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CCU Spring School Radio Astronomy for Chemists.


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CCU Spring School Radio Astronomy for Chemists Lucy M. Ziurys Department of Chemistry Department of Astronomy Arizona Radio Observatory University of Arizona Our Galaxy in Molecules Columbia-CfA Project CO 1-0 All Sky Survey Chemistry and Interstellar Molecules
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Slide 1

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

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Our Galaxy in Molecules Columbia-CfA Project CO 1-0 All Sky Survey Chemistry and Interstellar Molecules Molecular Astrophysics: 35 Years of Investigation  Universe is genuinely MOLECULAR in nature Molecular Gas is Widespread in the Galaxy and in External Galaxies Our Galaxy at Optical Wavelengths half of matter in inward 10 kpc of Galaxy is MOLECULAR (~10 10 M  ) Molecular mists biggest very much characterized articles in Galaxy (1 - 10 6 M  ) Unique tracers of substance/physical conditions in chilly, thick gas  New window on cosmic frameworks - no more domain of particles

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CRL 2688 Post-AGB Star From Interstellar Molecules.. Protostars in Orion: HCN 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 compelling situations Implications for Astrobiology/Origins of Life - Limits of Chemical Complexity Unknown CO in M51

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Known Interstellar Molecules

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Orion Molecular Clouds CRL 2688 Circumstellar Envelopes of Evolved Stars Physical Characteristics of Molecular Gas Primarily Found in Two Types of Objects Characteristics of Molecular Regions Cold : T ~ 10 - 100 K Dense : n ~ 10 3 - 10 7 particles/cm 3 (OR 10 - 13 - 10 - 9 mtorr) Clouds Collapse to Form Stars/Solar Systems Chemistry happens basically through 2-body ION-MOLECULE responses Kinetics administers the science, NOT thermodynamics Timescales for science: 10 3 - 10 6 years

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r Molecular Energy Levels Electronic ~ 10,000 cm - 1 Vibrational ~ 100-1000 cm - 1 Rotational ~ 10 cm - 1 Rotational Spectroscopy: How Molecules are Detected Cold Interstellar Gas: Rotational Levels Populated by means of Collisions Spontaneous Decay Produces Narrow Emission Lines Resolve Individual Rotational Transitions (Gas-Phase) Rotational vitality levels  Depend on Moments of Inertia I = μ r 2 E decay = B J(J+1) Identification by “Finger Print” Pattern Unique to a Given Chemical Compound

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Spectra acquired with Radio Telescopes C N High Resolution Spectral Data Many moves measured High flag to-clamor Resolve fine, hyperfine structure N =2 → 1 rotational move: 15 hyperfine segments

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Radio Telescopes: Some Technical Aspects Radio Telescope: - Consists of two primary segments - Telescope (reception apparatus) itself with control framework - Receiver in addition to related location hardware Antenna: - Panels on a super structure (aluminum with carbon fiber) - Power example or increase capacity g( θ , φ ) - Pencil pillar on sky with round opening Gain example is Airy example - First invalid at 1.22 λ/D: “diffraction-limited” - Describes HPBW ( θ b ) of recieving wire - At 12 m, θ b ~ 75″ – 40″ SMT HPBW

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Antenna reaction as far as Antenna Temperature T A T A = 1/4 π ∫ g( θ , φ ) T B ( θ , φ ) d - convolution of source and reception apparatus properties - imbed reception apparatus in Blackbody at T BB T A = T/4 π ∫ g( θ , φ ) d = T BB Various Efficiencies for Antenna reaction Aperture Efficiency η A - Response to a point source - η A ~ 0.5 - a measure of surface exactness of dish (on a par with 15 microns rms) Main Beam Efficiency η B - Percent of force in fundamental bar versus side projections - Response to developed source T A = 1/4 π ∫ gT B d ~ <T B > - η B ~ 0.7 – 0.9

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Directed to Sub-reflector Signals reflected from essential Into a radio Receiver To focal choice mirror Radio signs originate From sky Radio Telescope Optics - Cassegrain frameworks f/D proportion of essential is ~ 0.4 - 0.6

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Dewar window Lens Feedhorn Coupler Mixer Bias Isolator HEMT speaker Millimeter Telescope Receivers  sky HETERODYNE RECEIVERS with MULTIPLEXING SPECTROMETERS Sky signal (  sky ) lands at blender SIS intersection in a dewar, cooled to 4.2 K At Mixer, nearby oscillator (LO) signal (  LO ) is blended with sky sign Generates a sign at recurrence contrast (middle of the road recurrence),  IF   IF =  sky -  LO or  LO -  sky IF recurrence identified by HEMT enhancer IF Signal sent to the spectrometer (Backend) Not single flag however go  IF  0.5 GHz =  sky  0.5 GHz  LO To spectrometer backend  IF COMPLEX SYSTEMS

