To obtain high resolution spectroscopy (R = 1000, 2200) in the K-band, two Fabry-Perot etalons can be mounted in front of the camera. Their finesse and resolution for different wavelengths are tabulated in Tables 1 and 2. The Fabry-Perot optics were optimized for use with the 50 mas/pixel scale. In this case the shift in passband across the field of view is less than 0.4 nm. Transmission in the wavelength range 1.9 to 2.4 µm] is: 85 % for the low resolution etalon; and 65 % for the high resolution etalon.
Both etalons need to be calibrated each day by the 3.6-m Team. A scan of spectral lines as close as possible to the science line are recorded before each observing night using a spectral lamp. For a list of the available spectral lines see the Sharp II manual.
The combination of adaptive optics and coronographic techniques providing at the same time high angular resolution and high dynamic range is a powerful tool to study the close environment of bright objects in different fields of astrophysics.
Observatoire de Grenoble, in collaboration and under contract with ESO, has designed and manufactured a new coronograph to be used as a prefocal optics on ADONIS. The optical sketch of the coronograph is shown in the next figure:
It is composed of an occulting mask introduced at the output F/45
focus of ADONIS and a Lyot stop located on a pupil image inside the
SHARP IR camera.
Please note that there is no reason to use the coronograph with COMIC, the COMIC detector already being an antiblooming device.
The occulting mask is optically conjugated with the detector and the Lyot stop with the telescope pupil. The Lyot stop, also called apodizing mask, is used to block the diffracted light from the edges of the telescope primary and secondary mirrors and from the secondary mirror support (including the spider arms).
The coronograph focal plane unit allows to insert different occulting masks
at the ADONIS F/45 output focal plane. These masks will be mounted on dedicated barrels, each of them supporting up to 3 masks.
The observer will thus be
able to insert anyone of those 3 masks in the IR camera field of view by remotely moving a motorized linear stage from the ADOCAM control software.
Typically 30 seconds will be necessary to switch from one mask to
another one. If needed, there is also a way to manually move the mask
along the perpendicular axis (limited excursion range).
Please note that it is necessary to dismount the coronograph to exchange one barrel for another (20mn). This delicate manipulation should be avoided during the night.
We strongly recommmend the observer to keep the same barrel for a given night.
The actual diameters (within an accuracy of 5 %) of the masks are as follows:
|Mask size in arcsec (")|
The detection limit at 2" from the central object in K band for a total integration time of 6 mn with an occulting mask of 0.8" in diameter is typically 100 000 fainter (12.5 magnitude per pixel) than the peak intensity of the star observed without the mask, with the same angular resolution.
Any polarizer position angle can be set by the user via the ADOCAM software. A nice feature of ADOCAM is that a sequence of different polarizer angles can be executed automatically for which images are taken at each angle.
|Spectral range||1-9 µm|
|Grid period||0.25 µm|
|Transmission for polarization |
perpendicular to the wire grid at 1.5 µm
|Transmission for polarization |
parallel to the wire grid at 1.5 µm
|Degree of polarization at 1.5 µm||93 %|
This ADC is built of two pairs of prisms made of ZnSe and ZnS-Multispectral. Each pair of prisms is cemented. All the surfaces are coated for highest transmission. The average transmission of the complete ADC in the wavelength range from 1.1 to 2.45 µm is 95 %.