CanariCam Upgrade

 

Due to the installation of EMIR on the GTC Nasmyth A focus were CanariCam was originally located, the instrument was dismounted and went through a series of improvements. Among other things, the old cooling sistem was replaced with a new one. Then, on December 2019, the instrument was relocated to one of the 4 folded Cassegrain foci available at GTC (folded Cassegrain E). From the user point of view, the instrument remains unchanged and the expected performances should remain the same. The format of the fits files is as before, thus if you have your own reduction scripts they should still work. Differences, if any, could be expected only in polarimetry mode, because in the new focus the pupil position with respect to the detector has changed.

Canaricam on Folded Cassegrain focus Canaricam on Folded Cassegrain focus
Canaricam on its new position on Folded Cassegrain focus E at GTC.

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icon Instrumental Sensitivity

The instrument global performance and sensitivity remain unchanged. Details on the IQ and chopping-nodding behaviour can be found here, while imaging/spectroscopy sensitivities are identical to the ones previously achieved, already listed here (see also Figure below).

Canaricam instrumental sensitivity
Canaricam instrumental sensitivity in spectroscopy mode as measured at Nasmyth focus. In the new focal station no changes are expected.

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icon Istrumental polarization

A number of stars were observed on the night of 5th and 6th March 2020, in order to measure the level of instrument polarization and its position angle (PA). Standard chop-nod images in Si4-10.3 filter were obtained. From the analysis of these data it was found that the level of instrumental polarization is fully consistent with the pre-upgrade value of around 0.8 percent, which is a good confirmation that the global performances of the instrument did not changed.

Canaricam instrumental polarization
Canaricam instrumental polarization as measured in a series of images of Pollux (red points) and Sirius. The average value is fully consistent with the value measures before the instrument upgrade. The dashed line indiicated the 0.8% polarization level.

The polarization position angle, as expecteed, did change because most of the instrumental polarization is due to the 90 degrees reflection on M3, and on its new position on the folded Cassegrain focus the instrument "sees" M3 from a different orientation. The advantage of the current configuration is that now the instrument-M3 relative position never change (at the Nasmyth focus it did change with elevation). Actual measurements give the following simple relation for the instrumental polarization position angle (from detector Y direction):



PA = 60.4 – RMA

where RMA is the instrument rotator position (FITS header keywords ROTATOR1 and ROTATOR2). This is consistent with the old value of PA=-(RMA+Elevation)-29.6, because now M3 is always seen as when elevation was equal to 90 degrees, and the instrument has been mounted upside down, adding a 180 degrees term. Thus setting elevation=90 degrees and adding 180 the old relation transforms to PA=-(RMA+90)-29.6+180= 60.4-RMA.

Canaricam instrumental polarization Position Angle at folded Cassegrain focus

Canaricam instrumental polarization position angle at folded cassegrain focus. Compared to the previous situation, now the dependence on elevation disappeared and the polarization position angle only change according to the rotator position angle RMA. In this figure the old data from Nasmyth focus have been transformed setting elevation = 90 and adding 180 because the instrument is now mounted upside down. The five big stars represent the measurements obtained during the last commissioning run (March 2020). The line is the relation PA = 60.4-RMA.

In the next Figure an example of spectropolarimetry observation of the non polarized standard star HD31767 is shown. The intensity of the instrumental polarization is found at around 0.5%, consistent with what is observed in imaging mode. The polarization position angle is also around 60 degrees, again consistent with imaging mode.

Canaricam instrumental polarization in spectropolarimetry
Spectropolarimetry obsservation of the non polarized standard star HD31767. Both intensity and position angle of the instrumental polarization are consistent with results obtained in imaging mode.

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icon Canaricam contact persons at GTC

 

contact email @ gtc.iac.es
Riccardo Scarpa - main contact riccardo.scarpa
Daniel Reverte daniel.reverte

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icon Useful Documents

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icon More Information

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icon Acknowledgements

We thanks Chris Wright, Chris Packham, Enrique López, Frank Varosi, and the UF team for the huge help provided during the whole process of upgrade of CanariCam.

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Last modified: 14 May 2020

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