Rotang - IDL procedure for calculating the optimum rotation angle for ALFA

Rotang can either be run from the command line as described here or through the alfa_ang GUI. This documentation covers the basic options that a user will normally require, the detailed documentation contains a description of other parameters not covered here, including the output parameters, and of the minimisation algorithm.

To run rotang at Arecibo:

  1. Start IDL
  2. If you are not using the AGES account, you will need to setup IDL with the following commands:
    IDL> @phil
    IDL> @corinit
    IDL> addpath,'/share/ages/IDLSTUFF'
  3. Run Rotang:
    IDL> rotang,Date,RA,Dec,Time,/choice

Here Date takes the format YYMMDD (e.g. 041128 for the 28th of November, 2004). RA takes the format HHMMSS (e.g. 093210 for 09:32:10) and is in J2000 coordinates. Dec takes the format DDMMSS (eg 212003 for 21:20:03) and is in J2000 coordinates. Time takes the format HHMMSS (e.g. 063000 for 06:30, or -003000 for -0.5 hours). /choice is one of /ha (for Hour Angle), /lst (for Local Sideral Time) or /ast (for Atlantic Standard Time) and defines what Time refers to, e.g. rotang,041128,093210,212003,063000,/ast is asking for the best angle at 06:30 AST on 04-11-28 while rotang,041128,093210,212003,-003000,/ha is asking for the best angle at an hour angle of -0.5 hrs on the same day, and rotang,041128,093210,212003,090000,/lst is asking for the best angle at 09:00 LST.

Rotang also calculates the Azimuth and Zenith Angle fir every source. If the Zenith Angle is greater than 20 degrees, then the program will return that the source is down and will not calculate an optimum ALFA angle. If the source is above 20 degrees, it will return the optimum angle and the mean beam separation that this angle will give as well as full positional information for all of the seven beams, as shown below:

Date (YYMMDD):        41128
      jd          LST        AST        HA        az      za      angle   sep
 2453337.937   10:33:38    6:30: 0   + 1: 1:11   103.92   14.69    -81.2   1.80

Beam    dAz     dZA     AZ       ZA        RA         Dec      dRA        dDec
  0     0.0     0.0   103.925    14.692     9.536    21.334     0.00     0.00
  1  -306.8  -138.9   104.260    14.730     9.534    21.424    -6.32     5.41
  2   -50.3  -379.5   103.979    14.797     9.529    21.364   -26.24     1.80
  3   256.4  -240.6   103.645    14.759     9.531    21.274   -19.81    -3.61
  4   306.8   138.9   103.588    14.653     9.538    21.244     6.43    -5.42
  5    50.3   379.5   103.869    14.586     9.543    21.304    26.23    -1.81
  6  -256.4   240.6   104.207    14.625     9.542    21.394    19.92     3.60

Rotang was written by Robert Minchin and incorporates code from Phil Perilat and from the Cornell EGG. It relies on the aoidl routines written by Phil Perilat.

Original page written by Robert Minchin, 19th November 2004. Last modified 22nd November 2004 by Robert Minchin.