We present new high angular resolution observations at near-IR wavelengths of the core of the Luminous Blue Variable eta Carinae, using NAOS-CONICA at the VLT and VINCI at the VLT Interferometer (VLTI). The latter observations provide spatial information on a scale of 5 milli-arcsec or ~ 11 AU at the distance of eta Carinae. The present-day stellar wind of eta Carinae is resolved on a scale of several stellar radii. Assuming spherical symmetry, we find a mass loss rate of 1.6*E-3 Msun/yr and a wind clumping factor of 0.26. The VLTI data taken at a baseline of 24 m show that the object is elongated with a de-projected axis ratio of approximately 1.5; the major axis is aligned with that of the large bi-polar nebula that was ejected in the 19th century. The most likely explanation for this observation is a counter-intuitive model in which stellar rotation near the critical velocity causes enhanced mass loss along the rotation axis. This results from the large temperature difference between pole and equator in rapidly rotating stars. eta Carinae must rotate in excess of 90 percent of its critical velocity to account for the observed shape. The large outburst may have been shaped in a similar way. Our observations provide strong support for the existence of a theoretically predicted rotational instability, known as the Omega limit.Based on observations obtained at the European Southern Observatory.
Astronomy and Astrophysics
- Pub Date:
- October 2003
- stars: circumstellar matter: stellar winds: mass loss;
- stars: individual: eta Carinae;
- 5 pages, 3 figures, accepted for publication in A&