| The applet now loading into this page is intended help
you to plan your Michelle observations on UKIRT or Gemini by predicting
the spatial and spectral coverage at the array for any of Michelle's wide
range of configurations. The sensitivity figures should be taken only as
an optimistic guide, as the true performance won't be known until February 2004. If you have any problems,
the same information is available in the user guide here. |
| To use the applet, select the telescope and optical
path (imaging or spectroscopy) you plan to use, and choose the observing
wavelength using the scroll bar controls. The spectral resolving power
and wavelength coverage for the observation can then be refined by selecting
the appropriate diffraction grating and entrance slit. The diffraction
order, grating blaze wavelength and the angle of incidence (in degrees)
of light onto the grating are all reported in the box next to the grating
selector. |
| For imaging, the slit and grating selection controls
are replaced by a filter control, with the filters denoted by their centre
wavelength and fractional bandwidth (expressed as a percentage of the centre
wavelength). This control has now been updated to reflect the filters that
are actually fitted in the instrument (see also the filter
manifest in the filter wheel service manual). As more filters become
available, they will be added to the planner.
|
| The lower half of the panel shows the value of a selection
of instrumental parameters as a function of position on the detector array,
|
| Pixel Column - The data in this column refers to the
left (short wavelength), centre or right hand column of the SBRC 320 column,
240 row detector array.
|
| Wavelength[mm] - The detector's
wavelength coverage. You can also select Velocity [km/sec] as the displayed
unit. Values outside the N and Q windows of good atmospheric transmission
are now displayed in red text.
|
| Spectral Resolving Power - The dimensionless ratio l/Dl.
Spectral Bandwidth [mm] and Velocity Resolution
[km/sec] units are also provided via the choice control.
|
| Optical Efficiency [%] - This is Michelle's approximate,
estimated efficiency at transporting photons arriving at the top of the
atmosphere from an astronomical target through to the detector. At certain
wavelengths, especially when using the echelle, the wavelength dependent
efficiency of the diffraction gratings will cause this figure to drop well
below its maximum value of around 34% for the spectrometer. When the Fraction
of PSF Sampled [%] item in this control is selected for the spectrometer,
it calculates the fraction of the light (within the first dark diffraction
ring) from a point source that is vignetted by the entrance slit.
|
| FWHM in Spatial Direction [pixels] - This is the full
width of the contour of half-maximum intensity for a point source, along
a column for the spectrometer and across a diameter for the imager. The
Area of Detector Sampled [pixels] is a figure that is used in calculating
the instrument sensitivity, and refers to the unvignetted region used to
calculate the 'Fraction of PSF Sampled' figure above.
|
| Flux for S/N=1 in 1 minute [mJy] - This control displays
an optimistic estimate of the predicted sensitivity for the planned
observation in a variety of formats. The flux refers to the total flux
from the object, incident at the top of the atmosphere. The Flux Density
for S/N=1 in 1 minute [mJy/square arcsecond] refers to extended sources. NB: The sensitivities for the two broadband N and Q filters
are very uncertain, and depending on testing at UKIRT in February 2004, could be twice as poor as given here. |
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