preparation using the Interactive Mask Design Interface
|NEW ! IMDI
2.0 released. The new release of IMDI includes
support for the new E2V CCD
at LRS/Dolores and the new
set of grisms. In addition, some known issues in previous
have been fixed.
Getting the IMDI software:
the most recent version of the IMDI package to the
resident astronomer; be sure
installed in your system and included in the IDL_PATH.
Note for Linux Users. There are two
known issues when using IMDI with Linux X-window systems. The first is
IMDI display is not
restored (i.e. it remains black) when windows overlap. Second problem,
changes in the IDL color table are not supported with the 16/24-bit graphics that
is the default in Linux. As the results,
the color controls enabled by the COLOR button do not take immediate
effect on the displayed image. Both problems will be fixed in the
next version IMDI V.2.1. In the meantime, we suggest the following
workarounds. 1) Edit the X-windows parameter
(e.g., /etc/X11/xorg.conf) by adding the Option "BackingStore" (and the
"Virtual" option if you run IMDI on a small-screen laptop) as in this
Using the IMDI is intended to be self-explaining. Run it by typing "@ mos" from IDL (Vers. 5.4 or later). Images taken with the DOLoRes are displayed on a 3-window screen, from which targets are interactively picked up and centered. Slits are adjusted under control of a real-time anti-overlap algorithm.
|Opening a pre-imaging FITS file
using is the
first step. The program can read both ".fits"
and ".fts" image files. The upper window (``main window'') of the
is used for image selection, while the lower rigth window (``zoom
window'') is used for fine centering of the targets. The lower-left
section gives an overview of the field (currently unused). The color
look-up table of the
image can be modified using
Note, however, that MOS is the recommended lookup table (also VOLCANO was found to be useful in case of very faint targets).
|When IMDI is started, the basic setup information (CCD, grism table, etc ...) are read from a TNG/DOLoRes setup file provided with the release of the mask design software. Just choose your grism from the menu. The spectral range can be edited by changing the upper and lower wavelength in the small windows (you must hit the RETURN key in each field, due to a known limitation of IDL).|
You may notice that the default wavelength ranges for the grisms are
different from those listed in the DOLoRes documents. This is not a
the latter are effective ranges determined by the size of the CCD in
case of a central (long)slit, the default grism ranges for the MOS are
related to the wavelength range covered by the grisms.
||Some data on the target field are read from the FITS header and displayed in the middle part of the main panel. This information will be inherited by the mask files and transferred to the associated documentation.|
||Objects are selected by clicking once (left button of the mouse) on the main
window. Then click on the zoom window with the right button to center the target. The size of
the box can be changed by using the middle button.
Before that, choose the
appropriate centering method in the main panel. Rectangles are used to outline the
location of the spectra. These are computed using information in
the IMDI instrument database and
the image header. The slits are interactively adjusted by the user
control of an anti-overlap algorithm.
NOTE. Using "centroid", the slit appears mis-centered in the zoom window. This problem only affects the graphics, not the computed centroids, and should be ignored.
|The [import ascii]
function allows importing of a list of targets from an ASCII catalog
produced by automated image analysis and classification programs (e.g.,
or by hand. The first three columns must be IDENTIFIER, x_pixel,
y_pixel. Any further columns are ignored.
|Clicking on a target activates the
Control Panel. By this mechanism, you can either choose a new
or pick up and modify a previously defined target. The length, setting,
and angle of the slitlet are defined by sliders in a
way. The minimum length of slits is 8 pixels (2"), even if you specify
After interactive editing, save the slit, delete it, or just quit
changes. The buttons and in the main panel allow you to suspend mask editing at
any time and resume it later. The
"saved configuration" is a
temporary IDL structure not to be confused with the final
of the mask design.
|The IMDI anti-collision algorithm warns you in real time
about spectrum overlap by highlighting the overlapping spectra. Our
advice is not to pack the spectra too close to each other, letting some
extra space between spectra. This will make reduction much easier
Still, the final decision about accepting these warnings is left to user's responsibility, although there are software checks against slitlets violating severe mechanical constraints. In particular, slits too close to the edges are rejected by safety checks. An automatic slit optimizer is not foreseen with the first release of IMDI.
||A useful feature allowed by the mask design software (and by Mask-Mode MOS observations) is stacking of two rows of spectra. Using a low-dispersion grism in combination with an appropriate filter to reduce the spectrum length, more than one spectrum can be aligned along the dispersion direction. (Note, however, that this mode is not offered as a standard facility of DOLoRes.) A multiplex factor of 2 will allow up to 80-100 spectra per mask (10" slits).|
At least two reference stars, well spaced
the dispersion direction, must be included in each mask. The
of the reference holes (in practice, slits with minimal length) is
to speed up MOS pointing at the telescope. Of course, the two stars
must be on
same coordinate system as the targets.
Each mask slit setup, once
satisfactory, is saved to a mask-cutting file using After
finishing your design, for each mask you will end up with:
mask-cutting drawing in the standard Drawing Interchange File Format
(DXF), for instance held_AOT9_123_mask01.dxf;
documentation file, logging the DOLoRes and telescope setup associated
with the mask,
all useful information from the image header, and a listing of the
in plain ASCII format (e.g., held_AOT9_123_mask01 .log);
|a finding chart in postscript format (not yet available in the Window environment) (e.g., held_AOT9_123_mask01.ps).|
After packing all files and a
detailed README file in one gzipped-tar file (e.g., held_AOT9_123 .tgz), the P.I. shall notify the DOLoRes Staff Astronomer who will provide file
transfer instructions. Masks will be manufactured by TNG mechanics
staff in advance of the run. Do not forget to
specify in your e-mail the requested slit width (1.1 or 1.6 arcsec) for