It is challenging for MOSFIRE observers to acquire standard star spectra that cover the entire wavelength range accessible at the H and K passbands. A standard longslit in the center of the mask will not necessarily cover the full wavelength range applicable to slits at the edges of the field of view. To deal with this problem, we have developed:

As of Aug 2015, the MOSFIRE DRP does reduce the long2pos mask observations.

long2pos Slitmask

The long2pos slitmask consists of two 3-segment longslits for spectroscopy, plus a center alignment box for acquisition. The mask pattern is depicted in the image below and includes three slits:
  1. (at left) samples the higher wavelength range
  2. (in center) is for target alignment only
  3. (at right) samples the lower wavelength range


There are two options for gathering spectra with the mask: The procedures are similar and are described below.


Follow these steps to acquire the data:

Preliminary Steps

  1. Install the slitmask into the CSUMasks sub directory using the pull down option:

    MOSFIRE Utilities -> Spectrophotometric Observations -> Install long2pos CSU mask files

  2. For longslit only: load the long2pos mask into MAGMA.
  3. For longslit & Spectrophotometric data: load the long2pos_specphot mask into MAGMA.

Observing Steps

  1. Configure CSU
    1. Select either long2pos or the long2pos_specphot mask
    2. Click Setup Science Mask (not alignment mask!)
    3. Click Execute Mask to configure CSU
  2. Acquire Target
    1. Select the Bright Long tab on the Slitmask Alignment Tool
    2. Have OA acquire star with guider and send to SLIT pointing origin
    3. Click Pre-config filter to set filter and grating to nb1061-imaging.
    4. Click Acquire image
    5. Wait for exposure to display on SAT. The red + marks the center of the object and the yellow X marks the slit center.
    6. If the object center is incorrect, click on the center to move the red + to the correct location
    7. Click Move to Center to offset telescope
    8. Repeat previous 4 steps until object is centered
  3. Configure MOSFIRE
    1. On the Observing Mode subpanel, select the appropriate spectroscopy mode
    2. Optionally, on the Exposure Control subpanel, enter the desired datataking parameters for:
      • integration time
      • coadds
      • sampling mode (2 for CDS, 3 for MCDS, 4 for UTR)
      • number of reads
      and click APPLY instead of GO. Note that this step is optional because the automatic acquisition script for long2pos (see step 5 below) will prompt you to enter the exposure configuration with defaults set to whichever values you currently have in the Exposure Control subpanel.
  4. Coordinate with the OA
    If no guide star is avaliable in the MOSFIRE guider detector within the blue-shaded region shown in the following figure (e.g. star surrounded by a red circle), ask the OA to stop guiding.

    Note that the standard can be observed without guiding because the four exposures taken by the long2pos script occur in a very short timescale.
  5. Acquire spectra:
    Note the spectrophotometric mask version will acquire spectra in the narrow and wide slits while the long2pos mask only uses the narrow slits.
    1. Launch the datataking script from the background menu via

      MOSFIRE Utilities > Spectrophotometric Observations > Acquire spectra with long2pos mask