The Chandra Multiwavelength Project:Galactic Plane Survey Chandra X-ray Observatory National Optical Astronomy Observatory

The ChaMPlane survey is being conducted at the Harvard-Smithsonian Center for Astrophysics.
Database Description

A Step-by-Step Description of the ChaMPlane DS9 Virtual Observatory.

These images and the instructions that follow are the examples referred to in our paper: Grindlay et al 2005, ApJ, 2005

We'll begin this tutorial with the example screenshot from the appendix to our ApJ  Introduction paper, which shows several of the main features of our database system.
Then we'll take a step-by-step guide showing exactly how that figure was made. By the end of this tutorial you should be familiar with a subset of the  champlane/ds9 tools
and ready to make your own investigations using the system.
screenshot ds9

1: Connect to ChaMPlane and load toolkit

The first thing to do is launch  DS9, making sure that only one copy is running on your machine.
Next, you connect to  the ChaMPlane server by selecting Virtual Observatory from the DS9
Analysis menu. The images below show what you should see (scroll sideways).
Alternatively you can connect by  clicking on this link  (you must have DS9 running first.)


Browser screen displayed while champlane is loading on your machine.

After selecting "Champlane" from the list of  Virtual Observatory nodes, you will be presented with this screen, in DS9's internal web browser window.

Click on the "Activate Database" link to load our Champlane toolkit onto your DS9.

Almost immediately, the page on the right will be displayed, indicating that our system has sucessfully located your DS9 and has loaded the toolkit and a welcome image.

Loading text

2: Select a ChaMPlane Field:

Once the connection is made, Select "ChaMPlane Tools" from the ds9 Analysis menu. You will see that only the "ChaMPlane Field Finder" tool is available for use,
click on it with your mouse. You will then see a dialog box displaying all available fields in a drop-down menu. You have the option to select an image in V,R,I, or Ha filters.

Pick the ChaMPlane field you are interested in and the filter (V,R,I, or Halpha). An image of the full 36'x36' image will be loaded into your DS9 -this will be
a reduced memory image for fast network transfer- its function is to enable you to identify the exact area you are interested in, or to perform searches
on large areas of the field. Details of the fields such as co-ords, exposure details, extinction etc. 
are posted on our website. Basic calibration data is included in the fits headers, viewable in DS9 under the file menu.

In the example below, we select the field of the Galactic Black-Hole GRO J0422 in the R filter.

  J0422 image
fieldfinder dialog

3: Display the Chandra ACIS Field of View.

To display the field of view of the Chandra ACIS instrument, click on the tool "Overlay Chandra ACIS field of view".
You will now see a region overlay on the image, showing the outline of the ACIS CCD's which were switched on and aquiring data during this observation.
The aimpoint is indicated by a small diamond.J0422 with Chandra FoV
4: Locate X-ray Point Sources

A wide range of different database searches can be performed with our toolkit. All are "region driven" -this means
you simply select a region of the image by dragging with the mouse and then click on a search tool.
For the moment circular regions work best for this purpose as they are interpreted as a radius search.
Box regions may also be used, however the the search will return a radius search with r=(mean side)/2.

For example we can display all X-ray sources by drawing a big circle over the image, and clicking "Overlay Positions of Wavedetect X-ray Sources".
When making a new region be careful to avoid accidentally selecting an existing region. You can start the new region in a blank area and then drag it to the desired location.
X-ray source regions
X-ray data table
The small blue circles are 95% error circles for Chandra X-ray sources. Each is a selectable region
and can be used to drive further searching, e.g. for optical counterparts.
A table of X-ray source data is also output, listing parameters
such as RA, Dec, counts and flux in different energy bands.

5: Locate Ha Emission Sources:

ChaMPlane optical is a deep wide-field emission line survey using a narrow band Ha filter.
We provide a  tool to searching for emission line objects, display their positions
and catalog data. A table of photometric data output is shown to right of image below.

Ha emission sources are defined in 2 bands as Ha-R < 0.3  and -0.2 < Ha-R < -0.2
Which correspond to accretion sources (CVs, Be-XRB) and dMe stars respectively.
Young stellar objects are also strong Ha emitters. Filtering can be applied to restrict
emission candidates using Signal-to-noise ratio as described in Zhao et al (2005)
Two built in Signal/Noise ratio selections are SNR>10 or SNR>5.

