--> Observation Preparation | Gemini Observatory

Change page style: 

Observation Preparation

You are here

Observations with the TEXES instrument are taken somewhat differently than those of the regular Gemini instruments. The OT setup for TEXES observations are relatively simple and are used only for two purposes: first, they define the target and the guide star; second, they indicate various basic items of the TEXES configuration (cross-disperser, total requested length of the observation, slit orientation, and central wavelength).

This page guides you through the main steps and considerations for configuring TEXES observations in the Observing Tool:

Refer to the TEXES instrument pages for further details of the instrument capabilities. Example TEXES observations can be found in the OT library.

Further details on general (non-TEXES-specific) OT components can be found on the general OT web pages where an OT tutorial is also available.

TEXES Component

The detailed component editor for TEXES is accessed in the usual manner, by selecting the TEXES component in the science program editor as shown below:

TEXES component


There is a choice of four disperser combinations to be used with TEXES. These determine the spectral resolution at any wavelength as well as the slit length. Please see the TEXES configuration table for details:

  • Echelon + 32 l/mm echelle
  • Echelon + 75 l/mm grating
  • 32 l/mm echelle
  • 75 l/mm grating

Note that the slit dimensions illustrated in the Position Editor are wrong for some configurations. Please refer to the TEXES configuration table for the correct slit sizes.

Observation time

The total time to be spent observing the target object should be defined. The details about how this total exposure time will be achieved are determined at the telescope depending on the conditions, and need not be of concern to the PI. The PI only defines the total on-source time.

The PI also need not worry about defining the intervals for nodding along the slit in the normal spectroscopy mode. This also will be determined at the telescope by the TEXES team.

While there is a field for the number of exposures per observation, this also is not normally set by the PI and should be left as 1. The total exposure time (for example 1800 seconds as above) should be entered with 1 exposure.


The central wavelength for the observation needs to be set for each observation. There is no iterator component for TEXES, if you need many wavelengths for a given target then you can either define separate observations for each wavelength (if the individual observations are fairly long) or list the wavelengths in a note in the program (where the individual observations are short). In the latter case then please indicate the total observation time for all wavelengths in the requested exposure time.

Position angle

The facility Cassegrain Rotator can rotate the instrument to any desired angle. The angle (in conventional astronomical notation of degrees east of north) is set by typing in the "position angle" field. The view of the science field in the position editor will reflect the selected angle. Alternatively the angle may be set or adjusted in the position editor itself by interactively rotating the science field.

Guide Stars

The science target will be imported from the Phase-I proposal, and will be automatically set when the observation templates are applied. Each TEXES observation must have a peripheral wavefront sensor (PWFS) guide star defined. The OT will automatically initiate a UCAC4 guide star query and place the brightest allowed guide star in an Auto guide group. The Position Editor may be used to check for bad guide stars (double, resolved, an artifact around a bright star, etc), in which case the "Manual GS" button should be used to to open the Catalog Query Tool and select a manual guide star.

It is generally useful to indicate the target brightness near the wavelength of interest to aid in acquisition of the correct object.

The target tab

Gemini Observatory Participants