MeerKAT calibrator selection
User tool to find the closest, good calibrators to a target, as well as create a CSV catalogue file.
astrokat-targets.py -h
The tool requires that a target, or a catalogue file be specified.
A single target is specified with the --target argument,
while catalogue file containing multiple targets are provided with the --infile argument.
-
Format for specifying a single target is simply
--target <name> <ra> <dec>, currently only string format input for the (RA, DEC) coordinates are implemented,
HH:MM:SS.f DD:MM:SS.f -
In addition to the targets, the user must also specify the type of calibrators to select using the
--cal-tagsargument. Current available options aregain, bp, flux, or pol
| Tag | Calibrator Type |
|---|---|
| gain | select a gain calibrator |
| bp | add bandpass calibrator(s) |
| flux | add flux calibrator(s) |
| pol | select a polarisation calibrator |
-
MeerKAT standard calibrator catalogues are selected using observatory calibrator catalogues located in
katconfig/user/catalogues.
For users to access these catalogues the--cat-pathargument must be specified giving the full path to the folder where the desired catalogues are located. Currently, these catalogues are available in the repository under theastrokat/cataloguesfolder.
Important: The reader should note that the current implementation ofastrokat-targets.pyassume a specific calibrator naming convension:
Lband-<calibrator_clasification>-calibrators.csv.
The implementation will be updated as new requirements are identified based on usage. -
Optional input arguments such as
--pi,--contactand--prop-id, provides metadata that is added when the observation catalogue file is created. The purpose of this information is simply informational and is supplementary to the target specification. -
MeerKAT standard catalogues have a large number of gain calibrators available, but currently only a small number of primary calibrators such as bandpass, flux and polarisation are available. Thus,
astrokat-targets.pywill find the closest gain calibrator to the target, the closet bandpass and flux calibrators, as well as additional bandpass and flux calibrators to cover the entire LST time range that the target will be visible to ensure a primary calibrator is always visible. -
Currently, MeerKAT only has three flux calibrators with known flux models, as well as three polarisation calibrators. The number of calibrators will improve going forward, but sometimes to make selection between these few calibrators visually, add the
--all-calstag. This will display all calibrators in the selected catalogues (flux or polarisation) in the elevation plot.
Most basic implementation is to view available calibrators for a target
astrokat-targets.py --target 'NGC641_03D03' '01:38:13.250' '-42:37:41.000' --cal-tags gain bp flux --lst --cat-path catalogues/ --datetime '2019-02-07 04:37:28
Note the use of the --lst flag to display the tabulated rise and set times in LST. This is generally used for planning when catalogues are constructed and calibrators has to be selected.
Resulting in display output:
Observation Table for 2019/2/7 04:37:29 (UTC)
Times listed in LST for target rise and set times
Target visible when above 17.0 degrees
Sources Class RA Decl Rise Time Set Time Separation Notes
NGC641_03D03 radec target 1:38:13.25 -42:37:41.0 19:19:50.89 7:58:10.41 60.75 separation from Sun
J0010-4153 radec bpcal 0:10:52.52 -41:53:10.8 17:54:38.67 6:28:57.07 16.13 *** separation from NGC641_03D03
J0155-4048 radec gaincal 1:55:37.06 -40:48:42.4 19:42:01.46 8:10:46.03 3.72
J0408-6545 radec bpcal fluxcal 4:08:20.38 -65:45:09.6 20:11:15.45 12:05:43.79 31.01 ***
With the *** a visual aid to the user to draw attention that the closest calibrator found was more than 15 degrees away from the target.
If the Python matplotlib library is available, an elevation graph will also be displayed.
Useful additional options:
- To create a catalogue file a filename for the output catalogue has to be provided by adding the
--outfileargument.
astrokat-targets.py --prop-id 'SCI-dateinitials-nr' --pi 'No One' --contact 'dummy@ska.ac.za' --target 'NGC641_03D03' '01:38:13.250' '-42:37:41.000' --cal-tags gain bp flux --outfile test_NGC641_03D03.csv --lst --cat-path catalogues/
Observation catalogue test_NGC641_03D03.csv
The --outfile argument is very important when selecting flux and polarisation calibrators. These calibrators comes with flux model coefficients that must be added to the targets and is only done in the output file.
