Spectral Distributions

Here you can either enter your own input spectrum for the source, or you can choose one of the following from the Reference Data for Calibration and Tools spectral atlases:

Castelli & Kurucz Models

The Atlas9 Stellar Atmosphere Models by Castelli and Kurucz 2004

This 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 upon the opacities and abundances previously used by Kurucz (1990). The main improvements, as detailed in Castelli and Kurucz (2004), are the use of improved solar abundances and TiO lines.

For more information, see the relevant section of the CDBS Castelli & Kurucz webpage on astronomical catalogs, and the Castelli & Kurucz README file for this catalog. A complete set of files can be found at ftp://ftp.stsci.edu/cdbs/grid/ck04models/

Pickles Models

A Stellar Spectral Flux Library By A.J. Pickles (1998) (PASP 110, 863)

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.

For more information, see the Reference Data for Calibration and Tools Pickles webpage and the Pickles README file for this catalog. A complete set of files can be found at ftp://ftp.stsci.edu/cdbs/grid/pickles/

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 STIS 96-24, 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.

For more information, see the Reference Data for Calibration and Tools Kurucz webpage. A complete set of files can be found at ftp://ftp.stsci.edu/cdbs/grid/k93models/

Bruzual Spectra

The Bruzual Atlas contains 77 stellar spectra frequently used in the synthesis of galaxy spectra.

For more information, see the Reference Data for Calibration and Tools Bruzual webpage. A complete set of files can be found at ftp://ftp.stsci.edu/cdbs/grid/bz77/

HST Standard Star spectra

Several HST calibration standard spectra are available. Those provided here are the recommended spectra for the calibrator. These spectra are stored in the Calibration Database System (CDBS) and were originally 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 and later updated as new data became available. See also Comparison of White Dwarf Models with STIS Spectrophotometry by Bohlin 2000, AJ, 120, 437. The selection also includes a spectrum of the Sun.

More information, along with a list of the complete set of files, including older versions, can be found here. This page provides a table with the all the available Flux Standards and their CDBS name. In this table the order of preference for the choice of a standard flux distribution is from left to right in the Table, i.e. from the best in column 6 to the last choice with the lowest quality in column 9. In this case, models have higher fidelity and extend to longer wavelength ranges while the more outdated are those derived applying corrections to the original IUE and optical fluxes. Note that for the cases when the CALSPEC data is updated after the ETC software is released, the ETC will not be able to access the most recent files, but only those that were available at the time of the build. If the ETC produces an error when trying to access an HST Standard Star spectrum, review the update history at the bottom of the CALSPEC page to determine when the spectrum was updated. If it was updated after the current ETC version, you may want to use the previous version of the model, or download the most recent spectrum, and apply it as a user-supplied spectrum (see User-supplied Spectra).

To use this spectra you will have to identify the name of the file and put it in the ETC input box for “Other HST Spectra”. To make up the corresponding CDBS name using this table you need to paste together the information from several of the columns. Take as an example star G191B2B:

Star Name Spec. type V B-V CDBS Name Model STIS FOS+Oke IUE+Oke
G191B2B DA0 11.781 -0.33 G191B2B _MOD_007 _STISNIC_003 _FOS_003 _005

The file name for the spectra that has STIS data is made up with the CDBS prefix in column five, the extension given in column seven, and “.fits”. In this case you will end up with “g191b2b_stisnic_003.fits” (note that the file name is all lower case). To this file name you will also need to add the access mode for CALSPEC, which is “crcalspec$”. The final name to enter in the “Other HST Spectra” box would be ‘crcalspec$g191b2b_stisnic_003.fits’.

Note that spectra for HZ 4 and G93-48, the spectra was contaminated with Lyman Alpha emission; therefore the flux at this particular wavelength range was set to zero rather than interpolating the baseline continuum from neighboring wavelengths. Using these spectra for UV sensitive instruments might underestimate the flux in this wavelength range.

Note also that photometric calculations in vegamags use a slightly different Vega spectrum than the model available to the ETC listed in the menu for HST Standard Star Spectra. The version used by the ETC is the version used by pysynphot.

Non-Stellar Spectra

There are also many model spectra of non-stellar objects available from CDBS. These are, according to their classification:

Brown Dwarf Stars / Substellar Objects

  • gl229b.dat: Gliese 229B
  • gl752b_vb10_M8.asc: Gliese 752B
  • g1411_M2.asc: Gliese 411
  • gl406_M6.asc: Gliese 406

Digital form of the spectrum of Gliese 229B. This data is presented in the paper entitled “The Spectrum of Gliese 229B” by B. R. Oppenheimer, S. R. Kulkarni, K. Matthews and M. H. van Kerkwijk (1998, ApJ, 502, 932). Please contact Ben R. Oppenheimer before using this data in any publication or presentation.

Nebulae representative models:

  • orion: Orion Nebula
  • orion_smooth: Orion Nebula II
  • pn_smooth: Planetary Nebula (NGC 7009) including point source
  • pn_nebula_only_smooth: pn_smooth extended source with point source removed

Note other nebulae with different excitation classes may have very different spectral characteristics.

