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Starting Out With AIPS Tutorial
James M Anderson
This tutorial session is intended to get people familiar with the basic concepts of radio interferometry. The student will be introduced to interferometry data, visibilities, the (u,v) plane, calibration, and imaging.
Step 1 --- Figure Out What to Observe (Reduce)
I decided to try to make an image of the Sun, as the Solar KSP is a significant part of GLOW. The NRAO image archive has a nice image of the Sun at 1400 MHz located at http://images.nrao.edu/8
Image courtesy of NRAO/AUI
Let's try to reduce the data ourselves.
Step 2 --- Download the Data From the Archive
Conveniently, the NRAO image archive gives details about the observations used to make the image, so I downloaded the data from the NRAO data archive, making sure to select the “AIPS friendly” filename option.
This has resulted in two files on my hard drive in my current directory:
ls -l
total 54164
-rw-r—– 1 anderson zeall 21002240 2008-11-11 14:40 GD_1
-rw-r—– 1 anderson zeall 34392064 2008-11-11 14:41 GD_2
Step 3 --- Start up AIPS
aips
I have chosen to use user ID 100, at semi-random selection.
At first, most of the archane syntax used to enter commands to AIPS will be difficult. As this is a tutorial session which intends to teach you about radio interferometry, and not how to use AIPS, we will gloss over the technical challenges of interacting with AIPS.
In AIPS you the user interact with something called POPS. You give POPS information by setting variables called ADVERBS to specific values. You can tell POPS which TASK you plan to run by setting a TASK ADVERB. If you want to check the values of ADVERBs for the current TASK, you ask for INPUTS. Because POPS will try to figure out what you mean if you only input the first few letters of an ADVERB or VERB, you can often abbreviate this to just INP. Also note that since AIPS is case-insensitive by default, you could also just type inp. If you want help on a specific topic, ask for HELP. If you want even more explanation for something, say EXPLAIN. If you don't know what it is you are trying to do, but you have some vague notion, say APROPOS SOMETHING. Note that apostrophes, and in certain locations, the lack of an apostrophe are significant.
Step 4 --- Initial look at data
FILLM
The AIPS task to read raw VLA data into AIPS is called FILLM.
dowait=true
dohist=1
docrt=132
dotv=1
task 'fillm'
default
datain = 'PWD:GD_
nfiles=0
ncount=2
vlamode='S '
doweight=10
doconcat=true
douvcomp=0
cparm(2)=16
cparm(4)=28
cparm(8)=10./60
go
This sets us up to read the data, sets the VLA mode to Solar, tells AIPS not to change the source if the position appears to be moving (which the Sun does), sets the shadowing limit to 28 meters, and sets the CL table interval to 10 seconds.
