Spectroscopy

The examination of the physical properties of the Galactic Centre stars as well as of the central black hole requires high quality spectroscopic observations. In the last years we executed a variety of spectroscopic observation programs aiming at the following main goals:

Spectral classification of stars
Determination of stellar radial velocities
Mapping of interstellar matter
The determination of the spectral-energy-distribution of the NIR radiation emitted by Sgr A*

A SINFONI image of the immediate vicinity of Sgr A*

For determining the nature of the individual stars and their radial velocities as of the infrared flares emitted by Sgr A*, a variety of instruments has been used by our group to obtain the spectra of these objects:

SHARP I in speckle-spectroscopy mode
The integral field spectrograph 3D on the MPG 2.2m telescope in La Silla
ISAAC on the VLT UT1 (Antu) in Paranal
CGS4 on the UKIRT on Mauna Kea
The integral field spectrograph SPIFFI resp. SINFONI on the VLT UT4 (Yepun)

Since reaching the diffraction limit of a telescope requires the usage of speckle interferometry or adaptive optics systems, the spectroscopic data aquired so far is either of high spectral or high spatial resolution. Using the integral field spectrographs 3D and SPIFFI, radial velocities of the brightest stars could be determined. The VLT allowed high resolution spectroscopy of the innermost fast moving sources which gives hints on their physical nature.

State of the art for spectroscopic observations of the Galactic Centre is the NIR integral field spectrograph SINFONI, a combination of the spectrograph SPIFFI and the adaptive optics system MACAO. First observations were executed during the SINFONI commissioning in July 2004, providing a great amount of information about the stars in the immediate vicinity of the central black hole.