next up previous contents index
Next: Design requirements Up: CAOS - The new Previous: CAOS - The new   Contents   Index

Scientific motivation

The echelle spectrograph at OAC was designed to work at the F/15 cassegrain focus of the telescope and to record the spectra on photographic plates both at high resolution, in cross dispersion mode and low resolution, in single dispersion mode. Since 1993 the spectrograph is fed by a fiber link and placed in a gravity independent position at the first floor of the telescope dome. A dioptric multielements objective 300 mm focal legth F/2.8 - commercial objective CANON EF300; installed in 1997 to replace the original schmidt camera allow to use the full output beam of the fiber. The acquisition system consists of a CCD camera that is based on back-illuminated SITE 1024x1024 pixels (24x24 micron) that gives a spectral coverage from 3800 A to 8000 A, with 0.9 Å/pxl in single dispersion and 0.15 Å/pxl in cross dispersion. During 2000, it has been equipped with a polarimetric module for the measurement of the linear and circular polarization, allowing the determination of the four Stokes parameters. Present possible performaces are radial velocities with errors up to 0.5 km s$^{-1}$ and S/N = 100 in the H$_{\alpha}$ region for a V = 6 A0 star with T$_{\rm exp}$ = 15 minutes.

The present observational activity at the OAC appears to be strongly limited by the relatively low performance of the spectrograph, expecially as it concerns the spectropolarimetry where high S/N ratios and resolutions are necessary. After the previous changing, the spectrograph cannot be further improved and the acquisition of a new high efficiency spectrograph cannot be delayed.

With the scientific activity carried out at the OAC, the importance of a higher resolution is related to the spectropolarimetry with particular interest to the measure of stellar magnetic fields (Leone & Kurtz 2004); Doppler Imaging of active stars and binary systems; measuring starspots temperature from line depth ratios (Catalano et al. 2002); radial velocities (Catanzaro & Leto 2004), stellar atmosphere studies (i.e. determination of effective temperature, gravity, rotation velocity, micro macro-turbulence and abundances (Catanzaro, Leone & Leto 2004); modeling of Balmer lines in presence of expanding envelopes.

Moreover, it will be possible to carry out all those scientific programs that are usually based on R = 50000 spectrographs. As in the case of FEROS or ELODIE, with CAOS it will be possible to: Search for extra-solar planet systems; Asteroseismology, i.e. measurements of stellar oscillations; Long-term monitoring of hydrodynamic phenomena in hot stellar atmospheres by following the line-profile variations of photospheric and wind lines over their characteristic time scales from hours to months; Chromospheric variability by the simultaneous observation of the CaII H&K and H$_{\alpha}$; Observations of diffuse insterstellar clouds in the interstellar medium which have a typical velocity seperation of 6 km s$^{-1}$.


next up previous contents index
Next: Design requirements Up: CAOS - The new Previous: CAOS - The new   Contents   Index
Innocenza Busa' 2005-11-14