Moving Target Procedures

This page describes the Phase 2 procedures for Moving Target (i.e. Solar System target) programmes.


Programme Definition

Programmes for Moving Targets can be divided into two broad categories:

  • programmes with undefined targets at Phase 2 submission time, such as for example bright comets that may discovered during the course of the observing semester.
  • programmes with pre-defined targets at Phase 2 submission time, such as for example planetary satellites.

The procedures described here refer to both classes of programmes, with the difference that the submission of the ephemerides files for programs with undefined targets must take place at the time when the target becomes known rather than at the time of the Phase 2 deadline.

Programmes with undefined targets appearing at short notice (such as faint near-Earth asteroids) are considered to be Target of Opportunity programmes and should follow the established ToO procedures. Still, an ephemerides file must be submitted in such cases in the format described below at the time of triggering the ToO observations.


Ephemerides Files

Users must submit a detailed ephemerides file for each target for the whole duration of the ESO Period in question, or for the whole duration of the observability period in case that observations must be executed within a specific time window. The ephemerides files are ASCII files compatible with the VLT parameter file (PAF) format.

An ephemerides file may contain the following elements:

  • A PAF file header [compulsory].
  • Blank lines [optional].
  • Additional comment lines [optional].
    Each comment line must start with the hash (#) sign.
  • Additional lines for the contents of the ephemerides [compulsory].
    Each line containing ephemerides data should start with the identifier INS.EPHEM.RECORD and contain the data for one time interval.

The data following the INS.EPHEM.RECORD identifier must contain the following information in comma-separated variable (csv) format:

  • Date and time in UT for the ephemerides positions [compulsory].
    Date and time must follow the ISO format: yyyy-mm-ddThh:mm:ss.[ssss], e.g. 2012-07-30T06:45:01.0000.
  • Julian date and time for the ephemerides positions [optional].
    Julian date must be given as a real number: x.xxxx, e.g. 2454950.513888. The Julian date may be omitted; in this case this entry would be empty or consist or one or more spaces (so “INS.EPHEM.RECORD "2009-04-29T00:00:0.000,, 11 08 21.3414, +07 56 01.525, 0.00699139, 0.00082480, 11.9756, 58.065, *" would be a valid entry).
  • Topocentric astrometric right ascension and declination of the target (J2000 equinox ICRF or FK5 system) [compulsory].
    Please note that the VLT telescope control system already corrects for precession, nutation, annual aberration and refraction, so topocentric astrometric coordinates (and not apparent coordinates) are required. R.A. and Dec. must be in the sexagesimal format: hh mm ss.[ss] +/-dd mm ss.[s], e.g. 20 26 08.96, -22 51 09.9.
  • Topocentric apparent motions in right ascension (mu_alpha*cos delta) and declination (mu_delta), in arcsec/sec [compulsory].
    Apparent motions must be in real-number format: +/-s.[ssssssss], +/-s.[ssssssss], e.g. -0.00699139, 0.00082480.
  • Apparent magnitude of the target at the observing wavelength [optional].
    Apparent magnitudes must be given as a real number: +/- mm.[mm], e.g. 15.60.
  • Comments [optional].
    Any additional information, if applicable, such as the desired slit orientation. Free text. This information must be provided so that it can be entered directly in the OBs without any transformation: please consult the corresponding instrument user's manual for information regarding orientation conventions.

Please note that each data element in an INS.EPHEM.RECORD line should be separated by a comma, and either no or one blank space. Multiple blank space may, at present, cause problems with the verification of the ephemerides file.

The time intervals at which the ephemerides are given should be defined so that the displacement of the target does not exceed 30 arcsec (3 arcsec in the case of SINFONI due to its much smaller acquisition field of view) between two consecutive entries. The ephemerides files must be submitted as attachments to the OBs to which they refer. To attach them, use the options available under the Ephemerides Files menu in the P2PP main GUI (see the P2PP User Manual for a detailed explanation).

The number of entries per night of observations is limited to 300, which corresponds to a minimum time step of 5 minutes if the target can be observed the whole night. However, the file can include data for a whole period.

