Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21544109t&link_type=abstract
American Astronomical Society, AAS Meeting #215, #441.09; Bulletin of the American Astronomical Society, Vol. 42, p.402
Astronomy and Astrophysics
Astrophysics
Scientific paper
The Measurement Astrophysics group at UNM designed and built a novel microthermal device for characterizing atmospheric optical turbulence at astronomical observatories. This instrument is based on a Wheatstone bridge circuit and uses fine tungsten filaments as resistance temperature detectors. The device makes differential temperature measurements which are directly related to the index of refraction structure constant, Cn2, which quantifies the strength of optical turbulence.
The device is designed to work in two modes. In horizontal mode temperature differentials are measured between adjacent sensors. Measurements are combined to recover the differences over all pairwise sensor baselines. These measurements result in a spatial spectrum of turbulence. Measured turbulent spectra are then fit to standard turbulence models which yield estimates of the outer scale of turbulence and the slope of the power spectra. In vertical mode the device operates with pairs of microthermal sensors distributed vertically, each pair being separated horizontally by approximately one meter. Sensor pairs are suspended at multiple heights above the ground allowing measurement of atmospheric turbulence power as a function of altitude.
This device was used to monitor optical turbulence during a site testing campaign at the future LSST site on Cerro Pachón. We present preliminary results from operation in both vertical and horizontal modes from October 2008 to December 2009. The microthermal array remains in operation on Cerro Pachón, and continues to produce valuable atmospheric measurements.
Our results support the conclusion that Cerro Pachón is an excellent observatory site. The vertical turbulence profile decreases monotonically with height as expected, and the surface layer does not contribute a significant amount to the overall seeing measured at the site.
This work was supported by Air Force Grant No. FA9451-04-2-0355. Instrumentation and travel support was provided in part by the LSST Corporation under NSF Grant 0421087.
Andrew John
Claver Charles
Krabbendam Victor
McGraw Jason
Turner Jonathan
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