The solar experiment
The FIES solar-experiment box is situated outside next to the entrance
of the FIES building. The box contains a fiber that is pointing at
the sky, and an iodine cell (for staff see iodine cell safety
information ) for accurate wavelength calibration. The purpose of
the box is to look at the solar oscillations through observations of
the blue sky. The fiber can be connected to the FIES spectrograph to
obtain spectra of the blue sky.
The box has a handle at the top, with which one
can pull out the iodine cell from the beam (fully up), or push it into
the beam (fully down). The handle is very stiff, so you need to apply
lots of force (eat some eggs for breakfast).
The iodine cell is heated, and the control box is placed on top of the
calibration unit trolley in the front room. The controller unit can be
swithed on/off and the heater control can be enabled/disabled with the
The optical fiber that is aimed at the sky is relayed to the
calibration unit trolley in the front room, where it can be connected
to a different fiber that comes from the spectrograph (FIES fiber #5). This latter
fiber should be either connected to the solar box, or to the
calibration unit itself for normal operation of FIES.
When to switch the fibers
For normal use of FIES the blue spectrograph fiber should always be
connected to the calibration unit. To check that the fibers are connected
correctly for normal FIES observations, try the following on the FIES sequencer:
If you see a ThAr spectrum coming in, then all is fine.
When the spectrograph is connected to the solar box,
this means that with every spectrum taken with
FIES+TELESCOPE (any of fibers 1,3,4) you get a free simultaneous sky
spectrum as well (through fiber 5 and the solar box fiber).
Note that for a typical night-time stellar spectrum, you don't want this sky
spectrum. In this case the entrance window to the box needs to be blocked,
or the fibers need to be switched (see below).
Switching the fibers
To switch the fiber setup, follow the following instructions:
Open the top white door of the calibration unit in the FIES front room.
There is a small black-metal fiber connection 'unit' , with fibers connected to it.
Depending on the setup required, unscrew the blue spectrograph fiber (next to the empty spot)
and screw it onto the empty spot, such that the light from either the solar box or the calibration unit
will be fed to the blue spectrograph fiber.
Calibration unit connected to FIES, for normal FIES operation:
Solar box connected to FIES: