Main Stellar Spectrograph of the BTA

3. Instrumental capabilities of the spectrograph

Fig. 7. Theoretical optical resolving power of the MSS, depending on the phases of the moon under typical weather conditions.
Fig. 7. Theoretical optical resolving power of the MSS, depending on the phases of the moon under typical weather conditions.

The optical resolving power of the telescope with the MSS allows to observe stars of up to the 12 magnitude. The graph in Fig. 7 gives an idea about the spectrograph capabilities in the observations of faint point sources.

Currently, more than 90% of observational time with the MSS spectrograph is used in the spectropolarimeter mode with a diffraction grating 24.7œ. An order registers a 550 ? ?wide spectral region with a reciprocal linear dispersion of 9 ?/mm (0.1215 ?/pix) at a time. In the second spectral order the dispersion amounts to 13.5 ?/mm (0.1823 ?/pix).

Signal-to-noise value calculator (Javascript)

Moon phase New Moon First/Last quarter of the Moon Full Moon Spectral class B0 A0 F0 G0 K0 M0 Brightness of the star (mag.)

S/N ratio calculation Exposure time (s)
S/N reached:119

Time calculation Required S/N ratio
Required exposure time (s)424

The calculations are performed for the conditions: FWHM of the image 1.2-1.5?, z = 20œ, ?_c = 4550 ?, the circular polarization analyzer in conjunction with the image slicer, reciprocal linear dispersion 9 ?/mm (0.1215 ?/pix).