The 30m User Observing Guide


Contents

1 Start observing session

2 Prepare basic observing scripts

3 Userful webpage links for observations


This user guide book gives basic instructions to enable the beginner or occasional user start observations with the 30m IRAM telescope. In the future, more information about the preparation of observing scripts and miscellaneous related to observations will be appended here. Additional information is described by AoD of your observation week.

1 Start observing session

1.1 Pako, the observing software

1.1.1 Start Pako

To start Pako, the first step is to log-in to mrt-lx1 server, which is the main observing server, after log-in your account with a domain of mrt-enter.iram.es. For example,

   > ssh -X userid@mrt-enter.iram.es                    !e.g., 001-99@mrt-enter.iram.es
   001-99@mrt-lx2vm: $ slogin -X mrt-lx1                !or click pako an icon on the background screen.
   001-99@mrt-lx1: $ gopako                             !Go to the Pako directory.
   001-99@mrt-lx1: $ pakodisplay                        !Execute a Pako display window.
   001-99@mrt-lx1: $ pako                               !Execute Pako software.

Two necessary windows pop-up and they are a green Pako display (Figure 1) and a Greg plot window. If no Greg plot window appears, it is because Pako does not start, and probably the observer can see a message to remove ’.pakoLock’ file (rm .pakoLock). This error happens when an observer does not close Pako properly from previous observation session. The Pako display shows all input parameters (e.g., source name, velocity, topology, receiver, backend, and so forth). Thus it is essential re-checking whether all the inputs have updated after executing observing scripts.

pako_display.png

1.1.2 Observing precedures

A single script does not automatically do observations with the 30m telescope. It requires several steps that are needed to be done by an observer.

OPT 1: if your target is far from a current telescope position, it's useful to select the source before sending a setup script. This way saves 7-10 minutes of your observing time because the telescope moves while tuning receiver and backends by an operator.

      Pako> source `Planet'                      !When selecting planets, no need to load any catalog.
e.g., Pako> source Mars                          !This case gives a velocity of 0 \kms.
e.g., Pako> source Mars /velocity lsr 300.       !/velocity 'format of velocity' input_velocity.
      Pako> source continuum_source /catalog *   !To choose any continuum sources from the default catalog.
e.g., Pako> source 1757-240 /catalog *

Step 1: Send observation information to the control system

      Pako> @setup.pako                 !it includes Project ID, names of PI and observer, catalogs, and so forth.

Problem 1: an executed script crashes and returns error messages. Solution1: Please, re-check your script whether there are any mistakes in it. Re-execute the corrected script but before then, you need to exist the error mode which appears like Pako_1> or Pako_2> (there could be any numbers after Pako). For such case, please, type q' to escape out of it, i.e., Pako_1> q`.

Checklist1: please, check your source and line catalogues uploaded in Pako display window (Figure 1).

   Pako> @receiver.pako            ! Backend setup can be also included in the receiver setup script. 

Checklist2: please, check your receiver setup in the receiver part of Pako display window (Figure 1).

   Pako> @backend.pako 

Checklist3: please, check your backend setup in the backend part of Pako display window (Figure 1).

   Pako> calibrate.           !or just type 'cal'.
   Pako> start                !Without 'Start' command, calibrate mode does not start. 
                              !Always, the first Calibrate is for tuning receivers and backends. 
                              !Therefore, the results of the calibrate are not correct. 
                              !When an operator confirms tuning done, please send another calibrate observation. 
   Pako> start                !Since you already select calibrate as the current observing mode, 
                              !you don't need to type 'Calibrate' again. 

Checklist3: check Calibrate results whether important values of backends are updated. If not, ask an operator for feedback on what may have gone wrong. See Figure 2.

cal1.png

Step2: do pointing and then focus on a brightest source like Planets and bright continuum sources. Typical pointing ranges are Az: +/-15" and El: +/-5", and the focus limit is 1 mm > focus > - 2.8 mm. In case of doubt, ask the AoD.

    Pako> source 'Planet'                                        !or source 'continuum source' /catalog *
    Pako> @pointing.pako                                         !use a pointing script or type `pointing; start`.
    Pako> set pointing 'new_Az_correction' 'new_El_correction'
    Pako> @focus.pako                                            !use a focus script or tyep `focus; start`.
    Pako> set focus 'new_focus_correction'

When all the pointing and focus results are satisfied. Please, move the telescope to a pointing source nearby your target.

