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Astron. Astrophys. 360, 1019-1030 (2000)


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Doppler imaging of stellar surface structure

XIV. The double-lined pre-main-sequence binary V 824 Arae = HD 155555 *

K.G. Strassmeier 1 and J.B. Rice 2

1 Universität Wien, Institut für Astronomie, Türkenschanzstrasse 17, 1180 Wien, Austria (strassmeier@astro.univie.ac.at)
2 Brandon University, Department of Physics, Brandon, Manitoba R7A 6A9, Canada (rice@BrandonU.ca)

Received 8 February 2000 / Accepted 15 June 2000

Abstract

Photospheric Doppler images for both stellar components of the double-lined pre-main-sequence binary V 824 Ara reveal surface temperature inhomogeneities of up to 1800 K on both stars. The spot geometry on the hotter primary is dominated by an elongated, tilted, equatorial feature but our maps from two spectral regions consistently also show a polar spot cooler by 1700 K. The secondary star has spots mainly at low and very high latitudes but not a full-sized polar cap. A flux-tube simulation with appropriate stellar models for V 824 Ara suggests that any polar or high-latitude spot must have formed after flux-tube emergence. Generally, the low-latitude spots on both stellar components appear to be mostly concentrated on the hemispheres turned away from each other while the asymmetry of the polar spot on the primary points in the direction of the orbital motion.

We present new radial velocities and use them to re-evaluate the orbital elements and to derive absolute parameters for both stellar components. The absolute brightness and mass of the two stars suggest that they are very close to the main sequence - but not yet on the ZAMS - if an inclination of the orbital plane (and rotational axes) of 52o is adopted as suggested by the Doppler imaging. Since both stars are active, we solve for the inclinations of both stellar components separately and find that the values agree to within their uncertainties.

Key words: stars: activity – stars: starspots – stars: imaging – stars: individual: V 824 Ara – stars: late-type

* Based on observations collected at the European Southern Observatory

© European Southern Observatory (ESO) 2000

Online publication: August 23, 2000

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