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OATS-DAUT SEMINAR
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Speaker: Mike Bessell (Research School of A & A; The Australian Nation Univ.)

Title: Problems in Realisation of the Stromgren Photometric System and the new SKYMAPPER survey of the southern skies

Date: Wednesday, September 6th, 2006
Time: 12:00 noon
Venue: Villa Bazzoni

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Abstract:
In the 1950s much stellar work involved qualitative photographic spectral-types and often imprecise broad-band UBV photometry based on poorly defined historical wave bands. In the 1950s Stromgren introduced a 6 filter system to measure two parameters, H beta and the Balmer Jump in B, A and F stars. He later extended this to the uvby beta system using one glass filter and 6 interference filters and a 1P21 photomultiplier tube. The system has since been extended by others to include white dwarfs, K giants and dwarfs and FGK super-giants but severe and often little understood problems have occurred in the standardization owing to differences in passbands (especially the v filter) and to the restricted color and spectral type range of the original standards. Ironically, a narrow band system devised to overcome perceived limitations in the precision of broad-band photometric systems has resulted in poorly standardized photometry due to the great sensitivity of uvby photometry to the exact position of the passbands. The best current system is that of Olsen, Schuster and coworkers who use spectrometer defined bands. I will discuss this system compared to the original filter system and the complications and uncertainties associated with trying to realize the passbands of the Standard System in order to compute synthetic photometry. Finally, I will outline the new SKYMAPPER project, (http://www.mso.anu.edu.au/skymapper/index.php) which is a 1.35m telescope with an 8-sq degree field of view located at Siding Spring Observatory. It will have an integrated 16kx16k CCD mosaic with 0.5'' pixels covering 5.7-sq degrees and will be fully automated. It will conduct a multi-colour (6), multi-epoch (6) survey of the southern hemisphere known as the Stromlo Southern Sky Survey and commence in mid-2007. It should take 5 years to complete. It will reach to 22 mag and have a precision of 0.02-0.03 mag. Its photometric system will use the Stromgren u and the DDO38 violet band together with the SDSS griz bands. These bands are very well suited for stellar work being capable of providing precise temperatures, gravities and abundances for a wide range of stars. We anticipate being able to identify halo stars with metallicities below -3.5 dex and will use the Munari, Sordo, Castelli and Zwitter fluxes and Cassisi isochrones for calibration. ***********************************************************