Nordic Optical Telescope Text Size: Smaller Text Normal Text Larger Text

MOSCA Cookbook

Last updated October 22 2020
Please refer to the online version for the latest update

Table of Contents

Preparing Observations

Observing scripts

Observing scripts can be generated automatically through the Observing Script Generator or crafted manually. If done through the web, the script will be uploaded and within a few minutes available in ~obs/scripts/proposal-ID, where proposal-ID refers to the proposal ID entered in the web form (e.g. 38-042). If the directory does no exist, it will be created. If you make your observing scripts manually, first make the proposal ID directory (using mkdir) and place them therein.

The scripts are executed from the sequencer window, from the directory where they are placed. Note that if you are saving scripts or files elsewhere in the ~obs account, the directory will be cleaned up after every run and it will not be possible to recover them.

Create a TCS Target Catalogue

A source catalogue can be made well in advance of your observations by using the web interface, NOT Source Catalogue Creation. Note that it is also possible to enter targets on-the-fly and create a catalogue directly on the TCS while observing (See section, Loading Target Catalogue).

Exposure Time Calculator

The Exposure Time Calculator can be used to estimate the required exposure times for ALFOSC, NOTCam, FIES, MOSCA and StanCam (both in imaging and spectroscopy mode, where it is available).


MOSCA CCDs are linear (better than 0.2%) up to digital saturation (216ADU).
NOTE The full well of device (ext 3) W20-(0,0) has a strong position dependence with a limiting level of only 40 kADU (/52 ke-) in the bottom right corner, nearest the centre of the mosaic array.

Please find more information from MOSCA general characteristics and Detector pages.

MOSCA read out time

The read out time of the full mosaic is 36 seconds with 2x2 binning.

Afternoon Preparations

Overview of everyday afternoon tasks

  • Update the TCS target catalog if necessary, and upload it to the TCS.
  • Find out the TCS access code of the day on TCS status page 1
  • Shutdown the MOSCA BIAS programme:
    [obs@selena ~]$ shutdownobssys mosca
  • EXIT MOSCA obs-log on the lisa display
  • Startup the MOSCA software
    [obs@selena ~]$ startobssys mosca
    and remember to set the binning 2x2
  • Change directory to your working directory:
    [obs@selena ~][MOSCA]$ cd ~obs/scripts/43-999
  • Edit and test your scripts.
  • Take calibration frames , darks, biases, dome flats.

  • In case of an FIES override:
    • Shutdown the FIES+STANCAM Sequencer:
      [obs@verushka]$ shutdownobssys fies
    • Kill all remaining windows on the lisa display (excluding those of MOSCA)
    • Startup the FIES+STANCAM Sequencer
    • In all FIES/STANCAM Sequencer windows change the working directory to the one assigned to the override programme, for instance
      [obs@selena][STANCAM]$ cd ~obs/scripts/38-025
      [obs@verushka][FIES]$ cd ~obs/scripts/38-025
      as in this directory FIES observing scripts can be found and executed.
    • Run the requested calibration scripts, typically fies-calibs script in the FIES Sequencer.

TCS access code

Any instrument computer which needs access to the TCS, for instance to move the telescope during slit acquisition or dithering, will ask for the current TCS access code at start-up. This code is updated every day (around lunch time). When you are asked to supply the TCS access code, do the following:

  • On the TCS VT510 terminal, make sure that the brightness is turned up
  • On TCS type: Show-Page and then 1 (or type sh 1 for short)
  • The TCS access code is shown on the top part of the screen as: AccessCode xxxxxxxxxx

Starting the MOSCA Observing Software

  1. Go to the computer called lisa.

  2. Click on the line

    ' Willing to manage'

  3. Click on Accept.

  4. Log in with username obs. Password will be supplied by the staff.
  5. To start the observing system in a terminal window type:
    [obs@selena ~]$ startobssys mosca
  6. and enter the TCS Access code of the night in a popup window.
  7. Wait until the Talker displays the text "MOSCA Sequencer READY TO USE" or the UT is incrementing on the top right of the "CCD status" window.
    The lisa-screen should look like this .

  8. Images are stored in the directory /data/mosca.

  9. The automatic MOSCA observing log displays a listing of FITS headers for incoming data files. The System Talker lists incoming messages from the Sequencer. These two programs are displayed on the InfoSys monitor, and are automatically reset every afternoon. If you change between instruments you can change the obslog with the command e.g.:
    [obs@selena][MOSCA]$ mosca.showlog

  10. Change directory to your working directory (e.g.):
    [obs@selena ~][MOSCA]$ cd ~obs/scripts/43-999
  11. Start a new Sequencer terminal, if needed:
    In a terminal window type
    [obs@selena~]$ seqterm
    and choose the MOSCA option.

The computer florence is used for image analysis using IRAF/MSCRED. You can start iraf ecl by typing xgterm on a terminal window. On florence, images made by MOSCA are found in the directory /data/mosca/. Be advised that this directory is read-only.