# Observation catalogue for proposal ID SCI-dateinitials-nr
# PI: No One
# Contact details: dummy@ska.ac.za
J0010-4153 | 0008-421, radec bpcal, 0:10:52.52, -41:53:10.8, (145.0 20000.0 -16.93 15.39 -4.21 0.3496)
J0155-4048 | 0153-410, radec gaincal, 1:55:37.06, -40:48:42.4
J0408-6545 | 0408-658, radec bpcal fluxcal, 4:08:20.38, -65:45:09.6, (145.0 18000.0 -0.979 3.366 -1.122 0.0861)
NGC641_03D03, radec target, 1:38:13.25, -42:37:41.0
Scheduling an observation with an existing catalogue, or evaluating viability of a created catalogue for a specific observation date, the --view option can be added.
This will generate an updated elevation plot of catalogue targets, adding a desired date and time using the --datetime option and leaving out the --lst option will display the rise and set time in UCT at the selected time.
astrokat-targets.py --view test_NGC641_03D03.csv --horizon 20
astrokat-targets.py --view test_NGC641_03D03.csv --datetime '2018-04-06 12:34'
astrokat-targets.py --view test_NGC641_03D03.csv --text-only --solar-angle=55 --datetime '2018-04-06 12:34'
While the target elevation plot is the default display, for more intricate observations, more display options are available with the --view-tags option.
These can be specified as a list, e.g.: --view-tags elevation solarangle
| Tag | Graph Type |
|---|---|
| elevation | Elevation angle or catalogue sources over LST range for a 24hr period |
| solarangle | Solar separation angle of target over a year |
| riseset | Target rise and set times (UTC) over the duration of a year |
Providing multiple targets in an input file simply follows the typical target specification definition of the observation CSV catalogue files.
Default is to select the first target in the list of targets to find the indicated calibrators for.
This is not always desirable and to indicate which targets in the file to use when selecting calibrators the --calref tag must be added to that target's observation information.
The unique --calref tag now indicates which target or coordinate should be used when selected the closest calibrator sources.
# AR1 mosaic NGC641
# Catalogue for the AR1 mosaic tests
NGC641_02D02, radec target, 01:39:25.009, -42:14:49.216
NGC641_03D02, radec target, 01:37:01.491, -42:14:49.216
NGC641_02D03, radec target, 01:40:36.768, -42:37:41.000
NGC641_03D03, radec target calref, 01:38:13.250, -42:37:41.000
NGC641_04D03, radec target, 01:35:49.732, -42:37:41.000
NGC641_02D04, radec target, 01:39:25.009, -43:00:32.784
NGC641_03D04, radec target, 01:37:01.491, -43:00:32.784
Using the example input file above listing multiple galactic pointings
astrokat-targets.py --cal-tags gain bp flux --outfile mosaic_catalogue.csv --infile sample_targetlist_for_cals.csv --horizon 20 --cat-path catalogues/ --datetime '2018-11-14 11:32:31'
Producing screen output:
Observation catalogue mosaic_catalogue.csv
Observation Table for 2018/11/14 11:32:31
Times in UTC when target is above the default horizon = 20 degrees
Sources Class RA Decl Rise Time Set Time Separation Notes
NGC641_02D02 radec target 1:39:25.01 -42:14:49.2 14:39:36 02:38:09 115.45 separation from Sun
NGC641_02D03 radec target 1:40:36.77 -42:37:41.0 14:39:52 02:40:15 115.21
NGC641_02D04 radec target 1:39:25.01 -43:00:32.8 14:37:46 02:39:58 114.77
NGC641_03D02 radec target 1:37:01.49 -42:14:49.2 14:37:13 02:35:46 115.26
NGC641_03D03 radec target 1:38:13.25 -42:37:41.0 14:37:30 02:37:52 115.01
NGC641_03D04 radec target 1:37:01.49 -43:00:32.8 14:35:23 02:37:35 114.58
NGC641_04D03 radec target 1:35:49.73 -42:37:41.0 14:35:07 02:35:29 114.82
J0010-4153 radec bpcal 0:10:52.52 -41:53:10.8 13:12:18 01:09:07 16.13 *** separation from NGC641_03D03
