Fm: ACTR and Max Boccas

To : Telops, Scistaff

27 September 1999

Since the end of 1993, many improvements have been carried out at the 4m telescope to improve its image quality. The principal changes are: an active primary mirror support with lookup tables, a repolished f/8 secondary mirror, an image analyzer for the Cassegrain foci, removal of most heat sources inside the dome, active control of the primary temperature during the day, active ventilation of the primary cell at night and dome ventilation doors.

Periodically, a memo has been sent to TELOPS to establish procedures designed to take most advantage of these new functions and to monitor their impact. Over the years, some systems have failed and then been repaired, sometimes leaving confusion as regards the frequency of their operation (side port seeing camera for example). We think it is time to update these instructions. These official instructions should also help enlist the support of visiting astronomers when the night assistants have to explain to them the need to close or to take seeing measurements.

We are working on calibrating the weather humidity reading and setting up a web-based service with all ambient conditions (temperatures, wind,...) for quick analysis by the telescope operator and the astronomer.

We want particularly to ensure that seeing measurements are done EVERY night. They should become as regular as opening the dome. The most useful data will be taken between 2 and 3AM when the telescope and its environment are supposed to be best thermally equilibrated. PLEASE respect that time frame. The maximum time you can use for these measurements is (from the moment you say at loud voice "I start" until you say "Done"):

• seeing: 15 minutes
• IMAN collimation: 15 minutes

If all goes smoothly these operations can be executed in 5-10 minutes but you must allow yourself up to 15 minutes...

If the visiting astronomer is angry at these new rules, hand him over this memo politely and keep going.

Your collaboration will be very much appreciated: please send any comments or reports of problems to mboccas@noao.edu

ABSOLUTE closure when:

• wind > 45 mph in average (the telescope might still not shake badly but the air is dusty and will bring too much dirt inside the domes)

Dome re-opening: ONLY if RH < 85% for 30 consecutive minutes.

25 < Wind < 45 mph : avoid observing in the wind direction as it could jitter the telescope and will bring dirt inside the dome.

BEWARE PLEASE: Don't push the observing time beyond these limits! If you have trouble to be heard by the astronomer, please REPORT it (so we can politely make them clear about these rules and their obligations).

We are working on a script that will bring up automatically a warning window on the TCP display whenever RH>92% and/or Tmirror-Tdew<2, in order to ease the task of detecting closure situations.

1.2. Dome opening: no change from current procedureThe dome and the mirror cover have to be opened 30 minutes before sunset, orienting the shutter eastward to make sure no direct sunlight will enter the dome. Dome and mirror cover have to be closed at the end of the nigth.

1.3. Lateral sliding doors opening: no change from current procedureThese doors have to be opened just after sunset and left opened all night.

• If the wind > 15 mph in average, evaluate the image quality to decide whether to close them or not (elongated images mean you have to close the doors).

• If wind > 25 mph in average, ABSOLUTE closure (because of wind-shake on the telescope and deposit of dust).

• 30 min before sunset: Observer Support has the responsibility to turn OFF the cooler, turn ON the sucker and the extractors (P floor).

• End of the night: the night assistant has the responsibility to turn OFF the sucker and the extractors, and turn ON the cooler.

• Remember to check the status of the cooler and the extractor if you notice the seeing is very poor.
• Let's recall that a 1° temperature difference between the mirror surface and the ambient air will create additional mirror-seeing (typically up to 0.5" extra for 1° difference in certain conditions), thus our goal is to maintain the mirror temperature within 1° of the predicted temperature of the following night. During the night, you are invited to type "temp4m" and check that:

• the 4 sensors of the mirror are within a 0.5-1° range
• the mirror temperature, dome temperature and outside temperature are within a 1° range

• Any problems detected should be reported by email.
• The computer control does the following: whre Tgoal is the minimum of Tlow_dome / Toutside

1/ Tmirror < Tgoal - 2.5° : glycol valve closed (but ambient air is still blown onto the mirror)

2/ Tgoal + 1.7° < Tmirror < Tgoal -2.5°: glycol valve partially opened

3/ Tmirror > Tgoal + 1.7 ° : glycol valve fully opened

• If Tmirror < Tdew_point + 7 ° : the glycol valve will close
• The mirror cooling should NOT be turned off for instrument change unless you are really freezing to death. If ever you do turn it off, DON'T FORGET to turn it back on!

