Background

• Arcs. The tool allows you to acquire separate exposures in the HgNe, Xe, and CuAr lamps, or combine the lamps in a single exposure.
• Spectral flats. Acquire flatfield exposures with the current slit using either the dome or internal quartz halogen lamps.
• Pinhole flats. Acquire flatfield exposures through the MultiHoles mask using either the dome or internal quartz halogen lamps. These exposures may be useful in establishing the “trace” of the spectrum.
• Bias. Acquire bias exposures of 0 sec length to measure ESI fixed CCD pattern noise. Typically these are not required, since ESI has negligible pattern noise. Most observers simply remove the constant bias using the overscan sampling method.
• Darks. Acquire dark exposures of any length to measure and correct for dark current. ESI dark current is typically insignificant.

Recommendation

• Essentials:
  1. At least one combined arc using Hg+Xe+Cu (take 5 if time permits)
  2. At least three flats (take 10 if time permits)
• Useful if observing a source with no obvious continuum flux:
  1. At least one pinhole flat.
• Potentially useful:

Procedure

1. Configure the spectrograph for taking calibrations:
   • Close the hatch.
   • Extinguish lamps.
   • Configure for desired spectroscopic mode.
2. Launch the tool from the ESI background menu by selecting ESI Utilities > ESI Calibration Tool.
3. Under ARCS, select which lamps to observe, adjust the exposure times as needed, select the quantity, and determine whether you want the arcs to be combined (all selected lamps will be used in each exposure) or separate (only one type of lamp used in each exposure).
4. Under FLATS, set the number of spectral flats to acquire, and the desired exposure time.
5. Under PINHOLE FLATS, set the number of pinhole flats to acquire, and the desired exposure time.
6. Under BIAS, set the number of bias exposures to acquire. These are always 0 sec in exposure length.
7. Under DARKS, set the number of dark exposures to acquire and the desired exposure length.
8. Under OPTIONS, select Use dome flat lamps instead of internal? to use the dome flatfield lamps for the flat and pinhole flat exposures. De-select this option to use the internal quartz halogen lamps.
9. Under OPTIONS, select Shut down ESI when finished? to have the script shutdown the instrument software after the calibration exposures are completed. This allows you to go to sleep at the end of the night while the script completes your calibrations.
10. Click GO to start acquiring data with the esi_calib script.
11. Click RESET to restore the default exposure parameters for the currently-selected ESI slit.
12. Click QUIT to exit the GUI.