Header information
pcat
AIPS 1: Catalog on disk 1 AIPS 1: Cat Usid Mapname Class Seq Pt Last access Stat AIPS 1: 1 100 19810926 .L BAND. 1 UV 14-NOV-2008 21:35:31
getn 2
imhe
AIPS 1: Image=MULTI (UV) Filename=19810926 .L BAND. 1 AIPS 1: Telescope=VLA Receiver=VLA AIPS 1: Observer=GD User #= 100 AIPS 1: Observ. date=26-SEP-1981 Map date=14-NOV-2008 AIPS 1: # visibilities 556884 Sort order TB AIPS 1: Rand axes: UU-L-SIN VV-L-SIN WW-L-SIN BASELINE TIME1 AIPS 1: SOURCE FREQSEL AIPS 1: ---------------------------------------------------------------- AIPS 1: Type Pixels Coord value at Pixel Coord incr Rotat AIPS 1: COMPLEX 3 1.0000000E+00 1.00 1.0000000E+00 0.00 AIPS 1: STOKES 4 -1.0000000E+00 1.00 -1.0000000E+00 0.00 AIPS 1: FREQ 1 1.4461500E+09 1.00 1.2500000E+07 0.00 AIPS 1: IF 1 1.0000000E+00 1.00 1.0000000E+00 0.00 AIPS 1: RA 1 00 00 00.000 1.00 3600.000 0.00 AIPS 1: DEC 1 00 00 00.000 1.00 3600.000 0.00 AIPS 1: ---------------------------------------------------------------- AIPS 1: Coordinate equinox 0.00 AIPS 1: Maximum version number of extension files of type HI is 1 AIPS 1: Maximum version number of extension files of type AN is 1 AIPS 1: Maximum version number of extension files of type NX is 1 AIPS 1: Maximum version number of extension files of type SU is 1 AIPS 1: Maximum version number of extension files of type FQ is 1 AIPS 1: Maximum version number of extension files of type CL is 1 AIPS 1: Maximum version number of extension files of type TY is 1 AIPS 1: Maximum version number of extension files of type WX is 1 AIPS 1: Maximum version number of extension files of type OF is 1 AIPS 1: Keyword = 'CORRMODE' value = ' ' AIPS 1: Keyword = 'VLAIFS ' value = 'AC ' AIPS 1: Keyword = 'CORRCOEF' value = -1
LISTR --- scan listing
default listr
task 'listr'
indi 1
getn 2
optype 'scan'
docrt=132
go
vlb054 LISTR(31DEC08) 100 14-NOV-2008 21:42:46 Page 1 File = 19810926 .L BAND. 1 Vol = 1 Userid = 100 Freq = 1.446150006 GHz Ncor = 4 No. vis = 556884 Scan summary listing Scan Source Qual Calcode Sub Timerange FrqID START VIS END VIS 1 1148-001 : 0000 C 1 0/13:53:25 - 0/13:53:25 1 1 351 2 1148-001 : 0000 C 1 0/13:53:35 - 0/13:54:35 1 352 2808 3 SUN : 0000 1 0/13:59:05 - 0/13:59:35 1 2809 4212 4 SUN : 0000 1 0/14:05:15 - 0/14:09:35 1 4213 13689 5 1148-001 : 0000 C 1 0/14:18:05 - 0/14:19:35 1 13690 17199 6 SUN : 0000 1 0/14:20:15 - 0/14:24:35 1 17200 26676 7 SUN : 0000 1 0/14:30:05 - 0/14:34:35 1 26677 36504 8 1148-001 : 0000 C 1 0/14:43:05 - 0/14:44:35 1 36505 40014 9 SUN : 0000 1 0/14:45:15 - 0/14:49:35 1 40015 49491 10 SUN : 0000 1 0/14:55:05 - 0/14:59:25 1 49492 