2.6839          $-$ 0.0077    $+$ 0.0066
             $b$                                            0.28            $-$ 0.044     $+$ 0.036
             $i$                    \[deg\]                88.01            $-$ 0.28      $+$ 0.33
             $a$                    \[AU\]                 0.0368                       
        $a/R_{\star}$                                      7.986            $-$ 0.073     $+$ 0.074
        $\rho_{\star}$          \[g cm$^{-3}$\]            1.410            $-$ 0.039     $+$ 0.040
      $log \; g_{\star}$        \[cm s$^{-2}$\]            4.433            $-$ 0.008     $+$ 0.008
            $u_1$                                          0.359            $-$ 0.045     $+$ 0.042
            $u_2$                                         $-$0.029          $-$ 0.071     $+$ 0.077
            $M_p$              \[$\rm M_{jup}$\]         0.566$^*$          $-$ 0.025     $+$ 0.025
            $R_p$              \[$\rm R_{jup}$\]           0.993            $-$ 0.012     $+$ 0.012
           $\rho_p$             \[g cm$^{-3}$\]            0.715            $-$ 0.040     $+$ 0.041
         $log \; g_p$           \[cm s$^{-2}$\]            3.152            $-$ 0.022     $+$ 0.022
           $\Theta$                                        0.043            $-$ 0.002     $+$ 0.002
   \[tab:final param mcmc\]                                                             

  : Parameters for the XO-2 system.

$^\dagger$ From @Sing2011\
$^\ddag$ From @Fernandez2009\
$^*$ Using radial velocity measurements from @Burke2007\
$\Theta$: Safronov number

![White-light curve (top) and residuals (bottom) for after the MCMC analysis. Different colors represent the 6 groups of data. The best fit model yields a point-to-point precision of 350 ppm.[]{data-label="fig:white-light curve"}](fig9.png){width="11cm"}

Spectrum {#sec:Spectrum}
========

Instrumental parameters that affect the spectrum {#sec:Identifying NICMOS noise sources}
------------------------------------------------

To identify the main sources of systematics affecting the spectrum, we first build the XO-2 Stellar spectrum in a simple way: on each image, the flux is summed over each column of the 