NEWS ABOUT OASIS ...
The run in last January was
quite successful but affected by some bad weather. The OASIS Lyon Group has
also just released a new
version of the reduction software, XOasis. It is now
compatible with the EEV1 chip characteristics and is downloadable from their
OASIS Web site.
Now, concerning the future of OASIS at CFHT:
During the last SAC meeting, held in November in Waimea, we were informed
by the OASIS group in Lyon that OASIS stay at CFHT could be extended to the end of the 2002A
semester. OASIS will be returned to France in May 2002 and will not be available
again for CFHT Users. So, OASIS IS NOT AVAILABLE FOR 2002B ....
Status Update (02/13/02):
- Two detectors are available for OASIS. The first, Loral 3, has been
used since the arrival of the instrument here at CFHT. In June 2000,
a new chip, EEV1, has replaced EEV2 in its dewar, the detector previously
used for Gecko. This new device has a much better QE than Loral 3, a
smaller readout-noise and faster readout-time. Its characteristics can
be found here . However, since
it's a thin chip, fringing is very important over 7000A. The peak-to-valley
amplitude reached about 35% at 8500A. No useful science can be done in the
red range (> 7000 Ang.) of OASIS with EEV1. So, if your program
requires configurations in the red domain (e.g. LR2, MR3, MR6, MR7, HR5),
it is preferable to use Loral 3 instead of EEV1. However,
only ONE change of CCD will be allowed during an entire observing run with
OASIS. In other words, only one CCD will be mounted for a given program so
you can use one CCD or the other but not both.
The exposure time simulator has now integrated the characteristics of EEV1
and can be used for planning your observations with this device. The
pixels of EEV1 are smaller than Loral3 so, make sure to read the Instrument
Overview page to understand what it means for OASIS. For more information,
please contact me !
- An updated postscript version of the OASIS cookbook is now available! It
includes some guidelines for observing with OASIS and more! For Loral3, use
this version. For EEV1, use rather this version.
It might be useful for you if you're planning your observations with OASIS
so please, have a look! Since OASIS is still a "new" instrument, I am trying
to keep it updated with the new procedures and information. Do not be afraid
by the ``complicated'' look of the observing procedures. Observing with OASIS
is easy and it becomes quite automatic after a few hours...
- Good news! Analysis of set of data taken during the 2000 runs has shown
that the Atmospheric Dispersion Corrector (ADC) is working properly. This
device is essential for the very high spatial resolution of OASIS. Unfortunately,
this device was never fully used prior to the OASIS runs so we have discovered
problems in the way the device is controlled. Some hardware and software modifications
had to be implemented. At this moment, the correction is still not totally
optimized but residues are small at about 0.01"....
- All the AOB beamsplitters have been used! Their characteristics have been
gathered at CFHT and their coatings were found to be excellent and within
specifications. The transmission curves are now available on this page. Changing
beamsplitters is possible during an observing night but each operation results
in about 15 minutes lost on the sky. Observations MUST be planned to minimize
lost of observing time. However, we found that the splitters were not perfectly
aligned with each other and worse, that their position is not perfectly kept
if they are dismounted and remounted again. This means that for each beamsplitter
change, the wavefront sensor hotspot has to be redefined. This takes
some time so this is another reason to avoid changing beamsplitter too frequently
during a night.
- The f/8 mode of OASIS is fully implemented. Its availability makes OASIS
a very versatile instrument, well adapted to different seeing conditions.
The mode is easy to use except for a few complications in the telescope focussing
procedure. The interface has been modified so that the observers are automatically
prompted and asked to change the telescope focus, if necessary. It is then
very important that the observers arrive with a backup program that can make
use of this mode if the seeing becomes larger than 1.2" (i.e. limit for the
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