The dramatic change of the fossil magnetic field of HD 190073: evidence of the birth of the convective core in a Herbig star ?

Abstract

In the context of the ESPaDOnS and Narval spectropolarimetric surveys of Herbig Ae/Be stars, we discovered and then monitored the magnetic field of HD 190073 over more than four years, from 2004 to 2009. Our observations all displayed similar Zeeman signatures in the Stokes V spectra, indicating that HD 190073 hosted an aligned dipole, stable over many years, consistent with a fossil origin. We obtained new observations of the star in 2011 and 2012 and detected clear variations of the Zeeman signature on timescales of days to weeks, indicating that the configuration of its field has changed between 2009 and 2011. Such a sudden change of external structure of a fossil field has never previously been observed in any intermediate or high-mass star. HD 190073 is an almost entirely radiative pre-main sequence star, probably hosting a growing convective core. We propose that this dramatic change is the result of the interaction between the fossil field and the ignition of a dynamo field generated in the newly-born convective core.

4 pages, 5 figures, accepted for publication in A&A

References in corpus (4)

• Simulations of core convection in rotating A-type stars: Magnetic dynamo action
• The magnetic field of the pre-main sequence Herbig Ae star HD 190073
• EK Eridani: the tip of the iceberg of giants which have evolved from magnetic Ap stars
• The MiMeS Project: Magnetism in Massive Stars

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• Imaging the inner astronomical unit of Herbig Be star HD 190073
• High-cadence, High-resolution Spectroscopic Observations of Herbig Stars HD 98922 and V1295 Aquila
• Baroclinic Instability in Stellar Radiation Zones
• HARPS spectropolarimetry of three sharp-lined Herbig Ae stars: New insights
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• Baroclinic Instability in Differentially Rotating Stars
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