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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.
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