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, dome ventilation doors and active control of oil temperature.

Periodically, a memo has been sent to TELOPS to establish procedures designed to take maximum 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 humidity sensors 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 would be taken in the middle of the night (ideally at 2-3 AM) when the telescope and its environment are supposed to be best thermally equilibrated. In any cases, we request that the data be taken in a time frame going from 1 hour after evening twilight to 1 hour before morning twilight. It is the responsibility of the night assistant to TAKE THE INITIATIVE of planning early with the astronomer what will be the most convenient time to do it. 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 questions the rules, this memo can be used to explain them. We will have included in the time assignment letter explicit descriptions of the policy of requiring the seeing measurements.

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

The night assistant must check that all the environmental control functions explained below are working properly during the night.

ABSOLUTE closure when:

• wind > 45 mph on average (the telescope might still not shake badly but the air is dusty and will bring too much dirt inside the domes)
• humidity > 92 %, as indicated by the met tower (typing "weat") and no other sensor
• Tmirror - Tdew < 2°C. The values of Tmirror, Tdew and Tmirror-Tdew are shown in "temp4m", which is actualized every 10 minutes. See http://www.ctio.noao.edu/telescopes/opteng/wet.html for more information about dew point.

Dome re-opening: ONLY if RH < 85% for 30 consecutive minutes (in all cases, check outside that no water is dripping from the buildings).

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 permit observing beyond these limits! If you have trouble to be heard by the astronomer, please REPORT it (so we can politely explain the rules).

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.

The 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 night.

These doors have to be opened just after sunset and left opened all night.

• If the wind > 15 mph on 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 on 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 mirror 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 mirror cooler.
• Remember to check the status of the mirror 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). 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 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 4mtemp control system automatically controls the mirror temperature according to the following logic: where Tgoal is the lower of Tlow_dome and 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 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 done!

The cooling of the oil circulating under the R.A. rear and front pads is activated automatically when the pumps are turned ON by Observer support at sunset. The oil glycol valve is controlled (range is 1-2.25 V) by an equation involving the low dome and oil glycol temperature sensors. It is important that the oil cooling be working: if it is not, you can diagnostic it in "temp4m" (the "before pad" and "glycol" entries on the OIL line will quickly indicate around 30°).

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. This is to prevent Cass cage heat sources from creating 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 at 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 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 hours). We compensate that with a lookup table, which controls the pressure in 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 lose 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 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.

• Defocus: thermal expansion that can occur at night will cause the telescope to defocus. We will soon implement a program in the TCP that will alert the operator when the Serrurier truss (the telescope structure) temperature has changed enough to require a refocus. For typical focus settings at different foci, with different instruments and filters, see our web document: http://www.ctio.noao.edu/telescopes/4m/focus.html

• focus number increases when focal plane moves away from M1
• focus number is in microns neglecting the effect of the PFADC (the PFADC 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

• Once the Mosaic is focussed, type "seeing" (available from Oct 30th) 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 and the object must be selected near the zenith (airmass < 1.3).
• These images must be named "seeing.X.mmddyy" (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.
• A second sequence should be taken by the time it is one hour before morning twilight, preferably after the focus has been rechecked.
• In case some problems forced you to start late (i.e. after 11PM), only a single focus sequence will be required.

• focus number increases when focal plane (and M2) moves up
• the focus number represents microns of motion of the focal plane (not of M2)
• decrease focus setting 780 units per 1° increase in temperature

• 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). 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.

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

• On measurement at the beginning of the night, after doing the telescope zpoint and focussing the instrument.
• A second measurement by the time it is one hour before morning twilight
• In case some problems forced you to start late (i.e. after 11PM), only a single measurement will be required.
• Write the results (FWHM, Sx, Sy) in the seeing logbook and use the script "seeing monitor" (written by H. Tirado) accessible from the TCS workspace pull-down menu to log the results and additional information into the file /ut02/seeing/jacoby.log.

• focus number increases when focal plane (and M2) moves up
• the focus number represents microns of motion of the focal plane (not of M2)
• decrease focus setting by 2930 units per 1° increase in temperature
• all Tip-Tilt camera set-ups need to include the flexible exhaust pipe (to outside the Cass cage).

• 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). 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.

• 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 J filter. The exposure time is 20 sec and the object must be selected near the zenith (airmass < 1.3).
• These images must be named "seeing.X.mmddyy" (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.
• A second image should be taken by the time it is 1 hour before morning twilight, 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 will be required.
• For the time being, 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).

• 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)

PF check list for the night assistant

F/8 check list for the night assistant

F/14 check list for the night assistant