An example of a valid ephemerides file is shown below:

 

PAF.HDR.START;                                             # Start of PAF Header
PAF.TYPE                  "Instrument Setup";              # Type of PAF
PAF.ID                    "";                              # ID for PAF
PAF.NAME                  "Rhea_2013-04-29_2013-05-29.paf";# Name of PAF
PAF.DESC                  "Ephemeris / WWW_USER Thu Nov 30 19:36:05 2012  Pasadena, USA     / Horizons"
PAF.DESC                  "Target body name: Rhea (605)                      {source: SAT288}         "
PAF.DESC                  "Center body name: Earth (399)                     {source: DE405}          "
PAF.DESC                  "Center-site name: Cerro Paranal                                            "
PAF.DESC                  "Start time      : A.D. 2013-Apr-29 00:00:00.0000 UT                        "
PAF.DESC                  "Stop  time      : A.D. 2013-May-29 00:00:00.0000 UT                        "
PAF.DESC                  "Step-size       : 5 minutes                                                "
PAF.DESC                  "Target pole/equ : IAU_RHEA                        {East-longitude -}       "
PAF.DESC                  "Target radii    : 764.0 x 764.0 x 764.0 km        {Equator, meridian, pole}"
PAF.DESC                  "Atmos refraction: NO (AIRLESS)                                             "
PAF.CRTE.NAME             "crossEphem2Paf";                # Name of creator
PAF.HDR.END;                                               # End of PAF Header

#------------------------------------------------------------------------------
#                                         Date & Time (UT)       JD                       RA (J2000)     Dec (J2000)    dRA (“/s) dDEC (“/s) V-mag    Slit PA
#------------------------------------------------------------------------------
INS.EPHEM.RECORD          "2013-04-29T00:00:0.000, 2454950.500000000, 11 08 21.3414, +07 56 01.525, 0.00699139, 0.00082480, 11.9756,  58.065,  *"
INS.EPHEM.RECORD          "2013-04-29T00:05:0.000, 2454950.503472222, 11 08 21.3349, +07 56 01.652, 0.00698538, 0.00082479, 11.9761,  57.780,  *"
INS.EPHEM.RECORD          "2013-04-29T00:10:0.000, 2454950.506944444, 11 08 21.3286, +07 56 01.780, 0.00697939, 0.00082488, 11.9765,  57.493,  *"
INS.EPHEM.RECORD          "2013-04-29T00:15:0.000, 2454950.510416667, 11 08 21.3223, +07 56 01.907, 0.00697344, 0.00082505, 11.9770,  57.205,  *"
INS.EPHEM.RECORD          "2013-04-29T00:20:0.000, 2454950.513888889, 11 08 21.3160, +07 56 02.035, 0.00696752, 0.00082532, 11.9775,  56.916,  *"
INS.EPHEM.RECORD          "2013-04-29T00:25:0.000, 2454950.517361111, 11 08 21.3099, +07 56 02.163, 0.00696166, 0.00082567, 11.9780,  56.626,  *"
INS.EPHEM.RECORD          "2013-04-29T00:30:0.000, 2454950.520833333, 11 08 21.3039, +07 56 02.291, 0.00695586, 0.00082612, 11.9784,  56.335,  *"
INS.EPHEM.RECORD          "2013-04-29T00:35:0.000, 2454950.524305556, 11 08 21.2979, +07 56 02.419, 0.00695014, 0.00082665, 11.9789,  56.042,  *"
INS.EPHEM.RECORD          "2013-04-29T00:40:0.000, 2454950.527777778, 11 08 21.2920, +07 56 02.548, 0.00694449, 0.00082726, 11.9794,  55.748,  *"
INS.EPHEM.RECORD          "2013-04-29T00:45:0.000, 2454950.531250000, 11 08 21.2862, +07 56 02.676, 0.00693894, 0.00082796, 11.9799,  55.452,  *"
INS.EPHEM.RECORD          "2013-04-29T00:50:0.000, 2454950.534722222, 11 08 21.2805, +07 56 02.805, 0.00693349, 0.00082874, 11.9803,  55.156,  *"
INS.EPHEM.RECORD          "2013-04-29T00:55:0.000, 2454950.538194444, 11 08 21.2749, +07 56 02.933, 0.00692814, 0.00082960, 11.9808,  54.858,  *"
INS.EPHEM.RECORD          "2013-04-29T01:00:0.000, 2454950.541666667, 11 08 21.2694, +07 56 03.062, 0.00692292, 0.00083054, 11.9813,  54.559,  *"
INS.EPHEM.RECORD          "2013-04-29T01:05:0.000, 2454950.545138889, 11 08 21.2639, +07 56 03.191, 0.00691782, 0.00083155, 11.9817,  54.258,  *"
INS.EPHEM.RECORD          "2013-04-29T01:10:0.000, 2454950.548611111, 11 08 21.2585, +07 56 03.320, 0.00691286, 0.00083264, 11.9822,  53.956,  *"
INS.EPHEM.RECORD          "2013-04-29T01:15:0.000, 2454950.552083333, 11 08 21.2533, +07 56 03.449, 0.00690804, 0.00083380, 11.9827,  53.654,  *"
INS.EPHEM.RECORD          "2013-04-29T01:20:0.000, 2454950.555555556, 11 08 21.2481, +07 56 03.578, 0.00690338, 0.00083503, 11.9831,  53.350,  *"
INS.EPHEM.RECORD          "2013-04-29T01:25:0.000, 2454950.559027778, 11 08 21.2430, +07 56 03.707, 0.00689887, 0.00083633, 11.9836,  53.044,  *"
INS.EPHEM.RECORD          "2013-04-29T01:30:0.000, 2454950.562500000, 11 08 21.2379, +07 56 03.837, 0.00689453, 0.00083769, 11.9841,  52.738,  *"
INS.EPHEM.RECORD          "2013-04-29T01:35:0.000, 2454950.565972222, 11 08 21.2330, +07 56 03.966, 0.00689037, 0.00083911, 11.9845,  52.430,  *"
INS.EPHEM.RECORD          "2013-04-29T01:40:0.000, 2454950.569444444, 11 08 21.2282, +07 56 04.096, 0.00688639, 0.00084059, 11.9850,  52.121,  *"
INS.EPHEM.RECORD          "2013-04-29T01:45:0.000, 2454950.572916667, 11 08 21.2234, +07 56 04.226, 0.00688259, 0.00084213, 11.9855,  51.811,  *"
INS.EPHEM.RECORD          "2013-04-29T01:50:0.000, 2454950.576388889, 11 08 21.2187, +07 56 04.356, 0.00687899, 0.00084371, 11.9859,  51.500,  *"
INS.EPHEM.RECORD          "2013-04-29T01:55:0.000, 2454950.579861111, 11 08 21.2141, +07 56 04.486, 0.00687559, 0.00084535, 11.9864,  51.188,  *"
INS.EPHEM.RECORD          "2013-04-29T02:00:0.000, 2454950.583333333, 11 08 21.2096, +07 56 04.616, 0.00687239, 0.00084703, 11.9868,  50.874,  *"
INS.EPHEM.RECORD          "2013-04-29T02:05:0.000, 2454950.586805556, 11 08 21.2052, +07 56 04.746, 0.00686941, 0.00084875, 11.9873,  50.560,  *"


