User-Supplied Spectra

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” button 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 and column 2 should be the flux density (in for point sources, and in for diffuse sources).

Notes:

• The wavelengths in the first column must be in increasing order, with no duplicates.
• If your spectrum has zero or negative wavelength or flux values anywhere in the file, you will get a pysynphot error message.
• If your spectrum has NaN values for the flux anywhere in the file, these NaNs will be identified as the brightest pixel value in spectroscopic modes. This is because NaNs are inherently not comparable and will register as both the max() and the min() value of the array. You may wish to remove any rows containing NaNs.

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

Try to use a unique filename for this file, for example by 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 )

• column 2: flux density in for point sources,

  in 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.