Loading the TCS Target Catalogue

  • On the TCS, press the catalogue button CAT to view the object catalogue. If you want to erase the current catalogue that is displayed, type erase-catalogue on the TCS.
  • Load a source catalogue by typing read-catalogue on the TCS, where catname is the name of the catalogue. A source catalogue can be created by using the web interface or the objects can be added directly to the current TCS catalogue by pressing the key, Enter Object (2) and then type according to the example below:

    Name RA DEC Epoch ProperMotionRA ProperMotionDec Magnitude

    SN1995N 14:49:28.27 -10:10:15.40 2000.0 0.00 0.00 0.00
    The proper motion should be given in arcseconds/year

  • Add a catalogue of blank fields, if needed, for obtaining twilight flats fields by typing read blanks on the TCS.
  • To select an object, press the catalogue button CAT on the TCS, and then use key number 1 or 7 to move to the next or previous object, or use the Prev/Next buttons to scroll up/down an entire page. The telescope will move to the selected target when pressing the key Preset to selected (4), or if observing on the parallactic angle, pressing the key Preset to par ang (6).

Obtaining Calibration Frames

For many observing programs calibration frames can be secured in the afternoon. The type of calibration frames needed depend very much on your science goals and the instrument mode you are using. For further information see: MOSCA

During the afternoon it is recommended to take some bias frames and *dark* frames. The dark frames should have similar or longer integration time as your longest science exposures. Please let your duty officer known that you are taking dark exposures in order to keep the dome dark. In addition, it doesn't make any harm to take a set of dome flats however twilight flats do a good job as well.

Acquire at least two bias frames before starting your observations in the afternoon/evening and again in the end of your observing night. With two bias frames and with two flat fields of the same intensity level, gain and readout noise can be determined, e.g. by using the IRAF task findgain.

If there is a sudden large area of reduced sensitivity and the area is moving most likely it is a bug or spider. The only way to remove "a bug with wings" or a spider during an observing run is to lower the instrument and remove the offending bug.
Contact staff!!!

Start of the night

Overview of things to do at sunset

  • Power-on the telescope and open the dome following the procedure in the Cookbook

  • Once the telescope power is on, switch to MOSCA. Run the script
    [obs@selena]$ tcs.setup-tel-mosca
    in the Sequencer window. This script sets up the telescope for observing with MOSCA.

  • Starting at sunset, run any sky-flat scripts that are needed. Make sure that the you have set correct binning, typically 2x2 binning.

  • Focus the telescope. Use focusexpose-script and analyse the image using mosca.focus-auto sequencer script. NOTE! Do not autoguide while taking focus sequence.

  • When it is dark outside, switch on the two guiding monitors, and activate the guider at the TCS terminal or in a Sequencer window:
    Note that tv-on needs to be issued every time the telescope has been parked at zenith.

Telescope Startup Procedure

Return to the dome at least 30 minutes before twilight and follow the instructions below.

Weather precautions

Humidity Wind Dusty Wind Temperature
> 90% - Close telescope

After 20min < 90% the telescope can be reopened.
12 m/s - Close sideports and lower hatch 10 m/s - Close sideports and lower hatch If the humidity is > 90% and the temperature is
< 0° C close telescope and do not open until all ice has melted on the outside of the dome.
15 m/s - Observe down wind: at least 85 degrees in AZ away from wind 12 m/s - Close telescope
20 m/s - Close telescope

Telescope Control System (TCS)

  1. Turn up the brightness of the TCS screen (on right-hand side, below the screen).
  2. Look at the top-left of the TCS screen. If the item ST isincrementing, then the TCS is running, if not - then the TCS needs rebooting (rebooting the TCS should be done under guidance of a staff member). Type refresh if the screen looks strange.

Telescope power-on and Dome Opening

  1. Check the safety system in the computer room. Reset the system by turning the left key (marked as "First") and then the right key (marked as "Second"), one at a time (See TCS Manual Sect. 10.1 for procedure). If you hear a repeated clanking sound then the system has not reset, check the red lights above the keys to see if a safety stop or other item is set.
  2. Type on the TCS, power-on and confirm with y for yes. Look at the status page number 1 (type sh 1). On this page the status of the power units for the telescope motors can be viewed. When the TopUnitPower is on and the telescope is Idle, the telescope is ready to use. The power-on procedure takes about one minute in total.
  3. At sunset, if weather conditions are OK, open the upper hatch with the mirror covers closed. Press the key, START/STOP on the TCS and then the key Open Upper Hatch (7). Confirm by typing y for yes. It takes about 3.5 minutes to open the upper hatch.
  4. In the dome (While the upper hatch opens):
    • Open the side ports (only if weather conditions are OK).
      The side ports are motorized and opened/closed by pressing green buttons on the dome wall. See Sideport Operation .
    • Check that nothing is in the way of the telescope motion (altitude: 6.5° - 90°).
  5. Open the lower hatch (only if weather conditions are OK). On the TCS, press the keys Start/Stop and Open Lower Hatch (8). Confirm with a y. It takes about two minutes to open the lower hatch. The TCS will not allow opening of the lower hatch before the upper hatch has completed opening. In case you can only open the upper hatch, the maximum zenith distance for unvignetted observing is 55°, and at a zenith distance of about 70° roughly half of the mirror is vignetted.
  6. The mirror covers can be opened at the same time as the lower hatch. On the TCS, press the keys Start/Stop and Open Mirror Covers (9). Confirm with a y. It takes about 50 seconds to open the mirror covers. Please note that the power for hatches and mirror covers is completely independent of the telescope power and the electronics in the control room.

