DEIMOS TVANGLE Adjustment Procedure

Background

Accurate moves on the DEIMOS guider require that the DCS keyword TVANGL is set to the correct value. Although KSD 40 specifies that the value of TVANGL should be either 0 or 180, precedent exists for adjusting this value in order to set the guider angle correctly. This document describes how to measure and adjust the angle.

Requirements

DEIMOS on-sky
MAGIQ guider software running
SKYMAP software running (launch via ssh k2obs@k2server skymap)

Procedure

Acquire star field. Point DEIMOS to a region with a moderate density of stars visible on the guider. A total of 10 stars or more is ideal for determining the solution.
Save guider image. On the MAGIQ GUI, right-click on the image area and select Save as FITS to save the current guider image to the nightly directory.
Analyze guider image. Load and analyze the image using the SKYMAP GUI as follows:
- Ensure that the source is set to From FITS
- Click on Load FITS and select the image to analyze (the browse function should default to the current nightly directory). SKYMAP should load the FITS image and the corresponding DSS image, and identify stars in both images.
- Remove bogus stars in the guider image (at left) by either using the Less Stars/More Stars slider to restrict the brightness range, or by left-clicking on individual targets in the image to remove them.
- Click and drag on the right-hand side image to align the red markers (stars from DEIMOS guider image) with the green stars (stars from catalog).
- Click on Calc Delta to compute the offset in angle, which is displayed in the lower left corner as angle.
Update guider parameters.
- Log into k2-magiq-server as user magiq.
- Edit file /kroot/magiq/default/configData/KECK2/Cameras/deimos.xml.
- Modify the line for tvAngl, subtracting the angle value derived from SKYMAP from the value currently on that line.
- Save the modified version of deimos.xml.
- Have the OA kill and restart MAGIQ server (not the GUI), thus triggering the software to re-read the guider parameters.
Repeat as needed. Acquire a new image and check the angle as described above to obtain a new value of angle, which should be close to zero. Repeat above steps until values converge to zero.

Note

This procedure will only modify the MAGIQ guider parameters. It will not change the corresponding DCS keyword TVANGL, the value of which can be shown using
```
	show -s dcs tvangl
```

Figures

Skymap GUI

	DEIMOS TVANGLE Adjustment Procedure
DEIMOS Home Page NEWS Config form Slitmask database DEIMOS temps (internal) Index Keck Instrument Ready? Archive (KOA) Observer Home Page Tel Schedule Instruments Home Keck Home Observing Info ToO Policies Weather MK Forecast CFHT SkyProbe MK Seeing CFHT Cloudcam Summit Cams Keck Cloud Cams Planning Tools Starlist Tool Finding Charts IRSA Finder Charts Observing Planning Tool Offset/PA Tool Contact Us Contact Info Post-Observing Comment Form WWW Keck Web Site	Background Accurate moves on the DEIMOS guider require that the DCS keyword `TVANGL` is set to the correct value. Although KSD 40 specifies that the value of `TVANGL` should be either 0 or 180, precedent exists for adjusting this value in order to set the guider angle correctly. This document describes how to measure and adjust the angle. Requirements DEIMOS on-sky MAGIQ guider software running SKYMAP software running (launch via `ssh k2obs@k2server skymap`) Procedure Acquire star field. Point DEIMOS to a region with a moderate density of stars visible on the guider. A total of 10 stars or more is ideal for determining the solution. Save guider image. On the MAGIQ GUI, right-click on the image area and select `Save as FITS` to save the current guider image to the nightly directory. Analyze guider image. Load and analyze the image using the SKYMAP GUI as follows: Ensure that the source is set to `From FITS` Click on `Load FITS` and select the image to analyze (the browse function should default to the current nightly directory). SKYMAP should load the FITS image and the corresponding DSS image, and identify stars in both images. Remove bogus stars in the guider image (at left) by either using the `Less Stars/More Stars` slider to restrict the brightness range, or by left-clicking on individual targets in the image to remove them. Click and drag on the right-hand side image to align the red markers (stars from DEIMOS guider image) with the green stars (stars from catalog). Click on `Calc Delta` to compute the offset in angle, which is displayed in the lower left corner as `angle`. Update guider parameters. Log into `k2-magiq-server` as user `magiq`. Edit file `/kroot/magiq/default/configData/KECK2/Cameras/deimos.xml`. Modify the line for `tvAngl`, subtracting the `angle` value derived from SKYMAP from the value currently on that line. Save the modified version of `deimos.xml`. Have the OA kill and restart MAGIQ server (not the GUI), thus triggering the software to re-read the guider parameters. Repeat as needed. Acquire a new image and check the angle as described above to obtain a new value of `angle`, which should be close to zero. Repeat above steps until values converge to zero. Note This procedure will only modify the MAGIQ guider parameters. It will not change the corresponding DCS keyword `TVANGL`, the value of which can be shown using show -s dcs tvangl Figures Skymap GUI
Last modified: 07/10/2020 05:20 Send questions or comments to:DEIMOS Support