Output Parameters Help Page

This page contains information regarding the output parameters for the resulting spectra obtain with our Webtools. 

• λInitial (Å)

Starting restframe wavelength of the output spectra in Angstroms. If Redshift is different from 0.0, this value will be blue/redshifted accordingly.

• λFinal (Å)

End restframe wavelength of the output spectra in Angstroms. If Redshift is different from 0.0, this value will be blue/redshifted accordingly.  

• Δλ (Å/pix)

Spectral sampling of the output spectra in Angstroms. 

• Sampling

Type of sampling for the output spectra: linear, rebinned in Log10, or rebinned in Ln. When Log10 or Ln is selected, note that  the output spectrum is average of the input spectrum across each output wavelength  coordinate. This conserves flux-density (NOT total flux) in the rebinning process, which is likely what most users want from flux calibrated data.

• Redshift (z)

Redshift to be applied to the output spectra. At present only the wavelength vector is changed. No scaling is applied to the fluxes.

• Resolution

Full-Width Half Maximum (FWHM) of the output spectra. The stellar library or model spectra will be convolved with a Gaussian PSF to match the desired spectral resolution. During this step, particular attention will be paid as to whether the user requires the FWHM to be constant as a function of wavelength (in which case convolution will be performed in linear space), or constant in velocity (in which case convolution will be performed in logarithmic space). Select FWHM(Å) or σ (km/s) for each option respectively. 

• Format

Format of the output spectra. Options are ASCII or FITS (Flexible Image Transport System). Note that wavelengths provided refer to the centre of each pixel. For consistency this convention is adopted in the spectra in both ASCII and FITS formats. Therefore the CRVAL1 value in the header of the FITS files corresponds to the wavelength at the centre of the first pixel of the spectrum (and not at the beginning of the pixel). The definition of this keyword (CRVAL1) in the CFISTIO library gives the user the freedom to choose whether the reference point value refers to the center or somewhere else in a pixel (see the definitions here for details).

• Filters Response File

A file containing the list of filters through which the magnitudes have to be computed. If the default list is not suitable enter a new one with the same format. Each filter response should be separated by an header line starting with '#'. Note that the magnitudes provided for the Sloan Filters (as defined in our filters response file) will be in the AB system.

• Reference Zeropoint

The (Vega) spectra to be used to normalize the spectrum. The user can choose among the following options:

  1. Alpha Lyr:  from CALSPEC (see http://www.stsci.edu/hst/observatory/cdbs/calspec.html)
  2. Vega (CK94): Castelli & Kurucz 1994, A&A, 281, 817
  3. Vega (Hayes 1985): in Calibration of Fundamental Stellar Quantities, IAU Symposium 111. This is the default option, as it produces the closest results to those obtained with the photometric libraries used in thise website (see here for details).
  4. Vega (Koo): from David Koo, private communication
  5. AB system

Synthetic magnitudes are provided assuming a Vega magnitude of zero in all filters.