Set default telescope parameters

  1. This should be done in any sequencer terminal with
    [obs@selena]$ setup-tel-mosca
    This sets amongst other items, the default telescope focus and rotator angle, and auto-pos-full for fully automatic autoguiding when pointing to an object.


Field Rotator

In an alt-az telescope the field rotator is used to keep the orientation on the sky fixed while tracking. When the field rotator is in automatic mode, which is the default, the TCS command field-rotation value sets the rotator such that value is the angle between the sky and the instrument. The default value of the Field Rotator is different for each instrument and can be found in Table 1. The field-rotation value will be set to the default angle when executing the script setup-tel-mosca

The rotator-position is the physical position of the rotator with respect to the telescope fork, and it has a limit at +- 200 degrees. Its current value is shown on the TCS status display together with the time-to-reach-limit in minutes. Before reaching the limit, the TCS will send a warning and suggest you to turn the rotator 360 degrees at any convenient moment. This can be done manually with the TCS command ro-tu-360 after switching off autoguiding with ag-off. Note that this is possible only in the overlapping ranges [-200,-160] and [160,200]. If the limit is reached, the TCS will eventually, after repeated warnings, perform the full rotation automatically (whether or not an observation is ongoing).

The exposure commands for ALFOSC, FIES, MOSCA and StanCam check whether the rotator limit is reached within the exposure time, if this is larger than 300 seconds. For NOTCam, where typically multiple short exposures are made, this is not the case. If you want to follow the same target continuously for many hours, and you wish to avoid having to turn the rotator, for instance because you want your target on exactly the same pixels all the time (transit light curves), you might consider using a different field-rotation value, based on the time-to-reach-limit value displayed on the TCS UIF.

For the case that right after the telescope pointing the rotator will start off in the overlapping rotator range, the telescope can be told to automatically point using the rotator position that allows for maximum tracking time, with tcs.set-rotator-standard, which is the default behaviour. For details see the TCS documentation. If you have many pointings with relatively short exposures or you keep pointing towards the same region of the sky, you may save some pointing overheads by making the TCS choose the fastest rotator slew to reach either of the overlapping rotator ranges: set the rotator to fast mode using tcs.set-rotator-fast, which is a sticky command. To go back to the default mode, use the command tcs.set-rotator-standard .

Camera Probe

The Camera Probe is used for the standby Camera (StanCam) and for FIES and should be put in park position for all other instruments. Put the Camera Probe in the correct position by typing the TCS command as indicated in Table 1. The correct Camera-Probe position will be set when executing the script setup-tel-mosca

Sky Flats

If you are observing in imaging mode, obtain sky flats in the evening twilight with the filters you are going to use. If you know before hand that you might be requested to perform observations for a Target of Opportunity (ToO), it could be convenient to obtain sky flat fields in the standard filters (U, B, V, R, i) already in the evening. The type of calibration frames needed depend very much on your science goals and the instrument mode you are using. We recommend the documentation on the instrument pages. Please, check the User Guides available for: MOSCA

Below is a short guide of how to obtain twilight flat fields for optical imaging.

  • Remember to set tv-off on the TCS before making sky flat fields (adequate for morning flat fields, the TV monitor is often already off in the evening).
  • Choose a proper blank field from the blanks catalogue. A useful blank field target in the eastern sky that is not too low (i.e. RA 1-4 hours more than current ST).
  • point the telescope to the blank field:e.g.
    tcs.goto-object Blank03+31 from the sequencer terminal or
    goto-object Blank03+31 from the TCS.
    • You can also read the full catalogue:
    • Load a catalogue containing empty fields by typing read blanks on the TCS. Access the catalogue by pressing the key CAT and select an empty field with the keys 1, 7, or Prev, Next. Preset the telescope by pressing the key Preset to selected (4).
  • It is recommended to be close to the focus for each filter. Type foc-pos value where value is the default focus for the instrument and can be found in Table 1. Then type foc-del value where value is the focus offset (focus delta) for the filter, see full focus offset table and remember to change the value of the focus delta when you are changing filter.
  • Choose the desired filter
  • Make an exposure by typing expose t in the sequencer window where t is the exposure time in seconds. It is recommended to make a small offset between each image in order to be able to remove stars from the frames. To make an offset, choose the move mode Telescope RA/DEC of the TCS by pressing 5 on the numerical key pad until the right move mode is selected. Then make sure that the offset size is put to a suitable value by typing o-s x y on the TCS, where the value of x and y is in arcseconds (it is recommended to use an offset size of ten times the size of the FWHM of the seeing disk in order to easily filter out the stars). Make the actual offset while the CCD is reading out by pressing down AltFunc together with any of the arrow keys (make the offsets in the same direction). One keystroke corresponds to the value of the offset size. Repeat for next filter.

Focusing the Telescope

Focusing the Telescope with MOSCA

The telescope focus depends on temperature and zenith distance. These relations have been measured to a high accuracy and the corresponding corrections are applied in real time by the TCS (note that you will not see these corrections in the focus value displayed on the TCS since this value is kept constant to avoid confusing the observer).

Focusing with MOSCA

To focus the telescope with MOSCA is done easiest if you use scripts focusexpose, mosca.focus-auto (from a sequencer terminal) and select a focus star field close to the meridian and make sure both FASU A and FASU B are "Open". If you will use filter without known focus offsets you need to determine the focus offset.

