Observing with VATT



This document describes how to observe with PEPSI at Vatican Advanced Technology Telescope (VATT).

Observations are performed with following steps:
I Accessing PEPSI GUI
II Connecting with VATT
III Selecting and sending targets to VATT
IV Guiding
V Observing

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

I Accessing PEPSI GUI

  1. Either
    • use the PEPSI 4K monitor in the LBT control room,
    • connect to it from VATT
      • using ‘vattarchive’ server
      • login as ‘vattobserver’, passwd is at control room
      • type in terminal vncviewer -via ajarvinen@ssh.lbto.org -shared
      • environment (telemetry) status can be seen at
      • passwd is the standard pepsi passwd
    • observe remotely
      • from Linux machine
        • take VNC connection by typing in terminal vncviewer -via ajarvinen@ssh.lbto.org -shared
        • environment (telemetry) status can be seen at
        • passwd is given on need to know basis
        • in the end, close the VNC connection from the upper corner ‘x’ or F8, exit viewer
      • from Mac
        • one has to first make a VPN connection to vpn.lbto.org
        • username and passwd are given on need to know basis
        • and then take a VNC (with TigerVNCViewer) connection to server alpha.pepsi.lbto.org:1 (or :2) 
        • in the end, close the VNC connection with Fn+F8, exit viewer and disconnect VPN
    VNC view of PEPSI GUI (:1)

    VNC view of telemetry (:2)
  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 VATT

  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 VATT check button to connect and open ‘PEPSI VATT Control Interface‘:
    • Check that VATT radio button is selected:
  2. ‘VATT Telescope Control Interface’ and ‘VATT Guiding Camera’ windows should appear:


III Selecting and sending targets to VATT

  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 colour) you want to observe and send it to VATT. This does not yet move the telescope!
          • Note that target can be sent already during CCD readout!
        2. check that ‘PEPSI VATT Control Interface’ 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 program 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 program:
      4. Additional things to take into account when making observing programmes:
        • 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 specral 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
        • Exposure time depends on the used cross-disperser
        • One can have different exposure times for cross-dispersers in blue and in red arm
      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.
    • If for any reason the ‘PRESET‘ does not work, it is possible that the connection to VATT has been lost. Uncheck and re-check the VATT connection button (see II-1) to close and reopen the VATT windows.


IV Guiding

  1. Click ‘Guider’ to open guiding window to keep the target on the pinhole, check that ‘Pause’ is unchecked:
    • Offset buttons offsets the telescope in small steps so that the image of the direct-reflected image of the target moves on the guider CCD according to the directions of the buttons.
    • Offset step size specifies the offsets in arcsec. The default value is 1 arcsec.
    • The faster way to move the target into the pinhole is to click the target with the right button of the mouse (it does not matter if it seems that cursor is focused on the box instead of the star). The pinhole image itself is rather defocused, but the target should be sharp (status June 2019).
    • At this point you may re-focus with the help of the telescope operator. This is done by following counts in ‘PEPSI Photon Counter‘ window.  The larger the values, the better the focus. Note that no neutral density filter in ‘PEPSI Photon Counter’ should be inserted (ND0 selected when observing stars). If the sky gets too bright (or the target is too bright), it is possible that ND3 goes automatically in (as it should in that case). During summer 2018 the focus was around -1760 and summer 2019 around -1750.
    • Adjust exposure time, number of exposures, and binning according to brightness of the target. Exposure time is given in microseconds, max 0.5s. Binning should be kept at 4 for targets fainter than Vmag 6. It can be lowered for very bright targets. Number of exposures tells how many images are stacked for the guider.
  2. When the telescope adapter has been connected, you should check the hot spot coordinates (direct reflected image position). If you see the image of the star on the pinhole (doughnut) spilling over asymmetrically, correct hot spot coordinates. As reference, summer 2019 values were x=880 and y=566.
  3. When you are happy with the plots in ‘VATT Guider‘ window, start guiding by ‘Start’:
      • The upper most plot shows the cross profiles of the target in both X and Y direction and they should overlap and converge to zero. The second plot from top shows the guider offset and third FWHM of the star. The bottom plot shows how much flux the guiding camera gets. This gives a good indication of passing clouds.
    • Guiding in the next target can be started already while previous one is read out.
    • Normally, the gain value in ‘VATT Guider‘ window should be 0.3. If the star keeps jumping around and guiding does not see to work properly, try to change the gain value. At southern sky gain 0.8 is sometimes needed. FAP value 3 should be good.
    • In the morning, make sure that you ‘Pause‘ guiding to prevent GUI crash due to lost connection to VATT.


V 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.


VI 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 of the 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:

VII 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‘:


VIII 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 (summer 2019 130L is used):
  3. Click ‘START‘ button on Control Interface window:
    • Note that calibration settings (exposure times, etc.) get visible in the control interface after pressing ‘Start’.
  4. When calibration frames are ready, click ‘Calibs‘ again to close the calibration sequencer window and to be able to do anything else.


IX 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.

X Troubleshooting

  • When VATT computers have to be rebooted, the connection to them is lost and PEPSI software has to be closed and restarted.
    • Close it by clicking x in ‘PEPSI Spectrograph Control Interface’:
    • Start opening as described in the beginning of the instructions.
  • You have problems with pointing if
    • PEPSI VATT Control Interface’ Telescope section has either Azimuth or Altitude with red background
    • The cross profiles in ‘VATT Guider‘ window do not converge to zero
      • Contact telescope operator in order to solve the situation!
  • Sometimes the software program freezes or even crashes (STA Archon time out). If that happens, find the following terminal

and type Ctrl+c, wait some time and start everything again by typing ‘pepsi’


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.