Hi I worked with turtlebot distro hydro, i want to navigate my robot with rgbdslam so i roslaunch my turtlebot ,openni+rgbdslam, octomapserver, movebase, but after when i did roswtf i found this warning:

WARNING The following node subscriptions are unconnected:
 * /robot_tf_listener:
   * /robot_tf_listener/costmap/footprint
   * /tf_static
 * /rviz:
   * /move_base/global_costmap/costmap_updates
   * /move_base/local_costmap/costmap
   * /move_base/local_costmap/costmap_updates
   * /projected_map_updates
   * /tf_static
   * /particlecloud
   * /move_base/global_costmap/costmap
   * /move_base/TrajectoryPlannerROS/local_plan
   * /move_base/TrajectoryPlannerROS/global_plan
 * /octomap_server:
   * /tf_static
 * /camera/camera_nodelet_manager:
   * /tf_static
 * /mobile_base_nodelet_manager:
   * /mobile_base/commands/reset_odometry
   * /mobile_base/commands/external_power
   * /kobuki_safety_controller/disable
   * /mobile_base/commands/sound
   * /mobile_base/commands/digital_output
   * /mobile_base/commands/led1
   * /mobile_base/commands/led2
   * /kobuki_safety_controller/enable
   * /mobile_base/commands/motor_power
   * /cmd_vel_mux/input/teleop
   * /kobuki_safety_controller/reset
   * /mobile_base/commands/controller_info
 * /move_base:
   * /tf_static
   * /map
 * /pointcloud_to_laserscan:
   * /cloud_in
   * /tf_static
 * /rgbdslam:
   * /tf_static

so these nodes are subsribed to topics that no one is publishing to,I noticed that the tf_static topic is present in all these nodes. but i didn'tt understand what is this topic and which node is the reponsable to publish it.

I really need your help, Thanks in advance