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NEON Archive School, P. Padovani

Astrophysical Virtual Observatory (AVO) demo tutorial (prototype available at
http://www.euro-vo.org/twiki/bin/view/Avo/SwgDownload)

Open cluster membership

* fire up the AVO prototype portal as described on the installation page

* click on Load, enter target "pleiades" and radius "30 arcmin", press Submit

* click on Data Tree

* moving the cursor on the data tree "branches" one sees the field of view
of the various images

* load, for example, J-band, POSSII image 6.4 x 6.4 deg

* centre the image by clicking on "zoom" and then clicking over the cluster
centre

* we now need distance information on the stars; click on Load again, then
on "Vizier Catalogs"; enter "parallax" in the "Author, free text ..." field
click Submit

* select "The Hipparcos and Tycho Catalogues", then go back to the "Load"
window, add "/hip_main" to "I/239" (need to do that to avoid loading more
than one table, which confuses the plotting package), put in a radius
of "5 deg", then click "Submit"

* the catalog is now loaded (see right, above the POSSII image) and
the sources are overlaid on the image

* select with the cursor the central region: the selected sources get
highlighted and the catalog parameters appear in the window below the image;
moving the cursor over a column gives the column name

* we now want to plot an histogram of the Hipparcos parallaxes; we first
select with the cursor all stars in the image, then click on "Plugins" and
select "VOPlot". Select "Plx" for the x axis, then click on "Histogram".
Parallax for this cluster has to be around 8 - 9 mas (real value is
8.46+/-0.22 mas) and there are many foreground stars and a few background
ones

* we now want to plot a colour-magnitude diagram; we want first to correct
for reddening, using the relation (B-V)o = (B-V) - E(B-V) = (B-V) -
0.04 for this cluster. We need then to add a new column by "right
clicking" on the catalogue plane and selecting "Add a new column".
"Name" can be "(B-V)o". Click on "B-V" under "Pick up a column name",
and then enter "-0.04" after the column name. Then click on "Add a
new column".

* scroll the bottom bar all the way to the left, and check that indeed
a new column with the name "(B-V)o" has been added as the last column

* now we plot Vmag vs. (B-V)o for the cluster; we go back to the VOplot
window, click "Plot" and then select "Vmag" for the Y axis and "(B-V)o"
for the x axis, then click "Plot" again. Then click the "Rev" button above
"Vmag" to flip the Y axis. The Zero Age Mean Sequence (ZAMS) is clearly
visible. Select sources in the top left corner by using the cursor: the
corresponding sources get highlighted in the image. Note how they are mostly
in the centre. Click on "out" (bottom right) to see all the selected
sources. Notice how most of them have parallaxes ~ 8 - 9 mas

* now select with VOPlot the outliers (bottom right); look at the image,
now they appear to be mostly at the edge of the field. As before, look at
their parallaxes: now they are mostly foreground sources, with a couple of
background objects and some ~ 8 mas

* now we want to look for data available for selected sources in various
mission archives. We then select some sources in the image, for example
in the center, and then go to the Load window, click on "Missions in VizieR"
and select, for example, ESO, then hit Submit; do the same for HST and
then IUE. The pointings for the three missions are overlaid in the image

* select one IUE pointing, then click on the first column, which is
highlighted. One gets the entry in the INES catalogue in the Web
browser, with a link to a preview of the IUE spectrum

* now select one HST pointing; an "Image" link means that there is a preview
image available, a "Spectrum" link means that there is a preview spectrum
(clicking on "Image" loads it in the tree.) By clicking on the "Dataset"
column one is taken to the MAST archive, with information on the dataset.
Clicking on the "Catalog search" link one can then request the dataset.
Scrolling down and clicking on the highlighted "Proposal ID" number one
gets to the proposal page, with abstract, link to published papers (if
any), and a list of all the datasets belonging to that proposal.


Looking for optical counterparts of X-ray sources

* fire up the AVO prototype portal as described on the installation page

* click on Load, enter target CDFS and radius = 30 arcmin, press Submit

* click on Data Tree

* load V-band WFI preview image of whole CDFS as background: find tree
node GOODS-WFI, expand node V89, select item DEEP2C-FV-PREVIEW... and
press submit

* now we want to look for X-ray sources in the area; we go to Load, click on
Vizier Catalogs, select X-ray and the submit; select Alexander et
al. then add /cdfs then submit (MAKE SURE TO HAVE WFI IMAGE SELECTED
BEFORE DOING THAT)

* now overlay the FOV of GOODS-ACS-HST data and show how one can see
which X-ray sources are or not in the GOODS area; then select a few
sources on the image and show the catalog entries

* then open e.g. ACS F850LP box, then open version1.0 (these are the
5-epoch, stacked images), close WFI

* check box on sector 33, click submit and download the ACS image

* click in the center of the field, open version 1.0 for other filters,
see checked boxes in those as well

* hit submit and download all checked boxes (typically 3 ACS
images F435W, F775W, F850LP)

* close ACS

* make RGB of ACS images

* zoom out, see sources are mostly blue, notice tiny size of ACS
image compared to WFI

* now look for sources with VLT/FORS spectra: click on Load, click on VOdemo,
select "SSA server for VLT/FORS spectra", change radius to, say, 0.5
deg, hit Submit

* this loads the spectra into the tree, and one can see them all with
their position angles (needs cursor on top level "SSA server for
VLT/FORS spectra" in the tree); zoom in a little to be able to see the
slits on the objects in the ACS image

* right click on same text in the tree to create a catalog plane for
spectra (might need to change colour by using the "properties" button)

* to get to the spectra one selects a region and then clicks on the
"spectrum" link; this sends off a request to ESO, retrieves the FITS
file and displays it using SpeCView

AS OF VERSION 2.0 THE FOLLOWING PART IS OUT-OF-DATE, AS THE ACE
PLUG-IN IS NOT PART OF THE PROTOTYPE ANYMORE BUT IS NOW A WEB SERVICE

* now we want to create a catalog of ACS sources; select the ACS image, then
call ACE (Astronomical Catalog Extractor) from Plugins, then Open
the configuration file, F775W-v1-config.ace, which is important as it
tells ACE which settings to use for SExtractor (this file is available from
http://www.euro-vo.org/twiki/bin/view/Avo/ExtragalacticScenario/
demo_files.tar.gz)

* click on Extract; this tells the CDS server in Strasbourg to send
the image to ACE in Cambridge and then returns to the user the output
catalog whose sources are automatically overlaid

* now cross-correlate the optical and X-ray sources by using the Cross-match
service under Plugins; this creates a plane with the cross-matches
and a table which is a joint between the two input tables for the matching
sources; can first check typical X-ray positional errors using VOPlot; use
1.25 arcsec

* one could now create derived parameters, like X-ray-to-optical flux ratios
using the "add a column" feature