The Study of IFU for the Li Jiang 2.4m Telescope

ZHANG Jujia 张居甲

Yun Nan Astronomical Observatory . CAS

Sino-French IFU Workshop Nov.8 2010 Li Jiang

Outline

1. An Experiment of IFU for the 2.4m Telescope

2. The Application of IFU for the 2.4m Telescope

3. Conceptual Design of IFU for the 2.4m Telescope

4. Summary

1. An Experiment of IFU for the 2.4m Telescope

IFS encodes all the spectral and spatial information in the same exposure resulting in a two dimensional field of view for a given detector format.

I x y ( , , )Why Integral Field Spectrograph?

As we enter the age when 8 m class telescopes are producing science on a routine basis, single-object spectroscopy on small telescopes (apertures <4 m) is no longer competitive. There is a need to exploit the immense multiplex advantage that can be provided by the wide-field foci on small telescopes.

--Gary J. Hill et al. SPIE 2002

For the good seeing of GMG station and outstanding performance of Li Jing 2.4m telescope, that is a wonderful place to mount an IFU for the studying of local universe.

Collimator

Grating

Optics layout

Mechanical configuration

Hexagonal IFU Top Pseudo-Slit

Parameter

Fiber： 143m, F/6, 4m

Sampling： 1".5

Field of View： 8" x 10" (Hexagonal Field by 19 Fibers )

Dispersion： =1.83Å（ =5500Å, R≈3000）Wavelength arrange： 4000Å~7800Å

Solar absorption Spectrum

The integral emission spectrum of M42

Attached to the Cassegrain focus 2.4m Telescope2.4m Telescope

Orion Nebula

Problems

Low accuracy of fiber arrangement

It’s Hand Made without any machining equipment

Plan to contribute a system to do it

EpoxyUse common glue

SpectrographAgeing

2. The Application of IFU for the 2.4m Telescope

Nearby Galaxies: Velocity distributionMissive Black HolesAbundance and age

Global Clusters in the Milk Way: Star population evolution

HII regions in the Milk Way: Electron temperature and number density

Crowed field: Better background subtractionExtra Galaxies’ Planetary Nebulas or Global Clusters Supernova, AGN

From SAURON Project

Flexible parameters of IFUSpace Resolution (sampling): 0.5" : The average seeing at GMG is 1" (Sampling Theory) 1": For the bad seeing (Use Focal Reducer) ~3": For wider Field (LAMSOT or VIRUS-P at 2.4m telescope)Field of View:

30"~2'

Science Cases and requirements for the IFU

The velocity distribution and material abundance of galaxiesMaterial abundance (Visible)◆Hydrogen: R~2000 ◆Metalicity: R>6000◆H/Fe: R>15000Velocity (dependent on the magnitude and resolution)

10~100km/s

Wavelength range (for the low spectral resolution): 4000~9000 Å

2field~cost

If the IFU under fiber principle:With or without Lenslet array (fill factor: 95%or 65%)

3. The Conceptual Design of IFU for the 2.4m Telescope

3.1 Principle of IFULens Array? Fiber Array? Image Slicer?

For the better sky subtraction:Sky IFU or Nod and Shuffle Observation(Full field or faint object)

What kind of object would be observed

Science cases: specially for nearby galaxies

(Also Global Clusters and HII regions in the Milk Way)

Principle: Lens array and fibers

Sampling: 0.5"/1" or/and 1.5"/3" (F/8 to F/4 Focal Reducer)

FOV: 15"/30"(mosaic) or 45"/1.5'

Spectral resolution: 1K、 2K、 5K (even 10K)

Wavelength: 4000~9000 Å (Use High OH fiber made by Polymicro)

Micro-Lens: ~150m(with or without fore optics)

Fiber aperture: ~80m

Fiber length and amount: ~20m 900 fibers

Fiber focal ration: F/4

Grating: VPH Transmission Grating

CCD: 4Kx4K

3.2 One flexible design

Optics Layout （ Sketch ）

Lens range

CCD

Camera

VPH

Collimator

Fiber

slit and lens

Why ALL Fraction?Low spectrum resolution (chromatism correction will be not too hard)

Make optic units smaller

Micro lens

Front Optics

Lens array

Fiber

Focal Reducer

Sampling: 0.5"/1" or/and 1.5"/3"

3.3 Cooperate with MOS (LiMOS?)

If we have MOS and IFU why not Multi-IFUs

Same alike FLAMES-GIRAFFE at VLT-UT2 (Our French friends are familiar with it)

With MOS, Multi-IFUs and a wide fied IFU

The Multi-IFUs at 2.4m telescope can be used to study crowed field in the local universe

The small IFU under the same sampling with MOS and contains 4x4 fibers then can use the same fiber pedestal

Object IFU

MOS’ Fiber

Sampling: ~1.5"625 fibers for IFU 25 fibers for Sky150 fibers for MOS

4. Summary

IFU will be a powerful and wonderful equipment for 2.4m telescope to study local universe. (Wide field, low spatial resolution or Seeing limited, low-middle spectral resolution and visible)

IFU on the fiber principle will be preferred for 2.4m telescope.

To determine the parameters of IFU is an art of balance.

If we manufacture a IFU under fibers way:

Add MOS will not increases cost sharply

And then add multi-IFUs also wont increases cost obviously