58968 11 1148-001 : 0000 C 1 0/15:07:55 - 0/15:09:25 1 58969 62478 12 SUN : 0000 1 0/15:10:05 - 0/15:14:25 1 62479 71955 13 SUN : 0000 1 0/15:19:55 - 0/15:24:25 1 71956 81783 14 1148-001 : 0000 C 1 0/15:32:55 - 0/15:34:25 1 81784 85293 15 SUN : 0000 1 0/15:35:05 - 0/15:39:25 1 85294 94770 16 SUN : 0000 1 0/15:44:55 - 0/15:49:25 1 94771 104598 17 1148-001 : 0000 C 1 0/15:57:55 - 0/15:59:25 1 104599 108108 18 SUN : 0000 1 0/16:00:05 - 0/16:04:15 1 108109 117234 19 SUN : 0000 1 0/16:09:45 - 0/16:14:15 1 117235 127062 20 1148-001 : 0000 C 1 0/16:22:45 - 0/16:24:15 1 127063 130572 21 SUN : 0000 1 0/16:24:55 - 0/16:29:15 1 130573 140049 22 SUN : 0000 1 0/16:34:45 - 0/16:39:15 1 140050 149877 23 1148-001 : 0000 C 1 0/16:47:45 - 0/16:49:15 1 149878 153387 24 SUN : 0000 1 0/16:49:55 - 0/16:54:15 1 153388 162864 25 SUN : 0000 1 0/16:59:45 - 0/17:04:05 1 162865 172341 26 1148-001 : 0000 C 1 0/17:12:35 - 0/17:14:05 1 172342 175851 27 SUN : 0000 1 0/17:14:45 - 0/17:19:05 1 175852 185328 28 SUN : 0000 1 0/17:24:35 - 0/17:29:05 1 185329 195156 29 1148-001 : 0000 C 1 0/17:37:35 - 0/17:39:05 1 195157 198666 30 SUN : 0000 1 0/17:39:45 - 0/17:44:25 1 198667 208845 31 SUN : 0000 1 0/17:50:15 - 0/17:54:05 1 208846 217269 32 1148-001 : 0000 C 1 0/18:02:25 - 0/18:03:55 1 217270 220779 33 SUN : 0000 1 0/18:04:35 - 0/18:08:55 1 220780 230256 34 SUN : 0000 1 0/18:14:25 - 0/18:18:55 1 230257 240084 35 1148-001 : 0000 C 1 0/18:27:25 - 0/18:28:55 1 240085 243594 36 SUN : 0000 1 0/18:29:35 - 0/18:33:55 1 243595 253071 37 SUN : 0000 1 0/18:39:35 - 0/18:44:05 1 253072 262899 38 1148-001 : 0000 C 1 0/18:52:35 - 0/18:53:55 1 262900 266058 39 SUN : 0000 1 0/18:54:45 - 0/18:59:05 1 266059 275535 40 SUN : 0000 1 0/19:04:25 - 0/19:08:45 1 275536 285012 41 1148-001 : 0000 C 1 0/19:17:25 - 0/19:18:45 1 285013 288171 42 SUN : 0000 1 0/19:19:25 - 0/19:23:45 1 288172 297648 43 SUN : 0000 1 0/19:29:15 - 0/19:33:45 1 297649 307476 44 1148-001 : 0000 C 1 0/19:42:15 - 0/19:43:45 1 307477 310986 45 SUN : 0000 1 0/19:44:25 - 0/19:53:05 1 310987 329589 46 SUN : 0000 1 0/19:54:25 - 0/19:58:45 1 329590 339066 47 1148-001 : 0000 C 1 0/20:07:05 - 0/20:08:35 1 339067 342576 48 SUN : 0000 1 0/20:09:15 - 0/20:13:35 1 342577 352053 49 SUN : 0000 1 0/20:19:05 - 0/20:23:35 1 352054 361881 50 1148-001 : 0000 C 1 0/20:32:05 - 0/20:33:35 1 361882 365391 51 SUN : 0000 1 0/20:34:15 - 0/20:38:35 1 365392 374868 52 SUN : 0000 1 0/20:44:05 - 0/20:48:35 1 374869 384696 53 1148-001 : 0000 C 1 0/20:57:05 - 0/20:58:35 1 384697 388206 54 SUN : 0000 1 0/20:59:15 - 0/21:03:35 1 388207 397657 55 SUN : 0000 1 0/21:08:55 - 0/21:13:25 1 397658 407485 56 1148-001 : 0000 C 1 0/21:21:55 - 0/21:23:25 1 407486 410969 57 SUN : 0000 1 0/21:24:05 - 