REOSC Spectrograph

The REOCS is an echelle spectrograph which belongs to the Institute d'Astrophysique de Liege in Belgium and is currently on loan at CASLEO to be used with the 2.15 m telescope. This instrument can operate in a range of 3500 Å to 7500 Å and in two operating modes: cross dispersion (CD) and simple dispersion (SD). For the latter, the echelle grating is replaced by a flat mirror. It is important to point out that the spectrograph can operate beyond 7000 Å; however, as it was not designed for that purpose, its efficiency can be reduced.

reosc

The overall efficiency of the spectrograph in combination with the telescope and the detector has not yet been measured. A StellaCam or an ST-7 camera is used to observe the field.

The detector currently used with the REOSC spectrograph is a 1024 × 1024 pixels CCD TEK. The chip in this detector is thinned, it has no coating, and is back-illuminated. The main features of the chip are listed in the table below:

CCD Characteristics
Rows × columns 1024 × 1024
Pixel size 24 × 24 µm
Chip size 25 mm × 25 mm
gain #1 7.97 e-/ADU
gain #4 1.98 e-/ADU
Read-out noise (gain #1) 0.4 e-
Read-out noise (gain #4) 7.4 e-
Dark current 0.4 e-/hour/pixel
Operating temperature -120 °C

The graph shows the chip's quantum efficiency.

The detector-REOSC-telescope efficiency has not yet been measured; however, it is possible to estimate the integration times for CD assuming 0.3 Å/2 px in 4500 Å resolution; i.e. with a slot opening of 273 µm, equivalent to 3" in sky and with a seeing lower than such value. In these conditions, it is possible to obtain a S/N relation of 50 in 30 minutes of integration for a B=10 magnitude.

tek

In the case of SD and under the conditions mentioned above (unless the slot is opened 2 pixels which is equivalent to approximaltely 200 µm at the focal plane of the telescope and slightly over 2" on the sky) a 50 S/N relation in 30 integration minutes can be obtained for a 12 magnitude star.

Click here to view the REOSC operating manual and here for a technical report on the measurement of radial velocities with REOSC in simple dispersion mode.

Available gratings


Characteristics produced by the Echelle grating
λ [Å] m d [Å/mm] Fλ C λ [Å] R
3000 75 4.0 40 98 3019 12500
4000 56 5.3 71 130 4043 12600
5000 45 6.6 111 162 5031 12626
6000 37 7.9 162 194 6119 12658
7000 32 9.3 218 228 7076 12544
8000 28 10.6 286 260 8087 12578
9000 25 11.9 360 292 9057 12605


Crossed Dispersers Data
Gratings l/mm Blaze Disp. Resolution Spectral range
(Å) (Å/mm) (Å/pix) (Å)
340 1200 6000 44 1.0 1000
580 400 4000 124 2.9 2900
180 316 7500 160 3.8 3800
080 600 4000 84 2.0 2000
260 600 5000 85 2.0 2000
360a 1200 7500 44 1.0 1000
270 300 5000 166 4.0 4000
510 300 10000 170 4.0 4000
320 300 7600 168 4.0 4000

(a): In SD this grating can be used in second order centered at approximately 3800 Å with a 22 Å/mm dispersion and a 500 Å spectral range.

Comparison lamps


SIMPLE DISPERSION:

CROSSED DISPERSION: