- Gemini Office
This section describes the standard setting up procedures which are necessary before a night's observing with UHRF. UHRF is normally setup during the afternoon, either by the afternoon staff or by the support astronomer. Non-expert visiting astronomers at the telescope are not expected to know how to set up the instrument.
The following procedures are normally followed in order:
We also describe how to:
UHRF configuration files are created manually for each wavelength observed. Once a configuration file has been created, it is kept on disk and can be reused whenever the selected wavelength is observed. The files are stored in a directory named something like /instsoft/drama/local/ucles/r1_44/UhrfModel/. UHRF files normally start with an element name, for example the file NA_5980 contains the settings for the Na 5890 line.
You can also refer to the UHRF configurations summary for setup values optimized in previous UHRF runs.
- Make sure that Beam Rotator is OUT of the beam so that it does not interfere with the TV which needs to be repositioned to view the slicer. This may need to be done from the UCLES GUI, or from the Syntel micro.
- Make sure the slit angle offset is zero by entering 0.0 in the Slit Angle Offset: field of the UHRF tab, and then press CONFIGURE.
- Make sure the slit is horizontal (otherwise the slit angle is applied to the slicer which will be tilted) by entering -0.205 (units are degrees) in the Slit Angle: field, and then press CONFIGURE.
- Check that the Lamp and Post-Slit filter wheels are all in the CLEAR position.
- Check that the focal reducer is set to the correct value, i.e. Focal Reducer: is set to 3e5, 6E5, or 1E6 as appropriate for the camera resolution and focal station in use.
- The HeNe laser line has two possible configuration files for either the V or R gratings. Select the "Configure with Control File" sub-tab of UHRF, click on the blue "Load Control File" button, then click on either the LASER_6328V or LASER_6328R files, then click the blue "OK" button to start UHRF reconfiguring to this setting.
- Turn on the laser by selecting LASER from the Calibration Lamp: pull-down menu, then CONFIGURE.
- Load a CCD window such as the "vax" file eev2_x8 and take a 15 second Dummy frame at Normal read speed.
- The HeNe laser line should be clearly visible on the gaia display. The line may be grossly out of focus as seen below (e.g. in Aug 2007, we found the best focus to be near 46400 ADU, cf. the canonical value of 49400 ADU) and considerably tilted. On the gaia display, y = dispersion direction, and x = spatial direction. For the EEV2 CCD, red wavelengths are at the top and blue wavelengths are toward the bottom of the gaia display. Any overscan columns are on the right-hand edge.
- Move the laser line to the approximate center of the field by adjusting the theta and gamma angles. To move a line up, increase theta. To move a line rightwards, increase gamma. For 1E6 resolution the full window ~1900 x 500 ADU. For 3E5 resolution the full window is ~5700 x 1500 ADU.
The CCD rotation for UHRF is done such that the laser line is parallel to the CCD rows. Note that this is different to UCLES where orders seen from the quartz lamp are aligned parallel to the CCD columns. Make sure the laser line is in reasonable focus to begin with, then execute the RotateUHRF.tcl sequence. If working at 3E5 resolution, use theRotateUHRF_3E5.tcl sequence instead, which uses a narrower CCD window to better contain the laser line. The measured tilt of the laser line, and the micrometer adjustment required to correct for this, will be reported in a pop-up window. Double-check the line measurements to confirm they make sense.
Have the afternoon shift technician rotate the CCD in the Coude room in the usual way. For EEV2, a positive shift requires a decrease in the micrometer reading, and one full rotation of micrometer screw = 0.5 mm. Click the "Cancel" button to properly terminate the sequence, else the GUI will not allow you to execute another sequence. Repeat the procedure to see if the laser line is now correctly aligned; the CCD should be rotated to an accuracy of 0.1 mm or better.
The collimator focus procedure is done with a Hartmann test by taking two arc frames with the upper, then the lower Hartmann shutter closed. Simply execute theFocusUHRFLaser.tcl sequence, which takes the necessary exposures, then analyses them in two independent ways:
- a cut is made through the centre of each image, and the peak of the strongest line in each is found automatically from which the shift in pixels is determined;
- a cross-correlation of the two images is done, from which the shift in pixels is determined.
