User Supplied Spectrum
One of the features of the ETC is its ability handle a spectrum supplied by the user. In this version of the ETC this is accomplished by a direct upload from the machine where the user is running the web browser.
To use this option, you will need to:
- Prepare your spectrum file
- Specify your spectrum file in the ETC input form
The file will be uploaded when you click the "submit" botton at the top or bottom of the form. If the file is large or the computer has a slow internet connection it will take extra time for the browser to send the file to the ETC server.
Prepare your file
Prepare your input spectrum file with 2 columns:
- column 1: wavelength
- column 2: flux density
Column 1 should be the wavelength in Å, and column 2 should be the flux density (in erg cm-2 sec-1 Å-1 for point sources, and in erg cm-2 sec-1 Å-1 arcsec-2 for diffuse sources). The wavelengths in the first column must be in increasing order. Please note that if your spectrum has negative flux values you will get a pysynphot error message.
The user specified spectrum file should be in one of the following 2 file formats:
- ASCII table with the extension .dat
- FITS table with an extension .fits or .fit
SDAS tables (files with the .tab extension) are no longer supported. If you attempt to use an SDAS table file you will get an error. Try to use a unique filename for this file, for example using your last name as part of the filename.
Spectrum File Format
ASCII
If the file is an ASCII file, it must contain the following 2-columns:
- column 1: wavelength (in Å)
- column 2: flux density in erg cm-2 sec-1 Å-1 for point sources, in erg cm-2 sec-1 Å-1 arcsec-2 for diffuse sources
Any comment lines in the file must start with "#" in order to avoid confusion when it is used in the calculation.
SDAS
The SDAS table file format is not portable to different machine architectures and so support for it has been discontinued. We recommend using the TTools command "tcopy" to convert all SDAS files to FITS format.
FITS
If the file is a FITS binary table, it should have two columns labeled "WAVELENGTH" and "FLUX", again with the units specified for each column. The header of the FITS table should then include lines similar to these:
PCOUNT = 0 / GCOUNT = 1 / Only one group TFIELDS = 2 / Number of fields per row EXTNAME = 'f4v_v15_flam.tab' / Name of extension TTYPE1 = 'WAVELENGTH' / TBCOL1 = 1 / TFORM1 = 'E15.7 ' / TUNIT1 = 'angstroms' / TDISP1 = 'G15.7 ' / %15.7g TTYPE2 = 'FLUX ' / TBCOL2 = 17 / TFORM2 = 'E15.7 ' / TUNIT2 = 'flam ' / TDISP2 = 'G15.7 ' / %15.7g
Specify your spectrum
In section 3 of the ETC input form simply check the box next to "User Supplied Spectrum". You may then either type the path of the file in the input box or use the "browse" button next to the box and then navigate through the local file system to the file.