[obs@selena 42-999][MOSCA]$focusexpose [focus-startvalue] [focus stepsize] [tint]

which make 5 images, e.g. focusexpose 22000 75 12
!!!NOTE Do not autoguide and make sure the 'field-rotation' is set to -90!!!!

[obs@selena 42-999][MOSCA]$focus-auto [focus step-size] [file name]

For the focusexpose-script you have to give the initial TCS focus value and the focus step size, e.g. focus-auto 75 (for the last obtained image). If the exposure time is not provided the script will use the MOSCA default integration time ( tint).
The "mosca.focus-auto"-sequencer script analyses the image and estimates the best focus value.

A good first guess for the focus script is

focusexpose 22000 75 12
Set the telescope focus e.g.
tcs.focus-position 22120

or on the TCS by (e.g.)"foc-pos 22120".

!!!NOTE the smallest meaningful focus offset is about 20-30 TCS focus units.

A The full documentation and other methods of estimating the telescope focus can be found from MOSCA www-pages.
See also the focus offsets between the filters and the focus offsets between the CCDs .


It is recommended to have the telescope autoguide on an optical source close to your target object. The TCS is automatically selecting a star from the HST guide star catalogue. The guide probe is then automatically placed at the correct position to auto-guide on this star.

  1. After obtaining sky flats, switch on the two Guide TV monitors above the TCS monitor. When it is dark outside, type tv-on on the TCS to power on the TV guide camera. Alternatively, use in any Sequencer window
    The TCS command tv-off switches the TV camera off.
  2. On the TCS, type auto-pos-full to choose the fully automatic guiding mode. Note that this is the default guiding mode as set in tcs.setup-tel-<inst>. In this mode, a guide star will be automatically found, centered on the screen and autoguiding will be switched on (ag-on).
    If the guiding does not start automatically but you see a guide star on the TV monitor, type auto-pos-retry.

  3. The TV filter can be adjusted to the intensity of the guide star by typing tv-filt name on the TCS, where the options for name is Open, Closed, Grey, Red, Yellow or Blue. Choose an appropriate TV filter based on the brightness of the guiding object and keep an eye on the guide monitors during your observations so you can change TV filter after weather conditions and brightness of the guide stars.
  4. The autoguider TV focus is also set by the script tcs.setup-tel-<inst>. The TV focus is depending on instrument and can be adjusted by typing tv-foc value on the TCS, where the value for default focus is found in Table 1.
    If you wish the TV-focus to follow the telescope focus type au-t-f (Automatic-TV-Focus, default setting) on the TCS, else to restrict to only manual TV-focus settings type ma-t-f (Manual-TV-Focus).
    In automatic mode, after every pointing of the telescope the TV-focus will be set to a default value that takes the telescope-focus position into account. If that value is not adequate, you can recalibrate the TV-focus on the spot: after adjusting the tv-focus type calibrate-tv-focus in the TCS interface.
    Note, do not change the TV-focus while integrating or while placing an object on a slit. For example, the position of a star on ALFOSC CCD can move up to 1 second of arc by adjusting the TV focus by 25 units.
  5. If you want to choose a new guide star, type get-guide-star 2 (or 3,4,5, etc.) to get a new guide star from the guide server at the current pointing, followed by auto-pos-retry.
  6. On the TCS, the signal strength from the autoguider is shown as a number. A guiding value between 1 and 23 is useful. Put in a filter if the signal is above 24, otherwise the TV filter will be set to grey automatically. If the signal is close to 1 the autoguiding is not reliable (e.g. clouds and/or bad seeing). Set tv-filt open and check for clouds.
  7. Make sure that the smaller box, the sky box is placed outside the star box. If needed, move the sky box by selecting the function Sky Box with Change move mode (5) and move the box with the keystroke combination, Alt Function + arrow keys.

    Always turn-off autoguiding (ag-off) before moving the telescope.

Hints for manual guiding and tweaking of telescope pointing

If guiding mode is set to auto-pos-off, the guiding has to be activated manually. Furthermore, in case that the pointing is not optimal, some manual tweaking may be required.

For manual choosing of a guide star, start with preseting to target. Find a guide star on the screen and move the star box to the star by pressing the key change move mode (5) on the TCS several times until the option Star Box is shown. Move the box by using the keystroke combination Alt Funtion + arrow keys. Alternatively, choose the move mode Guide Probe to move the star into the box, or use the command move-g. To set the step size of the Guide Probe, type probe-step-size x y on the TCS, where x and y are in arcseconds.

In case the telescope pointing is not optimal, in particular if the guide star ends up outside the screen, a pointing correction can be made with the move mode called Telescope: press the key change move mode (5) on the TCS several times until the option Telescope is shown, and move the star by using the keystroke combination Alt Funtion + arrow keys. The step size of the Telescope is set with the command offset-size on the TCS UIF.

Alternatively, if no guide star can be found on the screen, use get-guide-star 2 (or 3,4,5, etc.) to get a new guide star from the guide server at the current pointing.

When the star is placed in the starbox, type ag-on on the TCS to switch on autoguiding. To switch off the autoguiding, type ag-off.

Guiding on moving targets

If you are observing moving targets, view the page Tracking of Moving Targets, in the Appendix.