Elliptical / Spiral / Starburst Galaxies:

  • elliptical: Elliptical #1 [1]
  • elliptical_smooth: Elliptical #2 [1]
  • el_cb2004a: Elliptical Benitez 2004a [2]
  • el_cww_fuv: Elliptical CWW FUV [3]
  • im_cb2004a: Im_B2004a [3]
  • spiral: Spiral [1]
  • s0_fuv_1: S0 [1]
  • sa_fuv_1: Sa [1]
  • sbc_cb2004a: Spiral Sbc Benitez 2004a [2]
  • sbc_cww: Sbc CWW [3]
  • scd_cb2004a: Scd B2004a [2]
  • sb2_b2004a: SB2_B2004a [4]
  • sb3_b2004a: SB3_B2004a [4]
  • ssp_25myr_z008: ssp_25Myr_z008 [5]
  • ssp_5myr_z008: ssp_5Myr_z008 [5]
  • ngc1068_template: NGC 1068, Seyfert 2 Galaxy [1]

[1] Representative models

[2] Coleman, Wu, Weedman 1980 templates recalibrated by Benitez et al. 2004, ApJS, 150, 1.

[3] Coleman, Wu, Weedman, 1980, ApJS, 43, 393.
Ultraviolet observations of nearby galaxies with the ANS are used to derive ultraviolet spectra for different galaxy types. These spectra are used with existing visible spectrophotometry to calculate K-corrections, and to predict colors and magnitudes for various galaxy types as a function of redshifts, to z = 2. No evolutionary effects are considered. It appears that the first-ranked cluster galaxies on blue emulsions should be spirals for z greater than or approximately equal to 0.5.

[4] Starburst galaxies form Kinney et al. 1996 (ApJ, 467, 38) recalibrated by Benitez et al. 2004.

[5] Young 5, 25 Myr old simple stellar populations with 0.4 times solar metallicity from Bruzual & Charlot 2003, MNRAS, 344, 1000.

Starburst galaxies (Kinney models):

  • sb1_kinney_fuv: E(B-V) = 0 - 0.10
  • sb2_kinney_fuv: E(B-V) = 0.11 - 0.21
  • sb3_kinney_fuv: E(B-V) = 0.25 - 0.35
  • sb4_kinney_fuv: E(B-V) = 0.39 - 0.50
  • sb5_kinney_fuv: E(B-V) = 0.51 - 0.60
  • sb6_kinney_fuv: E(B-V) = 0.61 - 0.70

From Kinney et al. 1996, ApJ, 467, 38.

Template UV-Optical spectra for starburst galaxies, from a combination of IUE data and of optical data with an aperture size matched to the IUE. The templates of the starburst galaxies are built according to color excess.

In order to make the templetes, all the spectra are shifted to the rest frame and corrected for the foreground Galactic extinction using the Seaton (1979) extinction curve. Within the starburst group, the UV-optical spectra are rescaled to a common flux value and are averaged, after weighting each spectrum by its SNR ratio to produce the final template.

BC03 models:

  • tau06_z02_1015_190: age = 1.01519 Gyr
  • tau06_z02_2500_000: age = 2.5 Gyr
  • tau06_z02_4500_000: age = 4.5 Gyr
  • tau06_z02_5000_000: age = 5.0 Gyr
  • tau06_z02_6000_000: age = 6.0 Gyr
  • tau06_z02_8000_000: age = 8.0 Gyr
  • tau06_z02_12000_000: age = 12.0 Gyr

Bruzual and Charlot 2003 (MNRAS, 344, 1000)
Tau models with solar metallicity, Tau = 0.6 Gyr, and exponentially decreasing star formation.


  • qso_template.dat: QSO (COS-based)
  • qso_template: QSO (LBQS-based)
  • qso_fos: QSO (FOS-based)
  • qso_sdss: QSO (SDSS-based) Vanden Berk et al. (2001)
  • qso_irtf_template: QSO (IRTF-based) Glikman, Helfand, and White (2006)

The COS-based AGN spectrum is taken from Stevans, Shull, Danforth, & Tilton 2014, ApJ, 794, 75. It is a composite spectrum drawn from 159 AGN at redshifts 0.001 < z_{\mbox{\tiny{AGN}}} < 1.476 observed in the FUV with COS. It covers restframe wavelengths from 475 to 1875 \AA. The composite rest-frame continuum can be characterized by a spectral index \alpha, where F_{\nu} is proportional to \nu^{\alpha}, with \alpha = -0.83\pm0.09 in the FUV (1200-2000 \AA) steepening to -1.41\pm0.15 in the EUV (500-1000 \AA). The composite also contains numerous FUV and EUV emission lines from metal ions. Full details are given in Stevans et al. (2014).

