The Coude Echelle Spectrographs

3.1 Observing with UCLES

Sections: Image Display Orientations | Controlling the spectrograph | Starting the VAX program | Configuring UCLES | The UCLES Setup Routine | Displaying the spectrograph status | Mechanisms to configure interactively | Focussing UCLES | Wavelength placement | Other useful commands

Observing with UHRF | Controlling the detector | Contents | Home

Image Display Orientations

EEV2 display on XMEM                      EEV2 display in IRAF/Figaro
--------------------                      ---------------------------
| red           : o |                     | blue                 : o |
|  :            : v |                     |  :                   : v |
|  :            : e |                     |  :                   : e |
|  :            : r |                     |  :                   : r |
|  : red...blue : s |                     |  :  red...blue       : s |
|  :            : c |                     |  :                   : c |
|  :            : a |                     |  :                   : a |
|  :            : n |                     |  :                   : n |
| blue          : . |                     | red                  : . |
---------------------                     ----------------------------

MITLL3 display on XMEM                    MITLL3 display in IRAF/Figaro
--------------------                      ---------------------------
| blue          : o |                     | red                  : o |
|  :            : v |                     |  :                   : v |
|  :            : e |                     |  :                   : e |
|  :            : r |                     |  :                   : r |
|  : blue...red : s |                     |  :  blue...red       : s |
|  :            : c |                     |  :                   : c |
|  :            : a |                     |  :                   : a |
|  :            : n |                     |  :                   : n |
| red           : . |                     | blue                 : . |
---------------------                     ----------------------------

Controlling the Spectrograph

Observers control UCLES through the VAX via a user interface based on the ADAM Interactive Command Language (ICL). This software in turn controls a SYNTEL micro-computer that handles all the low-level processing involved in configuring the instrument.

Starting the VAX Program

Usually the afternoon technician has already started up a VAX session on one of the xterms in the control room, but if not, login to the vax observer account (see whiteboard). After login completes...

$ UCLES
... start control program. NO to automatic setup.
$ UCLES
Set mode to UCLES

Note that you need to use a  separate OBSERVER window to the one running the detector.

You will be prompted for information on the detector.  We hope to reduce the number of prompts soon, as most take the default. Prompts that require an explicit answer are:
PUT IN THE DETAILS

 

Configuring UCLES

Before the observer starts to use UCLES, the support staff will have powered up the hardware and set up the detector. The detector will have been rotated to align an order near your chosen wavelength with the detector pixels, and the spectrograph focused to ensure that their is adequate travel to reach optimum
focus. For more information on these procedures, see Appendices C1, & C2 .

It is possible to demand any optical wavelength at the centre of the detector.

CENTRE grating lambda filename
computes the settings which centre wavelength lambda (in Angstroms) on the detector, using the specified grating. The settings are output to the named control file. (Hint: Use lambda as the filename too.)

CENTRE PEAK

centres on the blaze peak of the order in which lambda falls, rather than on lambda itself.

USE filename
adopts the named control file.

CONFIG SLAUTO

configures the hardware using the control file specified by USE. The SLAUTO keyword selects the maximum slit length that maintains an interorder gap of 1 pixel.
 

The UCLES setup routine

The command CENTRE causes the software to calculate the echelle grating angles to place the specified wavelength in the centre of the field. However, since the centre of the detector may not coincide precisely with the optical axis of the camera, it is usually necessary to determine small offsets to be applied to the calculated angles. Similarly, since the detector is rotated to align the orders with the detector, it is necessary to offset the calculated slit angle so that the slit image is perpendicular to the echelle orders. These offsets are determined by running the SETUP routine. While afternoon staff or the support astronomer may have already carried out this procedure for you, this part of the configuring process is the observer's responsibility.

When UCLES is run, it uses offsets determined the last time it was used. If you suspect that the offsets applied are wrong, i.e. if you can't recognize the ThAr spectrum, you may zero the offsets by using the command OFFSETS. Note also that the ThAr lamp polarity must be correct, or an unrecognizable spectrum will result.

• You must be running from a terminal with imaging capabilities, probably an xterminal in which case SETUP will want to create its own image display (FIGDISP) window; there must be no FIGDISP windows already active on this terminal.
• UCLES: SETUP
• SETUP prompts for a central wavelength, which should correspond to a moderately strong, easily recognised spectral line near the wavelength region of interest. SETUP configures the spectrograph to the requested central wavelength using the 79 lines/mm grating (since this gives the greatest order spacings), and turns on the ThAr lamp.

Take an exposure with this setup. Use a narrow window, e.g. TEK1K_SETUP. The image should resemble Figure 1.
• The program initiates a FIGARO IMAGE command. Note: This version of IMAGE will not recognize MAX, MIN or `\' as responses to these prompts.
• SETUP calls ICUR, producing an image cursor, and asks the user to mark three points along the target spectral line, which should be obvious near the centre of the field. Place the cursor at the left end, the middle and the right end of the spectral line, hitting the space bar on each occasion. Type Q when this is done.
• SETUP calls ROTCEN to calculate the offsets. The slit angle is determined by cross-correlating the ends of the spectral line. The program prompts for the range of data values to extract; the defaults are usually suitable. The position of the central point is used to determine the echelle angle offsets.

SETUP reconfigures the spectrograph with the new offsets and gives the option of repeating the process. This is advisable to ensure that the offsets were reasonable. The ech_theta and ech_gamma offsets should be of order 0.01.

