DECal is a spectrophotometric calibration system that will be implemented as part of the DES DECam project at the Blanco 4 meter at CTIO. The system uses a 2nm wide tunable source to measure the instrumental response function of the telescope from 300nm up to 1100nm. This calibration will be performed regularly to monitor any change in the transmission function. The system consists of a monochromator based tunable light source that provides illumination on a dome flat that is monitored by calibrated photodiodes and allow us to measure the throughput as a function of wavelength. Our system has an output power of 2 mW, equivalent to a flux of approximately 800 photons/s/pixel on DECam. We successfully deployed a prototype of this system at the Swope and DuPont telescopes at Las Campanas Observatory. This provided data to help reduce the systematic error budget of the Carnegie Supernova Project.

DECal Layout
Layout for the DES Calibration Project
DECal Screen
J-P Rheault working on the screen for DECal

This will be an upgrade to the current screen at the Blanco telescope. It is coated with a highly reflective, highly dispersive (Lambertian) coating, and is important for side illumination. The screen was shipped to Chile in Summer 2011, and was installed in October 2011.

DECal fiber
Fiber bundle for the DECal system

This custom made fiber bundle from Fibertech Optica will be fed into 4 modules spread evenly around the top ring of the telescope. The light from the fibers will then be evenly projected onto the flat field screen.

J-P Rheault and Steven Villanueva working on the DECal electronics
Prototype results
An example of the prototype results from the Carnegie Supernova Project
Second photometry release

For more information, please see our Publications page.