Using Aladin With APT In Phase II


The Aladin Tool (click here to see the movie) allows you visualize your HST observations. While the basic functions are the same as in Phase I, the context is different (you have real instead of draft apertures), and there is a save to proposal capability not available in Phase I. There are separate help files and movies on specific Aladin topics (such as blinking, reviewing mosaics, etc.).

In this document, the project is to image the nucleus of M51, as well as that of the companion galaxy with the WFC3. We have 2 exposures do to this - one on M51, and the second offset (using a POS TARG) to get the companion.

Before initiating Aladin, you should select the exposure(s) you wish to visualize. You can select your exposure(s) by either selecting the individual exposure or group of exposures in the heirarchical editor. If you wish to view an entire visit, you can select the Visit container, and if you wish to view the entire proposal, select the Visits container. Then select the Aladin button at the top of the display, which will bring up the Aladin viewer.

Note that the Aladin apertures are semi-transparent. If you want to adjust the transparency, then under each exposure in the Aladin Tree, adjust the slider to get the desired opacity. If you want to keep all the apertues for a Visit in sync, then use the slider onthe Visit rather than an exposure

You can change the image scale (Zoom) by either using the Zoom slider under the Aladin Tree, by clicking on the spot in the image you want the zoom centered and rotating the mouse wheel (forward will zoom in while backwards will zoom out), or selecting th Zoom button in the toolbar, centering on the area of interest, and clicking to zoom in (shift-click will zoom out). You can pan around the image by selecting the Pan function in the option bar. To disable the Pan, just move the cursor off of the display area.

In the APT window are controls for what is shown in the Aladin display.

The buttons along the top perform the following functions:

  • Create POS TARGs - when selected, any aperture position changes you perform in Aladin will be used to create POSition TARGet offsets, rather than changing the position of the target.
  • POS TARG Axes - when selected, the XY axes for POS TARGs are displayed
  • FOV - when selected, the HST Field of View is displayed.
  • Coverage Circles - when selected, circles indicating the region of the sky covered by the aperture that will always be imaged (inner) and may be imaged depending on Orientation (outer).
  • Orient Ranges - when selected, a circle indicating the valid (green) and invalid (red) orientations (based on values in the proposal).
  • Grid - when selected, a coordinate grid is displayed.
  • Apply Proper Motion to Epoch - when selected, the proper motion of the target is applied (and a motion vector displayed) in the Aladin display to the Epoch today+6 months.
  • BOT Data - when selected, results from the Bright Object Tool are displayed (see separate documentation on this tool).
  • Labels - when selected, each aperture is labeled with Observation/Exposure name
  • Load DSS - loads a DSS image (POSS2 Red) for the selected exposures. To load a different type/size of image, use the Aladin Load function.
  • Reset Orients - resets any Orient values you modified to those specified in the proposal.
  • Color Map - allows for the specification of the colors of plotted items (e.g. apertures).

  • After loading a DSS image, we see the aperture overlaid on the image.

    Adjusting the exposure

    We want to have the the nucleus centered on the UVIS chips, so we need to change the location of the aperture. Grab the aperture (make sure you see the hand icon), and move it to center the nucleus.

    We also want to have the indicated star in our image, so we need to change the orientation of the apeture. Grab the corner of the aperture (make sure you see the icon) and rotate the aperture.

    Note that our second exposure is now off the companion (since we changed both the object position and the orientation). We therefore need to change the POS TARG to accomodate these changes. If we moved the aperture now, we would change the position of the target (as we have already done), rather than change the POS TARG. We need to go back to the APT window and change the operating mode.

    To change the POS TARG, we need to click on the Create POS TARGs button. Also note the pending change for the coordinates that we made. If you change your mind about including the star in the image, you can Clear the changes to remove the target motion, and click on Reset Orients to remove the Orient change. At present, APT does not save any Orient changes made in Aladin, so these will need to be manually input.

    We can now go back to the Aladin window, grab the aperture (again, make sure you see the hand icon) and center on the companion galaxy.

    Now that we have completed our changes, we can go back to the APT window and commit them, as well as manually update the Orientation.

    Overlaying catalogs

    You can overlay catalogs in Aladin. Under the File Menu, select Load catalog.

    There you see the list of available catalogs. Note that you can also load images from your disk.

    Click on SIMBAD, which brings up the Server selector window, and then hit Submit. This will perform a search of the SIMBAD database for all objects in the field, and create a SIMBAD plane in the Aladin stack.

    Note that if you put your cursor on the Simbad plane, it will you the number of objects in the catalog. To get information on a SIMBAD source, go to Select mode in Aladin and click on one of the objects (note that object flashes, and you get the hand icon). The information on the object is displayed in the spreadsheet. To get the field definitions, put your cursor in the spreadsheet field.

    If you want to examine multiple objects, make a box around the area of interest, and all objects contained in that box will be shown in the spreadsheet. Putting your cursor on the object name in the spreadsheet will cause that object to flash in the image display.

    You can display multiple catalogs at the same time. If a given object is in mutliple catalogs, clicking on it will display the information for all catalogs in the spreadsheet.

    Finally, if you want to save a copy of the image, click on the SAVE option in the File Menu, and select the option appropriate for your needs.

    Last modified: June 2, 2016.