Fiber echelle: overview


Fiber echelle consists of the de-comissioned Blanco Echelle spectrograph in fixed configuration connected by optical fiber to the CTIO 1.5-m telescope. The instrument was used in service mode in 2008-2010. Fiber echelle is de-commissioned starting from 2011.

Spectral format: Fixed configuration covering wavelength range from 4010 to 7300 Angstroem without gaps. The order height is about 3 pixels FWHM.

Spectral resolution:

Efficiency: Estimated 1%. The star V=5 gives about 135 electrons/s in the extracted spectrum (standard slit setting 50 micron). Assuming 5-pixel height of the extracted spectrum and normal readout mode, the signal-to-noise ratio S/N near blaze maximum for exposure time t seconds and a star of magnitude V can be estimated as

S/N = Nph/sqrt(Nph + 18^2), Nph = 1.35 t 10^(-0.4V + 4)

See the plot below. Exposures longer than 20 min. are not recommended because of cosmic rays; take several exposures instead.

Detector: SITe, 2048x2048 pixels, 24-micron pixel size. Full readout in 27s (normal mode, gain 0.9 el/ADU) or 18s (fast mode, gain 3 el/ADU). Readout noise 8el (normal) and 9.5el (fast). Saturation level: 65536 counts in all modes (to be confirmed).

Comparison lamps: Thorium-Argon, Quartz (not simultaneous, light goes through the same fiber). Do not forget to take comparison exposures needed for your program!

Precise radial velocities: Iodine cell can be inserted in the beam before slit for precise radial-velolcity measurements. On bright stars, the precision can reach 3 m/s.

Entrance aperture: round, diameter 2.7 arcseconds.

Guiding: automatic, using light of the observed star falling outside entrance aperture.


Last update: March 3, 2011
atokovinin-AT-ctio.noao.edu