Workshop Ringberg-April 13-17, 2004

1. SUBMILLIMETER STUDY OF STAR FORMING REGIONS AND RADIATIVE TRANSFER MODELING -- AN APPROACH R. S. THAMPI, PRL, INDIA Workshop Ringberg-April 13-17, 2004

2. SUBMILLIMETER SCIENCE GOALS STUDY OF STAR FORMING REGIONS SUBMILLIMETER INSTUMENTATION DATA ANALYSIS RADIATIVE TRANSFER MODELING –AN APPROACH PLAN OF MY PRESENTATION OVER VIEW OF OUR PROGRAME Workshop Ringberg-April 13-17, 2004

3. SUBMILLIMETER PROGRAM First stars and galaxies in the early universe and their evolution Physics and Chemistry of ISM • SCIENCE • TECHNOLOGY • APPLICATIONS New solar systems in protostellar disks Cometary, planetary, and satellite bodiesand atmospheres Data Analysis-CLASS, Radiative transfer modeling-1D & 2D Astronomy and Astrophysics High resolution heterodyne receiver development for ground and Space born telescopes Planetary Science Fabrication of detectors ( Schottky, HEB and SIS) Medical Sciences Defence Local Oscillator development (OPML, Gunn Oscillator, BWO) Electronics &Communication Development of Back end Electronics (AOS,CTS and Filter bank) Plasma Physics Workshop Ringberg-April 13-17, 2004

4. SUBMILLIMETER ASTRONOMY A novel branch of astronomy is the study of atoms, molecules and dust particles in the Interstellar Medium by means of their submillimeter wavelength emissions. Many species such as complex molecules, simple hydride molecules and atoms can easily be detected in this way. The submillimeter band can be used to study STARS, our own galaxy and also distant galaxies to determine both the kinematics of the interstellar gas and its chemical constitution. SALIENT FEATURES OFSMM PROGRAM • STATE-OF-THE-ART HIGH RESOLUTION HETERODYNE RECEIVER DEVELOPMENT FOR SPACE BORN SUBMILLIMETER TELESCOPE • LABORATORY STUDY OF MOLECULES BEING PURSUED BY USING OPML AND GAS CELL • CTS, AOS AND FILTER BANK TYPE SPECTROMETER DEVELOPMENT • MIXERS, HEMT AND AUTO CORRELATOR DEVELOPMENT • SUBMILLIMETER RECEIVER DEVELOPMENT FOR GROUND BASED TELESCOPE FACILITY AT HANLE • SUBMILLIMETER HIGH RESOLUTION HETERODYNE RECEIVER SYSTEM USING SIS DETECTORS FOR BALOON PAYLOAD EXPERIMENT. • NOVEL SLOTTED WAVE GUIDE TECHNIQUES TO IMPROVE THE EFFICIENCY OF EXISTING OPML • DATA ANALYSIS USING CLASS AND IRAF SOFTWARES. • RADIATIVE TRANSFER MODELING FOR THE INTERPRETATION OF SUBMILLIMETER DATA. Workshop Ringberg-April 13-17, 2004

5. SUBMILLIMETER STUDY-SCIENCE GOALS WHY SUBMILLIMETER ASTRONOMY • TO FIND THE ANSWERS FOR THE FOLLOWING FUNDAMENTAL QUESTIONS • Did galaxies all form around the same time in the early universe, or is galaxy-formation an • ongoing process that continues today? • Did stars lead to galaxies, or galaxies to stars? • What kind of objects existed in the early universe? • How did they evolve over the years into the galaxies of today? • Submillimeter astronomy promises to yield a new view upon the Universe we live in, almost certainly shedding light upon many of the outstanding questions in modern astronomy. • Atmospheric constraints • Water vapor is the primary enemy of far- • IR/submillimeter astronomy. • Range λ= 30m – 300 m is unavailable from the ground. Other options: • Airplanes (40,000 ft.) – KAO, SOFIA • Balloons (120,000 ft.) • Satellites – IRAS, ISO, SWAS, SIRTF • 300 m – 1 mm range is partially available from high, dry mountains • (> 10,000 ft.) – Mauna Kea (CSO, JCMT, SMA); South Pole; Chile (ALMA) • λ> 1 mm – available from lower elevations • USES • Atomic and molecular spectroscopy • Transition frequency can be determined • Atom or molecule detected by remote • observation • Study of dust properties • Cooling mechanism that facilitate cloud • collapse • Molecular cloud composition and • chemistry • Early stages of star and planet formation Workshop Ringberg-April 13-17, 2004

