Acquiring Targets, the Red Slit, the Guide Map
Acquiring a target on OSMOS was a bit of a learning curve. The OSMOS 4x4k CCD can be used with two two different slits, a ‘centre’ slit and an ‘inner’ slit. The inner slit is best used if you would like to concentrate on the redder end of the spectrum, and is thus dubbed the red slit. The red slit is located just over 75% to the right edge of the CCD from the left side of the CCD. When looking for targets, you first take an image without a slit/disperser in the light-beam. The object will most likely be located very close to the centre of the CCD (as a result of focus and pointing maneuvers taken earlier in the night). It is now your job to move the object into the portion of the CCD covered by the red slit. This is done by:
1. Image the field and locate the object, while guiding using the guide camera
2. Put the red slit in the light beam and take another image; this results in a vertical bar on the CCD in the location of the CCD
3. Use the program oalign.py to calculate the separation between the centre of the object, and the centre of the slit:
oalign.py -l maskImage.fits fieldImage.fits *
this will calculate a number of steps (on the guide camera!!!) in the offset between object and slit. In order to move the telescope to match the two up you must:
4. turn guiding off momentarily
5. enter into the guider GUI the number of steps to move the guider camera, enter (watch the stars on the guide camera jump out by the entered steps
6. move the telescope back so the original guide star is back in the guide box, resume guiding
The object should now be in the slit.
NOTES: Important here is I was using the red slit. The inner slit is quite far from the centre of the chip, and the guide camera can only move so far. I found many times I was requiring the guide camera to make large movements that were TOO LARGE for its range of motion. As a result, I would have to move the guide camera most of the way, and then begin guiding on a DIFFERENT star. This would allow me to move the rest of the way. Note also that there is a ‘red slit’ option on the guide camera GUI that forces you to use guide stars that are in the proper spot to account for such large changes. I found that I could only switch to that option after making one small jump.
*this is considered a ‘back-up’ way of doing this. There should be another way, that I was unable to get to work, that uses propsero scripts.
HgNe comp lamp
The Mercury-Neon (HgNe) needs only 5 sec of integration for a good comparison spectrum, however, the lamp needs to be on for at least 40 sec. What happens is the Neon gas is first heated up, and that heated Neon gas is used to heat the Mercury gas. This takes approximately 30 sec; it is safe to wait 40 sec in order to be sure that the Mercury gas has been heated up. After the Mercury is heated up, the Neon gas is dialed down automatically leaving you with only a Mercury spectrum.