Among binary NEAs observed so far, our photometric datasets for these three sytems (together with 1996 FG3) are the longest coverages obtained, providing a unique opportunity to study an evolution of the mutual orbits of components of small binary asteroids.

The structure of this paper is as follows. In Section \[Model\], we present a model of the mutual orbit of the components of 1999 KW4 and 2001 SL9 constructed from our complete photometric datasets. Then in Sections \[ParamsKW4\] and \[ParamsSL9\], we summarize our results with already known parameters of the two binaries. In Section \[byorp\], we then discuss implications of the observed characteristics, especially on the BYORP theory, from the derived drifts of the mutual orbits.

Mutual orbit models of 1999 KW4 and and 2001 SL9 {#Model}
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Observational data {#KW4ObsData}
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            Time span             No. of nights            Telescope            References
  ------------------------------ --------------- ----------------------------- ------------
   2000-06-19.0 to 2000-06-29.0         5               0.65-m Ondřejov            P06
   2001-06-03.2 to 2001-06-20.9         7              0.41-m River Oaks           P06
                                        4               0.65-m Ondřejov            P06
   2016-06-07.9 to 2016-06-22.3         6               0.65-m Ondřejov         This work
                                        6          0.5-m Sugarloaf Mountain     This work
   2017-06-01.8 to 2017-06-27.0         8               0.65-m Ondřejov         This work
                                        6          0.5-m Sugarloaf Mountain     This work
   2018-06-05.9 to 2018-06-18.9         9               0.65-m Ondřejov         This work
   2019-05-31.1 to 