To convert from pixel shifts to the necessary focus adjustments, the following conversion scale is used:
- @1E6, a shift of +1 pixel means the focus value needs to be adjusted by -28.1 ADU
- @6E5, 1 pixel = -45 ADU
- @3E5, 1 pixel = -95.5 ADU
The collimator focus for UHRF has two different drives, giving coarse (Collimator Coarse Focus) and fine (Collimator Fine Focus) control. To set the focus, first use the coarse control. This sets the focus position to within about 30 ADU. Then use the fine control to adjust it to the final value. The fine control has a maximum range of around +/- 100 ADU and can be driven out of range. If this happens, the response will be something like:
"obey" UHRF_FFOCUS - action complete - text: 49623adu !!
instead of the requested position. In this case, you will need to reset the focus value using the coarse control - drive it up by 100 units or so (if that was the direction you were trying to go), then re-issue the Fine Focus setting. It is possible to set the focus position to an accuracy of 5 ADU, but repeated use of the "Update FF" button will show that this is about as accurate as the encoder can read anyway. It may be necessary to repeat the focus procedure if the initial focus was poor, but once a focus change of <20 ADU or so is needed, you may well end up getting stuck in a loop so don't bother with more than 2 or 3 iterations of this.
After focusing on the laser line, make sure both Hartmann shutters were opened at the end of the focus sequence and take another frame to measure the intrinsic instrumental resolution. Use the IRAF "imaexam" task and the "k" key to measure the FWHM of the line in pixels, then convert this to Angstroms using the formula:
where UFR = 0.3, 0.6, or 1.0 depending on whether the camera resolution is set to 3e5, 6e5, or 1e6 respectively; and PIX is the CCD pixel scale of 0.0135 mm for EEV2 or 0.015 mm for MITLL3.
Note that the instrumental resolution for UHRF can only be measured on the laser line as the ThAr lines are resolved. A best FWHM of 4 pixels or less should be achievable at 1E6, corresponding to a resolution >800,000. The ThAr lines will give 5-6 pixels at best for 1E6.
Be aware also that at 1E6 resolution, you should even be able to resolve adjacent modes of the laser in the wings of the line profile, as shown below on a logarithmic scale. This is a characteristic of all off-the-shelf lasers that not all adjacent modes are fully suppressed. Nevertheless, the width of the main peak can still be used to determine the resolution.
If the configuration file for the selected wavelength already exists then configure UHRF using that file. Select and turn on the ThAr lamp (it may be necessary to do this twice if no lines are seen in the arc exposure, as the lamp may not always strike). If necessary make adjustments to the echelle angles Theta and Gamma to recenter the order on the CCD. Make sure that the selected central wavelength allows for enough arc lines for wavelength calibration. Also check that the velocity shifts of the sources are within the observed range. Record the final grating angles.
To focus the collimator using the ThAr lamp, execute the sequence FocusUHRFThAr.tcl and follow the procedure described above for the laser line. The collimator must be refocussed each time the central wavelength is changed.
Make certain that the visible wavelength range is correct by checking the arc spectrum against the hardcopies of previous UHRF arc spectra kept in a purple comb-bound folder in the Control Room. It is helpful to add any new plots to this file.
Here are some example parameters used to set up on NA_5890:
Date: 24/3/97 @ 1E6
UXD = V
UF = 47473
SECOLL = 22.624 (32551ADU in listing)
UT = 38939
UT_offset = 0
UG = 20310
UG_offset = 0
SA = -0.205 degrees
SA_offset = 0
pixels = 24 x 96
SLIT SLICER (except for FLATS)
UHRF uses two filter wheels which are aligned on the same optical axis. Each filter wheel can hold up to eight filters. To select a filter, set one filter wheel to the CLEAR position and the other to the position with the correct filter. For blue wavelengths it is advisable to use a bandpass filter to cut out scattered red light. Examples are UG11 centred at 3300 Å and BG12 centred at 4000 Å. Note that the blue filters have some transmission losses and may also have strong red leaks. For red wavelengths, it is advisable to use a 'cut-on' filter such as RG630. These have a sharp cut-off profile at the short wavelength edge. The response of different filters can be plotted using Steve Lee's program curves.
