Mission Overview

New NLTE Model SEDs For OB Stars (NLTE-OBGRID)


Primary Investigator: Ralph Bohlin

HLSP Authors: Ralph Bohlin, Jessica Krick, Karl Gordon, Ivan Hubeny

Released: 2022-06-17

Updated: 2022-06-17

Primary Reference(s): Bohlin et al. 2022

DOI: 10.17909/bsbk-pj11

Citations: See ADS Statistics

Read Me

Spectra of 7 stars comparing NLTE vs. LTE models.
The SEDs scaled by λ4 and then scaled to unity near 6 μm for seven stars, using the LTE models for OB-stars (blue). Each star above G191B2B is offset by 0.15 on the y-axis. The green SEDs are the new NLTE models matched to the blue LTE models at 6800-7700 Å. The red SEDs are the three primary WDs from CALSPEC, as specified in Bohlin et al. (2020). Triangles illustrate the difference between the NLTE-OBGRID IRAC photometry and CALSPEC at the four IRAC pivot wavelengths. The most reliable IRAC1-2 photometry agrees much better with the NLTE models (green) than with the LTE models (blue) for the three stars at the top.


Ivan Hubeny has updated the TLusty OB NLTE model SED grids of Lanz & Hubeny (2003) and Lanz & Hubeny (2007) using a more complete hydrogen atom to produce more realistic IR flux predictions. In particular, the new NLTE spectra have a much better description of line confluences and of the contribution to the opacity in very high series members. In addition, there are improvements in the treatment of the hydrogen and He II continua from high levels, inclusion of more scattering opacity sources, and updates to the physics of level dissolution. Each model has 29957 points at constant spectral resolution of R=5000 and a micro-turbulent velocity of 2 km/s. The Asplund et al. (2009) element abundances are used for computing the spectra.

The grid contains 1082 model pairs of spectra and continua and covers effective temperature Teff in the range 15,000-55,000 K and surface gravity log(g) between 1.75 and 4.75, with steps of 0.25. The steps in Teff are 1,000 K between 15,000 and 29,000 K and 2,500 K between 30,000 and 55,000 K. As Teff rises, more of the unstable lower surface gravities are omitted. There are five metallicity values log Z=[M/H] of 0.301, 0.000, -0.301, -0.70, and -1.00, which correspond to Z=2, 1, 0.5, 0.2, and 0.1, where Z=1 is the solar value. The continuum spectra have a coarser wavelength scale than the spectra.

Both ASCII text and FITS versions of the SEDs are provided.  The wavelengths are in Angstroms measured in vacuum, while the fluxes are in erg/cm2/s/Angstrom.

Data Products

The SEDs are sorted into subdirectories "b-star" or "o-star", and have the following file naming convention:



  • <modcode> = Encapsulates the stellar parameters for this model.  Example: z02t23000g325v2.
    • <z##> = Metallicity, examples: "z02" corresponds to Z=0.2, "z20" corresponds to Z=2.0
    • <t#####> = Effective tempreature, examples: "t42500" corresponds to Teff = 42,500 K
    • <g###> = log(g), example: "g325" corresponds to a log(g) = 3.25
    • <v2> = Microturbulent velocity, which is set to 2 km/s for all SEDs.
  • "r5000" = a reminder that the spectral resolution is in steps of a constant 5000 Angstroms
  • <type> = "spec" or "cont" for the spectrum and continuum SEDs, respectively.
  • <ext> = "txt" or "fits" for ASCII text or FITS versions of the SEDs.

Data file types:

_spec.txt, _spec.fits SED spectra.
_cont.txt, _cont.fits SED continua.

Data Access


Download the set of SED models using the curl scripts provided. curl is likely already installed on most operating systems; if not, consult the official page for installation instructions prior to running these download scripts. The total size of the SED model grid after downloading them through the shell scripts are provided for reference in the table below.

Star Types SED FITS Files SED ASCII Files
B Stars hlsp_nlte-obgrid_tlusty208_model_b-star_r5000_v1_bulk-dl-fits.sh (~654 MB) hlsp_nlte-obgrid_tlusty208_model_b-star_r5000_v1_bulk-dl-txt.sh (~1.3 GB)
O Stars hlsp_nlte-obgrid_tlusty208_model_o-star_r5000_v1_bulk-dl-fits.sh (~244 MB) hlsp_nlte-obgrid_tlusty208_model_o-star_r5000_v1_bulk-dl-txt.sh (~472 MB)



Please remember to cite the appropriate paper(s) below and the DOI if you use these data in a published work. 

Note: These HLSP data products are licensed for use under CC BY 4.0.