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NOTCam Cookbook

Last updated October 24 2017
Please refer to the online version for the latest update

Table of Contents

Preparing NOTCam Observations

We refer to the more extensive NOTCam User's Guide as a preparatory reading about NOTCam in general, and imaging in particular, and for spectroscopy we refer to the NOTCam spectroscopy web pages.

Exposure Time Calculator

You need to determine the total on-source integration time needed to reach your required S/N ratio. Use the Exposure Time Calculator (ETC) , and note that it allows multiple exposures, as well as peak value estimates (useful to indicate linear range and saturation levels, but NB! note that this depends critically on the seeing).

The total time needed is typically spread out on many sky positions in order to allow an accurate subtraction of the sky background. For imaging it is recommended to stay only 1-2 minutes per sky position. Depending on the accuracy you need, you probably want (target + sky) to be within the linear range of the detector (i.e. < 25000 adu, though the non-linearity can be corrected for, see NOTCam calibrations). The background is high and variable, and for deep broad-band imaging (especially H and K) this may become the limiting factor regarding how long individual exposure time you can use. Otherwise the limiting factor is the peak value of the target. Both the seeing and the sky-background varies from night to night and within the night. Note that you can play around with different seeing values using the ETC, but the sky background it uses is fixed to typical values. In visitor mode you can make test exposures and modify your scripts on-the-fly, and in service mode you can ask that the observer makes sure a given target or background is staying within a given limiting value.

Dithering patterns

Decide what dithering pattern and dithering step size you will use. This depends on the spatial extent of your source. Ideally it is recommended to dither at least 10 times the FWHM of the objects. For point sources about 5-15" is typically used. The dithered target fields are used to estimate the sky (and dithering is also essential to get rid of bad pixel areas). In spectroscopy it is normal to dither along the slit, and a frequently used pattern is the so-called ABBA with a step size between A and B that is big enough for the spatial extent of the source. For slightly extended objects it is sufficient to increase the step size somewhat, while for more extended objects it is necessary to measure the sky completely OFF the target (this is called beam-switching), both for imaging and spectroscopy.

  • Small step dithering: A typically used dithering pattern is 3x3 grid or 4x4 grid. For bright targets or standard stars a 5-point dice will be sufficient. Available sequencer scripts are the notcam.9point or notcam.5point. Further details shown in section Imaging.
  • Beam-switching: There is an available sequencer script called notcam.beamswitch for extended target imaging, and one called notcam.ab3-beamswitch for extended target spectroscopy.
  • Along-the-slit dither for spectroscopy: The template scripts notcam.abba and notcam.ab3 are useful for point source spectroscopy.

You may use our available NOTCam Sequencer Scripts, which are executed from a sequencer window and accessible from any directory. Alternatively, prepare your scripts using the OB generator, which also gives you an estimate of the overheads. The OB generator lets you upload your scripts to the data acquisition computer in directory ~obs/scripts/proposal-ID where proposal-ID refers to your proposal ID which you must enter in the web form (e.g. 42-024). If the directory does not exist, it will be created. You may also copy template scripts to your own directory if you wish to modify these. Make the directory (mkdir) if it does not exist and within this directory type cp ~staff/notcam.script my.script.

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.

Readout Modes

Decide whether you will use the reset-read-read or ramp-sampling readout mode, and which exposure times you want per dither position. If you need short exposures, for instance to stay within the linear range of the array, the reset-read-read mode (exp, mexp) must be used. The ramp-sampling mode (frame) usually gives a lower noise and less overheads, and is preferred whenever longer exposures are possible. In imaging mode it is recommended to stay only 1-2 minutes per sky position before dithering.

How long exposures you can make depends on the background (notably for broad band imaging), your target, and potential bright stars in the field that can saturate and give nasty memory effects. These considerations depend on what you wish to do. With a seeing of 0.6'' a 9.5 mag star saturates in 6 seconds with the WF camera. Check the 2MASS database, for instance through SIMBAD, which is also useful to make NIR finding charts. The saturation issue is important if you need good photometric accuracy and may lead you to use shorter individual exposure times than originally planned. This has consequences for the choice of readout mode and the resulting overhead factor. If strong saturation is inevitable, and these pixels may affect your target, it is recommended to clear the array a couple of times after each integration. Each such clear command takes 3.5 seconds.

Complete OB generator scripts

Also in visitor mode is it possible to use the OB generator to generate complete scripts to be executed by the observer. These scripts combine telescope pointing, instrument setup, and observing scripts in one go.

The OB compiler for NOTCam is complete for imaging mode. You may also use the OB generator for spectroscopy, but the compiled scripts are semi-automatic only, and after pointing to target and setting all FITS headers correctly, the observer is required to run the appropriate scripts for slit acquisition, dithered exposures, and lamp calibration exposures manually.

In addition to coordinates, epoch, possible proper motion and finding chart, you can specify the desired orientation on the sky, which apart from default (DEF) for imaging, can be on the parallactic angle (PA) or any given position angle on the sky to be entered in degrees. Note that it is important to select your guide field area, which depends on your dithering step size (read instructions on the web form and for more details consult section Autoguiding below).

Overheads

Because of the many short exposures typically used in the infrared, overheads is an issue. NOTCam overheads are dominated by the relatively long readout time of 3.6 seconds (to be lowered to < 1 second with the new controller). See Overheads at the NOT for an overview. In order to estimate how overheads (due to readout, file storage and dithering) depend on the readout mode selected and their parameters t and N, you can use the OB generator. Alternatively, you may use the old script generator, for checking overheads, but note that it is deprecated and not available for creating/uploading scripts. Be aware that the exposure time is t x N seconds for the ramp-sampling mode (frame t N) and only t seconds in the case of the reset-read-read mode (mexp t N). Make preview and check the overheads.

In addition to the observing overheads calculated in the above step (i.e. to readout, telescope dither, and file storage), one must add the overheads to target acquisition: 3 minutes per target for imaging and 5 minutes per target for spectroscopy, also for any standards (e.g. telluric standards in spectroscopy). Check the NOT Standard Star Catalogues or the IR reference info for info about standard stars etc.

For spectroscopy you also need to add the overheads related to taking calibration lamps. This is done in-situ for each target (due to flexure) and involves closing the telescope mirror cover, because of the calibration unit is situated inside the baffle cover. This means 2 minutes overhead to closing/opening plus the actual calibration lamp exposures and readouts. See also recommended calibration lamp exposure times. For WF-cam spectroscopy in the J, H or K band the total time for wavelength calibration is typically 3.5 minutes.

Pointing Scripts (old)

In case you are not using the OB generator, you can make pointing scripts using the old pointing script generator.

Target acquisition with NOTCam is made easy and speeded up substantially by preparing OBs/scripts in advance, especially for spectroscopic mode, beam-switching and/or when another orientation than the default one (which for NOTCam is East up and North right!) is wanted. If you do not prepare OBs, nor pointing scripts, then you can submit a TCS Target Catalogue via the web.

You may load several catalogues in the same buffer on the TCS by typing on the TCS User Interface read name, where name is the name of your submitted catalogue, or any of the following potentially useful catalogues:

  1. blanks (blank fields for sky flats)
  2. focus.cat (focus stars/fields)
  3. notcamstd.cat (NOTCam JHKs standard fields)

Instrument Setup Scripts

In case you are not using OB generated scripts, the instrument setup scripts notcam.setup-ima and notcam.setup-spec for imaging and spectroscopy mode, respectively, are recommended for changing filters/cameras etc. because they also apply the corresponding focus-offsets automatically. For all NOTCam scripts you can type the command without parameters to get info on the usage, such as for instance:

[obs@marissa][NOTCAM]$ notcam.setup-ima
Error in arguments
Usage: notcam.setup-ima cam fid 

       cam = camera (wf, hr)
       fid = filter ID number (see below) 

Z  = 237
Y  = 236    Yn        = 222
            He-IA     = 213   Pa-Gamma  = 214  
J  = 201    Jcnt1.207 = 215   Pa-Beta   = 216  
H  = 203    Hcnt1.574 = 211    
            CH4-s     = 223   CH4-l     = 224  
            [FeII]    = 212   [FeII]cnt = 228 
Ks = 207    He-IB     = 217   H2-2.121  = 218  
            H2cnt     = 230   Br-Gamma  = 209 
K  = 208    He-IC     = 219   H2-2.251  = 220 
            Kcnt2.267 = 210   CO-(2-0)  = 221
Kp = 206  

Afternoon Preparations

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 catname.cat 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).

