User manual for PEPSI PFU


The pdf version of the manual can be downloaded from here.


Below is described how to observe with PEPSI Permanent Fiber Unit (PFU) at Large Binocular Telescope (LBT). All pictures can be clicked to enlarge them for details.

Observations are performed with following steps:
I Accessing PEPSI GUI
II Connecting with PFU
III Selecting and sending targets to LBT
IV Guiding
V Keeping target in pinhole
VI Observing

The document also describes following items:
VII Viewing obtained spectra
VIII Estimating S/N
IX Calibration frames
X Telemetry
XI Troubleshooting

I Accessing PEPSI GUI

  1. Either
    • use the PEPSI 4K monitor in the LBT control room, or
    • observe remotely
      • NOTE that you must request VPN access to LBTO beforehand – at least about 10 days before the run. Write to to get it with relevant information about your run!
      • first make a VPN connection (using Cisco AnyConnect)
      •  then take a VNC (with TigerVNCViewer) connection to server (or :5902) 
        • in the end, close the connection with (Fn+)F8, exit viewer and disconnect VPN
    VNC view of the user interface (:5901)

    VNC view of telemetry (:5902)
  2. The PEPSI user interface program should be kept running all the time.
    • If it is not running, click Activities in the left upper corner. You should get a menu having PEPSI logo. Click on that logo to open the program.
    • Or use a terminal to open it (if not, open a new terminal)
      • on pepsi@alpha type ‘pepsi’

II Connecting with PFU

  1. Now you should have ‘PEPSI Spectrograph Control Interface’ open.
    • In case PEPSI has been used for solar observations (SDI selected) and you have text ‘Waiting for Sun‘ in the ‘PEPSI Spectrograph Control Interface‘, click ‘Abort‘ to be able to start night observations.
    • Click on LBT check button to connect and open ‘PEPSI@LBT‘:
    • Check that PFU radio button is selected:
  2. A ‘PEPSI@LBT‘ window should appear:

III Selecting and sending targets to LBT

  1. Click ‘Program’ button on ‘PEPSI Spectrograph Control Interface’:
  2. When you
    1. already have an observing program, a ‘Observing Programmes‘ window and a ‘Target Visibility Plot‘ window opens. If not, go to ‘Table‘ menu, choose ‘Open or Close Table‘ and select the correct one.
        • If GUI had to be restarted, check that the correct program is open (YYYYMMDD.obs)!
          1. select the target (highlighted with teal color) you want to observe and send it to LBT. This does not yet move the telescope!
              • Note that target can be sent already during CCD readout!
          2. check that ‘PEPSI@LBT’ has the same target as you chose, or resend:
          3. check that ‘PEPSI Spectrograph Control Interface’ changed (target name, selected cross-dispersers, exposure time, etc.) according to selected target:
              • Note that the changes happen only after CCD readout has finished.
          4. if you need to change pre-defined exposure times, click ‘Edit fields’:
          5. a new window pops up and you can make the changes
              • Note that values in ‘PEPSI Spectrograph Control Interface’ do not change unless you send the target information again (see A.)
            • you can also change values in ‘PEPSI Spectrograph Control Interface’ directly, but then the visibility plot does not change and block will not remember the changes made in future
    2. don’t have any targets or you want to change targets
      1. click ‘add another object’ in ‘Observing programmes’ window:
      2. a new window having targets pops up:
      3. choose the target and send it to the observing block:
      4. Additional things to take into account when making observing programmes:
        • PEPSI observation modes.
          PEPSI observation modes.
        • The entire spectral range is from 383 to 912 nm but it can not be covered by a single exposure
        • PEPSI has two arms, blue and red, that cover spectral ranges 383-544 nm and 544-912 nm, respectively
        • Each arm has three cross-dispersers:
          • CD1 383-426 nm in blue arm
          • CD2 426-480 nm in blue arm
          • CD3 480-544 nm in blue arm
          • CD4 544-627 nm in red arm
          • CD5 627-741 nm in red arm
          • CD6 741-912 nm in red arm
        • Simultaneously, one can observe one wavelength region in blue and one in red, however, CDs 3 and 4 can not be used at the same time
        • Observations can be done using three different fibers, that is with three different resolutions:
          • 100 μm gives R=250,000
          • 200 μm gives R=130,000
          • 300 μm gives R=50,000
        • Exposure time depends on the target, the wanted resolution, and used cross-disperser (use Exposure Time Calculator)
        • One can have different exposure times and numbers of exposures for cross-dispersers in blue and in red arm (examples below)
          • 30 min in blue, 20 min in red ⇐ red is idle for 10 minutes
          • 30 min in blue, 2×15 min in red ⇐ both are ready around the same time
          • 3×10 min in blue, 6×5 min in red ⇐ both are ready around the same time, blue likely idle for some minutes due to read-out times (~ 80 sec / read-out)
      5. continue as in III-2-a.
  3. after the telescope operator gives the permission, click ‘PRESET
      • PRESET‘ to next target can be done already during CCD readout.
      • In case one of the telescope eyes does not move to the target, it is possible to make ‘PRESET‘ separately only with one of them.
      • Note that ‘Preset‘ can be done in four different modes, but only the first one should be used unless requested otherwise by the telescope operator:
        1. Active – the normal mode, uses wavefront sensor and guiding
        2. Guide – no wavefront sensor is used, guiding yes
        3. Acquire – only points and centres on hot spot
        4. Track – only points

