How to take spectra

Prior to taking spectra, the slit position should be determined and the object imaged to verify position.  If suitable guide stars exist, the Guider should be guiding (ask the TO). If the CSHELL guider cannot guide and it is not daytime, then the TO may be able to use the offset guider. It is best to move the telescope in the direction of the slit to position your object away from the array center and nod about half a slit length in the opposite direction in order to observe your source in both A and B beam positions. For example, if the slit is oriented East - West (default orientation), then you may wish to move the telescope 7.5" east and use a 15" West nod between frames if you are observing a point source. This would position your source spectrum nearly equally displaced from the array center in both the A and B frames when observing in a nod mode.

The mean of the A-B data pairs in a set of cycles can be accumulated in a buffer if you are taking many spectra of an object. The MeanFrame buffer is initially set to "N/A" to disable this feature. To turn it on, select an unused buffer from its list in the Observing Parameters Frame. This buffer will then contain the mean A-B for the current set of cycles.

0. Verify that the object is on the slit.

A. Put Direct Imaging Mirror (DIM) IN.

B. Make sure all lamps are off, the filter in NOT blanked, and the shutter is OPEN.

C. Set Itime.

D. Set Cycles and Coadd to 1.

E. Turn Autosave OFF.

F. Take image (press GO).

G. Move object to slit position. One way to do so is:

a. In DV image, click on objects current position.

b. Press f key.

c. Move cursor to desired position (but do NOT push mouse button).

d. Press t key.

e. Select TCS Offset tab in lower part of DV.

f. Check that angle and plate scale are correct (270 and 0.2 respectively for CSHELL in standard position)

g. Click Offset Telescope.

h. Verify that the telescope is guiding (either with the CSHELL guider or offset guider).

1. Change to mechanism positions for taking spectra.

A. Take Direct Imaging Mirror (DIM) OUT.

B. For wavelengths 1.1-1.57 μm when using the CVF, the blocker should be put in.

C. Verify that desired slit is IN.

2. Check exposure-related settings.

A. Turn Autosave ON and make sure desired values are entered for path, filename, object, etc.

B. Enter desired values for Itime, Coadds, and Cycles.

C. Select desired Obs Mode. If nodding, give values to TO.

D. Check wavelength (μm) or wavenumber (1/cm).

3. Press GO.

LAST UPDATE: February 1, 2010