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 NOTCam observing system

  1. On the Lisa terminal click on the line
    'marissa.not.iac.es Willing to manage'
    Log in with username obs and password is obtained from staff.

  2. Open two terminal windows. Start up the NOTCam Sequencer by typing in one of them (the other is intended for shutting down):
    [obs@marissa~]$ startobssys notcam
    • A window pops up asking for the TCS access code. Type it and press enter. If you type the wrong code a red error message appears and you must try again.

    • All the NOTCam software controlling the array and the instrument wheels will now start up. In the Talker (on the InfoSys monitor to the upper right) you will find information about the correct start of the different software components, or a corresponding error. If any errors about a program not starting are seen, please shut down the observing system and start it again. Wait for the green-coloured message line stating NOTCam is ready.

    • The wheel status shows Not initialized after each power-cycling of the motor controller. If this is the case, you have to click on the Initialize menu, and thereafter click on Init all movements. Then you have to click on a valid entry for each wheel (status buttons should turn green).


    The NOTCam obssystem and its various windows.

  3. Commands are given in any of the 3 Sequencer Terminals. The default startup directory is "/home/softremote/obs/" and you should type:
    [obs@marissa][NOTCAM]$ cd scripts/prop-ID/
    where prop/ID refers to your proposal ID number. This is where your uploaded scripts and finding charts are located. If the directory does not exist, then mkdir to create it. An extra Sequencer window is obtained by typing seqterm .

  4. Read out the array 3-4 times with the command:
    [obs@marissa][NOTCAM]$ dark 0
    to clean accumulated charge. The first images look strange. After the 4th exposure the images should look normal.

  5. For NOTCam there are two DS9 windows showing the incoming images, the left shows the raw data in real time (useful for ramp-sampling readout) and the right shows the postprocessed image, potentially sky-subtracted, with any overlays from postprocessing. Set 'zoom' to 'fit' and 'scale' to 'zscale' or according to your wishes. To examine the image type:
    [obs@marissa][NOTCAM]$ imexam
    it works as in IRAF, quit with q. For more commands related to display and postprocessing see NOTCam Postprocessing control scripts. If imexam hangs you can use killimexam, then type display to recover the DS9 and restart imexam.

  6. The automatic NOTCam 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:
    [obs@marissa][NOTCAM]$ instrument.showlog

  7. Data files will be saved in '/data/notcam/' a directory which is also cross mounted on the computer Florence, where you can do quick-look data reductions by starting up an IRAF session and enter the notcam package (see NOTCam data reduction. Data files have the format NCub120001.fits, where 'NC' is the image prefix for NOTCam images, 'u' is for 2011, 'b' is for February, '12' is for the date 12 in the month and '0001' is a running number. Never delete stored images!

  8. If you want to interrupt a script, then type Ctrl-C in the NOTCam Sequencer Window. This will stop the script, but you will have to wait for the on-going exposure to finish. The reason for this is that we do not have a working "abort" command for the NOTCam array.

  9. In order to close down the observing system, give the following command in a terminal window (not a sequencer window):
    [obs@marissa~]$ shutdownobssys notcam

Calibrations

If the detector has been idle for a while it is always recommended to clean accumulated charge by reading out the array a couple of times. This can be done in any of the following ways:

[obs@marissa][NOTCAM]$ notcam.clear
[obs@marissa][NOTCAM]$ notcam.dark 0
[obs@marissa][NOTCAM]$ notcam.clean3

where the latter is a combination of 3 times clear and one dark 0 to show the result. Repeat until the dark looks normal. Examples of how darks of 0 and 42 seconds integration time look like are found on the page NOTCam calibrations.

Darks

The NOTCam darks are poorly understood, see the NOTCam User's Guide for a comment. By using differential flats and sky-subtraction, the dark is automatically subtracted out, and you should not need to take darks for broad-band imaging. Darks are useful to estimate hot pixels, however, which vary with exposure time. Take darks with the same exposure time and readout mode as your observations.

[obs@marissa][NOTCAM]$ notcam.dark t
[obs@marissa][NOTCAM]$ notcam.mdark t N
[obs@marissa][NOTCAM]$ notcam.dframe t N

NB! Since the array needs time to stabilize on the low count levels, it is recommended to take N > 3 subsequent darks of the same integration time, and preferrably disregard the first one(s).

Domeflats

It is recommended to use skyflats rather than domeflats, but if all skyflats could not be taken within the available twilight slots, then domeflats are an alternative. Like skyflats, domeflats should be done differentially, i.e. with the lamp ON and OFF using the same exptime. Because of structure on the inside of the dome, as well as daylight leakage through hatches, it is recommended to move the telescope to an altitude of 45 degrees. In order to do this, telescope power must be ON. The NOTCam-QC-lamp is located above the entrance door, i.e. light comes from behind the telescope giving a diffuse distribution, and it is operated from the control room on the panel on the wall in front of you. Turn switch rightwards to the "on" marker. The intensity can be adjusted on the upper panel from 0 to 100 (default = 56).

Thus the procedure to take a set of differential domeflats is as follows:

switch NOTCam-QC-lamp ON
reset the safety system
TCS: power-on
TCS: alt 45
TCS: open-mirror-covers
[obs@marissa][NOTCAM]$ notcam.setup-ima cam filter-ID
[obs@marissa][NOTCAM]$ notcam.mexp t N
switch NOTCam-QC-lamp OFF
[obs@marissa][NOTCAM]$ notcam.mexp t N

The exposure time t is typically 5-7 for K bands, 10-15 for J and H used with the WF camera. For all narrowband filters used with the WF camera, the lamp intensity should be set to max (100), and the exptimes should be around 10 for #223 and #224 and around 40 or more for the rest. When finished, remember to:

switch NOTCam-QC-lamp OFF
TCS: zenith
TCS: close-mirror-covers

You do not have to power off the telescope if you start observing within an hour.

Spectroscopy

For spectroscopy you must determine two good X positions on the array where you would want to put your targets for the ABBA mode. The dispersion is vertical, blue-to-red from upper-to-lower on the stored images. Thus, you need two clean vertical regions for your spectra. Take your own domeflat to check for hot and cold bad pixels. For instance exp 10 in the K-band gives enough counts from thermal emission without having to switch on a lamp. Define your position A to be a good x < 512 region and find your position B at some good x > 512 region. The separation (B-A)*pix_size, where the pix_size is 0.234'' for the WF camera and 0.078'' for the HR camera, is the step size in arc seconds you need for your ABBA script (typically it should be 20-60''). Position A is the X value you need as input in the slit-acquisition script notcam.slitoff X Y. Note down these values. The Y value must be determined on every new pointing due to instrument flexure.

For spectroscopy you can switch between the different wavelength regions (Y,J,H, and K) using the script notcam.setup-spec which sets the internal focus according to the camera/slit/wavelength combination. Note that it does not move slit and grism wheels! Note also that K (208) rather than Ks (207) is used in order to cover 0.08 microns further towards the red, i.e. until about 2.36 microns.