Start Observing

When the telescope is focused it is time to start the observations. Visit the individual pages for instrument specific information: MOSCA

The software interfaces for the instruments are very similar looking, however MOSCA has still non-sequencer BIAS CCD Control-software. However, all the tcs commands , tcs scripts and postprocessing commands are available from the sequencer window. For instance, type tcs.setup-tel-mosca to set up the telescope for for observing with MOSCA. See the list of the most commonly used TCS sequencer commands. For a complete list of all sequencer commands, view the Sequencer Reference Manual.

If you are observing moving targets, view the page Tracking of Moving Targets.

Overview: observing an object at night

  • Point the telescope using the TCS terminal, or use the tcs.append-object and tcs.goto-object commands in a Sequencer window.
  • Make sure the telescope is autoguiding (auto-pos-full or ag-on)
  • Choose the desired filter by clicking on the FASU User Interface button or with script/command line
    [obs@selena 42-999][MOSCA]$ fasua 1
    or giving a command with the filter id
    [obs@selena 42-999][MOSCA]$mosca.wheels -f 111
  • Adjust the telescope focus
    [obs@selena 42-999][MOSCA]$mosca.focus-offset
    or using the "focus-delta"-command (e.g. for filter #111)
    [obs@selena 42-999][MOSCA]$tcs.focus-delta 100
  • Start integrating e.g.
    [obs@selena 42-999][MOSCA]$expose 120
  • Note the bias levels of the CCDs can be variable. It is recommended to keep on eye of the bias levels during the night.
  • The easiest way to observe with MOSCA is using a script ( MOSCA commands, TCS commands) and to run a script type e.g.
    [obs@selena 42-999][MOSCA]$my_script
  • Switch-off autoguiding
    from the TCS terminal ag-off
    or from the sequencer window
    [obs@selena 42-999][MOSCA]$
    before pointing the telescope to the next object

  • In case of a FIES override:
    • Write down the current telescope focus for MOSCA
    • Switch to FIES. In the FIES Sequencer window, run the script
      [obs@selena][FIES]$ tcs.setup-tel-fies
    • Run any scripts that are required by the override program
    • When ready, switch back to MOSCA. In a FIES/STANCAM or MOSCA Sequencer window, run the script
      [obs@verushka][FIES]$ tcs.setup-tel-mosca
    • Change the telescope focus, if needed

Start Observing - With MOSCA

In most cases one has more than one pointing per filter per object. The possibility is to type (all) the commands (exp, object, teloffset) on the command line (Sequencer terminal) and change the filters by clicking on the "FASU User Interface" or write a a script (MOSCA commands, TCS commands). The script can include TCS-commands like: tcs.append-object, tcs.goto-object, tcs.focus-delta etc and MOSCA-commands like: fasua, fasub (to change filter), teloffset, expose etc.

All saved images are automatically loaded into the MOSCA DS9 display and can be examined interactively (see MOSCA SEQUENCER Script Reference):

  • on seqterm type
    [obs@selena 42-999][MOSCA]$ imexam
  • If you want to offset the telescope to move a target from one position on the mosaic to another use targetoff-script
    [obs@selena 42-999][MOSCA]$ targetoff
  • If you want to disply an image from the same night as you are observing (from "/data/mosca" -directory)
    [obs@selena 42-999][MOSCA]$ display MOtk020010.fits
    or from other night (e.g. "/data/mosca/MOta15" -directory)
    [obs@selena 42-999][MOSCA]$ display MOta15/MOta150010.fits

Unfortunately the bias level of CCD[im4] is variable, hence it is recommended to take a bias frame every now and then in order to monitor the bias level changes. After the commissioning the instrument the top right CCD (W19) has shown to have variable bias level. The change of thirty ADUs in 30 minutes have been seen. This behaviour is under investigation. The other CCDs have shown little (a few ADUs) or no intra-night bias level changes.

Adjusting integration time

If you want to adjust the integration time while integrating use "addtime" command from the sequencee terminal. This can be used in either increasing (positive value) or reducing the given integration time (negative value). The FITS-header keyword 'EXPTIME' will have the correct shutter opening time.


Offsets the telescope in seconds of arc in detector x and y direction. This command is used, typically, when dithering or small (less than about one arc minute) offsets of the telescope. If you want to move a star from the centre of the FOV (the cross) to the centre of a given CCD, it is recommended to use mosca.targetoff. Note that teloffset works with any field angle.

Focus offsets

Most 100mm filters are about 5mm thick and are expected to have similar telescope focus values. The estimated focus offset is 19 units per millimetre, i.e. the estimated focus offset between filters #108 (I_int 817_163) and #116 (b_Str 468_19) is +19 TCS focus units. See the thickness of filters

StanCam and MOSCA together

You can use StanCam and MOSCA together, if needed.