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Mixer, intensifier, LO coupler and so forth incorporated with “Insert” One addition for every blender Two blenders for each recurrence band (one for each orthogonal polarization) Frequency scope dictated by Waveguide Band (WR 10, WR 8, and so on) Inserts into Dewar; cooled to 4.2 K Mixer Block Incorporation into “Insert” put into Dewar

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A Complete Receiver … Optics Card Cage Cryo lines cabling

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Heterodyne Receivers and Image Rejection With Mixers: o bserve two frequencies at the same time Upper sideband (USB):  IF =  sky -  LO Lower sideband (LSB):  IF =  LO -  sky Reject undesirable sideband to keep away from perplexity (SSB blender or optics) “Single” versus “Double” sideband recipient (SSB versus DSB) Typical dismissal: > 15 - 20 db EXAMPLE: NGC7027 12 CO: J=2 → 1 line T A *~ 8 K - decreased to 0.1 K in picture  20.6 db dismissal - LO shift NGC 7027 13 CO in LSB (signal sideband) 12 CO picture from USB

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IF System Block Diagram: SMT Left Rx room Right Rx room 345 Rx 1.5G Rx switch 1.5->5G Converter 5G Rx switch Rx switch/Total force/Attenuators 490 Rx Right Flange Rx New Rx Channel guiding Computer room BE switch AOS A,B,C Frequency controlling Filter banks IF Systems at Radio Telescopes Radio Telescopes: MULTIPLEX ADVANTAGE Simultaneously gather information over complete BW of IF Amplifier Must have hardware to neatly transform IF signs Mix IF sign down to base band Send into spectrometer

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Spectrometer “Backends” Backend isolates out sign as a component of recurrence  A range is created…  = 178.323 MHz Filter Banks at the SMT TYPES of BACKENDS Filter banks : Complex arrangement of capacitors, channels, and so on. Acousto-optic spectrometers (AOS) Autocorrelators : Digital gadgets (MAC)

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Square law locator Integrator Mux BPF Zero DAC Filter Card for 16 stations: 1 MHz determination channels Filter Card Block Diagram (one station)

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Telescope Control System Sophisticated Control System Coordinates telescope movement with information gathering and hardware Fast information securing/preparing Distributed nature of framework Each assignment controlled by discrete PCs Computer for telescope following, center position, each backend, and so forth. Proficient, synchronous operation Remote Observing  Trained administrators at site ARO Control System

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Observing Techniques Continuum strategies : Observe over wide band: 1.2 GHz (Digital Backend) 1) Pointing - Small adjustments for gravitational distortion of dish - one in azimuth, one in height 2) Focus - Move sub-reflector pivotally to best position Spectral Line routines - Observe unearthly lines - Background clamor subtracted out with an exchanging strategy Telescope Calibration - Measure a voltage from blender - Convert to Temperature Scale (T R * ) utilizing “Calibration Scan” - Voltage on sky (T sky ) and surrounding burden (T amb ) - Intrinsic “noise” of framework (T sys ), including hardware, reception apparatus, sky

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Pointing sweep or continuum 5-point: done on planet Jupiter Establish guiding constants in az and elv

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FOCUS examine on Jupiter Determine ideal position of sub-reflector

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Astronomical Sources Various sources “visible” at distinctive times of day Matter of position in sky”, i.e. Divine Coordinates Right Ascension (RA or α ) and Declination (dec or Î' ) Source overhead when RA = LST (Local Sidereal Time) “Catalog Tool” at ARO

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Spectral Line Techniques Position exchanging Switch telescope position between the source and clear sky (“off position”: 10-30 arcmin away in azimuth) Subtract “(ON – OFF)/OFF” to evacuate foundation Calibrate the power scale (voltage) by doing a “Cal scan” : T scale =T A * ( in K) Beam-exchanging  Nutate sub-reflector to get ON/OFF positions  Also start with Cal Scan Frequency exchanging  Change recurrence of LO ± 1-2 MHz Blank sky Molecular cloud (ON-OFF)/OFF and alignment all done in a split second in programming

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Data Calibration and Intensity Scales Data got promptly adjusted wit