CFHT, Instruments, Spectroscopy, ESPaDOnS

ESPaDOnS: an Echelle SpectroPolarimetric Device
for the Observation of Stars at CFHT

Graphical User Interface (GUI)

ESPaDOnS is controlled via a Graphical User Interface (GUI), with the following buttons (click on a link to access directly the section concerning that button):

In addition to the GUI, there is a Director window with additional information.

Note that only ONE instrument session can be used at the same time.

Top Menu Bar

When the 'espadons' session is started, the Top Menu Bar of the GUI appears at the top of the screen.

The buttons are presented in a logical and somewhat chronological way: one has to start by configuring the instrument and checking its status. Once the instrument is configured and ready, calibrations are taken. When everything is ready for science, the guider and exposure meter are started, and exposures can be taken. At the end of the night, one must click on the End of night button to put the instrument in a sleep (safe) mode.

The 'Engineering' button should not be used by observers unless directed by the Support Astronomer or Observing Assistant.

The sensors button presents the instrument's vitals: temperature, pressure, humidity. The Image Display allows to enable or disable the automatic display of images.

The TCS Info button (Telescope Control System) launches windows with information on telescope position, date and time, focus position, dome status, guiding, etc.

Each window (except the TCS information windows) has a Close Window button to close the window. A window that is 'lost' underneath other windows can be brought to the front by clicking on its button in the Top Menu Bar.

Configure [Back to top]

The Configure button is used at the beginning of every night (even if the mode has not changed) and whenever a change of mode is desired. The configuration consists of defining:

Please note that the readout noise values mentioned above are approximate only.

After the desired modifications have been entered, the user must press the button Apply Changes to configure the instrument; a confirmation pop-up window will appear to make sure this was the correct action requested. If only the Run ID and/or PI name and/or observer name have changed (like in the case where a night is shared among many PIs), the button Change Run ID Only can be used; the instrument will not be touched, saving a couple of minutes. If only the CCD readout mode is to be changed (and nothing is touched in the instrument), then the button Change Readout Mode Only has to be used.

This (re)configuration also creates a new subdirectory for the current night, where all the data will be saved (for example, /data/noeau/espadons/raw/25Jan05/). This is why the configuration has to be done every night, even if the instrument has not be touched: the configuration includes the creation of the necessary directory for the data.

The button Clear Fields may be used to clear all fields before entering values.

After the instrument has been configured, the instrument's focus must be done using the button Autofocus. The Autofocus routine takes 4 exposures, 2 inside focus and 2 outside focus, with the Hartmann mask up or down. The images are analyzed with 2 methods, and the optimal focus value is reported. The camera focus is also adjusted to this new optical focus value. The focus routine must be used only after the dewar has been filled for the night, since this operation may shift the camera focus.

Status [Back to top]

The status window reports the status of the instrument. Any text in red indicates that something is not at the correct position to take science exposures. When a science exposure is requested, all components are automatically moved to get the correct configuration.

The boxes at the very top indicate if the instrument is Idle or Busy, if the detector is Exposing or Reading, etc.

When one of the lamps is turned ON, the status box indicates so, and the icons change to yellow light bulbs. The flat field lamp is actually made of 2 lamps, one with a red filter, the other with a blue filter; the flux of each lamp is indicated in the boxes to the right (RED should be equal to 3, BLUE should be equal to 12).

The Atmospheric Dispersion Corrector (ADC) can be put IN the beam or OUT. The ADC is made of 2 prisms, whose positions are indicated in the 2 boxes at right; these positions are updated every 30 seconds. The parallactic angle and Alpha angles are also displayed. The non-negligible thickness of the ADC means that the telescope focus changes a lot if the ADC is IN the beam or OUT; after moving the ADC (IN or OUT), the star image will look like a big donut, and the telescope must be refocussed (by about 100 'old' units, or about 1.0mm).

The calibration wheel says 'Clear' for science observations, but has diffusers when some lamps are used.

The Neutral Density Filter is used for the guider, and not for the science beam. The setting is indicated in magnitudes, and the position of the variable density filter is also indicated. To the right, the current status of the guider is indicated: Idle, Acquiring, Guiding.

In polarimetric mode, the 2 rhombs are moved to preset positions. The top rhomb can also rotate continuously to measure the Stokes parameter that we call 'W', which is circular polarization with the linear to circular cross-talk eliminated. When this is the case, the box at the far right says 'spinning'.

In polarimetric mode, the Wollaston prism is used, whereas in spectroscopic mode, a wedge is used.

The Fabry-Perot is used for calibrations.

Just before the spectrograph, an agitator agitates the optical fibers to get rid of modal noise. The agitator should be ON for all exposures with light.

The shutter slit allows light to enter into the spectrograph.

The slicer and bench control the number of slices. The dekker is used to select which fiber's light is fed to the spectrograph.

The Hartmann mask is used only when doing the focus of the instrument, when it toggles between the UP and DOWN positions. For all other exposures, the Hartmann mask is OUT.

The camera focus is indicated in mm. This is the focus which is changed when focussing the spectrograph.

The spectrograph has an Exposure Meter with shutter that picks up a few percents of the incoming light and directs it to Avalanche Photodiodes. The Exposure Meter is used in realtime to verify that light is really getting into the spectrograph.

Sensors [Back to top]

Temperature sensors are located in the calibration module (where the lamps are), the polarimeter module, and in 4 locations inside the spectrograph. The spectrograph also has a humidity and a relative pressure sensors. Instant values are given, along with graphs over time.

