Rigel

A supergiant in Orion

Rigel, also identified as Beta Orionis and HD 34085, is a B8 Ia supergiant. Its blue-white appearance contrasts with red supergiants. The 2012 study by Moravveji and colleagues describes Alpha Cygni-type variability and membership of a multiple-star system. This profile concerns the supergiant component, rather than the combined extent of that system.

Interpreting the adopted size

We adopt the radius of 78.9 ± 7.4 solar radii listed in that study’s Table 1. It combines a limb-darkened angular diameter of 2.75 ± 0.01 milliarcseconds with an adopted distance of 264 ± 24 parsecs. This historical determination depends on distance; it is not the diameter of the entire extended atmosphere. The adopted effective temperature is 12,100 ± 150 K, attributed in the table to earlier spectroscopic analyses. Radius and temperature therefore do not come from the same measuring technique.

Following the variability

The campaign combined approximately 28 days of MOST satellite photometry with more than six years of spectroscopic monitoring. Radial velocities revealed 19 significant periodicities. Such variations probe the structure of a massive star, rather than providing an explosion date. Brightness oscillations and changes in spectral lines trace different processes and do not necessarily evolve together.

A probe of another atmosphere

In a Cassini image taken on 28 April 2006, Rigel appears behind Saturn’s atmospheric haze. NASA/JPL explains that the star’s changing brightness at different apparent heights helps investigate that haze. This is an alignment seen by the spacecraft, not evidence that Rigel is near Saturn. Both this observation and the pulsation campaign are historical results, not a live view of the star.

Interpreting the catalogue

The atlas retains the historical HYG distance of 264.5503 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.