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Astron. Astrophys. 328, 551-564

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Properties and nature of Be stars

XVIII. Spectral, light and colour variations of 4 Herculis*,**

P. Koubský1, P. Harmanec1, J. Kubát1, A.-M. Hubert2, H. Boi3, M. Floquet2, P. Hadrava1, G. Hill4, and J.R. Percy5

1Astronomický ústav, Akademie ved Ceské republiky, 251 65 Ondrejov, Czech Republic
2Observatoire de Paris, Section d'Astrophysique de Meudon, URA 335 du CNRS, F-92195 Meudon Cedex, France
3Faculty of Geodesy, University of Zagreb, Kaciceva 26, 41000 Zagreb, Croatia
4Department of Physics, University of Auckland, 38 Princess Street, Auckland, New Zealand
5Erindale Campus, University of Toronto, Mississauga, Ontario L5L 1C6, Canada

Received 28 April 1997 / Accepted 30 July 1997


An analysis of a rich series of spectroscopic and photometric observations of the Be star 4 Her led to the following conclusions:

  • 4 Her is another example of a long-term Be variable with a type of correlation between the brightness and emission strength, similar to 88 Her (V744 Her) and BU Tau (Pleione). It is argued that the formation of a new Be envelope of 4 Her starts with the creation of a slightly cooler pseudophotosphere at the equatorial regions of the star (seen under some intermediate inclination angle) which only gradually grows into an optically thin extended envelope.
  • Radial-velocity measurements of the centre of the H$\alpha$ emission and of the photospheric lines confirm the binary nature of the star. The first reliable orbital elements are presented. The 46-d orbit is nearly circular and has a semiamplitude of 5-8 . An LTE model atmosphere analysis of the photospheric spectrum of the primary leads to $\mbox{$T_{\rm{eff}}$}=12500{\rm K}$, $\log g = 4.0$, and $\mbox{$v\sin i$}=300 \mbox{km s$^{\rm -1}$}$. No direct evidence of the low-mass secondary was found and the possibility that the secondary fills its Roche lobe can be safely excluded.
  • The central quasi-emission bumps (CQEB) visible as "doubling" of some shell lines appear during the phase of the formation of a new shell. They are strongest during the light minimum and become fainter as the H$\alpha$ emission strengthens.
  • An unusual blue-shifted absorption component of the H$\alpha$ line, never reported before, re-appears strictly periodically in the V peak of the H$\alpha$ emission at a limited range of velocities and orbital phases.
  • It is argued that the observational facts about 4 Her are probably best reconciled by a model which assumes that the secondary is a hot and rotationally unstable object which looses mass towards the primary via a gas stream. However, some important findings remain unexplained.

Key words: stars: binaries: spectroscopic - stars: emission-line, Be - stars: variable - stars: individual: 4 Her

*This research is based on spectra from the Ondrejov and Haute Provence Observatories and on photometry from Hvar, Ondrejov, Mt. Kobau, Toronto, APT Phoenix-10, and AAVSO observers.
** Tables 1 and 2 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr ( or via http://cdsweb.u-strasbg.fr/Abstract.html

Send offprint requests to: P. Koubský (koubsky@sunstel.asu.cas.cz)

© European Southern Observatory (ESO) 1997

Online publication: November 24, 1997
Last change: March 26, 1998