Christoph Birk

The Carnegie Planet Finder Spectrograph: integration and commissioning

The Carnegie Planet Finder Spectrograph (PFS) has been commissioned for use with the 6.5 meter Magellan Clay telescope at Las Campanas Observatory in Chile. PFS is optimized for high precision measurements of stellar radial velocities to support an ongoing search for extrasolar planets. PFS uses an R4 echelle grating and a prism cross-disperser in a Littrow arrangement to provide complete wavelength coverage between 388 and 668 nm distributed across 64 orders. The spectral resolution is 38,000 with a 1 arcsecond wide slit. An iodine absorption cell is used to superimpose well-defined absorption features on the stellar spectra, providing a fiducial wavelength reference. Several uncommon features have been implemented in the pursuit of increased velocity stability. These include enclosing the echelle grating in a vacuum tank, actively controlling the temperature of the instrument, providing a time delayed integration mode to improve flatfielding, and actively controlling the telescope guiding and focus using an image of the target star on the slit. Data collected in the first five months of scientific operation indicate that velocity precision better than 1 m s-1 RMS is being achieved.

MAGIC: a new near-infrared camera for Calar Alto

This paper describes the basic design, operation, and initial performance of MAGIC, the new MPI fur Astronomie General-purpose Infrared Camera. MAGIC uses a 256 X 256 NICMOS3 HgCdTe detector array and has flexible optics and drive electronics that permit a variety of observing configurations. The camera was designed and built to MPIA specifications by Infrared Laboratories of Tucson, Arizona. MAGIC is based at the 3.5 meter telescope on Calar Alto, although it may be used at a number of other sites, including the 2.2 and 1.2 meter telescopes on Calar Alto and the 2.2 meter MPIA/ESO telescope at La Silla. The design of MAGIC places particular emphasis on wide field, deep imaging at the f/10 focus of the 3.5 m telescope and on providing some spectroscopic and speckle interferometric capability.

CHARM - A TIP-TILT TERTIARY SYSTEM FOR THE CALAR ALTO 3.5M TELESCOPE

We discuss a tip-tilt tertiary mirror system developed for the Calar Alto 3.5m telescope in Spain, that corrects the rapid image motion caused by atmospheric turbulence. Using either a visible or an infrared tip-tilt sensor, the image motion is reduced typically to less than 0\farcs03 rms (corresponding to 0.29 rad2 mean square wavefront tilt error) at 2.2\micron on a 3.5m telescope. The system is equipped with a CCD camera to measure the image motion in the visible. Alternatively, using a novel technique for reading out a subarray of an infrared detector, the infrared science camera can be used to measure the slope of the wavefront by taking short exposure images on a very small subarray while simultaneously taking long exposure images on the rest of the array. This enables the system to be used even in obscured regions where only infrared stars are available. Astronomical results from several observing runs with this system at the Calar Alto 3.5m telescope are presented.

Magic and charm: A novel approach to tip-tilt adaptive optics

Atmospheric seeing limits the FWHM of a point-source to ~1″, ~5–30 times larger than the diffraction limit of a ground-based 4-m telescope at wavelengths 0.5–2µm. Adaptive optics systems are being developed to eliminate this blurring, resulting in more detailed imaging, shorter integration times, and deeper detection limits. At optical wavelengths, high-order wavefront correction is needed, requiring some or all of sophisticated wavefront sensors, segmented/rubber mirrors, dedicated high speed computers, and artificial (laser) guide stars.

Thermal IR Imaging with MAX: Pushing the Limit of Single-Dish Ground Based Observations

Diffraction limited images (Strehl ratio > 0.3) are routinely taken at 10-20µm with the new MPIA thermal IR camera MAX at UKIRT. The high read-out rate of the MAX electronics allows us to study the spatial and temporal variations of the telescope point spread function introduced by atmosphere, telescope and mirror flexure, etc. Comparing data taken before and after the recent (August 1996) upgrade of the UKIRT top-end, we can analyze these variations and obtain information useful for effective interferometry at large telescopes.