Moving Target Procedures: Ephemeris Files
Ephemeris files compatible with observations at the VLT can easily be generated using our online form. For reference, we detail here the format specifications for such files, and we provide links to other tools that can be helpful when trying to generate ephemerides for ESO observations.
Format specifications
An ephemeris 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.
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, *"
Tools
An ephemeris file that complies with the above specifications may be generated with any tool. As already mentioned, the most practical way is certainly to use our online PAF ephemeris generator.
Another tool we can recommend is the JPL Horizons ephemerides generator. Its output can then be converted into PAF format using the crossEphem2Paf Tcl script (new version for P109), which converts it to the PAF format. There is also an on-line converter that performs the same task.
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 9 Visual mag. & Surface Brght (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 (new version for P109) tool use the following syntax:
- tclsh crossEphem2paf.tcl -i sourceFileName -o fileName.eph
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