• The cooling of the C floor and M floor in the dome is always ON. It is currently regulated manually.

• The large stirring fan on the M floor (inside the dome) should always be ON when the dome is closed and OFF when the dome is opened. This fan improves greatly the air circulation inside the dome. It can be turned off during instrument change or any other works around the telescope if the noise bothers you. But turn it back on when you are down!

These fans are located inside the chimney at the level of the primary mirror and suck ambient air into the mirror cell so as to form a laminar downward flow in the chimney, preventing any Cass cage heat sources to create convection in the light path in the chimney.

At all Cassegrain foci (F/8, F/14, F/30), Observer Support has to turn ON the chimney fans before sunset. The switch is on the power supply on the old console room desk. The night assistant must turn it OFF at the end of the night.

The current thermal plan in the building is not changed. Always leave the air conditioning full power. Do not use heat sources at level M, MZ and C. Always maintain the doors closed in the passageways (especially the glass door in front of the lift at GR floor, the cryocooler compressor and pump rooms).In general, respect the signs displayed in the building.

Until we have a graphical web interface, type "temp4m" and "weat" to check the temperatures and weather conditions. Type, "/ut02/seeing/temper/tlog4m" for graphical analysis. We are working on a web page for thermal related issues: http://www.ctio.noao.edu/telescopes/opteng/thermal.html

The image quality of the telescope can suffer deterioration mainly from 3 optical problems:

• Astigmatism: this is due to tiny slippage of M1 and/or deformation under its own gravity. Astigmatism will show up as elongated images, perpendicular on each side of the focus, especially for large H.A. (typically more than 2 H.A.). We compensate that with a lookup table, which activate the air bags under M1. Thus the TCP toggle "CORR" should always be ON, at all foci. Note that if the F/8 or F/14 secondary mirrors loose their vacuum, strong astigmatism will immediately show up (typically 2-4 microns as measured by iman).
• Coma: this aberration shows up in 2 cases: at Prime Focus if the primary mirror's axis is not aligned with the PFADC and in the 2-mirror configurations (F/8, F/14, F/30) when there is a misalignment between them. Coma produces images with a flare (a tail like a comet) which is identical (same amplitude and direction) on each side of the focus.

* focus number increases when focal plane goes away from M1

* focus number is in unit of microns before the PFADC (which has a power of 1.076, i.e. multiply the focus change by 1.076 to get the real motion in microns in the focal plane)

* decrease focus setting by 110 units per 1° increase in temperature

• Seeing measurement: TWICE per night

* Once the Mosaic is focussed, type "seeing" (available from Oct 30th 1999) to run a special script which takes a 7-exposure focus sequence, centered on the best focus, with 40 units focus steps, through the R filter. The exposure time is 20 sec near the zenith (airmass < 1.3).

* These images must named "seeingXmmddyy" (where X is successively 1 and 2). They are automatically stored in the appropriate archive.

* One sequence should be taken at the beginning of the night, after doing the telescope zpoint and focussing the instrument.

* One sequence should be taken between 2 and 3AM, preferably after the focus has been rechecked.

* In case some problems forced you to start late (i.e. after 11PM), only a single measurement between the time you start and 3AM will be required.

• CORR ON all the time.
• The toggle next to F/8 on the TCP status display should be OFF all the time (this is for an eventual coma lookup table).
• Temperature drift compensation:

* focus number increases when focal plane (and M2) goes up

* the focus number represent microns of motion of the focal plane

* decrease focus setting 780 units per 1° increase in temperature

• Collimation: this has to be checked according to the following procedure:

* on the first night of a F/8 run, check in the TCP menu that /Active_Control/Tilt_Secondary/Display_Tilt shows the tilt value (amplitude and azimuth) written on the white board and in the logbook. If this is not the case, choose /Absolute_Tilt and enter the right values. Next, run IMAN according to the instructions in the IMAN instruction book (a version is also available on the web although it does not provide the last guider box coordinates, which are written in the IMAN book). Write the new tilt values on the white board and in the logbook.

* at the beginning of each following night of the F/8 run, check /Display_Tilt as described above and correct with /Absolute_Tilt if necessary.

• Seeing measurement: TWICE per night with the side port seeing camera (use stars of mag 5-9 and take your time to ensure you focused well the camera). See a copy of the instruction manual in appendix.

