CCU Spring School March , 2009 CCU Spring School Radio Astronomy for Chemists Lucy M. Ziurys Department of Chemistry Department of Astronomy Arizona Radio Observatory University of Arizona

CCU Spring School March , 2009 Chemistry and Interstellar Molecules Our Galaxy at Optical Wavelengths Columbia-CfA Project CO 1-0 All Sky Survey Our Galaxy in Molecules Molecular Astrophysics: 35 Years of Investigation  Universe is truly MOLECULAR in nature Molecular Gas is Widespread in the Galaxy and in External Galaxies 50% of matter in inner 10 kpc of Galaxy is MOLECULAR (~10 10 M  ) Molecular clouds largest well-defined objects in Galaxy ( M  ) Unique tracers of chemical/physical conditions in cold, dense gas  New window on astronomical systems - no longer realm of atoms

CCU Spring School March , 2009 Galactic Structure (Milky Way, others) - Galaxy Morphology - Galactic Chemical Evolution Early Star Formation - Life Cycles of Molecular Clouds - Creation of Solar Systems Late Stages of Stellar Evolution - Properties of Giant Stars, Planetary Nebulae - Mass Loss and Processing of Material in ISM - Nucleosynthesis and Isotope Ratios Molecular Composition of ISM - Remarkably Active and Robust Chemistry - Molecules present in extreme environments Implications for Astrobiology/Origins of Life - Limits of Chemical Complexity Unknown From Interstellar Molecules.. CRL 2688 Post-AGB Star CO in M51 Protostars in Orion: HCN

CCU Spring School March , 2009 Known Interstellar Molecules H2H2 CNH2OH2OC3C3 NH 3 CH 3 SiH 4 CH 3 OHCH 3 CHOCH 3 COOHCH 3 CH 2 OH OHCF + H2SH2SMgNCH3O+H3O+ C3N-C3N- CH 4 NH 2 CHOCH 3 NH 2 HCOOCH 3 (CH 3 ) 2 O SOCOSO 2 NaCNH 2 COHCNOHCOOHCH 3 CNCH 3 CCHCH 3 C 3 NCH 3 CH 2 CN SO + CSN2H+N2H+ CH 2 H 2 CSHSCNHC 3 NCH 3 NCCH 2 CHCNC7HC7HHC 7 N SiOC2C2 HNOMgCNHNCOCH 2 NHCH 3 SHHC 5 NH2C6H2C6 CH 3 C 4 H SiSSiCHCPHOC + HNCSNH 2 CNC5HC5HC6HC6HCH 2 OHCHOC8HC8H NOCPNH 2 HCNCCCNH 2 CCOHC 2 CHOC6H-C6H- HC 6 HC8H-C8H- NSCO + H3+H3+ HNCHCO 2 + C4HC4HC2H4C2H4 c-CH 2 OCH 2 CH 2 CCHCNCH 3 CONH 2 HClSHN2ON2OAlNCCCCHC4H-C4H- H2C4H2C4 CH 2 CHOHCH 2 CHCHOCH 3 CHCH 2 NaClHDHCOSiCNc-C 3 Hc-C 3 H 2 HC 3 NH + NH 2 CH 2 CN KClHFHCO + SiNCCCCOCH 2 CNHC 4 H1011 AlClPOOCSH2D+H2D+ CCCSC5C5 HC 4 NCH 3 COCH 3 HC 9 N AlFAlOCCHHD 2 + HCCHSiC 4 C5NC5NCH 3 C 5 NCH 3 C 6 H PNHCS + KCNHCNH + H2C3H2C3 20 ions(CH 2 OH) 2 12 SiNc-SiC 2 CO 2 HCCNHCCNC6 ringsCH 3 CH 2 CHO CHCCOH 2 CNHNCCC116 Carbon Molecules13 CH + CCSc-SiC 3 H 2 COH + 20 RefractoriesHC 11 N NHCCPPH 3 WHAT ELSE ??? Total = 151

CCU Spring School March , 2009 Physical Characteristics of Molecular Gas CRL 2688 Circumstellar Envelopes of Evolved Stars Characteristics of Molecular Regions –Cold: T ~ K –Dense: n ~ particles/cm 3 (OR mtorr) –Clouds Collapse to Form Stars/Solar Systems –Chemistry occurs primarily via 2-body ION-MOLECULE reactions  Kinetics governs the chemistry, NOT thermodynamics  Timescales for chemistry: years Orion Molecular Clouds Primarily Found in Two Types of Objects

CCU Spring School March , 2009 Rotational Spectroscopy: How Molecules are Detected Cold Interstellar Gas: Rotational Levels Populated via Collisions Spontaneous Decay Produces Narrow Emission Lines Resolve Individual Rotational Transitions (Gas-Phase) Identification by “Finger Print” Pattern Unique to a Given Chemical Compound Rotational ~ 10 cm -1 Vibrational ~ cm -1 Electronic ~ 10,000 cm -1 Molecular Energy Levels I = μ r 2 r Rotational energy levels  Depend on Moments of Inertia E rot = B J(J+1)

