Magnetic AP Stars in the Hertzsprung-Russell Diagram

Details Magnetic AP Stars in the Hertzsprung-Russell Diagram Magnetic AP Stars in the Hertzsprung-Russell Diagram

Aug 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000apj...539..352h&link_type=abstract

The Astrophysical Journal, Volume 539, Issue 1, pp. 352-363.

Astronomy and Astrophysics

Astronomy

99

Stars: Hertzsprung-Russell Diagram, Stars: Chemically Peculiar, Stars: Evolution, Stars: Fundamental Parameters, Stars: Magnetic Fields

Scientific paper

The evolutionary state of magnetic Ap stars is rediscussed using the recently released Hipparcos data. The distribution of the magnetic Ap stars of mass below 3 Msolar in the H-R diagram differs from that of the normal stars in the same temperature range at a high level of significance. Magnetic stars are concentrated toward the center of the main-sequence band. This is shown in two forms of the H-R diagram: one where logL is plotted against logTeff and a version more directly tied to the observed quantities, showing the astrometry-based luminosity (Arenou & Luri) against the (B2-G)0 index of Geneva photometry. In particular, it is found that magnetic fields appear only in stars that have already completed at least approximately 30% of their main-sequence lifetime. No clear picture emerges as to the possible evolution of the magnetic field across the main sequence. Hints of some (loose) relations between magnetic field strength and other stellar parameters are found: stars with shorter periods tend to have stronger fields, as do higher temperature and higher mass stars. A marginal trend of the magnetic flux to be lower in more slowly rotating stars may possibly be seen as suggesting a dynamo origin for the field. No correlation between the rotation period and the fraction of the main-sequence lifetime completed is observed, indicating that the slow rotation in these stars must already have been achieved before they became observably magnetic. Based on data from the ESA Hipparcos satellite and on observations collected at the European Southern Observatory (La Silla, Chile; ESO programs Nos. 43.7-004, 44.7-012, 49.7-030, 50.7-067, 51.7-041, 52.7-063, 53.7-028, 54.E-0416, and 55.E-0751), at the Observatoire de Haute-Provence (Saint-Michel l'Observatoire, France), at Kitt Peak National Observatory, and at the Canada-France-Hawaii Telescope.

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