Custom filters can of course also be used. Mechanically, the filters must
have 70 mm diameter; several adapters are available for 50mm filters.
Optically, the required diameter is 70 mmm for
filterwheel I and 50mm for filterwheel II; use of smaller filters will
cause loss of light in filterwheel I and loss of field in filterwheel II.
We have developed a procedure to design the masks and to do the critical alignment of
sky and mask on the telescope. We offer all users to benefit from our experience and
to make the masks according to our recipee in our mechanical shop. For more details
see the manual .
15 May 2000: A 2x4k CCD with 15 micron pixels from EEV has been tested. Advantages
of this CCD are fast read-out and good cosmetics. Disadvantages are lower QE than
the standard SITE16a chip and very strong fringing in the red!
March 2000: the V-filter is broken. Obviously the cementing of the 2 glass
disks is peeling away. It will take several weeks to get a new one!
March 2000: the red500 grism (peak efficiency at 850 nm, dispersion of 0.6nm/arcsec)
is here and will be installed before the observing runs in May
August 1999: A new grism has been ordered which has its peak efficiency at 850 nm
and a dispersion of 0.6nm/arcsec; this grism will extend the spectroscopic
capabilities of MOSCA to the red.
April 1999: The LORAL 11i detector has been replaced by a better CCD which has much
less fringing in the near IR which was a nuisance with the LORAL chip.
The new CCD is a 2x4 k CCD with 15 micron pixels; this CCD has 4 bad columns
but otherwise is fine
CALIBRATION UNIT:
The calibration unit has 1 tungsten lamp as continuum source for
testing purposes and 3 spectral lamps for wavelength
calibration.
APERTURE UNIT:
The aperture unit allows to select between:
FILTERS:
Two filter wheels with 10 positions each are available and may be used
simultaneously. The instrument is equipped with
standard broad-band filters (U, B, BV, V, R, I, z). GRISMS:
A set of 7 grisms with dispersions from 3 to 12 Angstroem per arcsec
is available:
grism lambda lambda_central dispersion
[nm] [nm] [nm/arcsec]
-----------------------------------------------------
green_250 330-1000 570 1.2
red_500 540-1000 850 0.6
blue_500 330-650 480 0.6
green_500 430-820 550 0.6
blue_1000 330-510 400 0.3
green_1000 420-650 530 0.3
red_1000 570-820 680 0.3
----------------------------------------------------
Efficiency curves are given in the manual .
FPI:
A Fabry-Perot interferometer whith piezoelectrically controllable spacing
can be used as tunable filter at a spectral resolution of 15-20
Angstroems over the wavelength range 5500 to 9500
Angstroems. Order selection is done with filters in filter wheeel II.
It is very easy to use, and there is an automatic procedure to determine
the wavelength calibration. If you plan to use the FPI
make sure that a suitable order separation filter is available!
POLARIZING OPTICS
Since there is currently little interest to use polarizers, the realisation of
polarizing optics has been postponed to an undetermined date.
MOS
Multi object spectroscopy is possible using user supplied masks which
are put into the aperture unit. The masks have
to be prepared by the observer before the observing run; there is
no possibility to make masks on Calar Alto.
SCHEDULE/HISTORY
15 May 2000: the red500 grism has been installed. Since the space in the
grism wheel is limited, the focussing prism had to be taken out. The wavelength calibration
looks very nice, see manual. The grism could not be tested on the telescope, so
the efficiency is not yet known. 
latest news
the MOSCA team:
send questions or fan mail to fried@mpia-hd.mpg.de