CCU Spring School March , 2009 Spectra obtained with Radio Telescopes High Resolution Spectral Data Many transitions measured High signal-to-noise Resolve fine, hyperfine structure CN N =2→1 rotational transition: 15 hyperfine components

CCU Spring School March , 2009 Radio Telescopes: Some Technical Aspects Radio Telescope: - Consists of two main components - Telescope (antenna) itself with control system - Receiver plus associated detection electronics Antenna: - Panels on a super structure (aluminum with carbon fiber) - Power pattern or gain function g(θ,φ) - Pencil beam on sky with circular aperture Gain pattern is Airy pattern - First null at 1.22 λ/D: “diffraction-limited” - Describes HPBW ( θ b ) of antenna - At 12 m, θ b ~ 75″ – 40″ SMT HPBW

CCU Spring School March , 2009 Antenna response in terms of Antenna Temperature T A T A = 1/4π ∫ g(θ,φ) T B (θ,φ) d  - convolution of source and antenna properties - imbed antenna in Blackbody at T BB T A = T/4π ∫ g(θ,φ) d  = T BB Various Efficiencies for Antenna response Aperture Efficiency η A - Response to a point source - η A ~ a measure of surface accuracy of dish (as good as 15 microns rms) Main Beam Efficiency η B - Percent of power in main beam vs. side lobes - Response to extended source T A = 1/4π∫ gT B d  ~ - η B ~ 0.7 – 0.9

CCU Spring School March , 2009 Radio signals come From sky Signals reflected from primary Radio Telescope Optics Directed to Sub-reflector To central selection mirror Into a radio Receiver - Cassegrain systems - f/D ratio of primary is ~

CCU Spring School March , 2009 Dewar window Lens Feedhorn Coupler Mixer Bias Isolator HEMT amplifier HETERODYNE RECEIVERS with MULTIPLEXING SPECTROMETERS Sky signal ( sky ) arrives at mixer SIS junction in a dewar, cooled to 4.2 K At Mixer, local oscillator (LO) signal ( LO ) is mixed with sky signal Generates a signal at frequency difference (intermediate frequency), IF  IF = sky - LO or LO - sky IF frequency detected by HEMT amplifier IF Signal sent to the spectrometer (Backend) Not single signal but range IF  0.5 GHz = sky  0.5 GHz Millimeter Telescope Receivers LO sky IF To spectrometer backend COMPLEX SYSTEMS

CCU Spring School March , 2009 Mixer Block Mixer, amplifier, LO coupler etc built into “Insert” One insert per mixer Two mixers per frequency band (one for each orthogonal polarization) Frequency coverage determined by Waveguide Band (WR 10, WR 8, etc) Inserts into Dewar; cooled to 4.2 K Incorporation into “Insert” “Insert” put into Dewar

CCU Spring School March , 2009 A Complete Receiver … Optics Card Cage Cryo lines cabling

CCU Spring School March , 2009 Heterodyne Receivers and Image Rejection With Mixers: observe two frequencies simultaneously Upper sideband (USB): IF = sky - LO Lower sideband (LSB): IF = LO - sky Reject unwanted sideband to avoid confusion (SSB mixer or optics) “Single” vs. “Double” sideband receiver (SSB vs. DSB) 13 CO in LSB (signal sideband) 12 CO image from USB NGC 7027 Typical rejection: > db EXAMPLE: NGC CO: J=2 →1 line T A *~ 8 K - reduced to 0.1 K in image  20.6 db rejection - LO shift

CCU Spring School March , 2009 IF Systems at Radio Telescopes Radio Telescopes: MULTIPLEX ADVANTAGE Simultaneously collect data over complete BW of IF Amplifier Must have electronics to cleanly process IF signals Frequency steering AOS A,B,C Filter banks Rx switch/ Total power/ Attenuators IF System Block Diagram: SMT Channel steering 345 Rx 490 Rx New Rx 1.5G Rx switch Right Flange Rx BE switch 1.5->5G Converter 5G Rx switch Right Rx room Left Rx room Computer room Mix IF signal down to base band Send into spectrometer

CCU Spring School March , 2009 Spectrometer “Backends” TYPES of BACKENDS Filter banks: Complex set of capacitors, filters, etc. Acousto-optic spectrometers (AOS) Autocorrelators: Digital devices (MAC) Backend separates out signal as a function of frequency  A spectrum is created… = MHz Filter Banks at the SMT

CCU Spring School March , 2009 Filter Card Block Diagram (one channel) Mux BPF Zero DAC Square law detector Integrator Filter Card for 16 channels: 1 MHz resolution filters

CCU Spring School March , 2009 Telescope Control System Sophisticated Control System Coordinates telescope motion with data collection and electronics Fast data acquisition/processing Distributed nature of system  Each task controlled by separate computers  Computer for telescope tracking, focus position, each backend, etc. Efficient, synchronous operation Remote Observing  Trained operators at site ARO Control System

