The Coude Echelle Spectrographs
The Coude Echelle Spectrographs
Table 1 gives the efficiency measurements for UHRF, scaled for the
Tektronix CCD.
These figures were obtained in November 1994. The figure at 5890A was
confirmed in April 2000.
The efficiencies are expressed in three different units, explained
below.
Table 1: Efficiencies for UHRF + Tektronix.
| Lambda
(Å) |
AB(1hz/Å)
(magnitudes) |
J(100hz/0.01A))
(magnitudes) |
Pixel size
(Angstroms) |
| 4232 | 15.7 | 2.7 | 0.0024 |
| 5890 | 16.0 | 3.0 | 0.0033 |
| 7700 | 15.3 | 2.4 | 0.0043 |
Definitions
AB(1hz/Å) is defined as the ABlambda magnitude of a star which, observed at an airmass X=0 and with a wide slit, yields a count rate of 1 Hz/Å (i.e. atmospheric absorption and slit losses not included).
J(100hz/0.01A) is defined as theJohnson magnitudes yielding 100 e-/s/0.01A
through the image
slicer in 1.8" seeing at X=1.5 airmasses. It is assumed that S/N =
sqrt(N), where N is the number of photons per pixel (unbinned)
- i.e. readout noise is not included.
Pixel size is the dispersion in Angstroms/pixel (unbinned) for the Tek
CCD at R=1.0M
With the image slicer, we expect an increase of 30% in countrate in
1.5" seeing compared to
1.8" seeing.
See the detectors page for parameters needed to convert to different detectors, and to calculate the contribution of dark count and readout noise which can be significant for faint targets.
A campaign to update efficiency values has been unsuccessful due to
poor weather and is
continuing. Note, however, that the throughput of the slicer is highly
dependent on seeing
so efficiency calculations can only be approximate.