Sky Brightness \& Acoustic Soundings, Mt.Evans Observatory
Session 10 -- Remote Observing, Ground-Based Telescopes and Instruments
Display presentation, Monday, 9, 1995, 9:20am - 6:30pm

## [10.04] Sky Brightness \& Acoustic Soundings, Mt.Evans Observatory

R.E.Stencel, M.A.Dahm, M.Jalakas and D.Klebe (U.Denver Obs.), G.Emerson (Emerson Enterprises), C.Butenhoff and R.D.Gehrz (Astronomy, U.Minnesota)

As a part of the site survey for future telescope construction at the Mt. Evans Womble Observatory, Colorado [elev.4,303 meters], sky brightness and acoustic sounding measurements are underway. V band CCD observations of the photometrically calibrated cluster, NGC 7790 (Odewahn et al, 1992 PASP) were obtained during 1994 Aug/Sept. These measurements were then compared to a new sky brightness model, based on methods developed by Garstang (1989, 1991 PASP), which agreed with other observatory numbers and predicted a zenith sky brightness for Mt.Evans of 21.65 magnitudes/arcsec$^2$. The CCD data, taken during a period marked by forest fires in the Western U.S. indicate a near-zenith sky brightness observed of no brighter than 19.5 mag/arcsec$^2$. We plan to obtain additional observations to determine whether seasonal differences occur. Acoustic sounding observations of airflow over the Observatory were obtained during 1994 Sept, using the method outlined by Forbes et al. (1985 Apr. SPIE Symposium 551-34), as applied at Mauna Kea and other sites. Mt.Evans values for the atmospheric refractive index structure parameter, C$_n^2$, were found to be of order 10$^{-16}$ to 10$^{-18}$ m$^{-2/3}$. These values are indicative of an atmospheric correlation length of a few meters, and a long exposure seeing disk of $\theta_{FWHM}^V <$ 1 arcsec. Concurrent, in-dome seeing tests with the antique 0.6m Ealing-Beck R-C on site, indicate times of sub-arcsecond seeing, but further statistics are being developed. At the time of this writing, negotiations with the US Forest Service for permission to build a 4 meter class optical-IR telescope are proceeding well, and we would like to contact additional potential collaborators for said project. We are please to acknowledge the help of Fred Forbes (NOAO), the Radian Corp. and William Herschel Womble for assistance with the acoustic soundings.