Difference between revisions of "Mookodi"

Revision as of 16:55, 13 April 2022

Mookodi is a low resolution spectrograph and imager, designed to be operated fully robotically. It was designed and built by Liverpool John Moores University (LJMU), and installed on the Lesedi telescope in December 2021. It will undergo a period of science commissioning observations during the first trimester of 2022, with the ability to do spectroscopy and low-cadence imaging.

Instrument Description

Specifications

• Camera: Andor DU934P deep depletion camera, 1024 × 1024 CCD, 13 μm pixels
• Spectral range: 400.5 – 799.5 nm ^[1]
• Spectral resolution:

  Dispersion: 3.88 Å/px

  Resolution:

  80µm slit

  R = 301.0 @4671.23 Å

  R = 374.4 @5823.89 Å

  R= 492.5 @7642.02 Å

  160µm slit

  R = 172 @4671.23 Å

• Plate scale: 0.6 arcsec/px ± 0.06 arcsec/px ^[1]
• Field of view: 10' × 10'
• Slit: Long slit with narrow (80µm, 2") and wide (160µm, 4") sections.
• Filters:

  Filter Slide A: Full set of SDSS filters (u', g', r', i', z')

  Filter Slide B: Longpass order blocking (OB) filter, and clear filter. There are three empty slots in this slide available for future use.

1. ↑ ^{1.0 1.1} Preliminary values based on lab tests at LJMU or original spec. Actual values to be confirmed during commissioning.

Suitable Uses

• Spectroscopy
• Low-cadence imaging: the camera is not a frame transfer camera, and in normal operation exposures are readout after the closure of an iris shutter. The shutter is life-cycle limited and not suitable for high-cadence observations.
• High-cadence imaging: it is possible to deactivate the shutter but users should be aware that this will result in some readout smearing. There is also no GPS triggering of the exposures but the times recorded in the header (Keyword = DATE-OBS) is the start of the exposure and has been measured to be accurate within ~50ms of absolute time (see here TODO). NB. High cadence observing (e.g. multiple continues exposures with exposure times < 30sec) SHOULD NOT be done with the shutter on AUTO mode. It is very important to set the shutter to "ALWAYS OPEN" which will deactivate the shutter in the open state but flush the CCD before the start of each new exposure.

Operating Mookodi

Prepare the Lesedi telescope by following the Lesedi start-up recipes. As Mookodi is on the old SHOC port, any relic references to the SHOC port should be taken to mean the Mookodi port.

Mookodi can be operated via a web GUI. Fully scripted observations (incl. auto-focus of the instrument, automatically positioning a target on the slit, and activating auto-guiding) will be available soon.

Operation via the web GUI

Open the web GUI at mookodi.suth.saao.ac.za:5000. The GUI is roughly divided into five sections. From top to bottom: opto-mechanic configuration (lamps, slit, filters etc.), target acquisition (auto acquisition of a user defined sky-coordinate on a user specified x and y pixel position), exposure configuration (exposure time, binning etc.), higher level instrument control (start exposures, auto-focus instrument etc.), and an image display.