Problem2: for pointing and focus observation, we need to use beam switching (swbeam). Solution2: please, type 'swbeam' in pako or add it in your pointing/focus script at the beginning.

Problem3: there is no either pointing or focus results delivered. Solution3: do Calibrate with BBC backend again. In addition to that, check it with MIRA software (see Sect. 1.3).

Step3: do pointing on a nearby pointing source close to either a line calibration source or your target. In case of doubt, please ask the AoD.

    Pako> source 'a_nearby_target'              !it is not necessary that a nearby pointing source is always bright. 
    Pako> @pointing.pako                        !default setup is 'pointing /notf 4 /totf 30'

OPT 2: sometimes, the source might be too weak to obtain pointing results and no alternative source. By adjusting pointing parameters, /notf and /totf, we can improve pointing results. Here are two examples of it.

   e.g., Pako> pointing /notf 8 /totf 20             !increase the number of subscans of pointing,
   e.g., Pako> pointing /notf 12 /totf 20            !you can adjust either /notf or /toft. This is for weak source or under unstable weather conditions. 
                                                     !However, if you increase /totf too long, you can also introduce instability of sky condition.

Additional (important): Check the frequency tuning by observing a line calibrator with strong and known lines (e.g. IRC+10216, DR21, W3OH, OriIrc2, etc.). If line calibrate sources are not added in your source catalog, we can use the IRAM line catalog.

   Pako> source W3OH /catalog lines-J2000.sou 

Step4: Observing your tartget.

   Pako> @backend.pako 
   Pako> @OnOff.pako                          !or @OTF.pako, execute an observing mode script

Problem4: see an error message like 'E-BACKEND, /tPhase 0.06 in beamSwitching too small for FTS' . Solution4: depending on backends, right switching mode is required to be set. In this case, we need to put Total Power (swtotal) or swwobb. The beamswitching mode (swbeam) is used for pointing/focus observations. Therefore, to avoid such errors, add a right switching mode in your backend script before the line of backend setup.

1.2 Pointig and focus

When there is a stable atmosphere, we usually obtain good pointing and focus results as seen in Figure 3 and Figure 4.

Left plots in Figure 3 shows nice Gaussian plots measured along to Azimuth (Az) and Elevation (El) directions on a point-like source (i.e., planet and continuum sources). It gives new Az and El corrections (in red color) and size of beams. If the beam is well aligned, we expect similar peak fluxes and beam sizes in both directions. Since we tune several backends (e.g., FTS gives at least two and four cables connections), such pointing results are obtained for each backend part. In that case, either average or median values of all obtained values except for bad-quality values will be applied to final correction in Pako like Pako> set pointing 'average Az' 'average El'.

Regarding focus correction, we need to find a maximum received power. With a weak calibration source, it is tough to get, and thus we do focus on either planets or bright continuum source even though they are far from your target. Besides, to maximize collecting light for focus, it is necessary to do pointing before focus.

For pointing, input new corrections should be in ranges of Az:+/-5" and El:+/-15". For example, measured new corrections of pointing are Az of 9" and El of -25". Applied corrections would be Az of 5" and El of -15", and we need to repeat pointing. Then, pointing results with the applied corrections get close to values within the recommended ranges. A recommend range of focus correction is 1 mm > focus > -2.8 mm.

Besides, there are not many bright continuum sources at 0.8 mm wavelengths (E3 receiver setup). Thus, it is helpful using either 3 mm and 2 mm receivers in parallel when tuning either 1 mm or 0.8 mm receivers (Note: we cannot connect E0+E3 receivers combination). Observers have to be aware of a significant difference between different receivers. For instance, the focus of E3 (0.8 mm wavelength) is about 0.6mm smaller than the focus of E1 (2 mm wavelength), e.g., 2.2mm for E1 and -2.8mm for E3.

If a beam is not aligned and unfocused under stable weather condition, the pointing and focus results would be like plots in Figure 5Figure 6. In general, after applying the new corrections, good fitting results are expected, but it is always safe to repeat pointing and focus observations once again to confirm whether the beam is properly aligned.

