Spectral Distributions
Here you can either enter your own input spectrum for the source, the details of how are given in the next section, or you can choose one of the following:
Castelli & Kurucz Models: The atlas contains about 4300 stellar atmosphere models for a wide range of metallicities, effective temperatures and gravities. These LTE models with no convective overshooting computed by Fiorella Castelli, have improved opacities and abundances upon previously used by Kurucz (1990). The main improvements from previous opacity distribution functions listed in Castelli & Kurucz 2003 (IAU Symposium 210, Modelling of Stellar Atmospheres, Uppsala, Sweden, eds. N.E. Piskunov, W.W. Weiss. and D.F. Gray, 2003, ASP-S210). A complete set of files can be found at http://www.stsci.edu/ftp/cdbs/grid/ck04models
For more information, see also our Castelli & Kurucz page
Pickles Models: This library of wide spectral coverage, consists of 131 flux calibrated stellar spectra, encompassing all normal spectral types and luminosity classes at solar abundance, and metal-weak and metal-rich F-K dwarf and G-K giant components. Each spectrum in the library is a combination of several sources overlapping in wavelength coverage. The creator of the library has followed precise criteria to combine sources and to assemble the most reliable spectra. As part of the selection criteria prior to combination, all input sources were checked against the SIMBAD database and against the colors and line strengths as derived by the observed spectra themselves to make sure they had similar spectral types (A.J. Pickles 1998, PASP 110, 863). A complete set of files can be found at http://www.stsci.edu/ftp/cdbs/grid/pickles
For more information, see also our Pickles models page
Kurucz Models: There are 24 stellar spectra available. All are Kurucz models calculated from the Kurucz database (Dr. R. Kurucz, CD-ROM No. 13, GSFC) which have been installed in CDBS. These are the same spectra used as input spectra by Leitherer, et. al. 1996, in ISR ACS 96-024, MAMA Bright Object Limits for Astronomical Objects. See also The Solar Blind Channel Bright Object Limits for Astronomical Objects by Boffi & Bohlin 1999, ISR ACS 99-07. A complete set of files can be found at http://www.stsci.edu/ftp/cdbs/grid/k93models
HST Standard Star spectra: Several HST calibration standard spectra are available. These spectra are stored in CDBS and were chosen from the paper Spectrophotometric Standards from the Far-UV to the Near-IR on the White Dwarf Flux Scale by Bohlin 1996, AJ, 111, 1743. See also Comparison of White Dwarf Models with ACS Spectrophotometry by Bohlin 2000, AJ, 120, 437. The selection also includes a spectrum of the Sun. A complete set of files can be found at http://www.stsci.edu/hst/observatory/cdbs/calspec.html
Non-Stellar Objects: There are also a few model spectra of non-stellar objects available from CDBS, such as an elliptical galaxy, a Seyfert galaxy, the Orion nebula, and a planetary nebula. These options are not all available for all the instruments because their data do not cover the relevant spectral range. A word of caution is necessary on the use of these model spectra. These are only &ldquot;typical&rdquot; examples, and individual cases may well have very different spectra. For example, the PN spectrum is that of NGC 7009, but other PNe with different excitation classes may have very different spectral characteristics.
QSO: Two templates are offered with user supplied redshift. The QSO SDSS spectrum refers to a composite spectrum of a sample of QSOs, transformed to z=0 (Francis et al. 1991, ApJ, 373, 465). Other QSOs may have very different spectral characteristics and some caution is advised in using these model spectra. The QSO spectrum at zero redshift has a rather limited wavelength range (800 - 6000 A). As a result, using high redshifts may put the QSO spectrum beyond the wavelength region of the filter or grating bandpass, thereby causing the ETC to return an error. Conversely, using a QSO with a very low (or zero) redshift will result in a spectrum with no flux in the infrared, which would cause the ETC to return an error when using NICMOS. The QSO FOS-SVP composite spectra has been smoothed above 2900A and below 700A. More details about the FOS spectra can be obtained from http://archive.stsci.edu/prepds/composite_quasar/
Black-body: with a user specified temperature.
Power-law: The flux distribution is given by F(λ) = λn, where n is specified by the user.
Flat continuum: This is a special case of the power law, where n=0. This distribution is so named because the spectrum has constant (flat line) energy per either wavelength or frequency units. Please note that countrate calculations use photons per wavelength unit.