1. Opto-Mechanic Configuration:
   • Select the desired configuration for each component. The components moved in/out of the beam via pneumatics (eg. mirrors, slit, grism) and lamps will respond on the push of the button, and indicate when they are busy or in the desired configuration. To conserve lamp lifetime, do not leave them on unneccessary for extended periods of time.
   • Select the required filter via the dropdown menu under the Filter A or Filter B headings and press the SET button to activate the filter slides. The box above the dropdown indicates the name of the filter in position for each slide, or BUSY if the slide is still finding its requested position.
2. Target Acquisition: TO DO
3. Exposure Configuration:
   Select the desired configuration for each setting using the dropdown menu below the relevant heading, then press the SET button to issue the command to the camera.
   • Binning: Options are 1×1, 2×2, 3×3, and 4×4.
   • Gain: High (faint objects), medium, and low (bright objects)
   • Rate (readout rate): Fast (5 MHz) - read-noise of 13.6 electrons, and slow (0.05 MHz) - read-noise of 3.3 electrons (see Andor spec sheet link at the top of page)
   • Image Type: This has no physical effect on the instrument configuration and only populates a header keyword with the selection (possibly useful for automated data reduction)
   • Instrument Mode: This has no physical effect on the instrument configuration and only populates a header keyword with the selection (possibly useful for automated data reduction)
   • Number of exposures: The number of exposures to take at the set camera/instrument configuration. NB. see also high cadence imaging in the Suitable uses section at the top of this page.
   • Exposure time (in ms): Note the exposure time display does not update when the SET button is pushed, it only updates after the exposure is started. This is a known issue.
4. Higher Level Instrument Control:
   • Exposure Control:
     • Take exposure/Start: Starts an exposure with the SET exposure configuration
     • Abort: Aborts the current exposure.
   • Guider Control: TODO
   • Shutter Control: TODO
   • Save images: TODO
   • Exposure Information: TODO
   • Nudge telescope pointing: TODO
   • Focus control: TODO
   • CCD Temperature Control: Displays the current CCD temperature, and buttons for cooling down and warming up. The camera takes 10 - 15 minutes to cool, and will stabilise at approximately -70 ºC. Cool the camera at the start of observations and warm it up once you are done.
5. Image Display:
   • Contains an image display of the last completed exposure, using JS9.
   • A red and blue circle will appear where the preset values are for the pixel positions for the narrow and wide slit locations. Known bug: only appears after the second image is taken and only displays correctly for 1×1 binning.
   • TIPS: TODO.

Note: It is advisable that DARK frames should be taken with the shutter in the "ALWAYS CLOSED" mode. BIAS frames (especially if multiple frames are taken) SHOULD ALWAYS be taken with the shutter in the "ALWAYS CLOSED" mode since this will deactivate the iris-shutter in the closed state and prolong the lifetime, see also high cadence imaging in the Suitable uses section at the top of this page.

From a terminal window:

scp mookodi@mookodi.suth.saao.ac.za:/data/lesedi/mkd/yyyy/mmdd/* .<local path to copy to> 

Where yyyy is the year, mm is the month, and dd is the day. The convention is that the data rolls over to the current date at 1200 UTC, hence all the files from a given night are stored in the folder corresponding to the date at the start of the night. e.g. All observations started on the night of 2021/12/11 will be stored in /data/lesedi/mkd/2021/1211/.

Start-up Procedures

It should not ordinarily be necessary for an observer to perform these procedures. However, if a restart is necessary, or if recovering from an unplanned shutdown:

• The Mookodi host machine is set to boot automatically when powered.
• There are three services that need to be run before Mookodi can be operated via the web GUI: opto-mechanics, camera, and web server.

TODO - instructions on how to restart all services in the correct order with a single "restart_services" terminal command

Daily Rounds

This section contains information for the technicians performing daily rounds.

Evening

• Switch on the compressor
• Check that instrument services are running (opto-mech, camera, web service) by opening the web GUI and configuring the instrument as follows:
  • Slit IN
  • OB filter SET (Filter Slide B)
  • 1000 ms exposure SET, Start exposure
• This should produce a noisy image at the camera (visible in the image view window), and all instrument mechanisms should respond as commanded.
• Slit OUT, filter out SET
• If anything fails to respond as expected, follow the troubleshooting procedures.

Morning

• Switch off the compressor
• Check that the camera is warmed up

Troubleshooting

Known Issues

• FITS headers are not populated with instrument information currently. This is a priority for early 2022. Observers will need to record observation information manually.
• Exposure time display does not update when the SET button is pushed, it only updates after the exposure is started.
• The Abort button on the web GUI does not abort the exposure, even though it reads as such. Exposure can be aborted via the CLI in the interim.
• Filter slide A can time out when trying to reach a commanded position when Mookodi is in certain orientations.