For spectroscopy you may wish to take some halogen flats and some arcs in the afternoon. Below are the steps to use the calibration unit mounted on the inside of the baffle lid. It consists of a halogen lamp for flats and two arc lamps (argon and xenon) for wavelength calibration. Useful exposure times are found in the table Typical NOTCam calibration lamp exposure times. In the example below we use the WF camera, the K-band (208), the 128 micron slit (0.6" width) and Grism #1, and we want to take 5 halogen flats of 7 seconds each, 3 argon arcs of 10 seconds, and one xenon arc of 20 seconds.

[obs@marissa][NOTCAM]$ notcam.setup-spec cam filter-ID slit-ID grism-ID
[obs@marissa][NOTCAM]$ notcam.setup-spec WF 208 128 1
Manually put in the slit and the grism!
[obs@marissa][NOTCAM]$ notcam.calibexp [-n Nexp] [-o Object] [-LeaveMirrorClosed] [-lmc] lamp t
[obs@marissa][NOTCAM]$ notcam.calibexp -n 5 -lmc halogen 7
[obs@marissa][NOTCAM]$ notcam.calibexp -n 3 -lmc argon 10
[obs@marissa][NOTCAM]$ notcam.calibexp -lmc xenon 20

Note that the argon lamp may take some time to come on (up to 1 minute).

For reference, the commands used to switch on and off the calibration lamps are: tcs.baffle-lamp-2-on and tcs.baffle-lamp-2-off, where the number refers to the lamp (1 = halogen, 2 = argon, 3 = xenon). You can check the status of the baffle lamps (whether they have been command to ON or OFF) on the TCS status page 30, as well as in a small window in the NOTCam obssystem.

You may also use the wrapper script notcam.easy-calib that is meant for in-situ calibrations at night, and described under Quick instructions for Spectroscopy in this document. In this case, since the mirror cover is probably already closed, you should manually switch on the argon lamp one minute before starting the script.

Telescope Startup Procedure

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

NB! If you want NIR skyflats, it is important to start early enough in order not to miss the useful twilight window. This depends on how many and which filter/camera combinations you need.

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 12 m/s - Close telescope
20 m/s - Close telescope

Telescope settings and power

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 is incrementing, 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

  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.

Select your instrument

  1. When power is on, and if you are going to use NOTCam, then type in the sequencer window:
    [obs@marissa][NOTCAM]$ tcs.setup-tel-notcam
    to setup the telescope for observing with NOTCam. The focus is set to the default value for NOTCam, which should not be far from the real value you will find later when focusing. Note that if you switch between NOTCam, StanCam and FIES during the night, using setup-tel-notcam will set the focus to default value.

  2. Otherwise, if you are going to use StanCam, then go to another desktop, open any terminal, type ssh -l obs tessa and then startobssys stancam. In the sequencer window that pops up, type:
    [obs@tessa][STANCAM]$ tcs.setup-tel-stancam
    to setup the telescope for observing with StanCam. The default focus for StanCam is usually good enough. Now preset to your target, select the StanCam filter, and take an exposure as given in the example below (300 seconds R-band exposure):
    [obs@tessa][STANCAM]$ tcs.enter-object obj hh mm ss.s dd mm ss.s epoch pm-ra pm-dec mag
    [obs@tessa][STANCAM]$ tcs.guide-object obj
    [obs@tessa][STANCAM]$ tcs.ccd-filter 4
    [obs@tessa][STANCAM]$ stancam.expose 300
    Consult the StanCam Quick Guide for an overview, or for more details, see the StanCam Cookbook.


  3. Or, if you are going to use FIES, then make sure you first shut down StanCam (shutdownobssys stancam, go to another desktop, open any terminal, type ssh -X verushka and then startobssys fies. In one of the sequencer windows that pop up, type:
    [obs@marissa][NOTCAM]$ tcs.setup-tel-fies
    to setup the telescope for observing with FIES. For more details, see the FIES Cookbook. If you will use both FIES and StanCam, only startup FIES and run StanCam from the StanCam sequencer which is already available as part of FIES observing.

Dome Opening before Sunset

With NOTCam the procedure to take skyflats may need to be started before sunset. Therefore, it is vital to point to a blank field in the East before opening the dome! Do as follows:

  1. Load the blanks catalogue on the TCS by typing read blanks
  2. Find a blank field located in the east to avoid the setting sun (i.e. RA 1-4 hours more than the current ST). Point the telescope to it about 20 minutes before sunset using the TCS numerical key 4.
  3. If weather conditions are OK and the telescope points roughly towards the east (verify TCS azimuth, east = 270 degrees), then 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). Do not use too much force and use the handle for lifting the ports if needed (Note that the side ports are easily damaged).
    • 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.

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-notcam

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-notcam

Sky flats

The exact timing of the useful window for near-IR twilight skyflats depends on the sky quality (dust, temperature) and the altitude of your blank field. Only a few minutes too late, and you may get too low S/N or a useless flat-field sequence.

We recommend doing all NOTCam imaging skyflats in differential mode, i.e. taking bright and faint flats. This removes thermal emission as well as the dark. If you are using all broad band filters (ZYJHKs) with the WF camera we recommend the following order of the double (bright and faint) cycle: KsHJZY - KsHJZY. If you want JHKs with both cameras, then make sure you start early and follow the order in the table below.

NB! It is vital that the exposure time is the same in the bright and faint pairs, otherwise the differential approach breaks down. It is important to have a relatively high count level in the bright images (but < 25000 adu to stay within the linear range) and a relatively low level in the faint ones (for broad-band JHK filters this is anything between a few hundred adu for the J band to a few thousand for the K). For practical reasons we recommend exposure times in the range 3-20 seconds. The longer the exposure times, the longer it takes to do the sequence, and the fewer filter/camera combinations can be done in the available twilight window.

Below are the most useful commands for changing camera/filter, to take test exposures (repeatedly, until the levels are OK), and to run the skyflat script with telescope dithering.

[obs@marissa][NOTCAM]$ notcam.setup-ima cam filter-ID
[obs@marissa][NOTCAM]$ notcam.setup-ima hr 207
[obs@marissa][NOTCAM]$ exp 1
[obs@marissa][NOTCAM]$ notcam.skyflat exptime

The notcam.skyflat script takes 8 flats with the given exposure time, dithering the telescope in 10'' steps, and takes about 3-4 minutes. Change filter and restart the script. By using the notcam.setup-ima script to change filter/camera, the telescope focus is adjusted automatically. If you happen to saturate on the test exposures, run clean3.

Example of skyflat sequence for JHKs and both cameras.
Camera + filter Sequencer cmd: notcam. Typical exptime (t)
HR + Ks setup-ima hr 207 10
HR + H setup-ima hr 203 5
HR + J setup-ima hr 201 5
WF + Ks setup-ima wf 207 10
WF + H setup-ima wf 203 7
WF + J setup-ima wf 201 15

The typical exptimes given in the table above is an example where the observing sequence started 11 minutes before sunset, the pointing was ESE and the zenith distance 48 degrees. The sky intensity varies with pointing, sky quality and time of year. It is possible to take both cameras (HR and WF) in JHKs and that takes about 50 minutes in total. NB! Repeat exactly the same sequence in order to get the faint images.

Examples of how raw skyflat images should look like can be found in NOTCam calibration images. The structure is similar for all filters.

AutoGuiding - general instructions

AutoGuiding

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. 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.
  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 monitor 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.

AutoGuiding with NOTCam

NB! Autoguiding is recommended ALWAYS for optimal image quality, even with the short exposure times used in the infrared. It is also recommended during focusing.