When the atmosphere and weather are unstable, it is challenging to measure pointing and focus corrections, as seen in Figure 7Figure 8Figure 9. In particular, during the summer season, the pointing results are sometimes strongly affected by anomalous reflection, which causes broadening beam shapes. If the weather condition is extremely unstable and with high water vapor, you may not get any usable pointing and focus results (e.g., Figure 9). In such a case, we need to wait until the weather condition improves, and so check water vapor by carrying out calibrate observations every few minutes to check the weather evolution. Even if we obtain excellent pointing and then repeat multiple times of focus observations, we can also get bad focus results. For this case, please repeat pointing on a bright source with higher elevation and then do again focus.

1.3 How to use MIRA for checking pointing and focus results (as well as data)

   Step1: log in to mrt-lx9 (or mrt-lx3) ! start MIRA
         > cd ~/mira
         > mira
   Step2: check pointig and focus with MIRA
     MIRA> file in ~/observationData/imbfits
     MIRA> ftd                                !load and list the scans of the current day.
     MIRA> find /observed 2019-07-10          !it is also possible to choose a specific day.
           167 1226+023   calibrat      totalPower           BBC   2019-07-16   245
           168 1226+023   pointing      beamSwitching        BBC   2019-07-16   246
           169 1226+023   focus         beamSwitching        BBC   2019-07-16   247
     MIRA> scan 167                           !load and read calibrate scan  
     MIRA> scan 168                           !load and read pointing scan
     MIRA> solve 1 
   OPT 1: check individual subscans of pointing.
     MIRA> let dopause yes
     MIRA> solve 1
     MIRA_3> c

1.4 Xephem, the source displaying software

Xephem is a software displaying sources on a sky map, and it is for finding targets and pointing/focus sources in real-time on the sky. Xephem can only real .edb file format that is automatically generated when the observer type a source catalog in Pako (e.g., Pako>catalog source source-file.sou). You can run the software by clicking a Xephem icon on the screen. Otherwise, it is also possible in a terminal. If you cannot see a telescope icon indicating the telescope position, please close xephem windows and re-run it by typing  xephem & azElToXephem.py in a terminal.

xephem_win0.png

With starting Xephem, a small window of Xephem will appear, as shown in Figure 10. To see sources on the sky, click View' in the top bar and then choose Sky View' as marked with red boxes in Figure 10, and, afterwards, the Sky View window opens (see Figure 11). On the Sky View display, all your target and line calibration sources are presented in green symbols and text, and continuum sources for pointing and focus are marked in white color. In addition, most of the planets are shown in either yellow or orange colors, but Uranus is in dark gray color.

Figure 11

To show sources positions in real-time, the update button has to been click (Figure 12), and, if it does not work, you can click RT button (see Figure 13}).

xephem_win1.pngxephem_win2.png

To load or delete a source catalog, click Data' on the top panel and select '''Files'''. Then, another new window appears, and we can load a new catalog with click '''Files` in the xephem Database Files window (see Figure 14).

xephem_win2.pngxephem_cata1.png

1.4.1 SET TOPOLOGY

The 30m antenna has azimuth limits of 60 and 460 degrees which are an overlapped range approximately toward East-Northeast. Azimuth 360 degrees is due North.  SET TOPOLOGY only becomes important for sources with an azimuth in the overlapped range of 60 to 100 degrees (from the South) or 420 to 460 degrees (from the North) (see Figure 15).

The easiest way how to choose SET TOPOLOGY LOW or SET TOPOLOGY HIGH is to check the sources positions in Xephem. For example, if a target source locates 58 degrees and it will be 61 degrees in some time when the topology is low, the telescope cannot go to the position of 61 degrees directly and has to move about 360 degrees which will take about 10 minutes. When we repeat such movements often, we will misuse a significant time just moving the telescope. Therefore, for similar case, as mentioned earlier, we can just switch set topology low to high that allows us to move the telescope up to 100 degrees. In opposite, if your source is on a position of 101 degrees and will enter below 100 degrees, you choose set topology low instead of keeping set topology high, to avoid unnecessary moving of the telescope.

2 Prepare basic observing scripts

3 Userful webpage links for observations

The30mUserOservingGuide (last edited 2020-11-14 07:00:31 by bongio)