From phelbig@hs.uni-hamburg.de Wed Apr 17 14:03:20 1996 Path: solitaire.cv.nrao.edu!hearst.acc.Virginia.EDU!caen!newsxfer2.itd.umich.edu!newsfeed.internetmci.com!news.msfc.nasa.gov!pecos.msfc.nasa.gov!not-for-mail From: Phillip Helbig Newsgroups: sci.astro.research Subject: calculating cosmological distances the practical way Date: 16 Apr 1996 13:34:28 GMT Organization: Hamburger Sternwarte, Germany Lines: 74 Sender: astres@pecos.msfc.nasa.gov Approved: astres@pecos.msfc.nasa.gov Distribution: world Message-ID: <4l07l3$7mi@pecos.msfc.nasa.gov> Reply-To: Phillip Helbig NNTP-Posting-Host: pecos.msfc.nasa.gov Summary: announcement of FORTRAN code, user's guide, and paper about the theory Keywords: cosmology distances methods:numerical gravitational lensing Of fundamental importance for much of extragalactic astronomy and cosmology is the calculation of distances from redshifts. There are various types of distances, and the nonlinearity with redshift makes the problem of cosmological distance calculation much more involved than in the conventional case. In addition, closed solutions are only valid in special cases which correspond to cosmological models which might not be a good approximation to reality. Although a general solution in terms of elliptic integrals exists, a practical implementation is lacking. Even this complex approach, however, must neglect the influence of inhomogeneities on the calculation of distances from redshifts, which for realistic scenarios is comparable to the influence of the `conventional' cosmological parameters. The present programme by Perlmutter et al. to determine cosmological parameters through the magnitude-redshift relation for supernovae Ia is a contemporary example where interesting things can be learned by looking at the behaviour of distances at redshifts where the linear approximation is no longer valid. Another area is gravitational lensing, where lensing statistics will hopefully set the tightest constraints on the cosmological parameters (with the possible exception of a successor to COBE) in the near future. My colleague Rainer Kayser has derived a second-order differential equation for calculating distances from redshifts, valid in all Friedmann-Lemaitre cosmological models, including inhomogeneous ones, that is, where a certain fraction of the matter is distributed clumpily. (Classically, complete homogeneity is assumed.) This degree of inhomogeneity can also be a function of redshift. Together with Tom Schramm we've written a paper describing this method of distance calculation, which has been submitted to Astronomy and Astrophysics. We have also developed a numerical implementation in strictly standard FORTRAN77, designed for the practical cosmologist and extragalactic astronomer who needs a `black box' for converting between redshifts and distances. The box can be opened, as we make the source code available. The A&A paper (PostScript), the source code and a user's guide to the routines (PostScript) is available from ftp://ftp.uni-hamburg.de/pub/misc/astronomy/angsiz.uu or from the preprint servers as astro-ph 9603028 >from which it is ALSO possible to obtain only the A&A paper (choose `PostScript'; choosing source will give you the paper in LaTeX and a uuencoded compressed tar archive containing the PostScript user's guide and the FORTRAN routines). Another possibility is to check out http://www.hs.uni-hamburg.de/ english/persons/helbig/Research/Publications/Info/angsiz.html (all one one line, of course) and follow the links to what you need. The FORTRAN code is available as ASCII and the paper and user's guide are available as PostScript or as gzipped PostScript. Feel free to send me email with comments, questions, problems, bug reports etc. Put ANGSIZ in the subject line. If you desire, you can be placed on a mailing list to be informed of any changes in the code (bug fixes, etc.). If anyone has any problems with access by the methods outlined above, I can also send you everything by email (uuencoded compressed (or gzipped) tar (or BACKUP) archives) or even paper versions of the A&A paper and user's guide. (I've made no provisions for a paper version of the FORTRAN routines, i.e., punched cards, though I can send a printout of the code, of course:) -- Phillip Helbig Email ....................... phelbig@hs.uni-hamburg.de Hamburger Sternwarte Tel. ................................. +49 40 7252 4110 Gojenbergsweg 112 Fax .................................. +49 40 7252 4198 D-21029 Hamburg http://www.hs.uni-hamburg.de/english/persons/helbig.html I don't speak for the Hamburg Observatory; the Observatory doesn't speak for me