note that the GOODS team have given names to their SN candidates
based on mythologies ancient and contemporary. 

Consider the first candidate called Aphrodite. 

We will now load the ACS data from epochs 1 and 2 where this
SN candidate was discovered.

Firstly select the Aphrodite point. To identify it put the cursor over the
table row for Aphrodite, and the point will blink. 

Use to drag box in the window to select only this point, then click on 
the point so that it's coordinates are registeredin the GOODS load window.

Next open up the ACS F850LP (z-band) nodes in the data list. You will
see that some of the data has a checked box. These are the data for 
the coordinate you selected.

Load these data, one at a time by selecting them, (clicking on the text next
to the check box in the data list), then press the "Load image" button.

After the files have loaded into the stack, get the big picture by
selecting the preview in the stack and see the outlines of the
loaded images.
Note that these are cutouts from the ACS fields, not the full field
tile. This is done because the full 4kx4k (~70MB) ACS images are 
very taxing on the computer memory, so 1kx1k cutouts work much better.

Now zoom in on the the Aphrodite position in the epoch 1 image.
i.e select the epoch1 image by clicking on the triangle selector 
in the image stack next to the epoch1 plane.

Zoom out. The Aphrodite point may seem to have dissappeared, but 
this is because of a feature of the stack. Catalog planes must reside 
above the image plane in the stack i order to be projected on the
image. Planes can simply be moved by dragging, so move the SN Candiates
plane to the top of the stack. 

(Good time now to turn off the ACS FOV display) 

Zoom inon the SN point, and set both epoch images to the same 
zoom factor. 

epoch1 : a05.jpg
epoch2 : a06.jpg

Make a  2-colour image of the different epochs:
 Red- epoch 1, Blue - epoch 2
This makes the SN canadidate Aphorodite stand out a a blue-only
region because it wasn't present in the epoch 1 observations.

Let's pretty it up with a label, and show it with (a07.jpg) and 
without (a08.jpg) the SN candiate catalog plane.

Now, lets see if there is any corresponding EIS catalog points
measured in the vicintiy of the SN candidate.

Open the VizieR Catalogs window in the Server Selector window.
We want to look for catalog entries in a region around the SN, 
so press the grab coords button and then drag out a circle 
around the SN. This registers the coordinate in the load window
and also defines a radius. If the radius is 0.0, it is because we 
are dealing with such a small field - change it to 0.1.

Then enter the catalog name, in this case eis-cc/ubvri for the
EIS UBVRI catalog. Then hit submit. The plane is loaded into the
stack and we can see that there actually is one nearby catalog entry.
(a09.jpg)

We can also load the EIS, UBVRIJK catalog to include the extra IR 
measurements if available.
(a10.jpg)

So... what is this catalog entry? There appears to be nothing there
in the ACS images. How far in arcsec is it from the SN candidate? 
Perhaps we have resolution issues with the catalog that was built
from lower resolution data(?).
(EIS cat ID: 26472)

By using the "dist" button in the image window, we can see it is only
 0.91" away from the SN.
( To do this, select "dist", mark the endpoints using the cursor, and an
arrow appears. The default color may be difficult to see so use
the properties button to change to white for example. Then to see the
actual distance measurement, make sure to check the "dist" button again
to be in "dist" mode)
(a11.jpg)

To investigate the catalog entries, lets see the SED. Select the catalog point
with a drag box. (remeber to exit "dist" mode first)
See the magnitude values in the measurement window

(a12.jpg)

Now, press the SED button
(a13.jpg)

Note how we have plotted 2 SEDs. They overlap for the UBVRI observations
and the UBVRIJK catalog extends for two more data points.
Also note that there are many upper limit points, which
really represent the detection limit of the observations,
the only "real" data points are those in the U and B bands.



Perhaps loading the WFI data will shed some light on the
the catalog points,
So.. lets load WFI U and B images at this point.
See the outline of the much larger WFI cutouts
 (a14.jpg) and the highlighted data sets.

Inspecting the U frame, we can indeed see an optical source at the
catalog point.
(remember to put the catalogs to the top of the stack to
inspect them overlaid on the new images)
(a15.jpg)
and zoomed in (a16.jpg)

make a contour map of the ACS epoch 1 frame... (a17.jpg)

and overlay on the WFI-U image (a18.jpg)

It seems the object associated with the catalog point is not
'detected in the ACS image. (is this strange?)

(a19.jpg, a20.jpg)

Contour map of U-band: (a21.jpg) overlaid on the ACS image with 
ACS contours shows that the WFI position may be in error simply 
due to the lower resolution of that data.

(Although the offset of the ACS and WFI EIS catalog point for another source
 in the field is not so large)
(a22.jpg)

finally a nice RGB of epoch 1 data

various pretty pics a23.jpg - a27.jpg