Antares

A red star with an extended atmosphere

Antares, Alpha Scorpii and HD 148478, is conspicuous for its reddish colour in Scorpius. The supergiant component has a comparatively cool photosphere surrounded by an extended atmosphere. Ohnaka and colleagues’ 2013 study adopts the M1.5 Iab-b classification. Its light-emitting surface must be distinguished from the surrounding molecular layers: different wavelengths do not reveal an identical stellar edge.

Putting radius and temperature in context

This profile adopts an approximate radius of 680 solar radii, estimated in that paper from angular diameter and parallax. The relevant passage gives no individual error for the radius; a missing error does not mean zero uncertainty. The limb-darkened angular diameter measured in 2009 was 37.38 ± 0.06 milliarcseconds. The derived effective temperature is 3,660 ± 120 K. That calculation combines bolometric flux and angular size, with an uncertainty that includes assumed flux variability based on Betelgeuse.

What interferometry reveals

VLTI/AMBER combined telescope light to reconstruct continuum images and images within carbon monoxide lines. The 2013 study compared observations from 2009 and 2010 and found major changes in atmospheric gas motions. In 2017, ESO presented a two-dimensional atmospheric velocity map. Such maps distinguish material approaching or receding from the observer; they are not photographs of a solid surface.

Evolution and remaining questions

The 2013 comparison with evolutionary tracks suggested an initial mass of 15 ± 5 solar masses and an age of 11–15 million years. These are model inferences, not a direct weighing or the current mass. ESO’s 2017 release explains that the observed turbulence challenges an explanation relying on convection alone. Antares helps investigate mass loss from evolved stars, without those observations establishing a supernova date.

Interpreting the catalogue

The atlas retains the historical HYG distance of 169.7793 parsecs and its reference coordinates. That record, the catalogue spectral classification and the adopted research parameters come from different solutions. Positions have not been recalculated and one distance has not been substituted for another. The compared sizes are radii, not diameters; a scale illustration does not show present-day position or brightness.