From CARMA
DAY 1: Monday 9 July
INTRODUCTION to Millimeter Wavelength Interferometry
9-10 am Introduction. (Melvyn)
. Course outline
-- Day 1 : Basics to get you going.
-- Day 2-4:
Radio antennas, arrays, aperture synthesis, receivers and correlators.
Observing techniques, scheduling, calibration, data inspection, imaging
-- Day 5: Data analysis, future developments, VLBI.
. Source characteristics, instrumentation, and observing techniques
together define a matched filter to possible observations with
millimeter wavelength interferometers.
. Astronomy from comets to cosmology
-- emission mechanisms: thermal and non-thermal
-- source selection: astronomy, frequency, size, brightness sensitivity
. Atmospheric windows at optical, IR, and radio frequencies
. CARMA site characteristics
10-11 am APERTURE SYNTHESIS BASICS (Melvyn)
. Radio antennas: collecting area and resolution
. Aperture arrays
. response of a 2-element interferometer to point source.
. coordinate systems: (u,v,w), u,v tracks for different arrays.
. CARMA array characteristics. antennas, Rx bands, correlator.
. Aperture sysnthesis imaging.
. Mapping extended sources. resolving out extended structures
. Calibration, Imaging and Deconvolution.
11-12 am. Antenna tour (DaveW & Dick)
. Visit to telescopes. Intro to antenna hardware.
-- antenna structure
-- drive system
-- manual, computer control
-- limits and switches
-- cable wraps
12am - 1pm Lunch.
1-2 pm Intro to CARMA computers. (Marc)
. computers. data flow. archiving
- control computer: roadmap of machines, disks, directories and
subdirectories
. school data reduction and analysis space. login, passwords.
. basic observing procedures, on-line monitors and data inspection
- key programs:
2-3 pm Basic demos (students)
-- observe a point source (maser or quasar) and a planet.
-- plot amplitude and phase vs. uvdistance
-- constant amplitude for point source, Bessel function (with
phase flips) for planet
-- set up correlator in various modes, take spectra of Orion
3-4 pm OBSERVING PROCEDURES (Melvyn)
. Calibrations:
-- gain(t,f,p) - gain, bandpass, polarization, pointing.
. calibration intervals. V' = gain(t,f,p) x V + noise
. Observing scripts
. selecting suitable observations for the target sources.
-- sensitivity
-- source size; mosaicing.
. CARMA correlator capabilities; selecting a correlator settup.
. choosing calibrators for gain, bandpass, flux and pointing.
4-5 pm group discussion selecting student projects. (Douglas)
5-6 pm Intro to preparing CARMA observing scripts (Marc)
6 pm Dinner at the CARMA site.
Student projects observed on CARMA array overnight.
DAY 2: Tues 10 July
9-10 am DATA INSPECTION AND ANALYSIS (Melvyn)
. overview of data reduction procedure
. introduction to MIRIAD data reduction package.
. basic Miriad data format: header, history, uvdata, gains, bandpass
. inspecting uvdata: uvindex, uvlist, uvplt, uvspec
. selecting uvdata: keywords select= and line=
. flagging bad data with uvflag
. antenna based calibration; selfcal and mfcal. gpplt. gains bandpass polcal
. rewriting edited data sets with uvaver, uvcat, uvcal
10-11 IMAGING (Melvyn)
. Review of basic math: brightness distribution is FT of visibility data.
. FFT requires convolving onto a grid; choosing the pixel and image size.
-- mosaicing
. invert; choice of natural, uniform, robust weighting, effect on the
synthesized beam
. deconvolution algorithms: clean, maxen, mossdi, mosmem, restor
11-12 am Laptop tutorial reduction and analysis of student data (Melvyn)
12 - 1 pm Lunch at the CARMA site
1-2 pm. CARMA hardware - I. Receivers and Calibration (Dick)
- introduce system block diagram; receiver, cal load, local osc,
phaselocks, fiber, downconverter, correlator
- compute energy collected if observing 20 Jy source for 1 yr;
would need to observe for 10^5 yrs to heat 1 drop of water by 1 C
- receiver types:
- bolometers: not suitable for interferometry because they
don't preserve phase
- HEMT amplifiers: not yet competitive at 1mm
- heterodyne rcvr: downconvert to lower freq in a nonlinear device
- SIS mixers: photon-assisted tunneling; not a Josephson effect
- cryogenics; closed-cycle refrigerators, compressors
- local oscillator: Gunn oscillator
- must be synchronized between all antennas; discuss in lecture 2
- both USB and LSB are downconverted to IF; can be separated
with 90 degree phase switch; also defer to lecture 2
- combining LO and signal: mylar beamsplitter
- receiver and system temperature
- calibration:
- ideally, calibrate on loads outside the earth's atmosphere
- the chopper wheel method
- CARMA sensitivity calculator
2-3 pm. Demos on CARMA system
3-4 pm Planning observations and preparing observing scripts
4-5 pm Source selection and script preparation for student projects
5-6 pm students prepare observing scripts, analyze data.
