“Infrared Spectroscopic Imaging Survey (IRSIS) payload for an Indian Satellite”

S K Ghosh on behalf of IRSIS team

(TIFR, IUCAA, PRL, IIA, ARIES, Paris Observatory, IAS-Orsay)

(1st Indo-French Meeting, 04-Dec-2007)

Motivation & Scientific objectives for the IRSIS Proposal :

-Exploit the crucial gap in astronomical spectroscopic capability in the wavelength range 2 - 6 micron (left between HST-NICMOS cut-off & SPITZER-IRS cut-on)

- Need for Space borne experiments (Earth’s atmosphere : transparency, background)

-Being unexplored ‘territory’, enormous science potential even with an experiment with limited capabilities (i.e. limited sophistication & resources);

Primary science goals :

(i) Detection of several spectral lines & features from the Interstellar Medium (ISM) of our Galaxy (inaccessible from ground);

(ii) Spectra of stars in our Galaxy and nearby galaxies;

(iii) Complete census of Low Mass objects in the Solar neighbourhood (~ 30 pc).

Spectroscopic Survey at 1.7-6 m covering > 50% of the full sky (within 2 years) including the Galactic plane ;

Large volume of quantitative details leading to much better understanding of energetics & composition of the Interstellar Medium; Infrared characterization of (1) stars, and (2) various types of Solar system bodies.

Indian InfraRed Spectroscopic Imaging Survey (IRSIS)Scientific Objectives

1) Interstellar gas in the Galaxy (+ LMC, SMC, M31) : mapping the Galactic Plane in - PAH bands at 3.3 & 6.2 m (1.68 m harmonic), size distribution from relative strengths; PAD at 4.2 m; - recombination lines : Paschen-(20% of H) Brackett-(10%) ; - ro-vibration bands of molecular H2, HD ;

2) Interstellar & circumstellar solid matter : - very small grains (nanodiamonds from 5 m feature) ; - signatures of hydration of silicates (in absorption) ; - elongation vib modes of isolated OH (2.6-2.9 m) - carbonaceous matter ; - distribution of interstellar ices (H2O @ 3.07 m, CO2,CH4), ISM primitive solar nebula (Comet formation) ;

#1

Indian InfraRed Spectroscopic Imaging Survey (IRSIS) Scientific Objectives (continued …) #2

3) Stellar populations in the Galaxy (classification) : - precise study of evolved stars (giants, supergiants, PNe) - chemical composition (metallicity) - effective temperatures & luminosity classes (from CO & H2O indices) - stars with dense envelopes (H2O & NH3 ices @ 3.1m) - emission line objects (Be star, proto-planetary nebulae, Fe II lines, PAH bands in post-AGB nebulae, …)

4) Low mass stars in the solar neighbourhood : - complete census (dwarf stars : class M, L, T, brown dwarf characterized by molecular bands; e.g. CH4) - precise mass & age (using model)

Indian InfraRed Spectroscopic Imaging Survey (IRSIS) Scientific Objectives (continued …) #3

5) Star forming regions : census of the nearby complexes (Taurus, Ophiucus, etc) complete up to ~ 10 Jupiter masses ;

6) Population of distant (z ~ 2-3) starburst galaxies (from limited deep survey, ~ 30 sq. deg.) : first generation stars period of galaxy formation, (rest frame visible spectra shifted to IR) ; diffuse extragalactic background ;

7) Small bodies of solar system : ~ 3000 asteroids & comets, their mineral composition ; evolution of solar system ;

8) Unexpected discoveries from new survey … ??

Important spectral lines in the 1.7-6 m range inaccessible from the ground

Wavelength (m) Line identifier Type of target 1.87 Paschen- stars / ISM 1.96 [Si VI] PN 2.41 H2 (1-0, Q(1)) ISM 2.63 Brackett- stars / ISM 4.49 [Mg VI] PN 4.53 [Ar VI] PN 5.61 [Mg V] PN

Important spectral bands in the 1.7-6 m range inaccessible from the ground Wavelength (m) Line identifier Type of target

1.8 C2 Carbon stars 1.9 H2O M stars 2.4 CH4 Brown Dwarfs 2.7 OH in Silicates ISM 3.05 Ice (H2O) ISM 3.1 C2H2, HCN Carbon stars 3.3 PAH (in emission) ISM 3.5 nano-diamonds stars 4.2 Ice (CO2) ISM 4.6 CO M/C Stars 5.2 C3 Carbon stars 6.0 Ice (H2O) ISM 6.2 PAH (in emission) ISM

Examples of typical spectra : (rich !)

