  The installation and operation of a telescope in Antarctica represent
particular challenges, in particular the requirement to operate at extremely
cold temperatures, to cope with rapid temperature fluctuations and to prevent
frosting. Heating of electronic subsystems is a necessity, but solutions must
be found to avoid the turbulence induced by temperature fluctua- tions on the
optical paths. ASTEP 400 is a 40 cm Newton telescope installed at the Concordia
station, Dome C since 2010 for photometric observations of fields of stars and
their exoplanets. While the telescope is designed to spread star light on
several pixels to maximize photometric stability, we show that it is
nonetheless sensitive to the extreme variations of the seeing at the ground
level (between about 0.1 and 5 arcsec) and to temperature fluctuations between
--30 degrees C and --80 degrees C. We analyze both day-time and night-time
observations and obtain the magnitude of the seeing caused by the mirrors, dome
and camera. The most important effect arises from the heating of the primary
mirror which gives rise to a mirror seeing of 0.23 arcsec K--1 . We propose
solutions to mitigate these effects.