0/21:28:25 1 410970 420446 58 SUN : 0000 1 0/21:33:55 - 0/21:38:25 1 420447 430274 59 1148-001 : 0000 C 1 0/21:47:05 - 0/21:48:25 1 430275 433433 60 SUN : 0000 1 0/21:49:05 - 0/21:53:25 1 433434 442858 61 SUN : 0000 1 0/21:58:55 - 0/22:03:25 1 442859 452686 62 1148-001 : 0000 C 1 0/22:11:45 - 0/22:13:15 1 452687 456196 63 SUN : 0000 1 0/22:13:55 - 0/22:18:15 1 456197 465647 64 SUN : 0000 1 0/22:23:55 - 0/22:28:15 1 465648 475124 65 1148-001 : 0000 C 1 0/22:36:55 - 0/22:38:15 1 475125 478283 66 SUN : 0000 1 0/22:38:55 - 0/22:43:15 1 478284 487734 67 SUN : 0000 1 0/22:48:55 - 0/22:53:25 1 487735 497562 68 1148-001 : 0000 C 1 0/23:01:55 - 0/23:03:15 1 497563 500721 69 SUN : 0000 1 0/23:03:55 - 0/23:08:05 1 500722 509847 70 SUN : 0000 1 0/23:13:45 - 0/23:18:05 1 509848 519324 71 1148-001 : 0000 C 1 0/23:26:45 - 0/23:28:05 1 519325 522249 72 SUN : 0000 1 0/23:28:45 - 0/23:33:05 1 522250 531700 73 SUN : 0000 1 0/23:38:45 - 0/23:43:05 1 531701 540450 74 1148-001 : 0000 C 1 0/23:51:45 - 0/23:53:05 1 540451 543350 75 SUN : 0000 1 0/23:53:45 - 0/23:58:05 1 543351 552125 76 SUN : 0000 1 1/00:01:15 - 1/00:01:15 1 552126 552450 77 SUN : 0000 1 1/00:07:25 - 1/00:07:55 1 552451 553725 78 3C286 : 0000 B 1 1/00:21:35 - 1/00:22:55 1 553726 556884 Source summary Velocity type = ' ' Definition = ' ' ID Source Qual Calcode RA( 0.0) Dec( 0.0) IFlux QFlux UFlux VFlux No. vis 1 1148-001 : 0000 C 11:48:10.1300 -00:07:13.300 0.000 0.000 0.000 0.000 84072 2 SUN : 0000 12:10:30.1272 -01:08:22.648 0.000 0.000 0.000 0.000 469653 3 3C286 : 0000 B 13:28:49.6570 30:45:58.640 0.000 0.000 0.000 0.000 3159 ID Source Freq(GHz) Velocity(Km/s) Rest freq (GHz) 1 All Sources 1.4462 0.0000 0.0000 Frequency Table summary FQID IF# Freq(GHz) BW(kHz) Ch.Sep(kHz) Sideband 1 1 1.44615001 12500.0010 12500.0010 1 AIPS 1: Resumes
PRTAN
Print the Antenna positions — useful for thinking about calibration.
go prtan
vlb054 PRTAN(31DEC08) 100 14-NOV-2008 21:45:10 Page 1
File=19810926 .L BAND. 1 An.ver= 1 Vol= 1 User= 100
Array= VLA Freq= 1446.150006 MHz Ref.date= 26-SEP-1981
Array reference position in meters (Earth centered)
Array BX= -1601185.36500 BY= -5041977.54700 BZ= 3554875.87000
Polar X = 0.00000 Polar Y = 0.00000 arcsec
Earth rotation rate = 360.9856449713 degrees / IAT day
GST at UT=0 = 364.7139688925 degrees
UT1-UTC= 0.0000000 Data time(IAT )-UTC= 0.0000000 seconds
Solutions not yet determined for a particular FREQID
Ant 1 = VLA:_N2 BX= -30.0602 BY= -4.7835 BZ= 45.7022
Mount=ALAZ Axis offset= 0.0000 meters IFA IFB
Feed polarization type = R L
Ant 2 = VLA:_E5 BX= 51.8719 BY= 195.8466 BZ= -75.1013
Mount=ALAZ Axis offset= 0.0000 meters IFA IFB
Feed polarization type = R L
Ant 3 = VLA:_E9 BX= 139.6430 BY= 536.8956 BZ= -207.7424
