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Astron. Astrophys. 328, 551-564 (1997)

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Properties and nature of Be stars

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

P. Koubský 1, P. Harmanec 1, J. Kubát 1, A.-M. Hubert 2, H. Boi 3, M. Floquet 2, P. Hadrava 1, G. Hill 4 and J.R. Percy 5

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

Received 28 April 1997 / Accepted 30 July 1997

Abstract

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 [FORMULA] 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 km s [FORMULA]. An LTE model atmosphere analysis of the photospheric spectrum of the primary leads to [FORMULA], [FORMULA], and [FORMULA]. 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 [FORMULA] emission strengthens.
  • An unusual blue-shifted absorption component of the H [FORMULA] line, never reported before, re-appears strictly periodically in the V peak of the H [FORMULA] 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 Ondejov and Haute Provence Observatories and on photometry from Hvar, Ondejov, 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 (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html

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

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© European Southern Observatory (ESO) 1997

Online publication: March 26, 1998

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