Offset Guider Command Reference

• Telescope Control Commands
• Offset Guider Control
• Miscellaneous Commands
• Summary of Guide Commands
• Tricks

Telescope Control Commands

Note that this page refers to MIRELLA commands that either control the telescope or move the r-theta guider arm.

There are many mirella commands to move the telescope by small amounts. Of these the [float1] [float2] mtg command (see item 9 below) is the most useful. Some of the commands are not used with SpectroCam (the ones that refer to the ``Peritek'', for example). Except for en all of these commands that take parameters expect a float, but will take an integer from the integer stack if one is available, and the float stack is empty. Command en will not accept integers.

1. [float] e - Moves telescope [float] arcseconds east.

2. [float] n - Moves telescope [float] arcseconds north.

3. [float] s - Moves telescope [float] arcseconds south.

4. [float] w - Moves telescope [float] arcseconds west.

5. [float1] [float2] en - Moves telescope [float1] arcsecond east (RA) and [float2] arcseconds north (Dec). Negative values move south and west.

6. [float] mrates - Set rate for telescope motion moves in arcseconds/sec.

7. mtg01 - Moves the telescope so that the object under cursor 0 on the peritek will be displaced to the position of cursor 1. The autoguider is displaced so as to still track the same guide star. If either cursor 0 or cursor 1 is off, this command will not work.

8. mt01 - Moves the telescope so that the object under cursor 0 on the peritek will be displaced to the position of cursor 1. The autoguider is not adjusted. If either cursor 0 or cursor 1 is off, this command will not work. Be sure you want this command and not mtg01. This command should only be used when the autoguider is not in use.

9. [float1] [float2] mtg - Moves the telescope east by float1 and north by float2. The autoguider is moved to compensate for this shift in telescope position. The autoguider will continue to track the same guide star.

10. telstat - Reads and displays current telescope data.

11. telwait - Waits for telescope to complete a move before executing another command. Actually only waits for set motion motors to halt. The telescope may still be oscillating at that time, especially for large motions, so the sleep command should be used after telwait for best results.

Offset Guider Control

Remember, these commands control the guider arm, not the actual guiding parameters. If you are using the Shepher Autoguider, guiding parameters are controlled from the Shepherd Autoguider GUI. If you are using the Tip-Tilt Autoguider, guiding parameters are controlled from the MINC terminal located next to the SAM terminal, to the left of your Spectrocam 10 workstation.

All values required by commands in this section can be given as either float or integer, unless specified otherwise, in which case the restriction to only integer or float will be clearly made.

Note that the field of view of the offset guider guidehead is approx 15'', and one can move the head up to 220'' radially from the center of the camera field. The guidehead will start to vignette the camera field of view if placed at a distance less than 30'' from the center of the camera field. All position angles are measured E from N. and x are positive to the East, and and y are positive to the North.

1. ogs - shows parameters for the next position the guider has been programmed to move to, but does not move the guider. The guider remains at its current position.

2. og - moves guider to the previously programmed next position, and displays new guider position and associated parameters.

3. ogs [chr] [parm string] - Specifies a guider function and associated values to be assumed by that parameter when the guider is next moved. Does not move the guider. Thus, it is helpful to think of ogs [chr] [parm string] commands as a means of specifying the next guider position, without moving the guider from its current position. Typing og will execute the command.

4. og [chr] [parm string] - Specifies a guider function and associated values and moves the guider. The new guider position and associated parameters are displayed after the guider has been moved. Thus, it is helpful to think of og [chr] [parm string] commands as a means of specifying a new (or next) guider position, and simultaneously moving the guider from its current position to that new position. Note that this command is equivalent to ogs [chr] [parm string] followed by og.

   The following parameters are used in the above ogs and og guider commands in place of [chr]:

   c [] [] - Celestial coordinates to offset from current guider zero in RA (sec) and DEC (''). This is useful when the (RA,DEC) of an offset guide star are known along with the position of the target source.

   d - Differential refraction angle in arcseconds given as the difference in R_0 at sea level (see Allen 1973 for definition of R_0). Note: the guider head effective wavelength is ~ 0.65 um; R_0 (0.65 um) - R_0 (2.2 um) = 0''.6; R_0 (0.65 um) - R_0 (10 um) = 0''.8.

   i [u] [v] - Increment position from current guider position by (u,v) in units of last value of r or c.

   o [r] [] - Offset the origin of the guider co-ordinates to the base plate coordinates (r,). r is in arcseconds, and is in degrees.

   r [x] [y] - Rectangular coordinates from current guider offset origin in x(RA), y(DEC). Units are arcseconds, where positive values are East and North from zero to the offset position. For example, if the target is at zero and offset guide star is at 60''E, 60''N, then r 60 60 will move the guide head to the guide star.