6. Gas temperatures are from 10K in cold clouds to several thousand K • Molecular radiation often represents an important loss of energy, and this acts as a coolant, preventing the (collapsing) cloud from heating up. If the gas temperature remains sufficiently low, the gas pressure will rise and prevent the collapse. • Something like this must happen at the birth of both galaxies and stars • The cooling also tends to reduce the degree of ionisation and hence the ability of magnetic fields to support the gas against collapse • Through the molecules we can trace the physical conditions that allow these changes to continue. Molecular lines are excellent probes of the physical and chemical conditions in interstellar clouds, protostar envelopes, circumstellar shells around late-type stars, photon dominated regions etc. Furthermore molecular line transitions play a key role in probing the properties of galaxies and their evolution. The cooling in the molecular cloud region is effectuated by vibrational-rotational transitions in the present molecules • Collision between atoms and molecule heat or cool the gas • Good coolant -readily emit photons following a collision - present enough quantities so significant number of photons are emitted • CO, H2O, O2, C are main coolants • At lower densities and temperatures CO and O2 are the dominant coolants • At higher densities and temperatures water becomes the principle coolant • Hydrides also play an important role in cooling. MOLECULES AS COOLENTS Workshop Ringberg-April 13-17, 2004

7. ROLE OF HYDRIDES IN ISM • Simple hydride molecules are of great importance in astrophysics and astro-chemistry. • Physically they dominate the cooling of dense, warm phases of the ISM, such as the cores and disks of YSOs. • Chemically they are often stable end points of chemical reactions, or may represent important intermediate stages of the reaction chains, which can be used to test the validity of the process. • Due to the low moment of inertia, the hydrides rotate rapidly and so have their fundamental spectral lines in the submillimeter. • Depending on the cloud geometry and temperature profile they may be observed in emission or absorption. • Species such as HCl, HF, OH, CH, CH+, NH2, NH3, H2O, H2S, H3O+ and even H3+ have been detected. • For example, the most important coolant for many regions, H2O, has a possible range of deduced abundance of a factor of 1000. • In circum stellar envelopes and planetary nebulae, the CH and OH radicals are predicted to be the products of photochemical processes which depend on a variety of factors, and since CH and OH contain three of the most abundant elements in the stellar ejecta, their transitions near 2 THz will be critical indicators for these processes. In particular, CH has strong transitions at 180.6, 149.5, 149.2, and 125.0 m with low-lying energy levels. Workshop Ringberg-April 13-17, 2004

8. Workshop Ringberg-April 13-17, 2004

9. Because the star forming process occurs behind so much intervening dusty material, visible-light telescopes cannot see what is happening. By moving to the infrared, sub-millimeter and millimeter wavelength regions, where the effects of this obscuration are nearly negligible, astronomers can begin to directly probe regions where stars are actively being born The dense and cool material in the interstellar medium of galaxies plays an important role in the life cycle of stars, from the earliest phases of star formation to the shells around evolved stars and the gas and dust tori around active galactic nuclei. Line emission from atoms and molecules, and continuum emission from dust particles, at radio, (sub) millimeter and infrared wavelengths are indispensable tools in the study of a wide variety of astrophysical problems. • By what process do pre-stellar cores collapse to form stars? • What are the physical natures of the nascent stellar cores of the youngest protostars? • What organic matter is present in the circumstellar environments of protostars? • is there water, and where is it located? Stars are born from the material between other stars. In some regions of space, the density of gas and dust is much higher than the normal, and atoms are sufficiently shielded from destructive high-energy photons to interact with other atoms to form simple molecules. In the highest density central regions of such molecular clouds, material is so well shielded that delicate, complex molecules can form. It is from these molecular cloud cores that new stars (including our own Sun) are born. The study of the chemistry in such regions can not only lead to an improved understanding of the physical conditions in such a "stellar nursery", but also can provide clues to the composition of other star-forming (and possibly planet-forming and life-giving) solar systems. Knowing what physical conditions are needed to form molecular cloud complexes is important in understanding the star-forming evolution of galaxies, both in the current age and, perhaps most importantly, when galaxies were first forming. SUBMILLIMETER STUDY OF STAR FORMING REGIONS Workshop Ringberg-April 13-17, 2004