Mount=ALAZ Axis offset= -0.0033 meters IFA IFB
Feed polarization type = R L
Ant 4 = VLA:_E6 BX= 70.6548 BY= 267.7575 BZ= -102.8996
Mount=ALAZ Axis offset= 0.0078 meters IFA IFB
Feed polarization type = R L
Ant 5 = VLA:_N3 BX= -52.4373 BY= -8.2629 BZ= 78.6643
Mount=ALAZ Axis offset= 0.0000 meters IFA IFB
Feed polarization type = R L
Ant 6 = VLA:_W2 BX= 14.7735 BY= -37.1404 BZ= -20.2135
Mount=ALAZ Axis offset= 0.0000 meters IFA IFB
Feed polarization type = R L
Ant 7 = VLA:_W3 BX= 28.9195 BY= -74.4876 BZ= -41.0524
Mount=ALAZ Axis offset= -0.0036 meters IFA IFB
Feed polarization type = R L
Ant 8 = VLA:_W1 BX= 22.9920 BY= 3.4974 BZ= -32.4864
Mount=ALAZ Axis offset= 0.0084 meters IFA IFB
Feed polarization type = R L
Ant 9 = VLA:_E2 BX= 11.3328 BY= 40.6638 BZ= -15.1624
Mount=ALAZ Axis offset= 0.0000 meters IFA IFB
Feed polarization type = R L
Ant 10 = VLA:_OUT BX= 0.0000 BY= 0.0000 BZ= 0.0000
Mount=ALAZ Axis offset= 0.0000 meters IFA IFB
Feed polarization type = R L
Ant 11 = VLA:_E8 BX= 114.4257 BY= 438.6941 BZ= -169.4880
Mount=ALAZ Axis offset= 0.0048 meters IFA IFB
Feed polarization type = R L
Ant 12 = VLA:_E3 BX= 21.9945 BY= 81.5250 BZ= -30.9498
Mount=ALAZ Axis offset= 0.0000 meters IFA IFB
Feed polarization type = R L
Ant 13 = VLA:_E7 BX= 91.5227 BY= 348.8871 BZ= -134.4449
Mount=ALAZ Axis offset= 0.0000 meters IFA IFB
Feed polarization type = R L
Ant 14 = VLA:_W7 BX= 121.6261 BY= -319.1264 BZ= -177.5842
Mount=ALAZ Axis offset= 0.0000 meters IFA IFB
Feed polarization type = R L
Ant 15 = VLA:_W9 BX= 186.8061 BY= -491.1158 BZ= -273.5624
Mount=ALAZ Axis offset= 0.0000 meters IFA IFB
Feed polarization type = R L
Ant 16 = VLA:_E4 BX= 35.6150 BY= 133.6310 BZ= -51.1099
Mount=ALAZ Axis offset= -0.0051 meters IFA IFB
Feed polarization type = R L
Ant 17 = VLA:_W8 BX= 152.7524 BY= -401.2839 BZ= -223.4146
Mount=ALAZ Axis offset= 0.0000 meters IFA IFB
Feed polarization type = R L
Ant 18 = VLA:_E1 BX= 45.3386 BY= 7.0026 BZ= -65.4888
Mount=ALAZ Axis offset= 0.0000 meters IFA IFB
Feed polarization type = R L
Ant 19 = VLA:_N7 BX= -193.6105 BY= -30.2503 BZ= 286.4580
Mount=ALAZ Axis offset= -0.0030 meters IFA IFB
Feed polarization type = R L
Ant 20 = VLA:_N1 BX= 0.6703 BY= 0.0144 BZ= 0.5135
Mount=ALAZ Axis offset= 0.0045 meters IFA IFB
Feed polarization type = R L
Ant 21 = VLA:_N8 BX= -243.6039 BY= -38.0389 BZ= 360.0340
Mount=ALAZ Axis offset= 0.0000 meters IFA IFB
Feed polarization type = R L
Ant 22 = VLA:_W5 BX= 68.6012 BY= -179.2282 BZ= -99.5242
Mount=ALAZ Axis offset= 0.0000 meters IFA IFB
Feed polarization type = R L
Ant 23 = VLA:_N5 BX= -108.4301 BY= -16.9862 BZ= 161.0152
Mount=ALAZ Axis offset= 0.0000 meters IFA IFB
Feed polarization type = R L
Ant 24 = VLA:_N9 BX= -298.3837 BY= -46.5620 BZ= 440.6260
