& 2501 & 129 & 212 & 90\
$\ge$12 & 630 & 156 & 251 & 138\
all ($\ge$6)& 113395 & 147 & 244 & 34\

![image](matlab/141209-093108/corr){width="\columnwidth"} ![image](matlab/141209-093108/histogram){width="\columnwidth"}

![image](matlab/141210-144919/corr){width="\columnwidth"} ![image](matlab/141210-144919/histogram){width="\columnwidth"}

Discussion
==========

Consequences of the simplifying assumptions\[sec:limits\]
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#### Data gaps:

Our simulations show that TGAS is robust to data gaps according to a realistic distribution of acquisition dead time. The data gaps result in an inhomogeneous sky distribution of actual and formal errors, but do not significantly degrade the performance in well-observed regions. Affected areas can be recovered through additional observations after the first half year. The actual length of [*Gaia*]{} observations necessary for a good solution over the whole sky is difficult to estimate without detailed knowledge about the actual distribution of gaps. However, since the whole sky is nominally covered by multiple scans every half year (cf. Fig. \[fig:frac\]), it is reasonable to conclude that the required time is less than 1 yr.

#### Non-single stars:

A large fraction of the TGAS stars are in reality binaries or multiple stars, but not recognised as such in the [*Tycho*]{} Catalogue and thus treated as single in TGAS. Some of them will be resolved by [*Gaia*]{} thanks to its 