A spectrum taken with the full window ( e.g. TEK1K_SX2) should resemble that shown in Figure 2, though it may be at a different wavelength or with the 31.6 lines/mm grating in which case there will be many more orders, more closely spaced.


Figure 1 (left): UCLES, 10 sec ThAr lamp, SLAUTO, TEK1K_SETUP, 79 lines/mm grating at 5009.334 Å, XMEM orientation.
Figure 2 (right): Same setup as Figure 1, with the TEK1K_SX2 window. Note overscan strip on right hand edge.

 
 

Displaying the Spectrograph Status

DISPLAY
displays spectrograph configuration. Check that the filters selection is correct (usually out of the beam). Items in motion are marked by asterixes (*'s). Reverse video emphasizes anything in an unusual state.

DISPLAY OUTPUT= filename
writes the display to an ASCII file.

R item
reads a specific item, in default units e.g. R BR

RU item units

reads an item in specified units e.g. RU SW PIX

LIST
lists current configuration parameters

Mechanisms to Configure Interactively

Not all spectrograph mechanisms are affected by the control file. Slit dimensions, use of the beam rotator or focal modifiers, filter settings, calibration lamps, and TV mirror controls must all be set interactively.

CANCEL action
halts action currently being modified.

SLIT item
selects item = SLIT or SLICER.

SW x units
sets the slit width to x units, where units = MM, PIX, or ARCSEC.

SL x units
sets the slit length to x units, where units = MM, PIX, or ARCSEC, if not using SLAUTO.

SF1 n
sets slit filter wheel 1 to filter n. Similarly SF2n, LF1n, LF2n for the other slit and lamp filter wheels.

ARC lamp
directs the specified calibration lamp onto the slit, where lamp is one of QUARTZ, THAR, or LASER.

LOF
turns off the lamp, but doesn't move any optics.

TV SLIT = STAR
turns off the lamp, and removes the calibration lamp optics. Returns TV view to the slit.

TV WIDE
changes from slit view to a 1 arcmin field.

FM IN
selects the focal modifier, and FM OUT removes it.

If the beam rotator is to be used, there are several additional commands:

VERTICAL
inserts the beam rotator and maintains parallactic angle.

CANCELVERTICAL
halts the rotator, but leaves it in.

TRACKPA pa
inserts the beam rotator and maintains a particular position angle pa (in degrees).

CANCELPA
halts the rotator, but leaves it in.

BR OUT
removes the beam rotator from the optical path.

 

Many mechanisms have a limited range of travel. MIN and MAX are valid values to set them to their limits, e.g. SL MIN to obtain the shortest possible slit length. See Appendix C6 for a complete list of commands, and their limits.
 

Focussing UCLES

The depth of focus for UCLES is substantial and it will be rare that focus changes are required, but it should nevertheless be checked.

Configure spectrograph to the wavelength of interest. Select a narrow unbinned window ( e.g. TEK1K_SETUP or MITLL?)
 

PIXELS
... verify that UCLES knows the pixel size.
CONFIG SLAUTO
... configure spectrograph
SW 2 PIX
... use narrow slit with UCLES
ARC THAR
... select arc lamp
CF MIN
... set collimator
HP DOWN
... set Hartmann mask, take exposure.
HP UP
... flip Hartmann mask; take exposure.
CF MAX
... move collimator
HP UP
... take exposure with Hartmann up.
HP DOWN
... flip Hartmann mask; take exposure.

Start the AAT utilities menu on aatssf by logging into obsred and typing AAT. The focus routine can be found under "setups" ? Run FOCUS to compute a new collimator focus value.

 
CF x
... Set recommended focus...
HP OPEN
... remove Hartmann masks...
SW 1 PIX
... set narrow slit and take an exposure of the arc.

Check the width of the lines. In FIGARO this can be done by: YSTRACT a spectrum, and run EMLT to see the FWHM. For UCLES the FWHM should be about 1.7 Tek pixels.
 

Wavelength Placement

Even after doing a CONFIG, the spectrum positioning may need further adjustment if, for instance, partial orders are being recorded at one or both sides of the detector or the detector has bad columns, in which case it might be desirable to shift the spectrum in the cross-dispersion direction.

The most likely parameters to change are:

EG eg
adjusts the cross dispersion position, ECH_GAMMA, in degrees. Increasing ECH_GAMMA moves bluer wavelengths onto the detector. 1 unit (degree) corresponds to 24 mm on the detector.

ET et
adjusts the cross dispersion position, ECH_THETA = ET, in degrees. ET has the same scale as EG.

For UCLES observations with the Tek, bluer wavelengths in the order are at the bottom of the display, and bluer orders are at the right of the display. The overscan (if any) is on the right. FIGARO displays the image inverted vertically.
ADD MITLL2&3, DIRECTIONS FOR EG AND ET

Once satisfactory grating and focus settings are obtained, they can be locked into the control files with

ISET itemname value
where itemname is the full (not abbreviated) form of the parameter being set.

LIST
lists the contents of the current control file. LISTed items can be ISET.
 

Other Useful Commands

PIXELS
declares the pixel size if CCD binning has changed.

DCL dclcommand
executes a VAX DCL command.

SHUTDOWN
performs an orderly shutdown of lamps, power supplies, kills all UCLES tasks, and exits from ICL. Not usually necessary during a run.

EXIT
leaves the UCLES software.

HELP
accesses the online UCLES HELP library.

Ray Stathakis (ras@aaoepp.aao.gov.au)
Last Update: 26 November 2003 by Stuart Ryder