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Using AAVSO light curve generator I have plotted V and B magnitudes of Betelgeuse in the past 150 days to see trend of B-V color index. If dust would be the cause of the recent drop in the star brightness, I would expect redenning (in fact de-blueing) of the starlight, that is increase of B-V value. In fact, B-V changed only slightly and it the opposite direction. In case of interstellar reddening, I thinks that change of V magnitude is roughly 3 times greater than the change of B-V color index, which is not the case here.

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Is the change of B-V color index of Betelgeuse compatible with expected properties of circumstellar dust?

Leos Ondra
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The changes in Jupiter's B-V index are not compatible with the expected properties of circumstellar dust. Circumstellar disks cause Infrared excess, which would cause reddening, not a shortening of the wavelength, as you have observed. Reddening works by the absorption of the light from the circumstellar disk, and then reemitting the wavelength as longer wavelengths, not shorter ones, which would correspond to an increase of energy and violate the conservation of energy. A possible source for the brightness change is that Betelgeuse is a semiregular variable star, exhibiting brightness changes. On top of this, semiregular variable stars can have secondary pulsation periods around ten times longer than the original period.

Astrovis
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