High Resolution Spectroscopy with Extremely Large Telescopes Using Pupil Slicing Adaptive Optics
Abstract
Under seeing limited imaging conditions, high resolution spectroscopy (R ≥ 100,000 at visible wavelengths) on large aperture telescopes requires huge instruments. This will cause major problems in future Extremely Large Telescopes (ELTs; diameters D = 20 - 60 meters). With diffraction limited imaging using adaptive optics the size of the spectrograph will become independent of the telescope diameter since the image size shrinks at the same rate as the telescope diameter increases. However the complexity of adaptive optics at visible wavelengths will be very high, requiring a large number of deformable mirrors elements (50000 to 100000 for D = 50 meters). It is not likely that devices of that complexity will be available soon.In this paper we propose an intermediate step in that direction using so-called Pupil-Slicing Adaptive Optics (PSAO). In it the telescope aperture (its "pupil") will be divided into N equal sub-pupils. Each sub-pupil will have its own adaptive optics to give a diffraction limited image size corresponding to its diameter. The N resulting images are then combined on the entrance of a multi-mode fiber which feeds the high resolution spectrograph. The fiber scrambles the light and avoids variations of the position of the spectrum due to variations of the spectrograph slit illumination.As an example, we present a strawman design for a PSAO spectrograph for the Euro50, D = 50 meter telescope. It uses N = 18 and 4000 element MEMS deformable mirrors. Such mirrors are currently under development and are likely to be available at the time of the commissioning of the first ELT. A spectral resolution of around R = 200000 seems feasible for spectrographs less than 2 meters in size.
- Publication:
-
American Astronomical Society Meeting Abstracts #208
- Pub Date:
- June 2006
- Bibcode:
- 2006AAS...208.5504B