tweak5 Script


This page is part of the ING manual WHT-INGRID-2: INGRID IMPB Software Operations Manual


 
Usage: tweak5 int_time num_coavgs tcs_x_offset tcs_y_offset ["title"]
 
Category: Observing System Scripts
 
Description: The intention of this script is to move the telescope in a 5 point dither pattern, taking exposures at each point, whilst simultaneously autoguiding. Autoguiding is important on long exposures to ensure that the images remains sharp, and to reduce the number of processing steps during data reduction.

This command is identical to dither5 with the following exceptions:

  • the telescope is sent  tweak commands to perform its movements instead of offset. 
  • the output files have their OBJECT headers set to "T-1/5: <title>" where title is an optional argument which may be specified by the user.
The tweak5 scripts moves the telescope in the following pattern:
 
tweak5
    2                5 
1
    3                4 

The numbers in the table above indicate the positions at which the data acquisition cycles occur. As can be seen the normal movement is anti-clockwise.  The telescope always starts and ends at the centre of the pattern.

Internally, the script performs data acquisition by means of the ISP run command.  Thus, the observational data files which are generated have run numbers allocated in the normal way. The number of reads in the MNDR cycle may be modified using the numreads commands.

The geometry of the dither pattern is defined by the tcs_x_offset and tcs_y_offset arguments. It is possible to supply negative values, in which case the sequence of moves will be reflected  about the corresponding axis.
 
Arguments: int_time is the MNDR integration time specified in seconds to the nearest millisecond. The minimum integration time is determined by the speed with which the SDSU Controller can scan the Hawaii detector array (typically about 1.2 seconds).

num_coavgs specifies the number of coaverages in the observation sequence. num_coavgs should be a positive integer in the range 1 to 99. 

tcs_x_offset  specifies the geometry of the dither pattern in the telescope x axis. The offset is specified in arcseconds in terms of the distance from the centre of the pattern to the outlying points.

tcs_y_offset  specifies the geometry of the dither pattern in the telescope y axis. The offset is specified in arcseconds in terms of the distance from the centre of the pattern to the outlying points.

title is optional, but if specified provides additional information which is recorded in the FITS headers. The title string should be less than 11 characters and should be supplied in double quotes if more than one word.
 
Examples: tweak5 20 4 15 15 test17 - perform a 5 point dithered observation  using the telescope tweak command. The geometry of the dither pattern in x/y axes will be 15 x 15. At each point where the telescope stops a run will be taken with 20 second integration time and four coaverages.