Astrometric search for planets around M8–L2 dwarfs

Sahlmann et al. "Astrometric planet search around southern ultracool dwarfs I: First results including parallaxes of 20 M8-L2 dwarfs"
http://arxiv.org/abs/1403.1275
Using astrometry to search for giant planets around low-mass dwarfs. Unfortunately none are found (although it is noted that the giant planet frequency around such stars is not expected to be high).

Quote :

On the basis of Fig. 11, which excludes tight binaries, we found that none of the 18 targets hosts a giant planet more massive than ~5 MJ within 0.1–0.8 AU, where strictly speaking we cannot exclude their presence at orbital periods of one year (0.44 AU). Consequently, the upper limit on the occurrence of these giant planets within 0.1–0.8 AU around M/L-transition dwarfs is 9 %.

On the other hand, two new binary systems were discovered:

Quote :

We discovered two new binary systems with separations of 0.36 AU (JS13) and ~1 AU (Sahlmann et al. in prep.) and can exclude the presence of additional binaries within ~1.5 AU (Fig. 11). We thus found that the fraction of M8-L2 dwarfs that form tight (≲1 AU) binary systems is 10⁺¹¹₋₃ %. This results obtained from our astrometric observations agrees with the outcome of the radial velocity survey of Blake et al. (2010).

Lazorenko et al. "Astrometric planet search around southern ultracool dwarfs II: Astrometric reduction methods and a deep astrometric catalogue"
http://arxiv.org/abs/1403.4619

Description of the methods used and causes of systematic errors.