End of the night

Overview of things to do at the end of the night

Closing Down Procedure

Closing the telescope

  1. Before obtaining morning flats fields, turn the guide TV off by typing tv-off on the TCS.
  2. Put the telescope to zenith by pressing the key Start/Stop and then Zenith (0). This will park the guide probe and it also sets rot-man. Wait for Rotator -90°.
  3. Park the building by pressing key 4, Park Building. This process can take up to 8 minutes. Building will stop at Az ≈ 119°, Alt ≈ 90°.
  4. Close the mirror covers by pressing key 3, Close Mirror Covers. This takes 42 seconds.
  5. Close the lower hatch by pressing key 2, Close Lower Hatch. This takes about 3 minutes.
  6. Close the upper hatch by pressing key 1, Close Upper Hatch. This takes about 5 minutes. If timeout occurs or hatch does not move, see TCS Manual p. 43.
    NB: When the upper hatch has closed the dome cooling will start and the staircase cooling will stop.
  7. Close all 4 side-ports in the dome. Please, do not use violence. If the ports are stuck, use the handle to lift them before closing.
  8. Power down the telescope. After all of the above have been completed, type power-off on the TCS, then type sh 1 to display the telescope power units. Wait until all the telescope power displays show "off".
  9. Turn down the TCS screen brightness. Use the knob on the right-hand side of the TCS monitor, near the power switch. Never turn the TCS monitor off.
  10. Turn off monitors. Turn off the two autoguider monitors and dome TV camera monitor.
  11. Turn on the control room webcam and the dome webcams. Make sure that the webcams in the control room as well as in the dome are turned on before you leave.
  12. Have a look in the dome at hatches and telescope, to check for any faults that might have occurred.
  13. Complete the WWW report forms. Fill in and submit Internet NOT End-of-Night Report. Be sure to include any faults that occurred and submit a fault report, so we can attend to problems promptly. If it is the last night of the observing run, also fill in and submit Internet NOT End-of-Run Report.
  14. Lockup the dome. Lock the outer dome door when you leave the building.
  15. Clean up the kitchen/lounge area in the service building and switch off all lights when you leave.
  16. Lockup the outer door in the service building before leaving for the Residencia.

Stopping the MOSCA observing system

  1. To shutdown the observing system type in a terminal window
    [obs@selena ~]$ shutdownobssys mosca
  2. To exit the MOSCA Obs Log, click on the close icon in the frame of the MOSCA Obs Log window.

Data saving and retrieval

As of April 1st 2019 all data acquired using ALFOSC, NOTCam, StanCam, MOSCA and FIES are available for the observers and PIs via the Data Retrieval page, where also instructions are available.

In the period 2005 - 2019 all data was written to DVDs.

Observers requiring access to data from the NOT archive should contact NOT staff for details of the required procedure. General information on NOT FITS-headers can be found here.

Accessing raw and reduced data at night

The computer called florence is setup for you to make a quicklook analysis of the incoming data, e.g. using IRAF start iraf e.g.

  xgterm -sb -fn 9x15 -sl 400 -cr red -title IRAF -e ecl &

For the different instruments we have on-line reduction programs running, that deposit the reduced products on a disk accessible through florence.
The raw and reduced data files can be found on florence under directories

To copy the new data products over wifi to your own mobile computer, while in the NOT control room, use for example
  scp guest@florence:/data/fies/FI\*0001.fits .
  scp guest@florence:/data/reduced/fies/auto/FI\*0001.fits .
  scp guest@florence:/data/alfosc/AL\*0001.fits .
  scp guest@florence:/data/reduced/alfosc/sAL\*0001.fits .
  scp guest@florence:/data/notcam/NC\*0001.fits .
  scp guest@florence:/data/reduced/notcam/sNC\*0001.fits .
on your own mobile computer.

Archival requests

To obtain NOT data from our archive, first compile a list of file names of the calibration and science data to be retrieved, using our FITS archive. Note that this archive does not show the data obtained in the latest twelve months, due to the propriatary period.
Then please contact staff and send the list of file names to be retrieved, such that we can locate the data in our archive and make them available through FTP.

Compensation for override observations

If your program was interrupted by a Target-of-Opportunity or another override observing program, you are entitled to payback time. Such compensation for time lost during your allocated observing run (whether in visitor or service mode), is claimed back through the submission of Observing Blocks (OBs) using our OB Generator. The observations will be executed accordingly in service mode by staff during Nordice Service nights, and you will be informed by email when observations are made and where to retrieve the data.

Using the OB generator to claim payback time

Access the Observing Block Generator and login to your account, or if you are a new user, please register. When you are logged in, add your proposal for which you claim compensation time. There are help buttons at every level of the OB generator, and you can also get support and give feedback through If you have questions about how to define OBs and/or Observing Sequences, please contact

For your OBs to be carried out as compensation for time lost to overrides, please make sure to select OB Group type "Payback".


If you have ...

