13.1.1 XEPHEM

Next start the xephem program: type XEPHEM in one of the windows on an X-terminal. After about 30 seconds a window will pop up. Pull down the View menu and select Sky View. Another window will pop up showing a map of the sky with the pointing calibrators above 10 degrees elevation. If this window overlaps the Update bar on the first window, reposition one of them so that you can press Update periodically. Each time this is pressed, the object positions on the sky are recalculated for the present time. Pull down the View menu on the Sky View window and select Grid. An Azimuth-Elevation grid will appear. The circles are lines of constant elevation spaced 5 degrees apart from 10 to 85 degrees. The lines are drawn every 30 degrees of azimuth with south at the bottom and east at the left. The scroll bars can be used to change the view, but this is not recommended. The scroll bar at the left sets the size of the field of view. It should be 160 degrees so that the last elevation circle is for 10 degrees elevation. The scroll bar at the right selects which elevation should be at the center of the circle (90 degrees). The scroll bar at the bottom selects the azimuth at the bottom of the circle (180 degrees).

Find a blank Azimuth-Elevation grid in the Control Room. If one is not available, you can print another one by typing:

KRONEN> PLOT TEL$POINTING:SKY_TEMPLATE 
    or
FRANKE> PLOT TEL$POINTING:SKY_TEMPLATE

You should write the date and time on this sheet and mark the positions of the objects as they are observed in order to document the sky distribution of the (successful) measurements.

The names of the objects are written on the map alongside the dots marking their positions. The size of each dot is an indication of the radio flux from the object at 1.3 mm wavelength. (The dots for the planets also indicate their relative brightness, but these are on a different scale.) If one moves the mouse pointer onto the map and presses the left button, the Elevation (``Alt'') and Azimuth of the pointer are shown on the top corners and the Right Ascension and Declination in the bottom corners. If one drags the mouse button, the SEP value in the upper right corner shows how far you have moved. (This can be used to checking how far an object is from the sun.) If one points at an object and presses the right button, the name and coordinates of the object are printed. (This is particularly useful when the names overlap each other.) Some other options are also available with the right mouse button. Create Trail... lets you see where an object will move as time passes. The first time it pops up the following selections are recommended: Path-Right orientation, 1 Hour interval, time stamp None, and start Now. Press OK and the pop-up will disappear and the trail is drawn. If a different object is right-clicked, one can select Create Trail... then press OK in the pop-up and a trail with the previous selections will be drawn. Right-clicking an object that already has or once had a trail brings up an additional option, Trail, which can be used to re-draw or erase the original trail. The Point and Point & Zoom options should probably avoided as they change the center of the map and the magnification which then must be restored in order to get back to the view corresponding to the Azimuth- Elevation grid used to record the object positions.

The catalogs for the XEPHEM program are in the directory:

   KDATA:[SMT.CAT]          !SMT Catalog Directory
     or
   KRONEN$DUA2:[SMT.CAT]    !Long form of the same address.

The standard pointing sources are in the file:

BOLO.EDB

Any files you wish to use for XEPHEM must end in EDB. The format of the files is, alas, not the same as the OBST pointing catalogs (see Chapter 2). The reader is referred to the online help files for all the options possible in XEPHEM. (Hint: look in the HELP area in the Data Base window, which is brought up by clicking the Objects (Data Base) entry on the main XEPHEM menu.) There is also a hardcopy of the XEPHEM manual to be found in the ASTRO/CLASS/etc... manual at the back.

An example format is given below:

#My favorite pointing source
W3OH, f|S|B5, 02:23:16.5, +61:38:57, -8.2, 1950
#end of file!

The # is a comment line.

The next line is the source entry, in this case W3OH. If we parse the line up, we get the following breakdown.

     W3OH        ! Source Name, can include - or + or . or _
                 ! Examples: W3OH, 1757-240, 2230+114, G45.1, CW_Leo

     f|S|B5      ! Source type.  Depending on the choice, one has
                 ! the ability to provide very detailed information.
                 ! For example, here it is a fixed source (no proper
                 ! motion) (f), Stellar (S), spectral type B5.
                 ! If you examine the pointing list, we use this
                 ! as a default...
                 ! See the manual for the fancy stuff!

     02:23:16.5  ! RA
    +61:38:57    ! Dec
     -8.2        ! Magnitude of source - relative brightness
     1950        ! Epoch (optional - assumes 2000.0 if not given).

Following this example, you can create your own catalog file for use in XEPHEM if you wish.