Completed Upgrade Projects
Blue sensitive CCD for FORS1: The CCD is now offered in combination with FORS2, but only for visitor mode.
HIT-MS mode for FORS2 This allows for many pairs of spectra to be stored on the CCD before the chips is read-out. It is designed forfast spectrscopy of variable sources. See the user-manual for further details.
October 2006 - New FORS1 grism 1200B as Replacement of the FORS2 Echelle Mode: The low efficiency FORS2 Echelle mode was replaced by a newholographic grism for the spectral range 373-497nm and central wavelength 434nm. The spectral resolution would be 1430 (lambda / d lambda) for a1.0 arcsec slit with an expected grism throughput of >85%. See the user manual for more details.October 2004 - Rapid Response Mode (RRM) for FORS:Starting in Period 74, a new mode, the Rapid Response Mode (RRM), is offered for observations of transient phenomena such as gamma-raybursts (GRB) or supernovae in semi-automatic mode. More information on the RRM can be found on the RRM USG PhaseII webpages.
June 2004 - New Volume Phased Holographic Grism for FORS1:A new holographic grism, GRIS_1200g+96, with a spectral range from 431 to 549nm and a central wavelength of 488nm has been installed June 15 2004 on FORS1. The spectral resolution (lambda / d lambda) is 1650 (24.4 Å/mm or 0.59 Å/pixel) for a 1.0 arcsec slit.
April 2004 - High Time Resolution (HIT) Modes for FORS2:We have been working on the software to re-invent the HIT modes for FORS2 after the MIT detector switch. The imaging (HITI) mode was realized with allMOS slits set to the left side of the field of view. This will form a 6.8 arcminutes long slit to allow to observe nearby stars as a reference.For the spectroscopic mode (HITS) a pinhole will be used - to be punched into an MXU mask. Only the former cross-disperser grisms XGRIS_600B and XGRIS_300I will be available for HITS-mode (with similar optical parameters as the 300I and 600B standard grisms). High time resolution spectroscopy is only offered in visitor mode due to the required instrument re-configuration, which would compromise service mode scheduling. Only the one-shift modes are available.
April 2003 - External Calibration Units for FORS1 and FORS2:New auxiliary External Calibration Units (ECUs) have been installedfor FORS1 (since March 22, 2003) and FORS2 (April 14, 2003) to solve the "parasitic light" problem which was caused by direct back reflection from the LADC. The new calibration units illuminate the calibration screen (back side of the Cassegrain beam shutter) through a fiber bundle from above the LADC. All spectroscopic flat field calibrations are done witht he ECUs starting at the dates given above. Please note that the ECU scan be only used with the LADC prisms in park position and accordingly only at day time. The LADC park position is required not to illuminate the upper LADC prisms from the bottom.
April 2002 - Detector Upgrade for FORS2:The old Site 2kx2k, 24 µm pixels detector of FORS2 was replaced by a state of the art mosaic of two MIT 2kx4k, 15µm pixels, red-enhanced chips. The primary advantage is the higher sensitivity in the 700-1100 nm wavelength domain. Furthermore a lower readout noise will be achieved at much higher readout speed then with the Site CCD. The detector upgrade including all software changes on the instrument sidewere ready for operation in April 2002 after a temporary installation of the mosaic during the bright time in October/November 2001 for tests and commissioning.
October 2001 - Volume Phased Holographic Grisms for FORS2: A set of 5 volume phased holographic grisms has been purchased to optimize the performance for medium resolution spectroscopy in the red and near-infrared spectral ranges. The last grism 1200R is offered since October 1, 2001. The holographic grisms consist of a holographic grating in the middle and two prisms to tilt the dispersed lightback - the central wavelength will go straight through the grism.