Note that because of the dithering strategy used in the infrared, autoguiding should be done using the proper NOTCam guide area. The guide camera has to compensate for the movement of the telescope, but it has a limited area to move across due to the shape of the field used for the guider, as depicted by the grey area in the simplified sketch below (from original TCS manual). The small square at the lower right shows the FOV of the guide camera. Thus, depending on the dithering or beamswitch strategy of the observation, the original guide area must be reduced to smaller and even placed in specific areas to allow the requested movements.


OB scripts

If you have prepared your observations with the OB Generator or alternatively, using the Pointing Script Generator you will save time at the telescope, since you have already entered the proper NOTCam guide area, which means you have probably read this section before, and you can skip it now.

Manual pointing

If you point the telescope in the manual way, then if the instrument name on the TCS is NOTCAM, the default NOTCam guide area will be used, which is good enough for focusing and normal small step dithering (e.g. 3x3 dithers with 10-20" step size) as it allows a guaranteed 60'' step in any direction. If this is not sufficient, you must specify your guide area, according to your dithering mode, manually as follows, either on the TCS command line (example given in green for the reduced area, allowing a guaranteed 100'' step in any direction):

[TCS] ag-off
[TCS] get-guide-star N area
[TCS] g-g-s 1 NOTCAM-Re
[TCS] auto-pos-retry
wait until guiding

or, in the Sequencer terminal (example in green for beamswitch):

[obs@marissa~][NOTCAM]$ tcs.ag-off
[obs@marissa~][NOTCAM]$ tcs.get-guide-star N area
[obs@marissa~][NOTCAM]$ tcs.get-guide-star 1 NOTCAM-N-negX
[obs@marissa~][NOTCAM]$ tcs.auto-positioning-retry
wait until guiding

where the first input parameter, N, refers to the star number in the list of available guide stars found by the Guide Star Server, filtered and sorted according to brightness, while the second parameter area is the specified NOTCam guide area, i.e. either one of the fields listed below (e.g., NOTCAM-Re, NOTCAM-N-negX, NOTCAM-W-posY, ... etc. ).

If N = 1 the guide probe will move to the best guide star available for the selected area, and if you don't like this one (e.g. it appears double) or it is not there (e.g. an error in the catalogue), you can try N = 2.

NB! Note that the guide area you specified might accept the current guide star, in which case no movement occurs upon the command get-guide-star. Make sure the TCS status field says "guiding" before you continue.

Description of available guide areas

The default NOTCam guide area (NOTCam-De) guarantees that autoguiding can proceed with the same guide star during dithering for the typical small teloffsets. For any guide star an offset of 60'' from the initial pointing is guaranteed. This is valid for instance for the frequently used 9point (3x3 grid) dither with 10-20'' step size and for typicaly point source spectroscopy with an AB offset up to 60''.

If you are doing larger dithers or offsets, you want to use the reduced NOTCam guide area (NOTCam-Re) which guarantees an offset of up to 100'' in any direction away from the initial pointing.

If you do beam-switching or you step > 100'' away from the initial pointing (for instance using an ABBA dither with step size > 70"), you must select among the Beamswitch guide areas below - according to your beamswitch off-target direction. NB! The sky directions N,S,E,W are valid only for the default NOTCam field field-r -90 and refer to the direction in which you move the telescope. The positive/negative XY directions, however, refer to the movement of the target(!) on the array, and these are always valid, irrespectively of the field rotation. (Note that you may change the field-rotation to adjust the off-target direction on the sky.)

Below is a listing of all available NOTCam guide areas:

  • NOTCAM-De NOTCam_Default field (60'' step guaranteed)
  • NOTCAM-Ma NOTCam_Maximum field (not useful for dithering)
  • NOTCAM-Re NOTCam_Reduced field (100'' step guaranteed)

  • NOTCAM-Be-NS Beamswitch offset in NS direction
  • NOTCAM-Be-EW Beamswitch offset in EW direction

  • NOTCAM-S-posX Beamswitch offset to the South (target moves in positive X direction)
  • NOTCAM-N-negX Beamswitch offset to the North (target moves in negative X direction)
  • NOTCAM-E-negY Beamswitch offset to the East (target moves in negative Y direction)
  • NOTCAM-W-posY Beamswitch offset to the West (target moves in positive Y direction)

The above beamswitch guide areas are to be used with the observing script notcam.beamswitch where the beamswitch directions are given as S-posX, N-negX, E-negY, W-posY, as well as for any self-made beamswitch observing script. The maximum offset (away from pointing) allowed for these areas is 10' (EW) and 13' (NS). In all cases small step dithering of the order of 15'' is allowed in any directions.

Note that the guide system does not allow for large steps in all directions within one observation.

No guide star found?

Note that if there are very few guide stars at your target position (high galactic latitude, or a dark cloud), you may check out the NOT web tool for guide stars, where you can search for guide stars, even before your run, by entering target coords and instrument to use. If you do not find a suitable guide star at the offset direction you had planned, you may choose another, or potentially change the field rotation to another than the default field-r -90.

Focusing the telescope

Focusing the Telescope with NOTCAM

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).

The reference telescope focus for NOTCam is determined each night using the Focus Pyramid with the WF camera and the Ks filter, and the focus value is entered in either of the two ways:

[TCS] foc-pos 22560
[obs@marissa][NOTCAM]$ tcs.focus-position 22560

where the value in the above example is the default NOTCam focus, which is also set when running the telescope setup script for NOTCam:

[obs@marissa][NOTCAM]$ tcs.setup-tel-notcam

The focus pyramid is calibrated with the internal camera focus set to 5650 and 20, respectively, for the WF and HR camera. Because it is calibrated for the Ks filter, we recommend finding the reference focus for the WF-camera and the Ks filter and use the measured focus-offsets for other filters/camera combinations (see table below).

Imaging mode focus offsets.

WF Camera HR Camera

5650 20 Internal camera focus (fixed)
foc-pos 22560* 22560* Telescope value for K,K',Ks
foc-del 0 110 K, K', Ks
foc-del -45 70 H
foc-del -100 30 J
foc-del -160 -50 Y
foc-del -200 -75 Z
* Don't trust default values. Determine this value every night.

Note that the following instrument setup scripts automatically apply the focus offsets required for filter/camera/obsmode by modifying the tcs.focus-delta. They assume the foc-pos value currently set is the one for WF-camera imaging in the Ks filter (either the default NOTCam focus or the value the observer finds each night) and do not change this value!

[obs@marissa][NOTCAM]$ setup-ima cam filter-ID
[obs@marissa][NOTCAM]$ setup-spec cam filter-ID slit-ID grism-ID

The focus offset is wavelength dependent, so for the narrow-band filters the focus offset for the closest broad band filter should be used.

Focus fields

You can use the NOTCam standard star fields for focusing (notcamstd.cat) or you can use the NOT focus catalogue (focus.cat). Load the desired catalogue on the TCS:

[TCS] read focus.cat
[TCS] read notcamdstd.cat
In the TCS catalogue select a focus field and press numerical key [4] to go there. Make sure you are guiding!

How to: step by step

In order to focus the telescope for NOTCam you should use auto-guiding and sky-subtraction.

In the following recipe the first image is subtracted from the subsequent images by giving its full file name (NCxxxxxxxx.fits). The parameters given in green are example or suggested values/names.

[obs@marissa][NOTCAM]$ setup-focpyr WF
[obs@marissa][NOTCAM]$ exp 15
[obs@marissa][NOTCAM]$ setskysub imagename.fits
[obs@marissa][NOTCAM]$ teloffset -15 0
[obs@marissa][NOTCAM]$ exp 15
[obs@marissa][NOTCAM]$ focuspyr-auto

The output from focuspyr-auto gives you the offset to be applied to the current telescope foc-pos value. Iterate the last two steps until you converge. When finished, remember to take out the pyramid, or simply run the setup script:

[obs@marissa][NOTCAM]$ setup-ima cam filter-ID

Rather than using the fully automatic focuspyr-auto you may also use a manual command focuspyr. On the DS9 you put the cursor on the upper one of the 4 images of the star you wish to measure, then press 'a', and then press 'q', and the offset to be applied is output.

