Observations - General
As with any other astronomical target, everything we know about the Galactic
Center is based on the light which was sent out by the stars and which we
detect using telescopes. The information that can be gathered is:
- intensity of the stars' light (photometry)
- variation of the intensity at different wavelengths (spectroscopy)
- variation of the intensity with time (variability)
- polarization (polarimetry)
- positions of the stars (astrometry)
With current instrumentation, it is not possible to gather all information
at the same time. It is necessary to use different observing techniques
depending on what we want to learn.
Using direct imaging, it is possible to do photometry, astrometry, and,
if done over longer periods of time, also to study the variability of the
The variation of light intensity as a function of wavelength is done
in various ways. Narrow band imaging can be used if one is interested
in the distribution of light at a very specific wavelength. This has the
advantage of still recording full spatial information, but only this very
wavelength is observed. Long slit spectroscopy is applied when a greater
coverage of wavelengths is needed, but then the spatial information is lost.
The latest state-of-the-art technique is called imaging spectroscopy,
where both spatial and spectral information are gathered simultaniously.
The technique of polarimetry is very similar to imaging, but an
additional device is needed in front of the detector to record that information.
In order to do observations, you need of course a telescope. The observations
presented in these pages were gathered at different sites: ESO's New Technology
Telescope and the MPG's 2.2 Meter Telescope on La Silla, Chile, the UKIRT
on Mauna Kea, Hawaii, MPG's 3.5 Meter Telescope on Calar Alto, Spain, and
ESO's Very Large Telescope on Paranal, Chile. The instruments used include
SHARP I and 3D, which were both built by MPE, as well as instruments supplied
by the observatories: Omega Cass on Calar Alto, ISAAC on Paranal, and CGS4
on Mauna Kea.
© Infrared and Submillimeter Astronomy Group at MPE
24/11/2008, editor of this page: Thomas Ott