Contents

• Definitions and procedures
  • Standard Slitmasks
  • Internal lamps
  • Order-blocking filters
  • Procedure to handle dome flat lamps
• Direct-imaging recipes
  • Through-focus series using GOH-X mask with internal lamps
  • Through-focus series using GOH-X mask using dome lamps
  • Through-focus series using GOH-X mask and night sky
  • Direct images of slitmasks using internal lamps
• Spectroscopic recipes
  • Through-focus series using GOSPH-3 mask with internal lamps
  • Spectral twilight flats
  • Typical night-sky spectral intensities
• Direct imaging flat fields
  • Broadband dome flats
  • Broadband twilight flats
  • Typical sky counts in a dark-sky broadband exposure
• Spectroscopic flat fields
  • Internal spectroscopic flats using Qz lamp
  • Dome spectral flats
  • Archival slitless dome spectral flats
  • Archival GRATEFOP exposures
  • Slitless standard star spectra
• FCS exposure times
  • Direct imaging
  • Spectroscopy
• TV exposures
  • Broadband TV dome flats
  • TV through-focus using dome FLSPECTR lamps
  • TV through-focus using internal lamps

Definitions and procedures

Standard Slitmasks

• GOH-foo mask: Grid of holes mask; for direct-imaging focusing
• LOSH3 mask: Line-of-slitlets-and-holes; 4.5 arcmin from center of telescope focal plane; slitwidth = 0.5 arcsec; for spectroscopic focusing
• GOSpH3 mask: Grid-of-holes for spectroscopy; small holes distributed in two dimensions over the slitmask; for spectroscopic focusing

Internal lamps

• Qz - Quartz iodide continuum
• Ne - Neon
• Cd - Cadmium
• Ar - Argon
• Kr - Krypton
• Xe - Xenon
• Zn - Zinc
• Hg - Mercury
• NAKX - Ne, Ar, Kr, Xe
• NHCXZ - Ne, Hg, Cd, Xe, Zn

Order-blocking filters

One of these, or a broadband filter, must be in place at all times in order for the camera to be able to focus on the CCD mosaic.

• BAL12 (clear)
• GG400
• GG455
• GG495
• OG550

Procedure to handle dome flat lamps

1. Bring up the dome lamp control GUI found under Telescope GUIs → Dome Lamp Control GUI on the VNC pulldown menu.
2. Turn ON the desired dome flat lamps.
3. Alternatively you can use the DCS keywords for lamp control on a vm-deimos or polo terminal. The keyword that controls the imaging dome flat lamps is flimagin. The keyword that controls the spectal dome flat lamps is flspectr. The spectral lamps are brighter than the imaging lamps. These are some examples of utilization of the DCS keywords to turn on and off dome flat lamps:
   • To turn the spectral lamps on:

     	    modify -s dcs flimagin=0 flspectr=1

   • To turn both sets of lamps off:

     	    modify -s dcs flimagin=0 flspectr=0

4. In a vm-deimos or polo terminal type:

   modify -s dcs domecals=true

   This is required to let the summit crew know that you are are going to take dome flats and they cannot enter the dome.
5. Manually take the flats using the recommended times in the tables below.
6. Make sure to Turn OFF the dome flat lamps once you are done taking your flatfield frames.
7. In a vm-deimos or polo terminal type:

   modify -s dcs domecals=false

   This is required to let the summit crew know that you have finished taking dome flats and they can enter the dome.

Direct-imaging recipes

Through-focus series using GOH-X mask with internal lamps

Through-focus series using GOH-X mask using dome lamps

Follow de procedure to handle dome flat lamps and use the exposure recipes in the next table:

Through-focus series using GOH-X mask and night sky

Direct images of slitmasks using internal lamps

Spectroscopic recipes

Through-focus series using GOSPH-3 mask with internal lamps

Blue lines below 5500 A:

• Kr: 7 lines, 4273-4502 A, few hundred counts in 20 sec
• Cd: 3 lines, 4660-5085 A, few thousand counts in 2 sec; medium Ar
• Hg: 2 lines, 4046-4358 A, few thousand counts in 2 sec; strong Ar
• Xe: 11 lines, 4736-5695 A, few thousand counts in 100 sec
• Ar: 7 lines, 4158-4510 A, ~100 counts in 20 sec
• Zn: 3 lines, 4680-5181 A, few thousand counts in 2 sec; weak Ar
• Ne: 1 line, ~4900 A, few thousand counts in 20 sec

Spectral twilight flats

Exact times and counts depend on when taken. The following data are for a series of 5 exposures each taken at sunset in two gratings. The series started 4 minutes after sunset and was taken in the order shown. Spectral twilight flats should really start 15 minutes BEFORE sunset (note: special Director's permission is needed to open that early).

Typical night-sky spectral intensities

Direct imaging flat fields

Broadband dome flats

Follow de procedure to handle dome flat lamps and use the exposure recipes in the next table:

Broadband twilight flats

• Exact times and counts depend on when taken.
• These data are for a series of 10 exposures taken at dawn starting with Z and ending with B, two flats in each filter.
• The series ended 15 min before sunrise.

Typical sky counts in a dark-sky broadband exposure

Spectroscopic flat fields

Internal spectroscopic flats using Qz lamp

• Need 10 of these to get good S/N in blue.

Dome spectral flats

Follow de procedure to handle dome flat lamps and use the exposure recipes in the next table:

• Use 1.00 arcsec slitwidth with FLSPECTR lamp.
• Note: the dome spectral lamp on Keck II is too faint; CARA should install a brighter lamp if possible.

Archival slitless dome spectral flats

• To measure for px-px variations and condensation monitoring.
• Use FLIMAGIN.
• Take three exposures at each tilt and add together.

Archival GRATEFOP exposures

Iillumination comes from positioning LED on grating transport stage. Shines light directly through camera, illuminating bubbles in coupling fluid and other defects. Recipe:

• Spectroscopic mode, to get image of whole detector
• BAL12 or other blue cuton filter; focus the CCD for filter used (precaution, probably does not matter)
• Slider 3 (tilt and grating do not matter)
• Hatch closed
• modify -s deimot GRATEFOP=on
• Take 3×10 sec exposures
• modify -s deimot GRATEFOP=off

Slitless standard star spectra

• Good for stars in range 10.5-11.5 V mag.
• Use 50s exposure time for all gratings, tilts, and filters.

FCS exposure times

The FCS lamps are a bit too bright and need adjustment. The following are the data for the current brightnesses (2002 December) before adjustment.

Direct imaging

Spectroscopy

• Use the CuAr lamps for all gratings.
• Exposures are 10 sec below 5500 A and 1-5 sec beyond this.
• Peak counts in the blue are a few hundred.
• Peak counts in the red are a few×10,000.

TV exposures

Broadband TV dome flats

Follow de procedure to handle dome flat lamps and use the exposure recipes in the next table:

TV through-focus using dome FLSPECTR lamps

Follow de procedure to handle dome flat lamps and use the exposure recipes in the next table:

TV through-focus using internal lamps

• Try to use Qz whenever possible, as illumination is better.