 |
 |
 |
 |
 |
|
 |
|
|
|
|
|
Assumptions and input values.
The ETC assumes QE efficiency curves of the detectors and overall
throughput of the optical chain as of May 4 2007. Future changes will
be notified.
The total efficiency curves (filter EXCLUDED) are shown here.
In addition, the ETC assumes that the only source of background
(apart from dark current in the IR detectors) is Zodiacal light,
ignoring both thermal bakground and Earth shine. The former is due to
the low wavelength cutoff at λ<17000 Å, the latter is expected
becuase of the high orbit.
The intensity of the zodiacal light at different wavelengths has been
taken from (see link1
and
link2).
The read-out noise, dark current and other parameters are left free,
with some pre-defined choices, pending their final definition.
Brief description of the functionalities.
Overview
The ETC is pretty easy to use. The user has to set the input
parameters, and click "compute" at the bottom.
Unlike other ETCs, the output does not appear on a new page, but on
the same page, with updated numbers.
This allows to use the output of a computation as input to the next one.
By clicking on "View Detailed Pars" on bottom, the user can obtain
more details no the calculation, see and
download the simulated FITS image.
The ETC allows you to select the channel (Opt/IR) and the adopted
filter. For the latter, the user can design a custom filter of
arbitrary width and efficiency.
How to use the ETC.
First of all, you have to select between the Optical/IR channel with
the button on the upper frame.
In the central window, ("Input Parameters") the user can define the
filter set, the r.o.n. parameters and the background intensity, and
the shape of the target objects. Stars are defined as PSF-like
objects, while Spiral and Elliptical galaxies are assumed to have an
half-light-radius of 0.4", convolved with the PSF.
Note that the PSF is assumed to be 0.23" at λ=8500 Å,with a
diffraction-limited scaling at longer λ.
In the two lower panels the user can select the exposure time, S/N
and limiting magnitude.
The left panel is related to the Total observing time. The user can
select two out of three free parameters (Tortal exposure time, SNR,
Ttotal AB mags) and compute the third one, just by selecting the
relevant radio button.
The SNR is computed in a circular aperture with diameter 2.5xPSF,
while the magnitude is the Total magnitude of the target object.
The right panel allows the user to define the exposure time of the
single exposure, if the total exposure time is obtained with several
exposures. Here the user can either set the Number of Exposures, or
the exposure time, or the desired level of Sky counts or the
magnitude of the faintest saturated star.
Observing with DUNE.
DUNE will have a mosaic of detectors and will be operated in transit
mode. As a result, images will be acquired over multiple exposures
with the same exposure time. The current baseline foresees 4
detectors (along the scanning direction) for the optical and 5 for
the IR. If all optical detectors have the same filter, and IR ones
have three filters, the expected number of exposures will be 4 for
the optical and 2+2+1 for the IR, in each filter.
Assuming a drift time of about 1500 sec, the single exposure times
are 4x375 sec (opt) and 2x300 + 2x300 + 300 sec (IR).
This can be taken into account when using the ETC. In the right
panel, the user can specify the number of single exposures (or their
exposure time) contributing to the final image. The default values
are set in order to match the above quantitiies but the user is
allowed to change them.
...all formulas may be found in the official Large Binocular Camera ETC ( here)...
|
|
|
|
|
|
|
|
|
 |
|
 |
|
|
|
 |
|
 |
|
