Astron. Astrophys. 358, 639-650 (2000)

The atmospheric parameters and chemical composition of early B-type giants in h and  Persei

M. Vrancken ¹, D.J. Lennon ², P.L. Dufton ³ and D.L. Lambert <sup>4

1</sup> Royal Observatory of Belgium, Ringlaan 3, 1180 Brussel, Belgium
² Universitätssternwarte München, Scheinerstrasse 1, 81679 München, Germany
³ The Department of Pure and Applied Physics, The Queen's University of Belfast, Belfast BT7 1NN, Ireland
⁴ Department of Astronomy, University of Texas, Austin, TX 78712, USA

Received 23 September 1999 / Accepted 7 April 2000

Abstract

Atmospheric parameters and surface chemical compositions are presented for eight stars, classified as B1 or B2 but with a range of luminosity classes, in the northern double cluster h and  Persei. Echelle spectroscopy (covering the wavelength region 3900 to 4700 Å) and grating spectroscopy (of the Balmer, H and H lines) were analysed using non-LTE synthetic spectra based on LTE line-blanketed atmosphere structures. High microturbulences are found in our sample, and this quantity must be included in the computation of the non-LTE level populations; its effect is generally to decrease the derived metal abundances by typically 0.1 dex but by up to 0.4 dex. Our absolute abundances are in reasonable agreement with those previously found for main sequence B-type stars, while we find some evidence for small abundance variations (particularly for nitrogen) within our sample. One star (BD+56 678) appears to be a spectrum variable and at two epochs shows a highly enriched nitrogen spectrum. Our atmospheric parameters imply that two stars have previously been mis-identified as main sequence objects and a distance modulus, at the higher end of the values previously deduced. The observational HR diagram is consistent with stellar evolutionary models that explicitly include the effects of rotation.

Key words: line: formation stars: abundances stars: early-type stars: evolution Galaxy: open clusters and associations: individual: h and O Persei

Send offprint requests to: Philip Dufton (P.Dufton@qub.ac.uk)

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Contents

• 1. Introduction
• 2. Observations and reduction
  • 2.1. Grating spectroscopy
  • 2.2. Echelle spectroscopy
• 3. Model atmosphere analysis
  • 3.1. Model calculations
  • 3.2. Determination of the atmospheric parameters
• 4. Results and discussion
  • 4.1. Atmospheric parameters and spectral types
    • 4.1.1. The giants and dwarfs
    • 4.1.2. The bright giants/supergiants
  • 4.2. Absolute Metal abundances
    • 4.2.1. Carbon
    • 4.2.2. Nitrogen
    • 4.2.3. Oxygen
    • 4.2.4. Magnesium
    • 4.2.5. Aluminium
    • 4.2.6. Silicon
    • 4.2.7. General
  • 4.3. Relative abundances
    • 4.3.1. BD +56 578
  • 4.4. Distances
  • 4.5. Evolutionary status
• 5. Discussion and conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: June 8, 2000
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