  • ... cannot reset the safety system:
  • ... no light on the CCD -- check:
    • Dome open, mirror cover open
    • Lower hatch not obstructing at low altitude
    • Guide probe out of light path
    • Camera probe in correct position
    • FASU shutter open (if using ALFOSC)
    • Correct filter in instrument
    • Correct telescope focus
    • If it is cloudy
    • Check all the above again. If there still is a problem, then phone duty staff.
    • If MOSCA or StanCam image has a count level of 0, this can actually mean saturation and you should reduce the amount of light falling on the detector.
    • StanCam shutter controller has power (if using StanCam)
  • ... wrong field on CCD -- check:
    • Coordinates of field
    • Epoch of coordinates
    • No typos in entering coordinates in TCS
    • Field rotation is correct
  • ... no guide star on guide probe screen -- check:
    • Dome open, mirror cover open
    • Guide probe in correct position
    • Field and rotator angle
    • TV switched on
    • TV filter open
    • TV focus correct
    • Try typing in the X and Y values of another Guide Star fromthe The 10 brightest currently available Guide Stars
    • If it is cloudy
  • ... lost tracking/guiding:
    • How close to the zenith are you? (Good guiding and tracking is guaranteed only 5 degrees or more from zenith).
  • ... changing tv filter does not work:
    • at TCS type in the command 'Initialize-TV-Filter'.
  • ... ctrl x', 'ctrl g', 'ctrl t' and 'ctrl v' commands on the TCS give incorrect functionality, e.g. telescope offset rather than star box movement.
    • wrong function key menu on the TCS keyboard press keypad key 5.
  • ... "building crash":
  • ... other TCS problems
    • Press the keypad key labelled Log and then keypad 2 to see the latest entries in the TCS log.
  • ... acquisition: slitoff/fiboff unresponsive
    • Using the mouse to set the contrast while image is loading?
      Using the mouse to set the contrast while this process takes place can cause DS9 to crash. Best procedure is to wait tuning the contrast level until the image has been fully loaded into DS9, and zoom / contrast levels set.
      A DS9 crash while in 'imexam' while leave the postprocessing system in a non-workable state.
      Rather than shutting down the whole observing system to recover, it is in most cases sufficient to run the sequencer command 'killimexam'.
      See also next item.
  • ... ds9 shutting down while doing acquisition
    • Using the mouse to set the contrast while image is loading?
      Using the mouse to set the contrast while this process takes place can cause DS9 to crash. Best procedure is to wait tuning the contrast level until the image has been fully loaded into DS9, and zoom / contrast levels set.
      A DS9 crash while in 'imexam' while leave the postprocessing system in a non-workable state. Rather than shutting down the whole observing system to recover, it is in most cases sufficient to run the sequencer command 'killimexam'.
  • ... "sequencer/obssys" does not respond or behaves badly:
    • Standard procedure in such circumstances is to restart the observing system using 'shutdownobssys' (from a terminal window) followed by 'startobssys'.
  • ... lisa frozen, not responding, e.g. can not log out using the foot icon
    • if you have a working terminal, try "$ killall panel", wait until the panel restarts and then logout as usual
    • if there's no terminal available, you can use florence to ssh as obs into the observing computer you've been using, and type the killall command.
    • if you have no terminal available, etc. press the "Ctrl" and "Alt" keys and then press "Backspace". That will kill the X server and force a logout

If you encounter a fault or a problem with the instrument, the computers or the telescopeduring the night, then fill in a Fault Report.

A sudden large area of reduced sensitivity

If the area is moving most likely it is a bug or spider. The only way to remove "a bug with wings" or a spider during an observing run is to lower the instrument and remove the offending bug.
Contact staff!!!


Tables for Instrument Settings

instrument field-rot i-p-a camera probe foc-pos tv-foc orientation c-w-h
ALFOSC +90 0 (horizontal slits)±90 (vertical slits) c-p-p 22450 500 North ↑ East ← Horizontal slits: E-W (P.A. = ±90) 0.75
FIES 0 N/A c-p-s 22770 530 North ↓ East ← N/A
NOTCam -90 -90 c-p-p 22610 495 North → East ↑ 0.95
MOSCA -90 N/A c-p-p 22260 450 North ↑ East ← 0.55
StanCam 0 N/A c-p-c 22200 430 North ↑ East ← N/A
SOFIN 0 -90 c-p-p 22650 520 N/A 0.9
TurPol 0 N/A c-p-p 24350 650 North ↑ East → 0.12

Table 1a shows the values of the: field rotation(field-r), instrument-parallactic-angle (i-p-a), ccd probe, focusposition (foc-pos), TV focus (tv-foc), field orientation andcounter weight height (c-w-h) for the different instruments. On the TCS, type thecommand followed by the value, for instance field-r -90. The default focus value stated for NOTCam is for the K band in imaging mode using the WF camera (internal camera focus of 5650).

From To foc-delta
ALFOSC no filter StanCam R-filter (#10) -260
MOSCA R-filter (#106) StanCam R-filter (#10) -155
NOTCam Ks-filter (WF) StanCam R-filter (#10) -380

Table 1b shows the default focus offsets between the instruments.

Commonly Used TCS Commands

Command Comments
ag-on Turns autoguiding on
ag-off Turns autoguiding off
auto-positioning-full Turns the guide star auto positioning to full-automatic
auto-positioning-retry Try again to bring the guide star in the guide box
Moves the camera probe to ccd position (for StanCam)
camera-probe-park Moves the camera probe to park position (for ALFOSC)
Moves the camera probe to split position (for FIES)
field-rotation fieldangle Sets the field rotation to fieldangle
focus-position n Moves the telescope to focus position n
focus-delta n Applies a focus offset to the current telescope focus
get-guide-star 2 Find another guide star
instrument-parallactic-angle n Defines the parallactic angle for following presets
read-catalogue Reads the catalogue
tv-on Turns on the guide TV
tv-filter name Selects the guide TV filter where name can be either closed, grey, open, red, yellow or blue
tv-foc pos Changes the guide TV focus to position pos

append-object string appends an object to the TCS catalog
goto-object Object moves telescope to "Object"
find-object selects an object in the TCS catalog
preset-with-parallactic-angle-to-selected moves telescope to the selected object, with parallactic angle
For more commands, view the TCS SEQUENCER Command Reference.

Tracking of Moving Targets

At the NOT there are two main modes of tracking a moving object (planet, comet, asteroid, satellite): 1) differential tracking with auto-guiding and 2) differential tracking without auto-guiding. Which of these to use, depends in practice on the target speed and how long the observations take. We have been working with speeds as high as 700"/hour with auto-guiding.

