Gam Cas Halpha evolution

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Olivier GARDE
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Gam Cas Halpha evolution

Post by Olivier GARDE »

Here's a graph with two spectras of Gam Cas : one taken the 3Oth july and the other taken the 20th september

Image
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http://o.garde.free.fr/astro/Spectro1/Bienvenue.html
Ernst Pollmann
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Re: Gam Cas Halpha evolution

Post by Ernst Pollmann »

Dear colleagues,
V-brightnesses are among other things indicators for gas discs and their variability in Be stars that shine in the light of the hydrogen line (emission) Halpha. The Be star gamma Cas is a classic example of this.
Halpha EW versus Vmag.png
The attached plot impressively shows the growth of the hydrogen gas disk (ordinate: Halpha equivalent width) with increasing V-brightness from September 1998 to February 2021.
DSLR and CCD brightness measurements therefore also have a reasonable justification in this area.
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Ernst Pollmann
Robin Leadbeater
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Re: Gam Cas Halpha evolution

Post by Robin Leadbeater »

Hi Ernst,

I have sometimes wondered if a significant amount of H alpha flux ends up in a V brightness measurement. (H alpha is at the edge of the published V filter profiles.) B might be a more independent measure, though this is further from the H alpha continuum wavelength so is not as good a proxy as V for estimating the true absolute flux in H alpha rather than just EW. Have you any estimate of the effect of H alpha emission on the V brightness due to it being included in the V passband ?

I see this paper suggests approximately 37% of brightness variability in Be stars are related to variations in the disc

https://arxiv.org/abs/1609.08449

and the correlation between brightness and H alpha flux can be positive or negative

https://arxiv.org/abs/1301.3721v2

Cheers
Robin
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Ernst Pollmann
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Re: Gam Cas Halpha evolution

Post by Ernst Pollmann »

Robin,
this correlation plot could mean that the Halpha flux is growing faster than the continuum flux. On the other hand, it also means that the disc not only creates lines, but also contributes to the continuum flux (which is actually not new).
The ratio of the flux contributions of Halpha to the continuum is not explicitly known to me in the case of gamma Cas.
On the other hand, I am very familiar with the two publications mentioned.

Ernst
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