Institute of Astronomy  

 Bob Carswell's page


Bob Carswell
Institute of Astronomy

Madingley Road
Cambridge   CB3 0HA
Office: Hoyle 16

Phone:           +44.1223.337514
Switchboard: +44.1223.337548
Email:  rfc (at

The main use for this page is to provide links various versions of a Voigt profile fitting program. The code is now fairly stable, though there are probably bugs in the more obscure corners of it. The downloadable gzipped tarfile also includes another program, rdgen, which may be used to set up files for vpfit, and generally looking at spectroscopic data.

The most recent version, VPFIT12.3 (here as a gzipped tarfile) has passed the standard tests so should generally be OK. The documentation is included in the tarfile. Thre is also a version which uses true derivatives of functions, as opposed to finite differences. It is a gzipped tarfile VPFIT12.4. This has been less extensively tested, so please report any bugs/difficulties.

For those using Overleaf the most up-to-date version of the VPFIT documentation may be found at

VPFIT12.3 and higher includes the option to use the Kramers-Heisenberg profile which is appropriate for high very high HI column densities (it was incorrectly implemented in version 12.0). For details see Lee, Webb and Carswell, MNRAS, 449, 5555, 2020. Improvements include the implementation of a hybrid optimisation technique which is described in Webb, Carswell and Lee, MNRAS 508, 3620, 2021. Version 12.3 also removes some further minor bugs.

For the previous versions use VPFIT12.2. If you want older versions (vpfit12.1,12.0, 11.2,11.1, 11.0, 10.4, 9.5) then these are still available. Please ask, or, for now, look at vpfit.html.

A somewhat dated collection of data showing the redshift evolution of the Lyman alpha forest, covering redshifts up to z=6.3.

Other links

Last update: 22 June 2023
by rfc