An ephemerides file that complies with the above specifications may be generated with any tool.
One convenient way is to use the output of the JPL Horizons ephemerides generator as input to the crossEphem2Paf Tcl script, which converts it to the PAF format. Following are appropriate settings for the JPL Horizons tool:

  • In the "Current Settings" table set the value in the right column:
Current Settings
Ephemeris type OBSERVER
Target Body favorite target or reference object
Observer Location Cerro Paranal [309]
Time Span start and end of the ephemerides, time step
Display/Output download/save

 

  • The "Table Settings" parameters should have the following values:
Table Settings
observer quantities

1 Astrometric RA & DEC  

3 Rates: RA & DEC

(other quantities are optional)

day/time format Julian day
angle format hours/degrees minutes seconds
Refraction model airless model (no refraction)
Airmass Limit 2.6 (or smaller)
Elevation cutoff 20 (or larger)
Skip daylight checked
Extra precision checked
Reference system ICRF/J2000.0
CSV format checked

To convert the JPL Horizons output file (coma-separated variable (csv) format) into the correct PAF format described above with the crossEphem2paf.tcl tool use the following syntax:

  • tclsh crossEphem2paf.tcl -i sourceFileName -o fileName.eph

OB Requirements

In addition to the standard OB requirements (see the Phase 2 preparation procedures), OBs for moving targets must have the following features:

  • The OB Name must begin with the prefix MOV_
  • All OBs for moving targets must have an ephemerides file attached to it.
  • All OBs for moving targets must use time intervals. In case the timing of the observation itself does not matter, the time intervals should be set to the start and end times of the period covered in the ephemerides file. The ephemerides file should have a minimum of one entry per day for each time interval set in the OB.

 

Target Acquisition and Verification

Bright Targets

For targets brighter than V = 14, a DSS-based finding chart will be prepared by the ESO operations team to verify the acquisition of the target.

Faint Targets: Blind Presets

If a blind preset is enough for the purposes of the observation(i.e. if a pointing accuracy of order of one arcsecond is sufficient), the identification of the field-of-view will be carried out by the ESOastronomer in charge of performing the observations using a DSS-based finding chart. Normally no attempt will be made to identify the exact target.

Faint Targets: Accurate Presets

In cases where an accurate preset is needed (for example, spectroscopic observations), the user will need to provide two pre-imaging OBs for each science OB, with names containing the MOV_PRE_ prefix. The parameters of these OBs (instrument setup and integration time) must be identical in both pre-imaging OBs, and defined so that the target is visible in both images. The constraint set of pre-imaging OBs must also be identical to that of the science exposures that they precede. These two pre-imaging OBs will be executed with a time separation sufficient to detect the apparent motion of the target between both images. This time difference will be determined by the ESO operations team based on the user-supplied ephemerides. Note that the time needed to execute these pre-imaging OBs will be deducted from the total time allocated by the OPC.

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