Cushing et al (2006)

Comparison between measurements ( ) and theoretical models ( , )

Tsuji (2006)

(R ~ 200)

(M2 super-giant)

Example of topicality :

“Quality” of the Atmospheric Windows in the Near & Mid Infrared

(Kitt Peak; 2080 m; “best condition”)

1.0 2.2 2.61.4

Wavelength ( m)

Transmission

1.0

0.5

J H K

(#1)

IRSIS coverage

(… at Mauna Kea; 4200 m)

Wavelength (m)

Transmission

3.2 3.6

Atmospheric transmission …. (continued #2)

4.0 4.4

1.0

0.5

L’

IRSIS

Atmospheric transmission … (continued #3)

(… at Mauna Kea; 4200 m)

Wavelength (m)

Transmission

1.0

5.44.2

M

0.5

emissivity background

IRSIS

Atmospheric transmission … (continued #4)

(… at Mauna Kea; 4200 m)

Wavelength (m)

Transmission

1.0

0.5

6.0 10 14 22 28

N Q

IRSIS coverage

Atmospheric Backgrounds : affecting ground based observations -

- atmospheric “fluorescence” : AIRGLOW; OH- originates at ~ 100 km ; spatial & temporal variation too ! limits photometric accuracy ;

-at > 2.3 m, dominated by thermal emission (230-280 K; peak ~ 12 m) ; + emissivity of the telescope ;

- scattered moonlight

Infrared background at the ‘best’ site (Mauna Kea) (comparison with space platform)

Jy/(sq. arc-sec)

K L M

COBE

@ 4,200 m

IRSIS

We just saw –

Infrared astronomy (near/mid IR) from Space : has many advantages over Ground based ; (access to uninterrupted wavelength range; lower background, not varying with time ; etc)

Matured Satellite Platform/(s) available to us (Indians) ! (Courtesy : ISRO)

BUT, what is the international scene (competition) ?

Perspective vis-a-vis international scene

Given the international scene, is there a niche for Indian astronomers ?

Yes ! - Exploit ~ 2-6 m gap in Spectroscopic capabilities between IRS/Spitzer & NICMOS/ HST !!

- ASTRO-F is unsuitable for Spectroscopic Survey covering large fields ;

Concentrate on Spectroscopic Survey with emaphasis on features / lines inaccessible from the ground ;

Major strength : - Large sky coverage (Survey) with Spectroscopic dimension !

- simultaneous capability of Spectro-photometry of ‘point’ as well as ‘extended’ sources !

What are the major Technological challenges for realizing an Infrared spectrometer (~1.7-6 m ) with R ~ 100 ? - cryogenics (achieving ~ 80 K in Low Earth Orbit, Earth’s albedo) proven space grade cryo-coolers now (2004+) available commercially !

- space grade detector arrays with ‘astronomy’ grade performance; ~ 80 K operation ? recent developments from JWST efforts !

- fibers with transmission in 1-6 m new materials developed in France !

Technical feasibility ?

Summary of the proposed instrument (IRSIS) #1:

Wavelength coverage : 1.7—6.5 micronSky coverage : > 50%, including Galactic PlaneAngular resolution : 18”Spectral resolution, R = (/) ~ 100-120

Survey Sensitivity (3-sec) – Point source : @K (2.2 m) = 14 mag. Diffuse emision : SW (1.7-3.4 m) ~ 0.4 MJy/Sr LW (3.2-6.5 m) ~ 1.5 MJy/SrConfusion limit : 2,500 stars/sq. deg.

