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First step-Turning the table into a spiketrum

(You may find it useful to review the section on spiketra before reading on.)

Figaro usually deals with tables, which are tricky to manipulate directly, by turning them into spiketra, which can be manipulated like spectra, although they only have non zero values at points that correspond to those tabulated. No matter which type of published standard is involved, the first step is to generate a spiketrum from the table.

This requires a template spectrum to give the wavelength scale. The one to use is the observed standard spectrum, preferably already scrunched to a linear wavelength scale. (You can use unscrunched data, but it is not advised.) For example, suppose `standobs' is such a spectrum of the standard star HD 84937. There is a table of flux densities for this star (one of the Oke & Gunn standards) in the main Figaro directory, in the file `hd84937.tab'. The command

   ICL> gspike spectrum=standobs table=hd84937 spiketrum=hdspike

will generate a spiketrum called `hdspike' that can be used by the subsequent steps. If you want a look at it,

   ICL> splot hdspike reset accept

will show it as a series of vertical spikes, giving the flux density at each of the tabulated points in the wavelength range of the observation.

`gspike' will search directories for the table file in the usual Figaro order: first the default directory, then the user's Figaro directory (environment variable FIGARO_PROG_U), then the local and Figaro directory (FIGARO_PROG_L), and finally the main Figaro directory (FIGARO_PROG_S). So a table file in any of these will be found, should you need to create your own.



next up previous 78
Next: Second step-for Oke & Gunn data
Up: Flux calibration
Previous: Published standards

FIGARO A general data reduction system
Starlink User Note 86
Keith Shortridge, Horst Meyerdierks,
Malcolm Currie, Martin Clayton, Jon Lockley,
Anne Charles, Clive Davenhall,
Mark Taylor, Tim Ash, Tim Wilkins, Dave Axon,
John Palmer, Anthony Holloway and
Vito Graffagnino
2004 February 17
E-mail:ussc@star.rl.ac.uk

Copyright © 2008 Science and Technology Facilities Council