A.CALCINES, R.LÓPEZ, C.GRIVEL, M.COLLADOS*
[email protected]
[email protected]
[email protected]
[email protected]
EAST-ATST WORKSHOP 2009
CONCEPTS FOR A VISIBLE AND AN INFRARED HIGH RESOLUTION
MULTI-λ MULTI-SLIT SPECTROGRAPHS FOR EST
ABSTRACT:
λ (Å)
αspec(º)
L
Order
β(º)
L.D.
(Å /mm)
Sampling
(mÅ/px)
Resolution
Power
∆λ(Å)
3933.70
5.39
0.76
20
-4.43
0.30
6.01
327310
3.08
5248.80
6.84
0.78
15
-5.64
0.40
8.11
323604
4.15
6302.00
8.00
0.75
12
-9.55
0.52
10.50
300000
5.38
6563.00
8.29
0.79
12
-6.83
0.51
10.25
320009
5.25
7774.00
9.64
0.96
10
-8.89
0.63
12.53
310130
6.41
8498.00
10.45
1.00
9
-10.69
0.71
14.13
300613
7.23
λ (Å)
αsp(º)
L
Order
β(º)
L.D.
(Å /mm)
Sampling
(mÅ/px)
Resolution
Power
∆λ(Å)
8542.00
6.39
0.99
9
-7.02
0.68
13.5
315812
6.9
8662.00
6.48
0.97
9
-5.55
0.66
13.2
327393
6.8
10830.0
8.00
0.93
7
-9.69
0.90
18.1
300000
9.3
15650.0 11.42 0.92
5
-8.74
1.25
24.9
313676
12.7
This poster presents the preliminary study for a visible and an infrared high resolution,
multi-slit and multi-λ spectrographs for EST developed at IAC. Each spectrograph is
preceded by a predisperser illuminated by eight slits. In the focal plane, one detector
is used for each wavelength, with eight bands per detector corresponding to the eight
entrance slits. Ten wavelengths are observed simultaneously (six for the visible
spectral range and four for infrared). The wavelengths that have been considered to
show the feasibility of the concept are: Two Ca II IR lines, at 8542 Å and 8662 Å,
He I 10830Å and Fe I 15648Å for IR and Ca II 3933 Å, Fe I 5247-5250 Å and
6301-6302 Å, Hα 6563 Å, O I triplet at 7774 Å and Ca II IR 8498.Å for the visible
spectral range.
MULTI-SLITS:
The considered spectrographs
have 8 entrance slits. In these
optical designs only 4 are
showed due to the limitation of
the number of fields using
ZEMAX.
Tables 1, 2: Calculated parameters for the two spectrographs.
L is luminosity, α and β the input and output grating angles (taking as
reference the normal to the grating grooves), L.D. is the linear dispersion
and ∆λ is the spectral range of each spectral line in the detector, this
depends on λ.
PREDISPERSER:
IR (Г=0.55 ) VISIBLE(Г=0.41)
DIAMETERS
132.678mm
151.55mm
COL. FOCAL LENGTH 6633.90mm
7577.55mm
CAM. FOCAL
3680.68mm
3153.54mm
LENGTH
PD GRATING
GROOVES/MM
300
600
BLAZE ANGLE
9.7º
8.6º
SPECTROGRAPH:
IR(Г=0.74) VISIBLE(Г=0.99)
DIAMETERS
324.700mm
472.53mm
COL. FOCAL LENGTH 9007.19mm
9833.29mm
CAM. FOCAL
6697.09mm
9747.30mm
LENGTH
SP GRATING
GROOVES/MM
188
147
BLAZE ANGLE
47º
35
Table 3: Technical data for predispersers and
spectrographs. The input f/# that has been
considered is f/50, in both cases, despite the
telescope’s f/# is not definitely fixed. Both
predispersers work at first order. (Г is the angular
magnification).
LOCATION
ENTRANCE SLITS
Telescope focal plane
Nº OF SLITS
SLIT WIDTH
8
0.05”, 50µm for f/50
SEPARATION
BETWEEN SLITS
24.98, 24.80mm (*)
SLIT LENGTH
198.58mm
PREDISPERSER MASK
LOCATION
Predisperser focal plane
Nº OF SLITS
41, 25 (*)
SLIT WIDTH (mm)
Visible:0.57, 0.77, 0.98, 0.98, 1.21,
1.37 ir: 0.73,0.73, 1.0, 1.41
10.34, 13.77mm (*)
SEPARATION
BETWEEN SLITS
SLIT LENGTH
MASK SIZE
82.74, 110.18mm (*)
875.75, 890.89mm (*)
DETECTORS
LOCATION
Spectrograph focal plane
DETECTORS
4K x 4K
PIXEL SIZE
20 µm
DETECTOR SIZE
Nº OF DETECTORS
81.92mm x 81.92mm
5, 4 (*)
SLITS PER DETECTOR
8
MASK:
VISIBLE
A mask is located at the predisperser focal
plane. Some wavelengths share some slits. This
is shown in the figures below:
VISIBLE PREDISPERSER MASK
(I)
VISIBLE SPECTROGRAPH FOCAL PLANE
(II)
IR PREDISPERSER MASK
(III)
MULTI-λ:
ZEMAX Optical design of the visible spectrograph. At
the focal plane the multi-λ capability can be observed.
One detector is used for each λ and each λ is replied as
the number of entrance slits (eight times).
Figs. I,III: Location of the different wavelengths and their 8
corresponding slit fields in the predisperser focal plane. There
is a total of 41 predisperser slits in the visible mask, where
6302 Å and 6563 Å share 4 slits and 25 slits in the infrared
mask, where 8542 Å and 8662 Å share 7 slits.
IR SPECTROGRAPH FOCAL PLANE
(IV)
Figs. II, IV: Spectrograph focal plane and the location of the detectors, one per wavelength. 4 for IR and 6 for visible. This
figure shows the spectral range required for each wavelength, different en each case. In each detector, the wavelength
interval is replicated eight times (one per entrance slit) without overlapping.
The figure below shows the ZEMAX optical layout of the infrared spectrograph where the concepts: multi-slit, multi-λ and
predisperser mask can be seen. Ca II 8542 Å and 8662 Å share some predisperser slits.
IR
Table 4: Data for the multi-slit capability. Those
values with (*) correspond to visible and infrared
respectively. The same detector and pixel size
has been considered for both spectrographs.
NEXT STEPS:
IFU: These spectrograph designs will be used as the basis for integral field spectroscopy. Different alternatives for the integral field unit are currently
under study (fiber optics+microlenses and image-slicer). This poster shows the feasibility of the multi-slit multi-wavelength spectrograph concept, both for
visible and IR, but the final parameters might change with further studies.