Summary of the proposed instrument (IRSIS) #2 :

Medium size telescope : ~ 30 cm (dia) @~120K Instantaneous FoV : 15’ x 15’ (9 sub-fields - 5’x5’, each feeding one slit)

Micro-lenses + Infrared fiber-bundles couple Focal Plane to multiple slits of 2-channel spectrometer : Channel SW : 1.7—3.4 m; Channel LW : 3.2 – 6.5 m; Optical components for dispersion (Grating) Cooled (~ 80 K) detector arrays : 1024x1024 HgCdTe (x 2)

IRSIS :Basic Specs -

Typical expectations from IRSIS :

-Typical number of stellar spectra detected : ~ 2,000 per sq. degree (@ Galactic lat., b ~ 0 deg. ~ 500 per sq. degree (@ b ~ 45 deg.

-Detection of 3.3m PAH feature from the Galactic Plane with S/N ~ 100 (10 sec. int.);

-Number of L-Dwarfs discovered & classified : ~ 2,500;

-Number of Asteroids & Comets with detected spectral features : ~ 3,000;

Block diagram of IRSIS

Spectroscopic Imaging : Topology - Telescope focal plane Slit detector array

Simultaneous spectra from all sub-areas (fibers) of sky !

Concept from MUSE instrument (ESO-VLT)

Exploring 1-degee of freedom (telescope moves, spectrometer fixed to S/C deck) Very deep exposures for selected targets possible;

IRSIS with one degree of freedom : ??

(NOT TO SCALE)

Target low-power cryo-cooler with space heritage (K508 from M/s RICOR)

(220mW load @ 77 K)

Mass : 450 gmSize : 70-120 mmPower : 7 W (steady) 17 W (max)MTBF : 10,000 hrs

(Used in MMM payload of Chandrayaan-1)

Choice of Detector Arrays :

Tunable cut-off wavelength (3.4 & 6.5 m) HgCdTe (MCT) FPAsUltra-Low Dark Current at ~ 80 K

Exciting recent developments related to James Webb Space Telescope (JWST) useful !

Development of MBE process for successful fabrication of larger format arrays (upto 2048 x 2048)

Development of a powerful ASIC for driving the array and signal processing (SIDECAR),operational at cryogenic temperatures (30 K to RT)

Liquid Phase Epitaxy (LPE) Producible Alternative to CdTe for Epitaxy (PACE) PACE-1 Sapphire substrate

Molecular Beam Epitaxial (MBE)

Drastic reduction in Dark Current for MBE -

Identified Detector array : HAWAII-1RG

‘R’ Reference columns : Insensitive to temperature variations;

Big saving in Mass, Power; EMI/EMC

(ASIC cost ~ Rs. 200 Lakh!)

ASIC

DETECTOR

22 mm x 15 mm30 K RT< 0.1 Watt

SIDECAR : System Image Digitizing, Enhancing, Controlling And Retrieving

ASIC -

Fully software controlledselectableRead-Outscheme !

Orbit &Spacecraft specs -

(L2 ?)

900 km PolarSun-synchronous

Inertial,3-axis stab.

Mass budget -

Raw Power Budget -

Proposed plan for implementation (institutional responsibilities): a) TIFR : Overall system configuration, Telescope optics, Thermal (Passive/active Cooling), Detectors, Mechanical Structures, Data Handling, Interfaces with the Spacecraft-bus; b) IUCAA : Fiber optic system design; c) PRL : Optical design /development of Spectrometers; Ground based follow-up; d) IIA : Off-line data processing pipeline software; e) ARIES : Data analysis;

e) Paris Observatory + IAS-Orsay: Micro-lenses; Cryogenic Infrared Fibers (Anamorphoser)

Importantcomponents :

Realization strategy :

Status & Plans :ISRO’s Announcement of Opportunity (AO) : March 2006Proposal Deadline : July 31, 2006 (IRSIS version #1)

TIFR review (XI Plan) : September 2006Results of ISRO Review #1 : November 2006 (suggested improvements) IRSIS version #2 : January 2007 IRSIS-ISRO Technical meeting : March 2007 IRSIS version #3 : April 2007

Results of ISRO Review #2 : August 2007 (Phase 1 support : 2 years for Engineering Model)

Next actions : Detailed Project Report (DPR) by December 31, 2007 Baseline Design Review (BDR) ~ February 2008 ? Preliminary Design Review (PDR) ~ end-2008 ??

Thank you !