5.3 Calibration models 5.3.7 Photometric relationships with other photometric systems 5.4 Processing steps

5.3.8 Saturation correction

Author(s): Josep M. Carrasco

The current calibration is not perfectly accounting for saturation effects (see Figure 5.22 comparing residuals in the Hipparcos and Tycho-2 photometric transformations derived in Section 5.3.7 as a function of the magnitude).

In order to provide a tool to empirically correct this trend at bright magnitudes we fit here a relationship of this trend in Figure 5.22, combining both Hipparcos and Tycho-2 residuals. The resulting fitted relationships are the following:

$\displaystyle G^{\rm corr}-G$	$\displaystyle=$	$\displaystyle-0.047344+0.16405G-0.046799G^{2}+0.0035015G^{3}$
$\displaystyle G_{\rm BP}^{\rm corr}-G_{\rm BP}$	$\displaystyle=$	$\displaystyle-2.0384+0.95282G-0.11018G^{2}$
$\displaystyle G_{\rm RP}^{\rm corr}-G_{\rm RP}$	$\displaystyle=$	$\displaystyle-13.946+13.239G_{\rm RP}-4.23G_{\rm RP}^{2}+0.4532G_{\rm RP}^{3}$

The ranges of applicability for these relationships are the following:

•

$2.0<G_{\rm obs}<6.5$ mag for the $G$ relationship,
•

$2.0<G_{\rm obs}<4.0$ mag for the $G_{\rm BP}$ relationship, and
•

$2.0<G_{\rm obs}<3.5$ mag for the $G_{\rm RP}$ relationship.

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5.3.8 Saturation correction

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