• The toggle next to F/14 on the TCP status display should be OFF all the time (this is for an eventual coma lookup table).

• Temperature drift compensation:

* focus number increases when focal plane (and M2) goes up

* the focus number represent microns of motion of the focal plane

• Collimation: this has to be check according to the following practice:

* on the first night of a F/14 run, check in the TCP menu that /Active_Control/Tilt_Secondary/Display_Tilt shows the tilt value (amplitude and azimuth) written on the white board and in the logbook. If this is not the case, chose /Absolute_Tilt and enter the right values. Next, run IMAN according to the instructions in the IMAN instruction book (a version is also available on the web although it does not provide the last guider box coordinates which are written in the book). Write the new tilt values on the white board and in the logbook.

* at the beginning of each following night of the F/14 run, check /Display_Tilt as described above and correct with /Absolute_Tilt if necessary.

• Seeing measurement: TWICE per night

* Once the IR instrument (CIRIM, OSIRIS) is focussed, type "seeing" (available ?) to run a special script which takes 3 exposures (200 units before in-focus, centered on the best focus, 200 units out of focus) through the I filter. The exposure time is 20 sec near the zenith (airmass < 1.3).

* These images must be named "seeingXmmddyy" (where X is successively 1 and 2). They are automatically stored in the appropriate archive.

* One image should be taken at the beginning of the night, after doing the telescope zpoint and focussing the instrument. ). The spectro mode of Osiris needs to be focused in the imaging mode (both modes are parfocal), thus it is easy to take that first seeing sequence.

* One image should be taken between 2 and 3AM, preferably after the focus has been rechecked. If Osiris is used in spectro mode, you obviously need to change back to imaging mode to take this second seeing frame.

* In case some problems forced you to start late (i.e. after 11PM), only a single measurement between the time you start and 3AM will be required.

* For the time beeing, no seeing measurement is required with IRS. In the near future, we hope to do the seeing measurement with the Tip-Tilt camera for all IR instruments.

This focus will not be used in the short-term future (Mosaic will be left in the PF cage).

• CORR ON all the time.
• Temperature drift compensation:

* the focus numbers represent microns of motion of M2

* decrease focus setting by 104 units per 1° increase in temperature

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Instruction for the side port seeing camera (Jacoby's software)

An RCA camera (image intensifier tube) is installed permanently on the side of the rotator. It must be ready to use during ALL F/8 nights. The light is sent to that camera by putting the rotator mirror #3 IN and another tiny flat mirror IN (switch is on the rack on the right side of the TCP sun).

• Typical telescope focus for the measurement is 172000 (at 14°C). WRITE DOWN the current focus used by the instrument before refocusing for the seeing camera.
• Use a mag. 3-5 star.
• The autoguider must be disable to do the measurement.

• Make sure the switch on the black rack in the computer room is on the "seeing PC" position.
• Type "cd seeing" on the PC (same display and keyboard used by Iman), which will bring you to the start up screen and menu (use the ESC key to return to menu or quit)
• Press F10 to see the setup parameters and modify the entries so that:

- F2 scale is 0.13

- F4, F5 and F7 say no (toggle the F# key several times to enter the right field value)

- the rest is unchanged from the default values

- ESC to return to main menu

• Press key F2 "Select Star Manually''. Use the arrow keys to approximately center the box on the star (note that the "+'' key toggles between big steps and little steps for each use of an arrow key). Then press the "!'' key to automatically center the box, and ESC to return to the main menu.

• Press key F3 "Focus Aid''. You will see graphs showing FWHM, Star Peak, and Contrast, being updated in real time. If the scales on the graph are wrong, use the F10 key to change them.

• Adjust the TV signal level (gain, etc) so that the Star Peak level is clearly below saturation. Saturation appears to occur at 256 for the RCA camera (as shown in the F3 Focus Aid mode).

• Adjust the focus carefully by looking at the video display. In the Focus Aid, you need to make the FWHM as small as possible while making Star Peak and Contrast as large as possible. In practice, the FWHM graph is not very useful except that it becomes very noisy when you are way out of focus. The Star Peak is useful in good observing conditions.
• BEWARE: If the image is either out of focus or saturated, the result is not meaningful!

"Whole sample FWHM: ..."

+ several lines showing the details of the calculations in each sub-list