Dinner at the CARMA site.
Student projects observed on CARMA array overnight.
DAY 3: Wed 11 July
9-10 am CALIBRATION (Melvyn)
. Calibrations - gain, bandpass, polarization, pointing.
. Antenna based calibrations: amplitude and phase closure
. Atmospheric and instrumental phase characteristics
. Tsys and Jy/K
. Pointing
. correlator calibration techniques.
10-12 am calibration and analysis of student projects (all)
12 - 1 pm Lunch at the CARMA site
1-2 pm special topics in mapping (Melvyn)
- the missing short spacing problem; importance for getting correct
answers for spectral index, etc; negative sidelobes due
to extended structure; filling in missing spacings with
larger single dish or Ekers-Rots scheme
- mosaicing: setting up grid files, linear and nonlinear
mosaicing schemes
- heterogeneous array imaging
2-3 pm CARMA software system (Marc)
-- monitor system
-- computers
-- data flow
-- archiving
2-4 pm Laptop tutorial data reduction and analysis of student data
4-6 pm students prepare observing scripts, and analyze data.
Dinner at the CARMA site.
Student projects observed on CARMA array overnight.
DAY 4: Thurs 12 July
9-10 am CARMA hardware lecture 2 - local oscillators, phaselocks (Dick)
- review system block diagram, heterodyne system, local oscillator
- independent oscillators, 100 GHz, synchronized to fraction of
one cycle over periods of hours (sounds hard)
- basic phaselock: mix with reference, low pass filter, generate
correction voltage; keeps phase relationship fixed
- CARMA phaselock chain; synth, YIG, Gunn, 10 MHz, 50 MHz
- numerical example: synth = xxx, YIG = yyy, LO = zzz
- fiber system; linelength correction
- lobe rotation
- compute differential doppler shift due to earth's rotation
for 100 GHz signal incident on 2 antennas 10-m apart: 0.24 Hz
- lobe rotators
- interferometer response for a double sideband conversion system
- need to offset freq of 1st LO as well as insert delays;
can be understood as removing differential doppler shift
due to earth's rotation
- phaselocks; the LO system
- cable length measurement system
- phase switching; Walsh functions
- sideband separation by phase switching; note that only signals
common to an antenna pair can be separated; noise appears
in both sidebands
- fiber optic hardware
10-11 am calibration (Dick)
- converting to flux density; aperture efficiency; source
flux table
12 - 1 pm Lunch at the CARMA site
DAY 5: Fri 13 July
9-10 am CARMA hardware lecture 3 - correlator; software control (James)
- review system block diagram
- correlator is detector and spectrometer for the array
- XF vs FX
- delays, 2nd LO lobe rotation, sideband separation
- correlator modes
- FPGA's
- noise source
- basic architecture of computer control system, CAN nodes
observer's everyday responsibilities (Douglas)
- creating and running the master observing script
- data quality reports
- data archiving and disk management
polarization measurements (Melvyn)
- interferometer response LR, RL, etc in terms of Stokes parameters
- Walsh function polarization switching schemes
- instrumental leakage terms and how to solve for them
- mapping procedures
troubleshooting (Dick, Marc)
- generator, air conditioning
- the anticollision system
- cryogenics
- rcvr tuning
- computer hangups
- clocks; resetting the time
- rebooting procedure:
moving the antennas and calibrating a new array configuration (DaveW, Marc)
- changing IFLO connections in the pits
- running tilt, shimming the antennas
- entering new station coordinates
- finding pointing offsets.
- finding the delay centers
- TV and radio pointing
- finding a baseline
- entering new pointing offsets or baselines
12 - 1 pm Lunch at the CARMA site
- atmospheric phase fluctuations and what we plan to do about them
- like floppy backup structure on a big telescope; causes
decorrelation, ruins aperture efficiency
- show results at long and short baselines
- phase structure function
- calibrating by rapid switching; put calibrator in grid file;
observe weak nearby calibrator often, strong faraway
calibrator less often
- calibrating by observing the total power; need for extreme
gain stability; typical results
CARMA future plans (Douglas)
- A-configuration
- Carlstrom's 1 cm system
- wideband receivers
- 23-antenna CARMA array
. analysis of student data
Dinner at the CARMA site.
Student projects observed on CARMA array overnight.
DAY 6: Sat 14 July
hike and go home.