5. /a - og r -.001 0 - Sets the offset guider to the absolute setting of (-0.001,0), but only when og d 0 and og o 0 have been executed so that there is no offset and no differential refraction correction.

6. /b - og r +.001 0 - Sets the offset guider to the absolute setting of (+0.001,0), but only when og d 0 and og o 0 have been executed so that there is no offset and no differential refraction correction.

7. ogc [x] [y] - Using current telescope base plate ring angle, calculates guider coordinates (r,), which are equivalent to the specified (x,y), where (x,y) are in rectangular coordinates on the sky, measured in arcseconds from the current offset-guider zero position, and (r,) are polar co-ords on the baseplate, measured from the center of the baseplate. (r,) are used with the og o and ogs o commands to translate the origin of the co-ordinates in the base-plate.

8. ring [] - sets Cassegrain ring angle in software to value in degrees. If a value for is not specified, the current ring angle is displayed, after attempting to update the current ring angle by interrogating the telescope control computer. If a value for is specified, the current value for ring is set to that value. An attempt is then made to update the current ring angle by interrogating the telescope control computer. The current ring angle is then displayed. Thus, the software value of ring will always reflect the value returned by the telescope control computer, unless the link to the telescope control computer is unavailable. Under such circumstance, the current ring value is the last manually entered value. This enables the guider to be used even when the telescope control is not available for interrogation.

   WARNING: If you manually move the Cassegrain ring (from the Cass. cage, for example), it is necessary to use the ring command immediately, as Mirella will not know the new value until you do.

9. agon - Turns autoguiding on (if unlocked). This is the startup default value.

10. agoff - Turns autoguiding off (if unlocked). Good for pausing the guider without resetting (flattening) the tip-tilt mirror.

11. agl - Lock the autoguider in the current state.

12. agu - Unlock the autoguider.

Miscellaneous Commands

1. abam - Abort from motor timeout.

2. poff - Turn off photometry info on VT100 screen.

3. pon - Turn on photometry info on VT100 screen.

4. refresh - Refresh VT100 screen.

Summary of Guide Commands

1. og - Move the guider to the position specified in the last ogs command.

2. og i [x] [y] - Increment offset guider by x (RA) and y (DEC).

3. og r [x] [y] - set offset guider to absolute position (x,y) (RA,DEC).

4. og c [r] [] - set offset guider to absolute position (r,).

5. og d [dra] - set differential refraction angle in arcseconds given as the difference in R_0 at sea level (see Allen 1973 for definition of R_0). Note: the guider head effective wavelength is ~ 0.65 um ; R_0 (0.65 um) - R_0 (2.2 um) = 0'' .6; R_0 (0.65 um) - R_0 (10 um) = 0'' .8.

6. og o [r] [] - offset the origin of the guider co-ordinates to the baseplate coordinates (r,). r is in arcseconds, and is in degrees.

7. ogc [ddec] [dra] - calculate offset guider polar coordinates r and from ddec and dra using ring position.

8. ogs - shows parameters for the next position the guider has been programmed to move to, but does not move the guider. The guider remains at its current position.

9. ogs i [x] [y] - same as og i [x] [y] but does not move the guider.

10. ogs r [x] [y] - same as og r [x] [y], but does not move the guider.

11. ogs c [r] [] - same as og c [r] [] but does not move the guider.

12. ogs d [dra] - same as og d [dra] but does not move the guider.

13. ogs o [r] [] - same as og o [r] [] but does not move the guider.

14. [X] [Y] mtg - moves the telescope by X,Y and the guider the other way. NOTE: X and Y must be in floating point format.

Tricks

If you have been doing several mtg-s and have lost track of the current offset (r and d), type

og i [] [] (incrementally offset by and ).

This will show the current head position x = RA'' and y = Dec''.