Wide Field Camera 3
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Posted by Peter Linde and Arde Ardeberg on July 06, 1999 at 10:26:50:


From: Peter Linde 
Message-Id: <199907051957.VAA16716@nastol.astro.lu.se>
Subject: Comments on WF3 uvby filters
To: lupie@stsci.edu
Date: Mon, 5 Jul 1999 21:57:20 +0200 (METDST)


Dear Olivia Lupie,


Here follows our  comments on necessary filters for the WF3:



What types of science do you envision doing with the WFC3?

Answer:   With the HST, its WFPC2 and uvby photometry, we have just 
successfully completed a study of star formation history and chemical 
evolution based on (Me/H) and age data for individual stars in the dense 
core of the LMC Bar. Down to V=22, we obtain (Me/H) data for 
individual stars with an accuracy of better than 0.2 dex. Differential 
age data are accurate to better than 25 %. Together, these data permit 
tracing of galactic evolution of the LMC Bar over the latest 10 billion 
years. We feel that for our understanding of galactic evolution such 
data are badly needed for a reasonable sample of galaxies.

We envision a continuation of our studies of galactic evolution in other 
galaxies in the vicinity of the Galaxy. Given a reasonable sensitivity 
of the detector of the WFC3 (around 90 %), we can, without problems, 
reach a number of such galaxies with the HST, the WFC3 and uvby 
photometry. Suitable candidate galaxies are, with the corresponding 
limiting magnitudes for (Me/H) to an accuracy of 0.2 dex

Sculptor,           V=23
Draco,              V=23
Ursa Minor,         V=23
Fornax,             V=22
Leo II,             V=21
Leo I,              V=20.5

We note that studies as proposed can be made both for field stars in 
structural parts of galaxies with well-defined populations and in 
globular clusters in the same galaxies, all the time with individual 
stars as targets.



Of the filters currently on the straw man list .... ?

Answer:   The uvby filters. This is a unique set of filters for 
determination of high quality metallicities for individual stars. Data 
from uvby photometry provide high accuracy (Me/H) data and ages for 
individual stars much fainter than possible with spectroscopy of a 
resolution necessary for corresponding accuracy. From wide band 
photometry, no really reliable data on (Me/H) can be obtained.



Are there filters that are essential .... ?

We need the uvby filters, and they are on the list. Having the freedom 
to wish, we would like to propose u and y filters closer to the standard 
uvby system definition than at present available.



Given your expertise in the field, do you .... ?

We are quite satisfied with the list presently proposed, at the same 
time as we like to refer to our answer to the previous question.




Best regards,


Peter Linde              Arde Ardeberg



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