CCU Spring School March , 2009 Continuum methods: Observe over broad band: 1.2 GHz (Digital Backend) 1) Pointing - Small corrections for gravitational deformation of dish - one in azimuth, one in elevation 2) Focus - Move sub-reflector axially to best position Spectral Line methods - Observe spectral lines - Background noise subtracted out with a switching technique Telescope Calibration - Measure a voltage from mixer - Convert to Temperature Scale (T R * ) using “Calibration Scan” - Voltage on sky (T sky ) and ambient load (T amb ) - Intrinsic “noise” of system (T sys ), including electronics, antenna, sky Observing Techniques

CCU Spring School March , 2009 Pointing scan or continuum 5-point: done on planet Jupiter Establish pointing constants in az and elv

CCU Spring School March , 2009 FOCUS scan on Jupiter Determine optimal position of sub-reflector

CCU Spring School March , 2009 Various sources “visible” at different times of day Matter of position in sky”, i.e. Celestial Coordinates Right Ascension (RA or α) and Declination (dec or δ) Source overhead when RA = LST (Local Sidereal Time) Astronomical Sources “Catalog Tool” at ARO

CCU Spring School March , 2009 Position switching  Switch telescope position between the source and blank sky (“off position”: arcmin away in azimuth)  Subtract “(ON – OFF)/OFF” to remove background  Calibrate the intensity scale (voltage) by doing a “Cal scan” :T scale =T A * ( in K) Beam-switching  Nutate sub-reflector to get ON/OFF positions  Also begin with Cal Scan Frequency switching  Change frequency of LO ± 1-2 MHz Spectral Line Techniques Molecular cloud Blank sky (ON-OFF)/OFF and calibration all done instantly in software

CCU Spring School March , 2009 Data obtained immediately calibrated with background subtracted Background given by SYSTEM TEMPERATURE (T sys ) T sys changes with time T sys ~ 150 – 250 K with new ALMA 3 mm rxr at 12 m Spectral Line Intensity (T R * ) ~ – 10 K Want background subtracted No further reduction needed Only cosmetic: baseline subtraction, “bad channels”, etc) Look at data and ON-LINE decisions Change frequency, source, receiver, etc.  Optimize data return Flexibility for new discoveries Data Calibration and Intensity Scales

CCU Spring School March , 2009 Sensitivity Limits: T sys = system temperature For a noise level of 0.5 mK, signal average for ~100 hours (T sys ~ 300 K) Requires telescope systems to be very stable over long periods of time  can be accomplished with ARO rms = 2mk at 12+ hrs rms = 1 mK at 25 hrs rms = 0.5 mK at 100 hrs Extensive Signal-Averaging Collect data over 5-6 min as a single “scan” with a scan number Written to computer disk Average many scans for high S/N Radiometer Equation

CCU Spring School March , 2009 Spectrum after 15 hours T rms = K MOSTLY NOISE Spectrum after 30 hours rms = K MAYBE A LINE ??? Spectrum after 60 hours rms = K LINES APPEAR Searching for KCN: new molecule J(K a,K c ) = 16(0,16)  15(0,15) at GHz Signal Averaging: An Illustration IRC KCNU U

CCU Spring School March , 2009 Dual Polarization Capabilities J=2-1 line of HCO + near 178 GHz Orthogonal linear polarizations for 12 m receivers: Two independent measurements of the spectra Then average two spectra together for increased S/N

CCU Spring School March , 2009 Spectrum gives Intensity (T R * ) Convert T R * to T R (in K) via telescope efficiencies T R related to the opacity τ T B (or T L ) = f T ex (1 – e -τ ) Thin limit: T B (or T L ) = f T ex τ Thick limit: T B (or T L ) = f T ex f = beam filling factor (assume f = 1) Column Density (in cm -2 ) - Unsure of distance along line of sight - Estimate an abundance along a column N (in cm -2 ) - Column diameter given by telescope beam size θ b - N J ~ T B in thin limit - N tot = g J N J e - ΔEg’d /ζ rot From a Spectrum to an Abundance

CCU Spring School March , 2009 T rot = 27 ± 8 K N tot = 1.1 ± 0.4 x10 11 cm -2 KCN/H 2 ~ 3 x Rotational Diagrams Measure many transitions More accurate picture of abundance and excitation Population in the levels governs the intensity of the transitions By considering multiple transitions, column density (abundance) and temperature governing level population can be derived Create “Rotational Diagram” Also model with more sophisticated excitation code: LVG, Monte Carlo formalism, etc.

CCU Spring School March , 2009 Line Profiles Contain Kinematic Information

CCU Spring School March , 2009

(125, 185) (390, - 30) (130, - 180) (-15, 270) (-240, - 100) (-120, 240) (-372, 0) (-300, - 200) HCO + J = 1 → 0: Helix Nebula Spatial Mapping of Molecular Lines Beam Size

CCU Spring School March , 2009 Observing Plan for School Divide into three groups Eight hours of observing per day in shifts Conducting 2 part sequence of observations and data analysis Part I: Introduction with various sources and molecules AND calculations Part II: Real observations could lead to publishable results Part II: Begin a spectral line survey of C-Rich Stellar Envelope with new ALMA Band 3 Receiver

CCU Spring School March , 2009 Watch out for the Skunk !