10. SITE-MAP Workshop Ringberg-April 13-17, 2004

11. Submillimeter/Far Infrared • Cooled space-borne telescopes will permit huge sensitivity gains at these wavelengths, but these will be wasted without large format detector arrays. Direct detectors and heterodyne instruments are needed. The direct detectors need architectures and readout electronics that will scale to large arrays, and greatly improved sensitivity if they are to be used for spectroscopy. Heterodyne systems need more stable oscillators and quieter electronics, especially at the highest frequencies. Submillimeter astronomy borrows techniques used by both optical and radio astronomers. Heterodyne Receiver • Basic idea: • Illuminate mixer element with radiation from the sky, and also radiation from a transmitter (‘local oscillator’). • Beat frequencies get produced: • Vsky = V1 sin (w1t – f1) • VLO = V0 sin (w0t – f0) • Voutput = (Vsky + VLO)2 = • C sin [(w1-w0)t – f] + high frequency terms which get filtered out • Example:Line of interest at 645 GHz, LO at 644 GHz  line appears at (645 – 644) = 1 GHz, a frequency which spectrometers can deal with. SUBMILLIMETER INSTRUMENTATION Workshop Ringberg-April 13-17, 2004

12. OPML consists of two cavities CO2 and FIR designed to give high out put power in 9-11 micron (about 80 lines) with good frequency and amplitude stability coupled with powerful FIR emission in the 40 micron to 1.22 mm region. • The CO2 section of the laser is operated in a flowing gas mode to obtain highest output power. • The laser gain section is a single arm water discharge tube sealed with Brewster angled ZnSe windows in air cooled mounts. • The CO2 resonator consists of a partially reflecting ZnSe output coupling mirror and a blazed diffraction grating. • The output coupler is mounted on a piezo-electric transducer which allows fine control of the cavity length (and hence output frequency). • FIR laser comprises a ZnSe input Brewster window which forms a vacuum seal at one end of the laser, a flat chromium gold coated stainless steel input mirror at one end of the laser and a dichroic output coupler from which the FIR power is extracted to other end. • A water cooled oversized Pyrex waveguide of 35 mm inside diameter is used. • ZnSe • Brewster window • The stabilization of the system is done by using a part of FIR power and feed that back to the CO2 piezo-electric transducer which stabilized the CO2 and hence FIR laser. • Novel ideas were implemented to increase the efficiency of the existing laser system. • Presently we are using two FIR gases CH3OH and HCOOH which are able to give about 10 strong FIR transitions. • CO2 • + • N2 • + • He • Water • jackets • CO2 output coupler • ZnSe • AR coated 9-11 m lens • M1 • M2 • FIR Molecule • Brewster window OPTICALLY PUMPED MOLECULAR LASER Workshop Ringberg-April 13-17, 2004

13. Closed structure mounting • Metal & n type semiconductor used instead of p-n junction • Absence of p layer lower series resistance and capacitance • Majority carrier device, exhibiting no charge storage • For similar size & doping, it has significantly smaller capacitance than that of a p-n junction, which permits higher operational frequencies • Photo-voltaic quantum detector • Response time r ~0.87 ps • Anode diameter ~0.5 m • Evaporated Schottky barrier diode is fabricated by depositing a metal (Pt or Au) onto a vacuum cleaned GaAs surface • Thin lightly doped n-type epitaxial layer is grown on an n+ GaAs substrate • Guard ring eliminate unwanted edge breakdown SCHOTTKY DIODE Workshop Ringberg-April 13-17, 2004

14. Superconductor-Insulator- Superconductor (SIS) Mixer • Mixers using Superconductor Isolator Superconductor (SIS) tunnel junctions have been constructed that perform with noise equivalents of a few times the quantum limit at frequencies below∼700 GHz, the gap frequency of niobium. • At higher frequencies losses in the superconducting material rapidly degrade the performance. • By using different materials (e.g., NbTiN), this cut-off may be shifted to slightly above 1.2 THz • Niobium junction works up to 700 GHz • Niobium-Titanium-Nitride works up to 1.2THz • DSB noise tem. ~ 2-4 h/k, IF bandwidth 4-8 GHz Workshop Ringberg-April 13-17, 2004

15. Bolometers • Photon energy heats detector (hexagons) • Detected by sensor – thermistor (right) or superconducting device (future) –Wiring lithographed • Low T operation at 100-300mK, determined by background conditions State-of-the-art –Bolometers at 0.3 K: NEP = 10-16 W s1/2 –Bolometers at 0.1 K: NEP = 10-17 W s1/2 Workshop Ringberg-April 13-17, 2004

