5.8. Uvtospex

Many optical/UV spectra are delivered without a response matrix. Hubble COS spectra, for example, are delivered as data/error points on a wavelength grid. To include these spectra in a SPEX fit, a response matrix with a given spectral resolution should be created. Uvtospex is a tool to transform such optical spectra into SPEX format.

Note

Some UV/optical instruments do provide response matrices, for example XMM-Newton OM and Swift UVOT. Please see this thread to import Import UV/Optical data.

To create a spectrum in SPEX format from UV/Optical grating data, the spectrum needs to be stored in a text file with three columns. The uvtospex program shows the format when opening:

Your input spectral file should have 3 columns:
Column 1: wavelength in Angstrom
Column 2: flux in ergs/cm^2/s/Angstrom
Column 3: flux error in same units

Enter input file name spectrum: cos.txt

The program first asks for the ascii file name containing the spectrum. Then the output file name of the spo file needs to be provided:

Enter file name output spectrum (with .spo): cos.spo

To be able to create a response matrix for the spectrum, the spectral resolution of the instrument needs to be known. Uvtospex asks for the resolution in units of km/s (FWHM):

Enter spectral resolution (km/s):

It is assumed that this resolution in km/s is constant over the entire spectral range. Finally, the name of the output response file should be entered:

Enter file name output response (with .res):

The result should be a .res and .spo file containing the UV spectrum that can be read into SPEX.