Since September 2019 the OB generator allows for non-sidereal tracking.

The differential rates are given in the FITS headers in the keywords DTRCK_RA and DTRCK_DE.

Differential tracking with auto-guiding

In this mode, the telescope tracking is set to the differential rates, and in addition, the auto-guider is used with the star-box set in motion with the same rates. This works for as long as the box stays within the auto-guider TV-screen (approximately 70" field). When the limit is reached, auto-guiding is no longer working. It is possible to reposition the star-box and guide probe without affecting the telescope tracking, but there is a limit to how many times this can be done before reaching the limit of the available guide probe area. This depends on the RA/DEC rates, the field-rotator angle, and the initial location of the guide star inside the guide probe area. If this happens, you have to repoint to the target again.

We are working on improving differential tracking with autoguiding for fast targets such that the guide probe repositioning can be done automatically, and to select the optimal rotator position and guide probe area such that the largest number of repositionings is possible.

If your target moves less than 70" over the execution time of your observations, you can relax. If it moves more, you need to keep an eye on the star-box and manually re-position it as described under step 3 below.

Both the telescope tracking rate and the box-motion rate are given in RA/DEC coordinates, i.e. dDEC/dt and dRA/dt (in arcsec per hour), and the cos(DEC) correction is taken care of internally by the TCS. (In other words, if your RA-rate is given as dRA*cos(DEC), you have to divide by cos(DEC) before entering its value.)

  1. From ephemeris get the target's position and coordinate motion for the time of observation. Coordinate motion is the RA and DEC rates (dRA/dt and dDEC/dt) in arcseconds per hour. Or use our tool

    tcs.asteph targetname

    where "targetname" must be the official JPL Horizons name and surrounded by double quotes if it contains a space. It finds position and rates for this moment at La Palma location, converts from dRA/dt*cos(DEC) to dRA/dt, as required by our TCS, and lists the commands you need to point and start tracking/guiding. It is highly recommended to test asteph in the afternoon. See example below (in green):
  2. tcs.asteph "C/2019 Q4"
    ......... lots of lines output and at last .....

    These tasks should be given to the TCS:
    tcs.append-object Borisov_C-2019_Q4 09 05 03.48 +27 26 32.7 2000.0 0.0 0.0 17.72 Borisov_C-2019_Q4
    tcs.reposition-guide-probe 69.4705 -52.2498
    The position angle is , 126.947
    09 05 03.48 +27 26 32.7
  3. Cut and paste the three first sequencer commands listed by tcs.asteph (or point to your target in the normal way), wait until guiding, and then cut and paste the fourth command or run it as:

    tcs.reposition-guide-probe RA-rate DEC-rate

    This is a script which will 1) stop auto-guiding and box motion (if it was set in motion), 2) move the star box to an optimal position on the TV screen, 3) set the telescope tracking rates to RA-rate and DEC-rate, 4) start the box motion to the same rates, 5) move the guide probe to put the star in the box, and 6) start differential auto-guiding.
  4. If this is a relatively fast target, i.e. moving more than 70" during the time your observations take, you will have to keep an eye on the star box. When it reaches the other edge of the TV screen, it will stop guiding. The TCS will send warning beeps when there is 120, 90 and 60 seconds left. Make sure you take action before guiding stops by re-running the command:

    tcs.reposition-guide-probe RA-rate DEC-rate

    in another sequencer window. You can do this while exposing, although it is optimal during readout, in between exposures. This repositions the box and the guide probe and continues differential autoguiding without affecting the telescope tracking.
  5. There is a limit to how many times you can reposition the guide probe due to the limited guide probe area. If this happens, you have to start again from point 1.

  6. Stop differential guiding by (or in short on the TCS UIF b-m-sto).

    NB! Note that this does not reset the telescope tracking rates, and if you wish to stop the differential tracking, going back to normal tracking rates, then on the TCS UIF type set-rate 0 0. This resetting of the telescope tracking to sidereal rates is automatically done at every new telescope preset.

Tracking without auto-guiding. Rapidly Moving Targets

For more rapidly moving targets, use the set-rate command on the TCS to continuously move the telescope from a pre-calculated change in position. RA-rate and DEC-rate as above. In this mode auto-guiding is not used.

We are also upgrading the possibilities for very fast tracking (without autoguiding), and the software speed limit has been increased from 17"/s to more than 5000"/s. Observations were made of fast satellites where the RA/DEC rates were updated every second.

  1. Preset to your object.
  2. Set the rate of change by set-rate RA-rate DEC-rate (rate in arcsec per hour). The maximum differential rate is 20000000 arcsec/hour (≈ 5500 arcsec/s).
  3. Make the exposure.
  4. Reset by typing set-rate 0 0 on the TCS.

For Experts Only

If the target has an unknown or rapidly changing motion, you might want to adjust the rate of change in RA and DEC while tracking. Use the set-rate command on the TCS and use command recall with the up/down keys and edit the set-rate.

  1. Preset to object.
  2. Guess the starting set-rate RA-rate DEC-rate values.
  3. Do as described above with command recall.
  4. Do set-rate 0 0 or just preset to another object.

| Back to Top | Back to Title page | Back to NOT homepage |

Back to top