aTmCam for DES/CTIO

After the success with the aTmCam prototype, we built and deployed a final version of aTmCam at CTIO for Dark Energy Survey (DES). It is designed to enable the improved photometric calibration of data acquired by the Dark Energy Camera (DECam) at the CTIO 4m Blanco telescope.

aTmCam is installed on the concrete pad formerly used by the "El Enano" dome. The aTmCam installation consists of a 7-foot (2.1m) diameter Astro Haven dome, a Paramount MX+ commercial telescope mount and pier, four SBIG CCDs, and four photographic camera lenses that serve as telescopes. A photograph of the final system is shown below (Credit: Brian Nord, Fermilab).

Image 6

The principle is similar to the prototype; each CCD is coupled with a narrow-band filter that monitors the brightness of suitable standard stars throughout the night. Each narrowband filter is selected to monitor a different wavelength region of the atmospheric transmission, including regions dominated by the precipitable water vapor and aerosol optical depth. (see the figure below for the wavelength we selected.)

Image 7

The aTmCam system runs semi-autonomously. The scripted observations will be automatically initiated at the beginning of each night; the only interaction with the system from on-site personnel will be to open the dome at the beginning of the night and to close the dome at the end of the night and in case of bad weather by the telescope operators at the CTIO 4m Blanco telescope. We derive hourly atmospheric transmission models from the observations; these atmospheric transmission models will be used for the photometric calibration of Dark Energy Survey and achieve ~0.01 mag photometric precision.

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Astronomy Group
4242 TAMU
College Station, TX 77843-4242
Ph: (979) 845 7717
Texas A&M University - College of Science