P52-030: Monitoring the ROSETTA target comet 67P/Churyumov-Gerasimenko

PI: Harry Lehto (University of Turku)
Contact: hlehto@utu.fi, +358503586062

Half nights 13.3. and 14.3.

Visibility plots:
130316
140316

Instructions

Note: Pay attenttion to the first image(s) and check that the tail of the comet is also included in the image. If needed, do a teloffset after the first two images (the observing script gives you an opportunity for it).
If you do not see any comet in images something probably went wrong with coordinates and telescope pointing. In that case you can check the comet coordinates on this list or online and point the telescope manually.


A raw 200s image in V taken on Sep 8 2015 where the comet and tail are well positioned on the ccd.

Observing sequence for all nights: 1h 15 min total each.

V and R bands

V exposure 1 x 15 sec with no differential tracking
V exposure 1 x 200 sec with no differential tracking
V exposures 6 x 200 sec with differential tracking on (for imaging and astrometry)
V exposure 1 x 200 sec with no differential tracking
V exposure 1 x 15 sec with no differential tracking

R exposure 1 x 15 sec with no differential tracking
R exposure 1 x 200 sec with no differential tracking
R exposures 7 x 200 sec with differential tracking on (for imaging and astrometry)
R exposure 1 x 200 sec with no differential tracking
R exposure 1 x 15 sec with no differentail tracking

There is a script to execute the observations. See the detailed instructions.

Calibrations

Standard bias and flats please, i.e. twilight flats and "alfosc-calibs".

Coordinates

The pointing script is taking the coordinates from a file (67P_coordinates_p52.txt), but here we list coordinates for the scheduled nights and the proposed observing start times. In case some observations are performed on nights not listed below, the coordinates can be obtained from this webpage (click on ephemeris and change time span to correct date and in table setting check "Rates;RA&Dec" to get also the tracking speed).

Note that these are for specified UT with the real date. Differential tracking is important for comet tail identification and accurate photo- and astrometry.

Please note that for the nights where observing time is given as a range of time, RA-rate and Dec-rate on this table are for the start time of the observing window. The correct values that should be used will be printed in sequencer by the pointing script (values can also be found in file 67P_coordinates_p52.txt).

67P/Churyumov-Gerasimenko Perturbed ephemeris below is based on elements from MPC 89011.

67P (updated Oct 1, 2015)

Detailed instructions how to execute observations

• Go to the programme directory ~/scripts/52-030/ in ALFOSC sequencer

• Run the script comet67P_ALpointing.script for ALFOSC or comet67P_pointing.script for StanCam. This will take correct coordinates from the file 67P_coordinates_2015.txt, append them to the TCS and points the telescope there. For ALFOSC-script there is an extra "teloffset -62 -62" to have the tail on the detector.
  
  In case something goes wrong, you can enter the coordinates manually (e.g.tcs.append-object 67P_CG 18 47 36.2 -29 34 10 2000 0 0 0) and preset to the target with key "4".

• In the programme directory ~/scripts/52-030/ in ALFOSC sequencer run the script comet67P_AL.script. Or when using StanCam, run the script comet67P_ST.script.

  Note that this is not a "do-it-all" script and requires your attention.
  It will first take images with normal tracking then it asks you to turn on differential tracking, takes some more images and asks again to turn back to normal tracking for more images. This sequence happens twice, first for V filter then for R filter.

  • Please make sure that the tail of the comet is on the CCD as much as possible.

  • When the script asks you to turn on differential tracking do the following in TCS:

  • auto-pos-off

  • preset again to the target with "4"
    NOTE: if you moved the comet after the first image with teloffset to position it better on the CCD, you should make sure to preset to the new TCS target 67P_actual that the script has appended to the catalgoue.

  • star-box-position 320 100 (this seemed to be a good position for the guide box on February 28 ), keep an eye on the box during differential tracking so that it doesn't reach the side of the screen, you may need to choose a different starting point for it)

  • p-s-s 5 5 (sets the step size for next point)

  • then select the function Guide Probe Y-/Y+/X+/X- using Change move mod (5), and use either 'Alt Function'+'arrow' keys, or 'Ctrl'+'t,f,v,g' to move the probe so that the guide star falls on the box. In the end you can do "p-s-s 1 1" to fine tune the guidprobe movement. Start autoguiding with the TCS command ag-on when the star is placed in the box.

  • box-motion-start RA-rate Dec-rate (Sets the tracking rate, for which you should check the correct values for each night on the coordinates table).

    • When script asks you to turn off differential tracking do the following:

  • box-motion-stop (this stops differential tracking and moves the star box back to the center next time you preset)

  • auto-pos-full

  • Preset to target with key "4" (67P_actual). Autoguiding should be started automatically

More information about differential tracking in the cookbook.