Quick observing instructions NOTCam

Field Rotator

For general information about the field rotator see an earlier section in this cookbook called Field Rotator and Camera probe. Every instrument has its default field rotation angle, for NOTCam it is -90, selected as such to cause minimal spilling of LN2. The script tcs.setup-tel-notcam sets the field rotation to default, but you can use any orientation, for instance if you want to do spectroscopy on the parallactic angle (see NOTCam Spectroscopy ). For most imaging applications the default value is fine.

The figure below shows the sky orientation on the NOTCam array with different values of the field rotation. If you want a given sky position angle (PA), you have to calculate a new field rotation: new_field = -180 + PA, where PA is measured from North and eastwards. If you wish to modify your current field rotation, then calculate new_field = current_field + d_angle, where d_angle (in degrees) is positive for clockwise rotation and negative for counter-clockwise rotation, referring here to the direction you rotate your stars on the array. You can also use the Pointing Script Generator, where you enter a sky PA and the script calculates the correct field rotation angle. Note that for spectroscopy it is the slit position angle on the sky that counts, but this is taken care of in the Pointing Script Generator for spectroscopy. Your current field rotation is always given on the TCS status display.

Field rotation

NOTCam Imaging

Make sure you are in your home directory in the Sequencer Terminal, i.e. in ~obs/scripts/proposal-ID, where proposal-ID refers to your proposal ID number. This is where your submitted scripts have been uploaded, OB generated scripts, as well as alternative pointing scripts, and finding charts.

New! If you have used the OB generator to make scripts, the compiled OB scripts with finding charts will be uploaded to your script directory on the instrument computer. To run the script, type the script name in the sequencer window. This replaces the following steps (1 - 4) of (semi-)manual observing. Note that point 3 also describes how to set the on-line sky-subtraction manually.

  1. Point the telescope to your target by running the pointing script you made through the web interface Pointing Script Generator. Your finding chart will then pop up on the screen.

    Alternatively, load your previously made and submitted TCS Target Catalogue or enter your target coordinates directly by typing:
    [obs@marissa][NOTCAM]$ tcs.enter-object obj hh mm ss.s dd mm ss.s epoch pm-ra pm-dec mag

    and point the telescope in either of the two ways:

    [TCS] select target and press numerical key [4]
    [obs@marissa][NOTCAM]$ guide-object obj

    where obj is the name of the target as written in the TCS target catalogue.

  2. Setup the instrument with the camera and filter of your choice, for instance WF-camera and Ks band:
    [obs@marissa][NOTCAM]$ notcam.setup-ima WF 207
  3. Before starting your dither scripts you may want to take a test exposure to verify the field and the peak count levels. Nnon-linearity reaches 1.4% at about 25000 ADU, and saturation starts at 56000 ADU (see the calibration page for details about the non-linearity and how to correct for it):
    [obs@marissa][NOTCAM]$ notcam.frames 4 4
    [obs@marissa][NOTCAM]$ notcam.teloffset 10 0
    [obs@marissa][NOTCAM]$ notcam.setskysub 1
    [obs@marissa][NOTCAM]$ notcam.frames 4 4
    The above sequence of commands takes two 16 second exposures separated by a 10'' telescope offset with the sky-subtraction set to previous image. You can modify the on-line sky-subtraction shown on the DS9 as follows:
    [obs@marissa][NOTCAM]$ notcam.setskysub N/no/filename
    [obs@marissa][NOTCAM]$ notcam.setskysub 1
    [obs@marissa][NOTCAM]$ notcam.setskysub no
    [obs@marissa][NOTCAM]$ notcam.setskysub NCwb240045.fits
    where the argument N subtracts the N'th previous image. Typically setskysub 1 , but if you use mexp t N you will want setskysub N+1. The command is sticky and every new image will be displayed accordingly. You can manually re-display the last image with the command display, or any image with the command display imagename .

    raw skysub
    Left: Raw WFC Ks-band image.
    Right: Sky-subtracted Ks-band image using previous image in a dither.

  4. Observe your targets using your own previously made observing scripts, or our set of NOTCam template dither scripts. Useful examples are listed:
    • [obs@marissa][NOTCAM]$ notcam.9point frame 8 6 my-object 10 2 3

      This does a 9point dither (3x3 grid) and at each position takes an exposure using the exposure command frame 8 6 (which gives a 48s exptime). The dither step size is 10'' and a skew of 2'' is applied to tilt the grid. The dither is run 3 times. Recommended for deep imaging where it is vital that the sky can be well calibrated.

    • [obs@marissa][NOTCAM]$ notcam.5point exp 4 1 my-object 15 3 1

      This does a 5point (dice) dither, and at each position takes an exposure using the exposure command exp 4 (note that you need to add N=1 as input). The dither step size is 15'' and a skew of 3'' is applied to tilt the grid. The dither is not repeated. Useful for bright targets where you don't worry so much about the sky.

    • [obs@marissa][NOTCAM]$ notcam.beamswitch frame 6 10 my-object S-posX 240 10 2

      This is a beamswitch mode going alternatingly ON and OFF target. At each position the exposure mode frame 6 10 (giving an exptime of 60s) is used. The OFF field is in the direction S-posX at the distance 240'' from the ON field. Both the ON and the OFF fields are being dithered by 10'' step sizes in a 3x3 grid fashion, using a skew of 2'' to tilt the grids. Useful for extended targets. The beam-switch direction can be either of: S-posX, N-negX, E-negY, W-posY and the step-size is in arc seconds. (NB! Note that the sky directions N,S,E,W are valid only for the default NOTCam field field-r -90 and refer to the direction in which you move the telescope. The positive/negative XY directions, however, refer to the movement of the target(!) on the array, and these are always valid, i.e. for any field rotation.)

    • [obs@marissa][NOTCAM]$ notcam.loop-frame 3.6 3

      Staring mode observing, using the exposure mode frame 3.6 3 (giving an exptime of 10.8s). The script is repeatedly taking exposures until interrrupted with Ctrl-C. The same type of loop script exists for the exposure mode exp t.

If you want to modify an existing NOTCam script, you can copy the original to your own directory and edit it (NB! it is vital that you call it something different!)

[obs@marissa~][NOTCAM]$ cp ~staff/notcam.as05-jhk my.as05-jhk

You can load a NIR standard star catalogue on the TCS by typing read JHKstd_leggett.cat or read JHKstd_hunt.cat. Reference papers: Leggett et al. 2006, MNRAS 373, 781-792 and Hunt et al. 1998, AJ 115, 2594. Or you may use our Selected JHKs standard fields for NOTCam and load them on the TCS by typing read notcamstd.cat. For these last sources there are sequencer scripts that make telescope pointing as well as the full JHKs cycle (see NOTCam Sequencer Scripts).

Field FS Other name RA(J2000) Dec(J2000) K-mag # stars expmode script Tot time
AS05 6 Feige 22 02 30 17.5 05 16 25 13.4-13.5 2 frames 3.6 5 notcam.as05-jhk 11 min
AS16 14 Rub 149 07 24 15.4 -00 32 49 11.0-14.3 5 frames 3.6 3 notcam.as16-jhk 10 min
AS19 17 M67-IV-27 08 51 20.2 11 52 43 9.7-12.4 3 expose 4 notcam.as19-jhk 9 min
AS26 23 M3-VZ193 13 41 45.4 28 29 50 11.4-12.4 2 frames 3.6 3 notcam.as26-jhk 10 min
AS33 35 . 18 27 13.6 04 03 10 11.7-13.2 3 frames 3.6 3 notcam.as33-jhk 10 min
Ser-std 143 Ser-EC68,EC84 18 29 51.2 01 11 48 11-12.9 2 frames 3.6 5 notcam.serstd-jhk 12 min
AS40 . NGC 7790 23 58 50.2 61 10 02 9.4-10.8 6 expose 4 notcam.as40-jhk 9 min

An IRAF package called notcam.cl is available for Quick Look reductions while observing. It is run off-line on the "Florence" computer where the data disk is cross-mounted (thus no need to copy raw data!). Check the Data reduction section in the NOTCam User's Guide for instructions.

