University of Heidelberg

Synthetic Spectra of B Main-Sequence Stars from 3000 - 10000 Å

Computational Details

As announced in Gummersbach & Kaufer (1996), we use the LTE static plane-parallel line-blanketed ATLAS9 model atmospheres of Kurucz (1991). The appropriate Opacity Distribution Functions (ODFs) are taken from Kurucz (1993). We run a modified version of the ATLAS9 UNIX implementation of Lemke (1995) available at the CCP7 server (Jeffery 1996). The chosen parameters are

  • Gravity log g = 4.0
  • Microturbulence xi = 2 km/s
  • Solar metallicity
  • Little frequency grid
  • 15 iterations
  • 64 depth levels from log tau = -5 ... +4.

Our spectrum synthesis BHTLI04 is based on the BHT (Baschek et al. 1966) LTE line-formation code. We make use of the recent CD-ROM of Kurucz & Bell (1995) containing explicit wavelengths, oscillator strengths, and excitation energies of 530000 atomic lines. It replaces the Kurucz & Peytremann (1975) line list. In line formation, the chosen parameters are

  • Microturbulence xi = 10 km/s.
  • Solar abundances from Grevesse & Noels (1993)
  • Convolved instrumental profile of lambda/Delta lambda = 20000
  • Convolved rotational profile of v sini = 40 km/s
  • Limb-darkening coefficients epsilon = 0.2 ... 0.4 from Gray (1992) depending on Teff .

The displayed spectrum shows all lines with computed equivalent widths of Wlambda > 1 mÅ. This includes absorption lines of

  • H I
  • He I/II
  • C I/II/III/IV
  • N I/II/III/IV
  • O I/II/III
  • Ne I/II/III
  • Na I/II
  • Mg I/II
  • Al I/II/III
  • Si I/II/III/IV
  • S I/II/III/IV
  • Cl I/II/III/IV
  • Ar I/II/III/IV
  • K I/II
  • Ca I/II/III
  • Sc II
  • Ti I/II/III/IV
  • V II
  • Cr I/II/III
  • Mn I/II/III
  • Fe I/II/III/IV
  • Co I/II
  • Ni I/II/III/IV
  • Cu I

The 40 strongest lines in the selected wavelength range have an actual identification giving lambda, ion, and Wlambda [mÅ]. To yield more identifications just reduce the wavelength range. For each effective temperature the corresponding spectral type O9-A0 is given.

For sake of completeness the He lines have been treated as metallic lines in the computation. Therefore, their equivalent widths are considerably underestimated compared to He lines in real B stars. The hydrogen lines, however, are computed with the theory of Griem (1962) which yield almost the same results as the VCS theory. They should be rather reliable except in the blue parts of both Balmer and Paschen jump which contain some numerical noise. Furthermore, please note that due to computational problems the Paschen lines of the 15000-K model between 8300 and 8450 Å are missing. Clearly, any possible NLTE effects in line cores and/or high-temperature models are neglected.

To facilitate the comparison with actual spectra we also included the positions of several interstellar features possibly present in observed spectra:

  • 39 Diffuse Interstellar Bands (DIBs) with Wlambda > 100 mÅ between 4000 and 10000 Å from Herbig (1995)
  • 29 interstellar absorption lines of NaI, KI, CaI/II, TiII, FeI, CH, CH+, and CN between 3000 and 8000 Å from Scheffler & Elsässer (1992).

All these interstellar lines are marked with a question mark (?) instead of an actual equivalent width.

In summary, due to the conceptual limitations the present synthetic spectra should not be used for any line-profile fitting. Instead, they are mainly intended to provide a reliable tool for line identification and a temperature-dependent search for unblended lines of interest.

References

  • Baschek B., Holweger H., Traving G. (1966): Abhandl. Hamburger Sternwarte VIII, Nr. 1, 26
  • Gray D.F. (1992): The Observation and Analysis of Stellar Photospheres, Cambridge University Press, Cambridge, 2nd edition
  • Grevesse N., Noels A. (1993) in Hauck B., Paltani S., Rabouch D. (eds.): La Formation des Éléments, Association Vaudoise des Chercheurs en Physique, Lausanne, p. 245
  • Griem H.R. (1962): ApJ 136, 422
  • Gummersbach C.A., Kaufer A. (1996): The Hot Star Newsletter 22, 16
  • Herbig G.H. (1995): ARA&A 33, 19 (Tab. A1)
  • Jeffery C.S. (1996): QJRAS 37, 39
  • Kurucz R.L. (1991) in Crivellari L. et al. (eds.): Stellar Atmospheres - Beyond Classical Models, Kluwer, Dordrecht, p. 441
  • Kurucz R.L. (1993): Kurucz CD-ROM No. 2 - Opacities for Stellar Atmospheres: [+0.0],[+0.5],[+1.0], Smithonian Astrophysical Observatory, Cambridge
  • Kurucz R.L., Bell B. (1995): Kurucz CD-ROM No. 23 - Atomic Line List, Smithonian Astrophysical Observatory, Cambridge
  • Kurucz R.L., Peytremann E. (1975): SAO Spec. Rep. 362, 1219
  • Lemke M. (1995): Anonymous FTP at ftp://ccp7.arm.ac.uk/ccp7/Soft/atlas.unix.tar.Z
  • Scheffler H., Elsässer H. (1992): Bau und Physik der Galaxis, BI, Mannheim, 2. Aufl. (Tab. III.4)
For any comments or suggestions turn to O.Stahl@lsw.uni-heidelberg.de
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