Calibration [Back to top]

After the instrument is configured and focussed, calibrations must be taken. The Default Settings will prepare the appropriate exposures for the current configuration. A type of exposure can be selected or unselected by clicking on the check box at left. Once an exposure type has been selected, it is possible to change the number of exposures or the exposure times. Once everything is set, all calibrations will be taken after clicking on the button GO.

Guider [Back to top]

The top boxes of the Viewer/Guider Camera window indicate what is the status of the Guider (Idle, Guiding), if the acquisition and guiding are ON or OFF.

The first top section is used to adjust the neutral density filter so the light of the star has an adequate brightness for guiding, and to setup the window size and guiding zone for the guider. The units are arcsec. The window is usually centered (x-cen=y-cen=0), and a typical window size is 20 arcsec. If the sky hole is not used, one might make the window smaller, for example, only 10 arcsec on a side. The guiding zone is also usually centered, and has a radius of 2.0 arcsec. If the seeing is bad, a bigger guiding zone of 2.5 arcsec might work better. By clicking on the Set Defaults button, commonly used default values are entered. Once a change has been made, the button Apply Changes must be used.

After setting the guider, the options in the second section are used. The acquisition mode takes images without moving the telescope (guiding); this mode is used to recognize the field and center the star in the hole. Guiding corrections can be calculated without sending the corrections to the telescope (2d option), or with sending the corrections (i.e., guiding). Each mode is selected with the right check box, and the exposure time can be modified. Once a mode has been selected, it is enabled after clicking on the GO button. Acquisition or guiding are stopped by clicking on the Stop button.

The image produced by the Guiding Camera is presented in a separate window. At the top of this window, the Seeing and Magnitude estimates are presented, along with the telescope corrections calculated. If the star is actually in the hole, the seeing and magnitude estimates will not make much sense since the star is not completely seen. At the top right corner, a status box indicates if Guiding is active or not.

A button Set Guiding Zone can be used to shift the guiding zone from its default location; this is rarely used. The button Center Star is used to center the target into the hole. After clicking on that button, the cursor in the guider display will change to a star icon, which can be positioned over the star (actually, anywhere in the window, since the star is not detected by the algorithm). After clicking on the star, it will be moved in the hole.

The optional graph shows how the magnitude of the star changes with time.

Exposure Meter [Back to top]

The Exposure Meter is used to check in real time if the light of the target is really getting into the spectrograph, and to follow any change in sky conditions (passing clouds for example). The Exposure Meter can be manually turned ON or OFF, and its shutter can be opened or closed. The optional graph shows how the counts vary with time, hence revealing clouds if here are any. The number of counts recorded during an exposure is saved in the FITS files under the keyword EEMCNTS.

Expose [Back to top]

The top boxes of the Expose window give feedback on what is being executed.

The top panel is there for information only, repeating the configuration chosen. This is to ensure the desired configuration has really been configured.

A menu allows to take every type of exposure possible, although usually the calibration exposures are taken through the Calibration form. Therefore, the Exposure Type is usually set to Star.

The Stokes parameter to measure is always 'I' (intensity) in either of the spectroscopic modes. It can be any combination of Q, U, V, or W in the polarimetric mode. Each Stokes parameter (Q, U, V, W) necessitates 4 exposures. Please note that the W mode currently does not work, and does not produce 0% circular polarization when a highly polarized flat field exposure is used as a source of light.

The object name and comment field will be saved in the FITS keywords OBJECT and CMMTOBS. An additional keyword, CMMTSEQ, will automatically track which Stokes parameter is being measured, and which one of the 4 needed exposure is being taken. It is recommended to stay away from special characters! Letters, numbers, plus and minus signs, and white spaces work.

The number of sequences is actually the number of exposures in spectroscopic mode, and the number of sets of 4 exposures for the polarimetric mode. The exposure time entered is in seconds.

Before being able to see the target on the guider display, the button Ready for Science has to be pushed. This will remove from the beam any calibration component that blocks the beam.

At low airmasses, the Atmospheric Dispersion Correction can be used. The non-negligible thickness of the ADC means that the telescope focus changes a lot if the ADC is IN the beam or OUT; after moving the ADC (IN or OUT), the star image will look like a big donut, and the telescope must be refocussed (by about 100 'old' units, or about 1.0mm). Since the ADC does not absorb light or polarize, it is recommended that it be left in the beam for the whole night.

When everything is ready, use the GO button.

The STOP button stops the all the actions that were planned, stops the current exposure, and reads it; the next exposures that were planned are canceled. The BREAK button breaks a sequence of exposures (if the number next to the Sequence box is 2 or higher), stops the current exposure and reads it. When using the STOP and BREAK buttons, expect repeated commands to be sent through director (quit and stop), along with yellow or red error messages, indicating that the exposure was stopped.

Image Display [Back to top]

This window can be used to turn off the automatic display of the images with ds9. A browse button allows one to pick a specific file to display.

TCS info [Back to top]

The TCS Info button (Telescope Control System) launches a menu, from which one can get Telescope information (see image below), dome position information (including position of Sun and Moon, distance between target and Moon, Moon phase, wind direction, target altitude and azimuth), and guiding information (corrections performed by the telescope in arcsec in RA and DEC), by clicking on the Status button of that menu.

End of night [Back to top]

The End of Night button is used to put the instrument into a safe mode after a night of observing, stopping the guiding camera, for example.

Director [Back to top]

In addition to the GUI, there is a Director window which shows:

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This CFHT Web page is maintained by Nadine Manset (manset -=AT=-