J0155-4048 radec gaincal 1:55:37.06 -40:48:42.4 14:59:06 02:50:56 3.72
J0408-6545 radec bpcal fluxcal 4:08:20.38 -65:45:09.6 15:46:16 06:27:16 31.01 ***
Creates the catalogue file:
# AR1 mosaic NGC641
# Catalogue for the AR1 mosaic tests
# Observation catalogue for proposal ID None
# PI: None
# Contact details: None
J0010-4153 | 0008-421, radec bpcal, 0:10:52.52, -41:53:10.8, (145.0 20000.0 -16.93 15.39 -4.21 0.3496)
J0155-4048 | 0153-410, radec gaincal, 1:55:37.06, -40:48:42.4
J0408-6545 | 0408-658, radec bpcal fluxcal, 4:08:20.38, -65:45:09.6, (145.0 18000.0 -0.979 3.366 -1.122 0.0861)
NGC641_02D02, radec target, 1:39:25.01, -42:14:49.2
NGC641_02D03, radec target, 1:40:36.77, -42:37:41.0
NGC641_02D04, radec target, 1:39:25.01, -43:00:32.8
NGC641_03D02, radec target, 1:37:01.49, -42:14:49.2
NGC641_03D03, radec target, 1:38:13.25, -42:37:41.0
NGC641_03D04, radec target, 1:37:01.49, -43:00:32.8
NGC641_04D03, radec target, 1:35:49.73, -42:37:41.0
Elevation plot:
If the --datetime argument is not specified, the current time will be used for all time conversions and elevation calculations. The impact of the --datetime argument can be shown in the following examples, using the 55 minimum solar separation angle threshold, --solar-angle, to highlight the differences:
astrokat-targets.py --cal-tags gain bp flux --infile sample_targetlist_for_cals.csv --datetime '2018-04-06 12:34' --text-only --horizon 20 --cat-path catalogues/
Observation Table for 2018/4/6 12:34:00
Times in UTC when target is above the default horizon = 20 degrees
Sources Class RA Decl Rise Time Set Time Separation Notes
NGC641_02D02 radec target 1:39:25.01 -42:14:49.2 05:12:22 17:10:57 49.50 separation from Sun
NGC641_02D03 radec target 1:40:36.77 -42:37:41.0 05:12:39 17:13:03 49.92
NGC641_02D04 radec target 1:39:25.01 -43:00:32.8 05:10:33 17:12:46 50.25
NGC641_03D02 radec target 1:37:01.49 -42:14:49.2 05:09:59 17:08:34 49.41
NGC641_03D03 radec target 1:38:13.25 -42:37:41.0 05:10:16 17:10:40 49.83
NGC641_03D04 radec target 1:37:01.49 -43:00:32.8 05:08:10 17:10:23 50.15
NGC641_04D03 radec target 1:35:49.73 -42:37:41.0 05:07:53 17:08:17 49.74
J0010-4153 radec bpcal 0:10:52.52 -41:53:10.8 03:45:05 15:41:54 16.13 *** separation from NGC641_03D03
J0155-4048 radec gaincal 1:55:37.06 -40:48:42.4 05:31:52 17:23:44 3.72
J0408-6545 radec bpcal fluxcal 4:08:20.38 -65:45:09.6 06:19:00 21:00:05 31.01 ***
J1939-6342 radec bpcal fluxcal 19:39:25.05 -63:42:43.6 22:04:06 12:23:00 52.49 ***
Compared to the output by specifying a required solar separation angle larger than the default 20 degrees.
astrokat-targets.py --cal-tags gain bp flux --infile sample_targetlist_for_cals.csv --datetime '2018-04-06 12:34' --solar-angle=55 --text-only --horizon 20 --cat-path catalogues/
Observation Table for 2018/4/6 12:34:00
Times in UTC when target is above the default horizon = 20 degrees
Sources Class RA Decl Rise Time Set Time Separation Notes
NGC641_02D02 radec target 1:39:25.01 -42:14:49.2 05:12:22 17:10:57 49.50 *** separation from Sun
NGC641_02D03 radec target 1:40:36.77 -42:37:41.0 05:12:39 17:13:03 49.92 ***
NGC641_02D04 radec target 1:39:25.01 -43:00:32.8 05:10:33 17:12:46 50.25 ***
NGC641_03D02 radec target 1:37:01.49 -42:14:49.2 05:09:59 17:08:34 49.41 ***
NGC641_03D03 radec target 1:38:13.25 -42:37:41.0 05:10:16 17:10:40 49.83 ***
NGC641_03D04 radec target 1:37:01.49 -43:00:32.8 05:08:10 17:10:23 50.15 ***
NGC641_04D03 radec target 1:35:49.73 -42:37:41.0 05:07:53 17:08:17 49.74 ***
J0010-4153 radec bpcal 0:10:52.52 -41:53:10.8 03:45:05 15:41:54 16.13 *** separation from NGC641_03D03
