<p>The changes in Jupiter's B-V index are not compatible with the expected properties of circumstellar dust. Circumstellar disks cause <em>Infrared</em> 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.</p>

CC BY-SA 4.0
2024-03-09T18:53:31.300Z
2024-03-09T18:53:31.300Z
Astrovis
<p>Using AAVSO <a href="https://www.aavso.org/lcg" rel="noreferrer">light curve generator</a> 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 <em>opposite</em> direction. In case of <em>interstellar</em> 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.</p>

<p><a href="https://i.sstatic.net/Bw24z.jpg" rel="noreferrer"><img src="https://i.sstatic.net/Bw24z.jpg" alt="enter image description here"></a></p>

<p>Is the change of B-V color index of Betelgeuse compatible with expected properties of <em>circumstellar</em> dust?   </p>

CC BY-SA 4.0
2020-02-16T01:47:40.007Z
Different and unanswered, but related: [Does the current “fainting” of Betelgeuse show any spectral trends that differ from it's normal variability?](https://astronomy.stackexchange.com/q/34545/7982) I wonder if this data can be an answer to that question?
uhoh
<photometry><dust><variable-star><extinction><betelgeuse>
Color index B-V of the dimming Betelgeuse
Leos Ondra
# Color index B-V of the dimming Betelgeuse

(Asked by: username_0 on 2020-02-15)

Using AAVSO [light curve generator](https://www.aavso.org/lcg) 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.

[![enter image description here](https://i.sstatic.net/Bw24z.jpg)](https://i.sstatic.net/Bw24z.jpg)

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

**Tags:** photometry, dust, variable-star, extinction, betelgeuse
> **Comments:**
> **username_1**: Different and unanswered, but related: [Does the current “fainting” of Betelgeuse show any spectral trends that differ from it's normal variability?](https://astronomy.stackexchange.com/q/34545/7982) I wonder if this data can be an answer to that question?  

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## 1 answers

### Answer by username_2 on 2024-03-09. Score: 1

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.


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