Betelgeuse

Re: Betelgeuse

Postby Robin Leadbeater » Thu Feb 13, 2020 10:58 pm

Hi James

James Foster wrote:It still looks like Betelgeuse EW at Ha has decreased significantly since last year.


I agree. Dividing my spectra for 2020-02-04 by 2019-12-28 confirms that the H alpha absorption has indeed reduced since the end of last year.

betelgeuse_20200204_div_20191228_Leadbeater.png
betelgeuse_20200204_div_20191228_Leadbeater.png (53.56 KiB) Viewed 2939 times


Cheers
Robin
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Re: Betelgeuse

Postby Christian Buil » Sat Feb 15, 2020 2:42 pm

High resolution spectra of Betelgeuse (VHIRES-MO, R=38 000) :

Image

Le profil Halpha est modifié entre décembre 2019 et février 2020 de manière subtile (le décalage spectral est de l'ordre de 4,5 km/s), mais il est très difficile de dire s'il s'agit d'une évolution banale à la surface de l'étoile ou si la raison est l'événement actuel. On sait à présent d'après les dernières observation VLT (imagerie directe), qu'il s'agit très probablement d'un nuage obscurs qui occulte une partie du disque. Est-ce que cette asymétrie sur la brillance du disque constatée peut produire un tel décalage Doppler (modification du champ de vitesse en rotation de l'astre) ?
(note, j'ai corrigé la vitesse héliocentrique et les raies telluriques sont retirées).



Christian Buil
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Re: Betelgeuse

Postby Robin Leadbeater » Sat Feb 15, 2020 6:36 pm

Very interesting Christian. 4.5km/s is certainly of the right order
https://www.obspm.fr/the-slow-rotation- ... ml?lang=fr
The line is also narrower as well as would be expected if part of the star is obscured

Cheers
Robin
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Re: Betelgeuse

Postby Robin Leadbeater » Sat Feb 15, 2020 7:54 pm

Here is a comparison between the doppler and VLT image assuming the VLT image is orientated the same. (The VLT image was taken in December though so might not represent the current state)

Betelgeuse.png
Betelgeuse.png (160.77 KiB) Viewed 2823 times


There is a high resolution UVES spectrum from 2002 here

http://www.eso.org/sci/observing/tools/ ... tonow.html

how does H alpha compare with now?

Cheers
Robin
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Re: Betelgeuse

Postby Hamish Barker » Thu Feb 20, 2020 2:41 am

Hi All,

I finally made time to take a spectrum with my L200. My guide camera isn't very good and the guiding optics seem out of collimation (lots of astigmatism), so it was hard to tell when i was on the slit, and it was getting late, so only 1x8 seconds exposure, then a hurried reference using Mintaka (O9III) before it all got too low behind the garage.

So not a very good result, lots of noise, doubtful reference/camera response correction etc, but a start! I also took a division of the spectra with M4v reference spectrum from the Vspec library. There does seem to be an absorption at 7051A (TiO?) and perhaps incompletely corrected Atmospheric O2 band at 6867A. The big peak in the division spectrum at 5890 I'm not sure if is just my instrument not having picked up the depth of the Na absorption line, or perhaps there really is something happening there.

I'll try to improve (left everything hooked up and threw a tarp over it) if the weather is clear tonight, with more exposures and hopefully I'll be able get the guider collimation sorted with a T42 tilt plate between the spectrograph and focuser.

Hamish
Attachments
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Betelgeuse-2020-02-19-1233UTC.png
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Re: Betelgeuse

Postby Paolo Berardi » Wed Feb 26, 2020 5:42 pm

A paper on the Betelgeuse dimming (optical spectrophotometric based analysis):

Betelgeuse Just Isn’t That Cool: Effective Temperature Alone Cannot Explain the Recent Dimming of Betelgeuse
Emily M. Levesque, Philip Massey

https://arxiv.org/abs/2002.10463

Clear skies,
Paolo
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