The LBQS composite QSO spectrum refers to a sample of QSOs transformed to z=0 (Francis et al. 1991, ApJ, 373, 465). The FOS-SVP composite QSO spectrum has been smoothed above 2900 \AA and below 700 \AA. More details about the FOS spectra can be obtained from https://archive.stsci.edu/prepds/composite_quasar/

The SDSS-based QSO spectrum comes from http://iopscience.iop.org/1538-3881/122/2/549/fulltext/datafile1.txt from “Composite Quasar Spectra From the Sloan Digital Sky Survey” by Vanden Berk D.E. et al. 2001, AJ, 122, 549.
Abstract excerpts: We have created a variety of composite quasar spectra using a homogeneous data set of over 2200 spectra from the SDSS. The input spectra cover an observed wavelength range of 3800 - 9200 \AA at a resolution of 1800. The median composite covers a rest wavelength range from 800 - 8555 \AA and reaches a peak signal-to-noise ratio of over 300 per 1 \AA resolution element in the rest frame. We have identified over 80 emission-line features in the spectrum.

The IRTF quasar is from Glikman E., Helfand D.J., White R.L. ApJ 2006, 640, 579.
Abstract: We present a near-infrared quasar composite spectrum spanning the wavelength range 0.58-3.5 \mu m. The spectrum has been constructed from observations of 27 quasars obtained at the NASA IRTF telescope and satisfying the criteria K_s < 14.5 and M_i < -23; the redshift range is 0.118 < z < 0.418. The signal-to-noise ratio is moderate, reaching a maximum of 150 between 1.6 and 1.9 \mu m. While a power-law fit to the continuum of the composite spectrum requires two breaks, a single power-law slope of \alpha = -0.92 plus a 1260 K blackbody provides an excellent description of the spectrum from H_\alpha to 3.5 \mu m, strongly suggesting the presence of significant quantities of hot dust in this blue-selected quasar sample. We measure intensities and line widths for 10 lines, finding that the Paschen line ratios rule out case B recombination. We compute K-corrections for the J, H, K, and Spitzer 3.6 \mu m bands, which will be useful in analyzing observations of quasars up to z = 10.

Other QSOs may have very different spectral characteristics and some caution is advised in using these model spectra. The QSO spectra at zero redshift have limited wavelength ranges. 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 WFC3/IR.

Infrared Galaxies:

  • 05189m2524_fullsed: Ultra Luminous IR Galaxy IRAS05189-2524
  • 12112p0305_fullsed: Ultra Luminous IR Galaxy IRAS12112+0305
  • 14348m1447_fullsed: Ultra Luminous IR Galaxy IRAS14348-1447
  • 15250p3609_fullsed: Ultra Luminous IR Galaxy IRAS15250+3609
  • 22491m1808_fullsed: Ultra Luminous IR Galaxy IRAS22491-1808
  • arp220_fullsed: Merger ARP220
  • m82_fullsed: Merger M82
  • mrk1014_fullsed: Ultra Luminous IR QSO MRK1014
  • mrk231_fullsed: Type-1 Seyfert Galaxy MRK231
  • mrk273_fullsed: Merger MRK273
  • mrk463_fullsed: Ultra Luminous IR Galaxy MRK463
  • ngc6240_fullsed: NGC6240: Ultra Luminous IR Galaxy (merger)
  • ugc5101_fullsed: Peculiar Galaxy U1GGC5101

Examples of galaxy spectra are taken from the Spectral Atlas of Infrared Luminous Galaxies. This atlas contains a set of spectrum templates of nearby infrared-luminous galaxies covering the wavelength range 0.1 to 1000 \mu m. Data were collected from the NASA Extragalactic Database (NED), and included photometry from the U-band through the K-band in the near-infrared. Photometry from the Infrared Astronomical Satellite (IRAS) as well as spectra from the Spitzer/Infrared Spectrograph (Armus et al. 2004, 2007) have been incorporated.

The optical/NIR data were fitted using two stellar components (a young component and an evolved component) so that the U to K band fluxes of the galaxies are reproduced. The far-infrared spectral energy distribution (SED) was fitted using the dust continuum models in Chary & Elbaz (2001). The Spitzer mid-infrared spectra were scaled to agree with the IRAS flux densities. The one exception is the template of M82 which was reconstructed from ISO data (Chary & Elbaz 2001). The range of mid-infrared SEDs in these templates illustrate the strength of polycyclic aromatic hydrocarbon (PAH) features and silicate features which might be present in real galaxies. Specifically, the features occur at wavelengths (in microns) of:

3.3: PAH emission
6.2: PAH emission
7.7: PAH emission
8.6: PAH emission
9.7: Broad Silicate, typically in absorption; can be seen in emission in AGN
11.3: PAH emission
12.7: PAH emission
18: Broad Silicate, typically in absorption; can be seen in emission in AGN.

These SEDs do not yet incorporate results on these galaxies from GALEX, Planck, and Herschel.

Because the templates are constructed using a combination of real data and models, artificial discontinuities at certain wavelengths may be noticeable.


with a user specified temperature.


The flux distribution is given by

F(\lambda) = \lambda^n

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 count rate calculations use photons per wavelength unit.