Betelgeuse: A red giant in its final phase

Betelgeuse (alpha Orionis) is one of the most recognisable stars in the night sky. Located in the contellation of Orion, it is (usually) bright, with magnitude of V~0.6.

Betelgeuse is a red supergiant. It left the main sequence about 1 million years ago, and has been a red supergiant for about 40,000 years. The radius of Betelgeuse is at least the size of the orbit of Mars, and at maximum diameter may possibly equal the orbit of Jupiter. It is a core-collapse SN II progenitor, which means that eventually, Betelgeuse will burn enough of its hydrogen that its core will collapse and it will explode as a supernova. This will occur sometime in the next 100,000 years. When it explodes, as seen from Earth, it is expected to (briefly) outshine the full Moon.

Betelgeuse is a semi-regular pulsating star: the brightness (or magnitude) varies. Betelgeuse's variability was first noticed in 1836, and in December 1852 it was thought by Herschel to be "the brightest star in the northern hemisphere", rivaling Rigel.

However, recently Betelgeuse has significantly dimmed. Although in 1927 and 1941 the magnitude of Betelgeuse dropped below V=1.2, in early 2020 is faded to to its faintest brightness than any time in the past ~150 years, before brightening again in spring 2020. In late summer 2020, Betelgeuse appeared to begin to fade again.

The drop in flux could be due to two effects: the oscillations in the upper atmosphere may have entered a new state, causing the star to expand and cool; (ii) a significant dust production event could have occured, causing increased attenuation. More speculatively, Betelgeuse could be about to go supernovae.

The goal of this project is to measure the magnitude of Betelgeuse in several bands (over the course of a few weeks), plot the light curve, and interpret the data.

Measuring the magnitude of such a bright star is not trivial, and so some novel techniques are required to carry out such an experiment.

Some useful links:

Recent newsletter from AAVSO

AAVSO science alert (including a V-band light curve)

AAVSO science alert

science alert

Sky and Telescope Article


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