Posted by Peter Linde and Arde Ardeberg on July 06, 1999 at 10:26:50:
From: Peter LindeMessage-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 ---------------------------------------------------------------------------- Peter Linde Tel: +46-46-222 4701 Lund Observatory E-mail: peter@astro.lu.se (Internet) Box 43 Fax: +46-46-222 4614 S-221 00 Lund WWW: http://www.astro.lu.se Sweden