If the seeing improves, it is recommended to redo the focusing on a focus field at high altitude. The telescope focus position foc-pos should always be set to the focus value for the WF-camera K-band.

If you wish to rotate the image on the DS9 display to have North Up and East Left, you can click on Zoom and then tick the Align button, or alternatively using the command line you can toggle alignment on/off with the sticky command:

[obs@marissa~][NOTCAM]$ notcam.wsc-align yes/no

Be aware that working at zenith distances larger than 60 degrees may cause some spilling of LN2, and subsequently cause a slight temperature increase of the detector. For a typical night the detector temperature has been found to change by +-0.1 degrees only.

NB! In order to have a stabilized detector where all effects subtract out well, it is recommended to take an exposure equal in time and readout mode to the one you use in your scripts before starting the script, i.e. take the target acquisition image the same way you would observe. At every change of integration time and/or filter the background level changes and the array needs to stabilize again. Alternatively, you can just skip the first image during data reductions.

For this same reason, it is not recommended to use the clear command in the beginning of each script if you plan to repeat the same script in order to get deep images. The clear command is useful if you have saturated, however, and want to get rid of memory effects.

NOTCam Spectroscopy

Make sure you are in your home directory in the Sequencer Terminal, i.e. in ~obs/scripts/proposal-ID, where proposal-ID refers to your proposal ID number. This is where your submitted OB scripts have been uploaded.

Note on focus

The default NOTCam telescope focus is defined as the best focus for WF-camera imaging in the Ks band (internal focus set at 5650). This value is determined using the Focus Pyramid in the beginning of each night (see above section on Focusing) and its value is typically close to the default value: 22560

The default telescope focus for spectroscopic mode is about 200 units lower for WF-cam spectroscopy and about 150 units higher for HR-cam spectroscopy. This is due to the different internal focus values needed for each camera/filter/slit combination in order to have the slits in focus. Both the telescope offsets mentioned above as well as the internal camera focus values for each setting are accounted for automatically when using the setup script:

[obs@marissa][NOTCAM]$ notcam.setup-spec cam filter-ID slit-ID grism-ID
[obs@marissa][NOTCAM]$ notcam.setup-spec WF 208 128 1

where the example is given for K-band WF-camera spectroscopy using the default 0.6" (128 micron) wide slit and grism #1.

Target acquisition

It is recommended to always use autoguiding. Automatic acquisition of guide star and starting of autoguiding is done if you have set the command tcs.auto-positioning-full. Note that for most spectroscopic observations with NOTCam, the dither along the slit is typically smaller than 60'' and you may therefore use the default guide area. This may not always apply:

  1. If your dither step is between 60'' and 100" you should use the so-called "Reduced" guide area. This situation is easily solved by preparing in advance your OB generator script. Alternatively, use the old Pointing Script Generator. If you point the telescope manually, you have to do as follows when the telescope preset reached to your target:

    [obs@marissa~][NOTCAM]$ tcs.ag-off
    [obs@marissa~][NOTCAM]$ tcs.get-guide-star 1 NOTCam-Re
    [obs@marissa~][NOTCAM]$ tcs.auto-positioning-retry
  2. If your dither step is larger than 100'', you have to specify an even smaller guide area, for instance NOTCAM-S-posX, since for typical ABBA/AB3 scripts the dither is towards positive X. For more details on guide areas see the section on Autoguiding with NOTCam above.

The default field rotation for NOTCam is field-r -90, but for your spectroscopic observations you may want another field angle, either because you want two targets in the slit, or because you wish to observe your target on the parallactic angle. This is prepared in advance using the OB generator , or alternatively, the old Pointing Script Generator. If not, you have to do as follows:

  1. In the first case you can either determine beforehand the position angle of the slit on the sky (P.A. measured from North and Eastwards). Then on the TCS give the new field-r value as (-90 + P.A.). Point to your target using the normal "Preset" button which is function key 4 in the Catalogue (CAT) menu. Alternatively, you can use the script
    [obs@marissa~][NOTCAM]$ notcam.slitrot
    when pointing at your target. It allows you to select your two targets interactively inside the imexam environment and gives as output the new field-rotation angle you have to use.
  2. In the latter case, when you point the telescope to your target, use the "Preset w par ang" which is function 6 in the Catalogue (CAT) menu. When comparing with your finding chart note that your field will be rotated differently for each target. On the DS9 you can click on the Zoom menu and the button Align to get your field aligned with North Up and East Left. (Note that for the "Preset w par ang" to work correctly, i.e. to orient the slit vertically with respect to the horizon, the instrument-parallactic-angle 90 must be defined in the TCS, but this is automatically done when the telescope is setup for NOTCam with the tcs.setup-tel-notcam command.)

Again, both the field-rotation as well as the guide-area setting can be well planned in advance and entered into the OB generator , alternatively, the old Pointing Script Generator.

Also, note that on the DS9 display you can align the image to have North Up and East Left by clicking on Zoom and then the Align button, or alternatively on the command line you can toggle alignment on/off with the sticky command:

[obs@marissa~][NOTCAM]$ notcam.wsc-align yes/no

Slit acquisition

There is an interactive script for NOTCam slit acquisition called notcam.acquisition that works similarly as alfosc.acquisition, but with a few important additions:

  1. it allows for sky subtraction of the acquisition image, and
  2. it takes an image of the slit to estimate the slit position per pointing (due to flexure), and
  3. to diminish the persistency problem, it reminds you to add a narrow-band filter from filter wheel 1 (click on the UIF) during acquisition of very bright stars. Note that in good seeing (FWHM=0.6'') an 8th mag star saturates in 0.5 seconds (the minimum effective exptime). If by accident a bright star falls in the slit on the first slit image and there are memory effects left even after two acquisition images, then it is recommended to run a notcam.clean3 before taking the spectra.

[obs@marissa][NOTCAM]$ notcam.acquisition -c -q -noslitim cam slit filter-ID expotime
[obs@marissa][NOTCAM]$ notcam.acquisition -c -q WF 128 208 0.5

The above example (in green) is for WF spectroscopy in the K-band. The script is interactive and prompts you for actions. Follow the instructions given in the sequencer window.
NB! the -noslitim flag is only to be used if you just measured the slit position at this pointing!

The -c flag makes a slitview exposure of the target on slit, and the -q flag queries the user for possible iterations. The normal procedure is to take a slit image at every new pointing and measure the slit position, but if you know what you are doing, you can skip this with the -noslitim flag. The script needs to know which camera you use (HR or WF), which slit (128 or 44), and which broad-band filter to sort the orders (Z = 237, Y = 236, J = 201, H = 203, Ks = 207, or K = 208).