J0155-4048 radec gaincal 1:55:37.06 -40:48:42.4 05:31:52 17:23:44 3.72
J0408-6545 radec bpcal fluxcal 4:08:20.38 -65:45:09.6 06:19:00 21:00:05 31.01 ***
J1939-6342 radec bpcal fluxcal 19:39:25.05 -63:42:43.6 22:04:06 12:23:00 52.49 ***
Solar system body observations rely on the bodies defined by PyEphem's Planet objects
import ephem
from pprint import pprint
pprint(ephem._libastro.builtin_planets())
Using the names of these objects the rise/set times, as well as closest calibrators can be calculated
astrokat-targets.py --body Moon --cat-path catalogues/ --text-only --lst
astrokat-targets.py --body Moon --cat-path catalogues/ --cal-tags gain flux pol --text-only --lst --outfile lunar.csv
Note the use of the special tag in the observation catalogue CSV file
> cat lunar.csv
# Observation catalogue for proposal ID None
# PI: None
# Contact details: None
J0059+0006 | 0056-001, radec gaincal, 0:59:05.51, 0:06:51.6, (74.0 8400.0 -0.9051 1.8362 -0.6141 0.0518)
J0137+3309 | 3C48, radec polcal, 1:37:41.30, 33:09:35.1, (50.0 50000.0 0.524 1.7377 -0.6396 0.0498)
J0408-6545 | 0408-658, radec bpcal fluxcal, 4:08:20.38, -65:45:09.1, (145.0 18000.0 -0.979 3.3662 -1.1216 0.0861)
J0521+1638 | 3C138, radec polcal, 5:21:09.89, 16:38:22.1, (50.0 50000.0 1.3781 0.1619 -0.065 -0.01)
Moon, special
For objects such as comets a heliocentric elliptical orbit is assumed with the orbital position from as specified through the XEphem EDB database.
The example use ephemeris from Minor Planet & Comet Ephemeris Service
https://www.minorplanetcenter.net/iau/MPEph/MPEph.html
astrokat-targets.py --xephem "C/2002 Y1" "C/2002 Y1 (Juels-Holvorcem)~e~103.7816~166.2194~128.8232~242.5695~0.0002609~0.99705756~0.0000~04/13.2508/2003~2000~g 6.5~4.0" --cal-tags gain flux --lst --cat-path catalogues/ --datetime '2019-02-07 16:30:00' --text-only --outfile C_2002_Y1.csv
Since the orbital elements moves fast, regular update for observations dates are required to keep the catalogue and observation files up to date
> cat C_2002_Y1.csv
# Observation catalogue for proposal ID None
# PI: None
# Contact details: None
C/2002 Y1 | C/2002 Y1 (Juels-Holvorcem), xephem solarsys target, C/2002 Y1~e~103.7816~166.2194~128.8232~242.5695~0~0.9970576~0~4/13.2508/2003~1/01/2000~g6.5~4~0
J0408-6545 | 0408-658, radec bpcal fluxcal, 4:08:20.38, -65:45:09.1, (145.0 18000.0 -0.979 3.3662 -1.1216 0.0861)
J0906-6829 | 0906-682, radec gaincal, 9:06:52.44, -68:29:39.8, (145.0 20000.0 0.768 1.3416 -0.6601 0.0573)
View the results
astrokat-targets.py --view C_2002_Y1.csv
- The default folder for the standard calibrator catalogues are
katconfig/user/catalogues/. This folder requires the katconfig repository which is not always available.
Unhandled exception <type 'exceptions.RuntimeError'> : Could not access calibrator catalogue default location
add explicit location of catalogue folder using --cat-path <dirname>
The standard catalogues will be made available in a separate repository for local use, with the updated command
astrokat-targets.py --prop-id 'SCI-dateinitials-nr' --pi 'No One' --contact 'dummy@ska.ac.za' --target 'NGC641_03D03' '01:38:13.250' '-42:37:41.000' --cal-tags gain bp flux --outfile test_NGC641_03D03.csv --cat-path astrokat/calibrators/
- The generation graphical output such as the elevation plot and PDF report creation is not always available on the observation systems. If the python
matplotlibpackage is not available, the script will default to the text output displayed to screen and indicate this to the user with the output:
Required matplotlib functionalities not available
Cannot create elevation plot or generate report
Only producing catalogue file and output to screen