If you use a filter of 0 and transmit of 1 the halo starts to show up,
but the real problem is that the scattering is too high.  A lot of people
do this starting out.  Generally I start with a scattering or .05 and go
from there.  The only other problem is that the halo container is
slightly visible.  This is something hard to fix, but adjusting the
transmission of the pigment of the sphere can hide it somewhat.  Here's
your source code with a few modifications:

global_settings {
  adc_bailout 0.003922
  ambient_light <1.0,1.0,1.0>
  assumed_gamma 1.9
  hf_gray_16 off
  irid_wavelength <0.247059,0.176471,0.137255>
  max_intersections 64
  max_trace_level 10
  number_of_waves 10
}

background { color <0.000,0.000,0.000> }


atmosphere {
  type 1
  distance     40.0
  color <0.8,0.8,1.0,0.0,1.0>
  scattering   0.05
  samples      5
  jitter       0.0
  aa_threshold 1.0
  aa_level     3
}


camera {
  location  <-12.000, -20.000, 15.000>
  direction <0.0,     0.0,  1.8317>
  sky       <0.0,     0.0,  1.0>
  up        <0.0,     0.0,  1.0>
  right     <1.33333,  0.0,  0.0>
  look_at   <0.000, 0.000, 0.000>
}

light_source {
  <0.000, 0.000, 18.812>
  color  rgb <1.000, 1.000, 1.000>
  spotlight
    point_at  <0.000, 0.000, 17.812>
    falloff   9.22
      radius    4.66
}

#declare Texture =
   texture
   {
      pigment
      {
         color rgbft <1.0, 1.0, 1.0, 0, .8>
      }
      finish
      {
         ambient 0.0
         diffuse 0.0
         brilliance 0.0
         phong_size 0.0
         roughness 0.0
      }
      halo
      {
         emitting
         linear
         spherical_mapping
         color_map
         {
            [ 0.0     rgbft <1.0, 1.0, 0.0, 0.0, 1.0> ]
            [ 0.088968  rgbft <1.0, 1.0, 0.0, 0.0, 0.0> ]
            [ 0.373665  rgbft <1.0, 0.0, 0.0, 0.0, 0.0> ]
            [ 1.0     rgbft <1.0, 0.0, 0.0, 0.0, 1.0> ]
         }
         turbulence 1.0
         scale  0.5
      }
   }

sphere {

  <0,0,0>,1
  texture {
    Texture
  }
  hollow
  scale 2.297393
}

P.S I had a little fun with it and changed the halo to a dust halo.
Looks pretty neat

halo
      {
         dust
         linear
         spherical_mapping
         color_map
         {
            [ 0.0     rgbft <1.0, 1.0, 0.0, 0.0, 1.0> ]
            [ 0.088968  rgbft <1.0, 1.0, 0.0, 1.0, 0.0> ]
            [ 0.373665  rgbft <1.0, 0.0, 0.0, 1.0, 0.0> ]
            [ 1.0     rgbft <1.0, 0.0, 0.0, 0.0, 1.0> ]
         }
         turbulence 1.0
         scale  0.5
      }


Harmen Mesker wrote:

> Dear Johannes,
>
> If tried this, but unfortunately this didn't help. This is an example
> of source code which produces the wrong result:
>

<snip>

> If I comment out the atmosphere section, the halo does show up. Maybe
> you can find the error in the source code?
>
> Thanks for your help,
>
> Greetings,
>
> Harmen.

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