16. f(t) F() CH + • The intermediate frequency signal obtained from the first mixer needs amplification by chain • of IF amplifiers to acquire suitable level required for further signal processing. • The HEMT (High Electron Mobility Transistor) amplifier can give very high gain and also provide • very high frequency operation with lowest noise figure. • The RF mixers are useful for further down converting the signal. • The Chirp Transform Spectrometer (CTS) is state-of-the-art spectrometer giving very high • frequency resolution and wide bandwidth. • The Filter Bank spectrometer is very bulky and suitable for ground based applications. • The Acousto-Optic spectrometer can give much wider bandwidth but its frequency resolution is limited to very low value. • The very high sensitivity spectrum analyzer, signal sources and high end oscilloscopes are useful for observing different characteristics of the signal. M-C structure CH - • Reflective Array Compressor (RAC) SAW device for space applications • Digital Waveform Generation (DWG) technique is better alternative • Direct Digital Chirp Synthesizer (DDCS) is suitable for ground applications • Aimed Specifications • Frequency Resolution = 20 kHz • Bandwidth = 200 MHz • Dynamic Range = 40 dB BACKEND ELECTRONICS Workshop Ringberg-April 13-17, 2004

17. Heterodyne receiver setup using CO2 pumped FIR LASER. Schottky barrier detector with corner cube antenna Filter bank. Lithography setup Spectrum analyzer and other backend electronics. . • LABORATORY SETUP Workshop Ringberg-April 13-17, 2004

18. The observational data provides information on • The morphology of dust and gas emission; • The SED's and energy budgets of the proto stellar cores; and • The density and temperature profiles of the clumps. • Models can simulate the velocity fields and density structures in the heads and tails closely matching observations. • Modeling is a very important process that basically allows us to compare observations to what we think might be going on in a given physical system. • Models that make different assumptions about the disk size, shape, and the properties of the dust grains. We can assume different things about the disk in order to make the model fit the data. • For themodeling of spectral lines one has to solve the corresponding radiative transfer equation. When we make models of circum stellar disks, we make certain assumptions about the properties of the disk and the grains that compose it. The telescopes measure the amount of Energy being emitted from a star (and also a disk that might be surrounding it) at a particular wavelength. This data is then plotted on an SED where we can see how well our models fit the data RADIATIVE TRANSFER MODELING Why modeling of star forming regions ? Star forming interstellar clouds are in fact complex systems: they have irregular three-dimensional shapes and complicated velocity fields, the densities extend over many orders of magnitude, and the temperatures range from about 10K to several million K. There are myriads of reactions going on among the particles. The relevant geometric scales range from atomic sizes to light years. We then compare these models with observations taken from telescopes and satellites Workshop Ringberg-April 13-17, 2004

19. RT EQUATION Observer Synthetic Spectra Task 1: Spectra Radiative Transfer Model T1 t1>> 1 T2 t2 Atmospheric Thermal Structure and Composition Stellar Spectra Atmospheric and surface optical properties Using more than one transition from the same molecule can give detailed information on its excitation temperature, which in turn is related to the kinetic temperature and density of the gas, and velocity component along the line of sight, using the Doppler shift. Combining this with optically thin emission from isotopomer species, the depth along the line of sight can be studied. The wealth of molecular lines can together give a full description of the physics and chemistry of STAR FORMING REGIONS Workshop Ringberg-April 13-17, 2004

20. INTERPRETATION OF SMM DATA COMPARISON WITH MODELS UNDERSTANDING OF PHYSICS AND CHEMISTRY OF STAR FORMING REGIONS DATA REDUCTION - CLASS Work Plan on Modeling aspects • To calculate the radiative transfer and excitation of molecular lines • To develop New dust models taking into account the evolution of grain properties in ISM sites. • Predict the submm dust Galactic emission • Characterize dust properties changes by modeling the emission of ISM objects (molecular clouds with or without embedded star, diffuse clouds, dense and cold cores,…), • To understand the physics of the photoevaporative flows that surround globules - and the role of the shock in inducing collapse and triggering star formation. • Model of the molecular-ionised gas interface to simulate the pressures, densities and excitation of the gas, and to understand how it is associated with the collapse of the molecular core just inside the neutral gas. PRESENT DUST SHELL MODLLING USING DUSTY (Zeljko Ivezic), 1-D MODEL USING RATRAN FUTURE DEVELOPMENT OF 1-D, 2-D CODES FOR SMM MISSION DATA ANALYSIS AND RADIATIVE TRANSFER MODELING Workshop Ringberg-April 13-17, 2004

21. ICSST 04 INTERNATIONAL CONFERENCE ON SUBMILLIMETER SCIENCE AND TECHNOLOGY- ICSST04 THANK YOU Workshop Ringberg-April 13-17, 2004