Mount=ALAZ Axis offset= 0.0000 meters IFA IFB
Feed polarization type = R L
Ant 25 = VLA:_N6 BX= -148.4545 BY= -23.2162 BZ= 219.9871
Mount=ALAZ Axis offset= 0.0000 meters IFA IFB
Feed polarization type = R L
Ant 26 = VLA:_N4 BX= -74.8318 BY= -11.7331 BZ= 111.6208
Mount=ALAZ Axis offset= 0.0000 meters IFA IFB
Feed polarization type = R L
Ant 27 = VLA:_W6 BX= 93.5170 BY= -245.0012 BZ= -136.2284
Mount=ALAZ Axis offset= 0.0000 meters IFA IFB
Feed polarization type = R L
Ant 28 = VLA:_W4 BX= 46.9220 BY= -122.0267 BZ= -67.6047
Mount=ALAZ Axis offset= 0.0000 meters IFA IFB
Feed polarization type = R L
Ant 29 = VPT:_OUT BX= 0.0000 BY= 0.0000 BZ= 0.0000
Mount=ALAZ Axis offset= 0.0000 meters IFA IFB
Feed polarization type = R L
Location Of VLA Antennas
N9 (24)
N8 (21)
N7 (19)
N6 (25)
N5 (23)
N4 (26)
N3 ( 5)
N2 ( 1)
N1 (20)
( 8) W1 E1 (18)
( 6) W2 E2 ( 9)
( 7) W3 E3 (12)
(28) W4 E4 (16)
(22) W5 E5 ( 2)
(27) W6 E6 ( 4)
(14) W7 E7 (13)
(17) W8 E8 (11)
(15) W9 E9 ( 3)
VLA:_OUT (10)
VPT:_OUT (29)
AIPS 1: Resumes
The really important part for you, the data reducer, is the antenna layout at the bottom. This tells you in a nice graphical form where each antenna is located. This helps you to figure out which baselines are small, and which baselines are long. This is also useful for figuring out other things related to antenna position and baseline direction.
SETJY
task 'setjy'
source '3c286',' '
optype 'calc'
aparm(2)=3
go
vlb054> SETJY1: Task SETJY (release of 31DEC08) begins vlb054> SETJY1: **WARNING: OPCODE=CALC AND FREQID = -1 vlb054> SETJY1: FREQID WILL BE RESET TO 1, CHECK YOUR RESULTS CAREFULLY vlb054> SETJY1: A source model for this calibrator may be available vlb054> SETJY1: Use the verb CALDIR to see if there is one vlb054> SETJY1: / Flux calculated using known spectrum vlb054> SETJY1: BIF = 1 EIF = 1 /Range of IFs vlb054> SETJY1: '3C286 ' IF = 1 FLUX =14.5979 (Jy calcd) vlb054> SETJY1: / Using (1990) VLA or Reynolds (1934-638) coefficients vlb054> SETJY1: Appears to have ended successfully vlb054> SETJY1: vlb054 31DEC08 TST: Cpu= 0.0 Real= 0
CALRD
task 'calrd'
object '3c286'
band 'l'
go
vlb054> CALRD1: Task CALRD (release of 31DEC08) begins vlb054> CALRD1: Reading disk file AIPSTARS:3C286_L.MODEL vlb054> CALRD1: Create 3C286_L .MODEL . 1 (MA) on disk 1 cno 5 vlb054> CALRD1: Appears to have ended successfully vlb054> CALRD1: vlb054 31DEC08 TST: Cpu= 0.0 Real= 0
So it looks like the calibration data image was put into catalog entry number 5.
CALIB
task 'calib'
getn 2
calsour '3c286',' '
uvrange 0
antennas 0
refant 24
weightit 1
in2di 1
get2n 5
ncomp 0
solmode 'A&P'
aparm(6) 2
minamper 10
minphser 10
docalib 1
solint 1
solsub 2
cparm(3) 10
cparm(4) 10