Manual slit acquisition (old)

Because of instrument flexure, the slit position may vary slightly with telescope pointing, thus for each new target it is recommended to take a short image (t = 2-5 sec) of the slit to measure its Y-value at the X-position you defined as a good in the afternoon. (Lately, defining position A at X=430 with an offset of 42.12" has been found to be a good location, but check the array for bad pixels.) Use imexam and measure on the DS9 the Y-position of the slit (at your desired X-value for position A) using the key 'k'. The step by step procedure for acquisition on the slit is therefore as follows:

[obs@marissa][NOTCAM]$ setup-spec cam filter-ID slit-ID grism-ID
Put in the slit! No grism!
[obs@marissa][NOTCAM]$ exp t
[obs@marissa][NOTCAM]$ imexam
Note down XY. Take out the slit!
[obs@marissa][NOTCAM]$ exp t
[obs@marissa~][NOTCAM]$ slitoff X Y
[obs@marissa][NOTCAM]$ exp t
[obs@marissa~][NOTCAM]$ slitoff X Y

Where one iteration of the slitoff task usually is enough to have the star centered on the slit with high precision. Follow descriptions which typically ask you to locate your target with the cursor and then press

  • 'a' for gaussian centering or
  • 'x' for using this exact pixel value,

and then type 'q' to quit. Now the telescope moves and the guide probe follows. (The acquisition image should be taken with the broad-band filter you will use for spectroscopy.) Comment: If your target is brighter than the sky, then you may use the slit image as a "sky-subtraction" image

[obs@marissa][NOTCAM]$ setskysub imagename
[obs@marissa][NOTCAM]$ setskysub NCvj010015.fits

and you will automatically see where your target lands on the negative slit image. If your target is fainter than the sky, you will have to take two aquisition images as a start, with a teloffset in between, such that you can use the first one as the sky-sbutraction image.

Taking spectra and calibration lamps

When you are satisfied with the slit acquisition, you can start the dither script. The ABBA dither is a frequently used mode, but an improved AB3 dither mode is also offered. (Be aware that the first exposure must be discarded in all cases.) The AB3 mode takes 6 spectra in an ABABAB pattern. The AB3-beamswitch mode allows you to do spectroscopy of extended targets. You may use and find more details about the available dither scripts. Examples of use:

[obs@marissa][NOTCAM]$ abba t N object step-size
[obs@marissa][NOTCAM]$ abba 10 10 HIP2435 42

[obs@marissa][NOTCAM]$ ab3 t N object step-size
[obs@marissa][NOTCAM]$ ab3 30 10 mytarget 42

[obs@marissa][NOTCAM]$ ab3-beamswitch t N object direction off-beam step-size
[obs@marissa][NOTCAM]$ ab3-beamswitch 30 10 mytarget W-posY 120 15

to give as input the parameters t and N in the notcam.frames t N command. In the above ABBA example the exptime per dither position is 100 seconds. The teloffset step-size (in arc seconds) is between position A and B for ABBA and AB3. For AB3-beamswitch the off-beam is the beamswitch step going in the direction direction, while the step-size is the small-step dithering along the slit for both ON and OFF target spectra (useful for removing bad pixels). Note that only the ramp-sampling readout mode is offered for spectroscopy, using the exposure command frame t N, and the minimum exposure time is 3.6 seconds with frame 3.6 1. The scripts put in the grism if it is not already in the path.

HspecA HspecABdiff
Left: Raw WFC H-band spectrum of a star at position A (x=425). Curved horizontal lines are sky lines (exptime = 130s).
Right: Sky-subtracted A-B position H-band spectrum.

The spectra are oriented vertically on the IR array with blue-to-red wavelengths going from the top to the bottom.

The notcam.abba and the notcam.ab3 scripts use the automatic quickspec option on incoming images to extract the individual spectra with an optimal sky-subtraction setting. This sky-subtraction setting is also used for the DS9 display. The quickspec settings can be modified using quickspec-config and you can manually run it on any spectroscopy image with the command quickspec filename .

It is highly recommended to take wavelength calibration lamps while pointing at your target due to flexure of the instrument. It is also easier to deal with fringing having spectral flats taken in-situ. The calibration unit for NOTCam is mounted on the inside of the baffle cover, and for this reason it is necessary to close mirror covers when using these lamps.

Closing and opening the mirror-covers takes 1.5 minutes, and in order to minimize extra overheads, we recommend the use of the script notcam.easy-calib for in-situ calibrations at night after taking the target spectra. Neither the slit nor the grism is moved, notcam.setup-spec is used to change between wavelength regions, and notcam.calibexp to perform the calibrations. The script takes 1 argon, 1 xenon, and 3 halogen lamp images per wavelength region using the default calibration lamp exposure times, and you can take up to 5 wavelength regions at the time. The total time needed is about 2 minutes per wavelength region plus 1.5 minutes for the mirror cover movement. When finished, you should be back guiding on your guide-star, with the target aligned in the slit, ready to continue on this target, if neeeded.

[obs@marissa][NOTCAM]$ easy-calib fid1 [fid2] [fid3] [fid4] [fid5]
[obs@marissa][NOTCAM]$ easy-calib 208
[obs@marissa][NOTCAM]$ easy-calib 208 203 201
[obs@marissa][NOTCAM]$ easy-calib 208 203 201 236 237

Due to the slowness of the argon spectral lamp in switching on, the script switches on this lamp already while closing the mirror-covers. Then all the argon lamp images for all wavelength regions are taken first. After this, xenon and halogen lamps are taken per region. The wavelength regions are defined by the filter ID-number of the broad-band filters: 208 = K, 203 = H, 201 = J, 236 = Y, 237 = Z.

If you want to obtain calibration images in a more manual fashion, use the notcam.calibexp script to take the number of lamps you wish. The script will stop auto-guiding, turn off TV, close mirror covers, switch lamp on, take exposure, switch lamp off, and, depending on your choice, either 1) leave mirror covers closed (if you set -lmc), or 2) re-open, switch on TV, set back the correct TV-filter, and re-acquire autoguiding. Here follows an example:

[obs@marissa][NOTCAM]$ calibexp -lmc lamp exptime
[obs@marissa][NOTCAM]$ calibexp -lmc halogen 7
[obs@marissa][NOTCAM]$ calibexp -n 2 -lmc argon 10
[obs@marissa][NOTCAM]$ setup-spec wf 203 128 1
[obs@marissa][NOTCAM]$ calibexp -lmc halogen 7
[obs@marissa][NOTCAM]$ calibexp -n 2 argon 2

Standard stars

Don't forget to take telluric standard stars at each target pointing. See NIR telluric standard stars (Gemini page).

At the end of the night

  1. When the background starts to become high in the morning twilight it is time to turn off the sensitive guide tv. On the TCS type tv-off. Turn also off the two autoguider monitors.

  2. If you want to take twilight sky flats, find a blank field in the western sky which is not too low (i.e. RA a couple of hours less than ST). Point to it at least 40 minutes before sunrise.

  3. You might need to continue until after the sun is up. Therefore: Close sideports first!

  4. Take test exposures and start the script
    [obs@marissa~][NOTCAM]$ notcam.skyflat t
    with t=3 for WF-Cam and ZYJHKs filters about 40 min before sunrise. Do the filter cycle the oposite way now: YZJHKs-YZJHKs. If you want only WF-camera JHKs flats, it should be sufficient to start 30 minutes before sunrise with the faint flats, using an exposure time of 3-5 seconds.

    Note that the timing is a bit tricky for morning flats. How fast the sky brightness increases in the different bands varies with temperature and sky conditions in general, as well as with the altitude of the blank field. Good luck!

  5. The TCS warns you about 5 minutes before sunrise that it will autoclose the telescope in 5 minutes. If you need to continue with flats after sunrise, this is possible by using the TCS command:
    TCS: keep-telescope-open xx
    which lets you keep on xx minutes more.
  6. If you wish to take darks at the end of the night, there is a script available called notcam.notcam-calibs that can be started when the dome is closed (and lights are off), and you can leave it running. The script takes a date-string (for instance NCwi14) as input parameter and checks all data obtained on this date in order to take 6 darks in each of the used exposure modes. Depending on the observations made, this can take some time.
    [obs@marissa~][NOTCAM]$ notcam-calibs NCwi14

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.