The results produced by this tool can be inspected on a star by star basis using the output regions
and the "inspect_Ha" tool. (described next).
Ha source regions added  
Halpha photometry

Red points and text labels indicate Ha emission objects selected using the "Locate Ha objects" tool.
A table of photometric data is also displayed, the ID column matches the labels drawn on the image.

6: Display the X-ray Image for the Selected Region

Having located some interesting Ha emission-line stars within the ACIS field, we can now examine the X-ray image
and perform the same kinds of overlays and searches on it. Here we selected a portion of the lower right ACIS-I CCD
with a circle region, and then clicked "View X-ray image for Selected Region" on the ChaMPlane tools menu. At this point,
make sure you have "Tile" mode selected under ds9's "Frame" menu, this enables you to display multiple images side-by-side.
The tool will extract an adaptively smoothed image from the X-ray data, corresponding to the slected region specified on the
optical image. In the screen below,  source regions were added to the X-ray image by selecting a circle and repeating the steps
above, but we could equally well have done "save regions" on the optical image followed by "load regions" on the X-ray image.
Both images have the same FK5 World Coordinate sytem (WCS). Looking at the right panel below, we immediately see that the
two Halpha emitters located in our selection region have X-ray counterparts.

dual optical Xray image

Hint: Try choosing the "Cross-Hairs" tool (from ds9's "Edit" menu) and then selecting "Lock crosshairs to WCS" under the "Frame" menu, this enable you to very easily compare the locations of objects in multiple images of the same field -for example those obtained in different wavebands, or different instruments.

We have now performed all the steps needed to replicate our example figure, which is reproduced below to show all the elements displayed together: optical image, X-ray image, optical photometry, X-ray source details and various region-overlays.

screenshot ds9

End of Tasks Described / Illustrated in Screenshot from Appendix to ApJ PAPER.

Below  are  more  ChaMPlane tool descriptions and demonstrations, which will be updated as we add more functionality to our VO server.

Extract Full Resolution Optical Image of Selected Region:

Select a region of interest on the full-field image using a square box. This section
will be extracted from the full resolution fits image in our database, and displayed
in a new frame. All header information is preserved and the image can be inspected in situ or
downloaded using File --> Save.  

List All Optical database Entries for Selected Region:

Select a (ideally circular) region on an image, a Photometry catalog will be
displayed for all stars within the selected region. The catalog can be saved/downloaded.

Search 1

Select a region and search for OPTICAL sources based on a single selection
criterion. e.g. V magnitude brighter than 21. All objects in the "OPT" catalog (see above)
lying in the selected region and matching the search criterion will be listed. The output includes all relevant photometry parameters.

Search 2

As above, but now apply two selection criteria simaltaneously. e.g. V brighter than 22 and
Vsharp set to exclude non-stars. The selected entries can be displayed in catalog form, and/or overlaid on the image.
If overlay is selected, the displayed region can themselves be used as a basis for further inspection. (see X-inspect, Ha inspect)

Plot Optical Data:

Make a graph of any pair of optical photometry quantities for all objects lying within a selected (circular) region.
e.g. plot R versus H-R. Any bad or missing values will be automatically excluded.
A cut in Signal/Noise ratio can be applied. (to both quantities).
(Note in the magnitude system, SNR=1.09/Error)


A general Visual-Verification tool for inspecting full resolution images of a large number of
sources. First display circular regions on an image (other shapes will be ignored)
and then activate this tool. There is an option to overlay the positions, ID numbers and
magnitudes of all Champlane optical sources for comparison with your targets.
Comments are collected in a dialog box and saved in a file, which is displayed upon termination
of the tast. Type a "?" in the comment field to exit.   In this example the red circle is a user defined region, and the green circles with text
are all the Champlane optical sources in the field, with Rmagnitudes displayed.

Inspect Ha

First display circular regions on an image, one for each source. Each region must have a label corresponding to
its ChaMPlane optical ID number. (For example use "Locate Ha sources" tool to produce such a set of regions).
The "inspect Ha" tool will display full resolution "thumbnail" R-band and Ha-band images for each source in turn
and collect your comments in a file which is displayed upon temination of the task. You can exit the tool at any
point by typing a "?" in the comment field.

Notes on IRAF Compatibility

Since DS9 is compatible with IRAF, it is possible to run interactive IRAF tools such as IMEXAM on the ChaMPlane data.
Due to the way IRAF links to the image data it is neccesary to save the image locally before attempting to measure it with  IRAF.
Just click File---> Save on the DS9 menu before proceeding.