aTmCam Prototype











After using a concept testing system to demonstrate that brightness measurements of stars at a few wavelengths can be used to derive a model for the transmission of the atmosphere, we built a prototype version of aTmCam and have used the prototype at Cerro Tololo Inter-American Observatory (CTIO) for ~40 nights of observing in Oct-Nov 2012 and Sept-Oct 2013 to determined the angular and temporal scale of meaningful changes in the atmosphere.

The aTmCam prototype consists of four Celestron f/10 8-inch telescopes mounted on two Celestron CGEM mounts. Each telescope is fitted with an SBIG ST-8300M CCD and a filter centered near a part of the spectrum sensitive to a particular component of the atmospheric throughput, with a different filter in each telescope. The figure below shows a photograph of (half of) the prototype being deployed at CTIO in October 2012.

Image 5 We have derived the precipitable water vapor (PWV) and aerosol optical depth (AOD) from the measured color of the stars using the aTmCam Prototype. We achieve a precision of ~0.6 mm of PWV and ~0.03 in AOD. We see that the precipitable water vapor can change over one night, while aerosol optical depths are generally quite stable. During our observing runs, we conclude that we need to measure the PWV only once per hour if we require PWV estimates accurate to 1mm. We also observe no significant PWV variation over an angle of ~90 degrees on the sky.

Read more about the aTmCam Prototype
  • SPIE 2014 Conference Preceeding
  • SPIE 2014 Poster


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