Data saving and retrieval

As of 2005 all data acquired using ALFOSC, NOTCAM, STANCAM, MOSCA, and FIES is written to DVD every morning by staff. It is the duty of either the allocated support astronomer or duty technician to put the data on DVD. No one other than the above personnel may use the DVD burners in the NOT service building. DVDs for visiting observers will be placed in the visitors mailbox in the NOT service building.

One copy of each night's data of a run will be made for the visiting observer, free of charge. Each DVD holds a maximum of 4.7 Gbyte of data, generally one DVD is used per night. One copy of each night's data will additionally be made for the NOT archive. 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. 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
  /data/<instrument-name>/
  /data/reduced/<instrument-name>/

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 obsupport@not.iac.es. If you have questions about how to define OBs and/or Observing Sequences, please contact service@not.iac.es.

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

Troubleshooting

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.

Troubleshooting - NOTCam

  1. If imexam stalls, which is known to happen if you press "t" or "g", type in another sequencer terminal:
    [obs@marissa~][NOTCAM]$ notcam.killimexam

  2. If the above did not help and you still experience problems with the postprocessing DS9 display, the best trouble shooting is to kill it properly using the command:
    [obs@marissa~][NOTCAM]$ notcam.killpostprocess
    [obs@marissa~][NOTCAM]$ notcam.setdisplay
    [obs@marissa~][NOTCAM]$ notcam.display-start

    NB! Note that this will terminate any running observing scripts! Remember to reset the Scale and the Zoom on the new DS9 window to see your image properly.

  3. If the automatic observing log gets stuck, which usually happens if connection to the database is lost, the easiest way to "fix" this is to type in a sequencer window the command:
    [obs@marissa~][NOTCAM]$ notcam.reset-log

    If anything goes wrong with this wrapper script, it will instruct you how to proceed.

  4. If you wish to abort a script, do so by typing in the sequencer:
    [obs@marissa~][NOTCAM]$ Ctrl-C

    which will stop the script, but NB! you will have to wait for the ongoing exposure to finish! The reason is that there is no working "abort" command for the NOTCam detector controller.

  5. It is known that Ctrl-C in the Sequencer Window, although it is the only way to interrupt a script, may cause the Sequencer to crash completely. Also, the error message "BIAS got sigpipe and dying" requires restarting the NOTCam sequencer. Do as follows:
    [obs@marissa][NOTCAM]$ shutdownobssys notcam
    [obs@marissa][NOTCAM]$ startobssys notcam
  6. The NOTCam "Buzzer" is supposed to control that the shutter works perfectly. If it makes noise, you may press the reset button on the Buzzer (on the wall in front of you) to stop the noise, but unfortunately you have to wait until the exposure ends. Sorry! Most probably it picked up noise and there is no problem with the shutter. To verify that the shutter behaves well, however, check the behaviour of the two LED lights. The correct behaviour is that the right LED is lit during every exposure and the left LED is lit during every second exposure. If the left light is blinking, this is an indication that the shutter is out of synchronization, and you should click on the Initialize menu on the NOTCam User Interface, and then on Init Shutter.

  7. If the actual exposure time is shorter than the requested exposure time, then you need to power cycle the NOTCam Array Controller.
    [obs@marissa][NOTCAM]$ shutdownobssys notcam
    Go to the dome and power cycle the array controller!
    [obs@marissa][NOTCAM]$ startobssys notcam

  8. If during observations you get an image which looks as follows:


    Condensation on the entrance window.

    then there is water condensed on the entrance window of NOTCam. This can happen if the humidity inside the dome is very high over a long time and/or there is some problem with the vacuum in the cryostat. Observations can not be continued. Call staff!

  9. If you find evidence of a large dust speck in your images, it might be a good idea to move the telescope down and up, perhaps turn the rotator with the telescope down, to try to get rid of it, although this may not help. The image below is an example of a large, out-of-focus particle, here seen in a ratio of flats. The particle is just barely visible in raw images, unless it moves between frames and you spot it in difference images (e.g. sky-subtraction is on). In the example below, a ratio flat from one night to the next (engineering grade array), the largest difference inside the dust speck is on a 3% level. The rest of the image has a value of 1 within 0.001 to 0.01, and a standard deviation around the mean of 0.004.


    Large dust speck seen in ratio flat field.

    If the particle is on the entrance window, then NOTCam can be dismounted and the entrance window inspected and cleaned. Before doing this, change to the other camera and make a ratio image of domeflats with the two cameras. This should reveal whether the particle is on the camera lens inside NOTCam.

  10. Interference pattern due to pick-up noise may re-occur, and is not easy to get rid of. The effect is always strongest for the upper two quadrants. See the example below for difference darks before (left) and after (right) eliminating the strong pick-up noise in 2003.
    Difference darks with pick-up noise (left) and without (right).
    BEFORE AFTER

  11. In all cases of doubt, contact staff!

Appendix

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 22400 480 North ↑ East ← Horizontal slits: E-W (P.A. = ±90) 0.75
FIES 0 N/A c-p-s 22720 530 North ↓ East ← N/A
NOTCam -90 -90 c-p-p 22560 495 North → East ↑ 0.95
MOSCA -90 N/A c-p-p 22210 450 North ↑ East ← 0.55
StanCam 0 N/A c-p-c 22150 430 North ↑ East ← N/A
SOFIN 0 -90 c-p-p 22600 520 N/A 0.9
TurPol 0 N/A c-p-p 24300 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 Instrument Commands

Command Comments
CNTR-C kill ongoing command or script
abort kill ongoing exposure

object text Sets the value of the FITS keyword OBJECT to text
autosave_on Turns on autosave. For off, type autosave_off
rempath link Sets the remote saving path to specified link
remsave_on Turns on remote saving. For off, type remsave_off
bin n Sets the binning factor in both X and Y directions to n
xbeg n Sets the X beginning to n (use ybeg for y).
xsize n Sets the X size to n (use ysize for y).
expose t Makes an exposure of t seconds. To abort the exposure press Ctrl-C and type abort in the sequencer window.
mexpose t n Makes n exposures of t seconds
dark t Makes an dark exposure of t seconds
mdark t n Makes n dark exposure of t seconds
teloffset n m Offsets the telescope in the CCD X,Y direction by the amount n in the X direction and m in the Y direction. n and m are given in arcseconds.
resetxy Resets the CCD to unbinned full-size readout
For more commands, view the Sequencer Reference Manual.

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
camera-probe-stancam
camera-probe-ccd
Moves the camera probe to ccd position (for StanCam)
camera-probe-park Moves the camera probe to park position (for ALFOSC)
camera-probe-fies
camera-probe-split
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
instrument-parallactic-angle n Defines the parallactic angle for following presets
read-catalogue name.cat 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.

NB! Note that the OB generator does not yet allow for differential tracking, and special observing scripts must be made. For manual observing see below.

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 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 your target moves less than 70" over the execution time of your observations, you can safely use this approach. If not, you need to keep an eye on the star-box and (for the time being) manually re-position it by typing a command (see point 7).

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. Calculate your object's coordinate motion in RA and DEC rates in advance (rates are in arcseconds per hour).
  2. Point to your target in the normal way, wait until guiding, and then run the script:

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

    This script 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 auto-guiding.
  3. If this is a relatively fast target, i.e. moving more than 70" during the time your observations take, you will have to make sure that the star box does not reach the other edge of the TV screen, in which case it will stop guiding. Before it does, you can run the script:

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

    in another sequencer window, while observing, or in between exposures, to reposition the box and the guide probe without affecting the telescope tracking.
  4. Stop differential guiding by tcs.box-motion-stop (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.

  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 rate is 60,000 arcsec/hour (≈ 17 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.

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