The position seen by the TV is offset from the true position due to the different optical paths. This wavelength-dependent position offset is minimized using a LAMBDA offset in the CCS. This is an essential procedure for UHRF! First tape or place a filter of known wavelength in front of the TV lens. This should be chosen to be close to the observing wavelength so that the lambda offset is small. Standard filters include the B(4400), V(5500), R(7000) and I(9000). Most filters are kept in a wooden box in the dark room on the 6th floor. The night assistant should then be requested to do a lambda offset in the CCS, from the filter wavelength to the wavelength of the observations.
The lamp filters wheels 1 and 2 should both be in position 1 (clear) except when the quartz lamp is on. This is mounted in the LF2=8 position. The filter wheel is returned to the correct position when the lamp is turned off.
This section gives an example of how to solve for the grating angles to set up a UHRF configuration file for a new central wavelength. This process is very tedious and should normally be done well in advance of an observing run.
In general it is best to solve for new configurations using the 3E5 resolution with the EEV CCD as this gives the most wavelength coverage. The grating angles are the same for each resolution so, once created, configuration files can be used for any resolution. In the following example we set up a configuration file at 3859 A using 1E6.
The aim of this excercise is to find initial values for the parameters:
- UXD = cross dispersing element
- UT = echelle theta angle
- UG = echelle gamma angle
- UFC = collimator focus position
- USC = Secondary collimator focus position
The steps taken to fix these parameters are as follows:
- Determine the order number and UXD using Appendix A3 of the UCLES/UHRF manual. This shows that at 3859 Å UXD = B and m = 149.
- Run the ray trace program /epping/sdr/UHRF/ras/routines/22decuhrf.e. This gives model solutions corresponding to the blaze peak of the selected order. Note that this is only an initial estimate of the solution. The output values from 22decuhrf.e are incorrect due to errors in the model and to non-linearities in the ADU to mm conversions.
Enter the target lambda and order number. Record the UFC and USC readings in both ADU and mm and the wavelength and order of the blaze peak.
UFC = coarse focus
USC = secondary collimator focus
For this example
UFC = 27803.649, ADU = -42.082 mm
USC = 21221.706, ADU = -9.012 mm
BLAZE PEAK = 3846.974 in order 149
(XBD grating has blaze peak at 3959.42 A)
- Now run two further programs in /epping/sdr/UHRF/ras/routines/, ufc.e and usc.e. Enter values in mm from previous output and record the new values in ADU. These correct the previous values for non-linearities in the system.
UFC ip = -42.082 mm, output = 27769 ADU
USC ip = -9.012 mm, output = 21154 ADU
STATUS = 0 (all OK)
These ADU values are now 'real'.
- Set the initial values for UT and UG. For all orders the UT of the blaze peak is 33000 ADU. UG values are given in Appendix C12 of the UCLES manual. We now have:
UT = 33000
UG = 15825
UFC = 27769
UXD = B (corresponds to 9 on the Syntel computer)
Enter these values manually into UHRF.
- Take a quartz frame. If necessary adjust UG to centre the order(s) on the gaia display.
- Take an arc frame to identify the blaze peak for the order. At this stage we have determined values which correspond to the blaze peak of the selected order (149). To check this, identify the arc lines using an arc atlas. If necessary focus the collimator. If OK carry on; if not, rerun the programs and check your values.
- Step across the order to the desired wavelength by taking repeated arc frames until the the selected wavelength is reached. Do this bit by bit so that the arc lines can always be identified. We did this in about 15 goes! When line is correctly centred on CCD, redo focus one last time and check it.
- Ask Minh Vuong to record the settings in a configuration file. The solution here for 3859 was:
UHRF_XDISP = B
UHRF_THETA = 27950
UHRF_GAMMA = 15700
UHRF_FOCUS = 27086
UHRF_SECOLL = 21165
Enter the new solution into the master configurations list. Place a copy of a grey scale image of the gaia display and any spectral plots with identified arc lines for reference in the binder in the Control Room.