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Publié : 1er février 2011

3D simulations Spectro-photocentric and consequences on Gaia measurements

Dear Colleagues,

We are pleased announce that the paper "Radiative hydrodynamics simulations of red supergiant stars. III. Spectro-photocentric variability, photometric variability, and consequences on Gaia measurements" has been accepted by Astronomy and Astrophysics.

We explored the impact of the granulation on the photocentric and photometric variability. We quantify these effects in order to better characterise the error that could possibly alter the parallax measured by Gaia. For this purpose, we use 3D radiative-hydrodynamics simulations of convection with CO5BOLD and the post-processing radiative transfer code OPTIM3D to compute intensity maps and spectra in the Gaia G band [325 – 1030 nm].

We provided astrometric and photometric predictions from 3D simulations of RSGs that are used to evaluate the possible degradation of the astrometric parameters of evolved stars derived by Gaia. The number of bright giant and supergiant stars whose Gaia parallaxes will be altered by the photocentric noise ranges from a few tens to several thousands.

In the worst situation, In the blue photometric band the fluctuations go up to 0.28 mag and up to 0.15 mag in the red filter ; while the degradation of the astrometric fit caused by this photocentric noise will be noticeable up to about 5 kpc for the brightest supergiants. Moreover, parallaxes of Betelgeuse-like supergiants are affected by an error of the order of a few percents.

We also show that the photocentric noise, as predicted by the 3D simulation, does account for a substantial part of the supplementary ’cosmic noise’ that affects Hipparcos measurements of Betelgeuse and Antares.

Arxiv link : http://arxiv.org/abs/1012.5234

Best regards, Andrea Chiavassa