IV Guiding

Collimating, guiding, and also focusing is done by the telescope operator. Do not do anything unless asked.

  • Engageopens the hatches so that the telescope operator can put the star in the position.
  • Guideropens guiding windows

V Keeping target in pinhole

VI Observing

Start observations by clicking ‘Start’ in ‘PEPSI Spectrograph Control Interface’:

  • If the exposure needs to be interrupted for any reason, use ‘Stop’ in case you want to save the data obtained so far orAbort’ in case the exposure time was not long enough for useful data.

VII Viewing obtained spectra

It is good to take a look at the spectra in order to see if you should change exposure times etc.

  1. Select the spectrum (highlighted with teal colour) you want to look at from ‘FITS Image Browser‘ with Enter or click the arrow icon to send it to ‘Spectrum viewer‘. One can also look at multiple spectra by selecting them and clicking double arrow icon.
  2. The active window in ‘Spectrum viewer‘ has a cyan frame. Select the area you want to look at closer by drawing a red box with, for example, a mouse:
  3. To see a summed spectrum from selected area
    1. Press ‘Enter‘, or
    2. Click the normal ‘Sigma‘ icon (one dimensional cross-cut in horizontal direction) on top of the viewer (the other sigma makes it in vertical direction)
  4. Now you have a spectrum plot where you can see the ADUs:

VIII Estimating S/N

  1. Select an area with mouse from highest continuum values to lowest (don’t be distracted by high fabry-perot peaks):
  2. Click ‘Sun‘ icon on top of the spectrum viewer:
  3. You get a pop-up window there the S/N estimate is given, save that information into fits list by clicking ‘Save‘:

IX Calibration frames

After the observing night is over, it is time to take the calibration
frames. Check that you have stopped guiding and guider camera is on pause.

In the ‘PEPSI Spectrograph Control Interface’ window:

  1. Click ‘Calibs‘ button to get a pop-up window:
  2. Check that for wanted fiber(s) ThAr, FPE, and Traces are chosen:
  3. Click ‘START‘ button on Control Interface window:
  4. When calibration frames are ready, click ‘Calibs‘ again to close the calibration sequencer window and to be able to do anything else.

X Telemetry

    • It is essential to check the telemetry from time to time:
    • If something is wrong and you are not trained to fix the problem, contact a person who is!
    • The most important is the ‘Pressure‘ in PEPSI Chamber window. If ‘In’ value has red background, and one sees that pressure curves follow each others, everything is not fine.
    • Other important measure is ‘Dewar heater‘ in PEPSI CCD window. If it approaches 0, the dewar pressure rises and pumping is needed.

XI Troubleshooting

  • Sometimes the software program freezes or even crashes (STA Archon time out). If that happens, find the following terminal

and type Ctrl+c and start all over again.

If terminal gives ‘Lost connection with Camera’, one can go to ‘PEPSI Control Unit’ Maintenance, but in order to do that, you should know what you are doing. Moxa-Power-Ccd Controllers, wait 10 seconds. In case of pressure problem, use again Maintenance.