Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.naic.edu/~astro/School/Talks/large_pdf/condon_cont_2.pdf Äàòà èçìåíåíèÿ: Tue Jul 12 03:49:49 2005 Äàòà èíäåêñèðîâàíèÿ: Sun Dec 23 04:14:14 2007 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: m 13

National Radio Astronomy Observatory
July 11, 2005 NAIC/NRAO Single-dish Summer School

Continuum Observing
Jim Condon

Continuum Emission and Single Dishes
· Continuum sources produce steady, broadband noise · So do receiver noise and drift, atmospheric emission, ground pickup, confusion, etc. · Single dishes can image large areas and low-brightness sources · Single dishes can use array feeds, wide bandwidths, and incoherent detectors
National Radio Astronomy Observatory July 11, 2005 ­ Single -dish Summer School

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Astronomical Continuum Sources
Synchrotron (dash-dot curve), free-free (dashes), and dust (dots) emission typical of spiral galaxies

National Radio Astronomy Observatory July 11, 2005 ­ Single -dish Summer School

408 MHz continuum emission, galactic coordinates

Haslam et al. 1982, A&AS, 47, 1 (see Chris Salter)
National Radio Astronomy Observatory July 11, 2005 ­ Single -dish Summer School

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National Radio Astronomy Observatory July 11, 2005 ­ Single -dish Summer School

Orion Nebula HII region at 8.4 GHz

National Radio Astronomy Observatory July 11, 2005 ­ Single -dish Summer School

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The Galactic dark cloud G11.11-0.12 in absorption at 8 microns (left) and in emission at 850 microns (right)

National Radio Astronomy Observatory July 11, 2005 ­ Single -dish Summer School

SCUBA on the JCMT

National Radio Astronomy Observatory July 11, 2005 ­ Single -dish Summer School

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850 micron SCUBA/JCMT image of the HDFN

National Radio Astronomy Observatory July 11, 2005 ­ Single -dish Summer School

Dust emission at high redshifts

National Radio Astronomy Observatory July 11, 2005 ­ Single -dish Summer School

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Strong continuum point sources as observing tools
· · · · Sanity checks Pointing, focus, and surface setting Intensity and polarization calibration Offset pointing corrections

National Radio Astronomy Observatory July 11, 2005 ­ Single -dish Summer School

A cross scan yields the pointing offset, beamwidth, and antenna temperature

National Radio Astronomy Observatory July 11, 2005 ­ Single -dish Summer School

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Distributions of normalized gain G resulting from Gaussian pointing errors with rms = HPBW

National Radio Astronomy Observatory July 11, 2005 ­ Single -dish Summer School

Pointing errors: ·Setting ·Gravitational ·Thermal ·Refraction

Different ial expansio n fro m solar heat ing bent the 300-foot telescope away fro m the Sun (near = 13h 20m).
National Radio Astronomy Observatory July 11, 2005 ­ Single -dish Summer School

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This dense grid of pointing calibrators can be used to reduce tracking errors north of = -40°.

National Radio Astronomy Observatory July 11, 2005 ­ Single -dish Summer School

Axial Focus
GBT focal ellipsoid axial FWHM 4

National Radio Astronomy Observatory July 11, 2005 ­ Single -dish Summer School

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Telescope setting by OOF holography

National Radio Astronomy Observatory July 11, 2005 ­ Single -dish Summer School

Telescope surface-error maps: before: = 370 µ m after: = 210µ m

National Radio Astronomy Observatory July 11, 2005 ­ Single -dish Summer School

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Flux-density and polarization calibrators:
Baars, J. W. M., Genzel, R., Pauliny-Toth, I. I. K., & Witzel, A. 1977, A&A, 61, 99 Ott, M. et al. 1994, A&A, 284, 331 http://134.104.64.34/JN/effbg_rx/kalirie. htm http://www.aoc.nrao.edu/~gtaylor/calib. html http://www.aoc.nrao.edu/~gtaylor/calman/po lcal. html ftp://ftp.atnf.csiro.au/pub/atnfdocs/guides/at.cat

Single-dish position calibrators:
Condon, J. J., & Yin, Q. F. 2001, PASP, 113, 362 ftp://ftp.cv.nrao.edu/NRAO-staff/jcondon/PCALS3.3 http://wiki.gb. nrao.edu/bin/view/PTCS/PointingFocusCatalog
National Radio Astronomy Observatory July 11, 2005 ­ Single -dish Summer School

Single-dish continuum observations of faint and/or extended sources
· · · · · Thermal noise 1/f noise (receiver and atmosphere) Confusion Baselines RFI

National Radio Astronomy Observatory July 11, 2005 ­ Single -dish Summer School

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Radiometer equation for a real receiver

National Radio Astronomy Observatory July 11, 2005 ­ Single -dish Summer School

Postdetection power spectrum showing 1/f noise at low frequencies and refrigerator microphonics near 1.2 Hz.

k

Use < 1/(2

k

): on-the-fly mapping, Dicke switching, ...

National Radio Astronomy Observatory July 11, 2005 ­ Single -dish Summer School

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Confusion
Profile plot of 45 deg² near the NGP imaged with 12 arcmin resolution at 1.4 GHz. The strongest source shown has S 1.5 Jy.

National Radio Astronomy Observatory July 11, 2005 ­ Single -dish Summer School

NVSS (45 arcsec FWHM) grayscale under GB (12 arcmin FWHM) contours illustrates source blending

National Radio Astronomy Observatory July 11, 2005 ­ Single -dish Summer School

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The confusion amplitude P(D) distribution [for n(s) = kS-2.1]

D = image brightness (e.g., Jy/beam) D = 0 mean is not a good baseline; use running median instead
National Radio Astronomy Observatory July 11, 2005 ­ Single -dish Summer School

"RMS" confusion

National Radio Astronomy Observatory July 11, 2005 ­ Single -dish Summer School

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The 5 extragalactic confusion limits for Arecibo (d = 220 m) and the GBT (d = 100 m).

National Radio Astronomy Observatory July 11, 2005 ­ Single -dish Summer School

Baselines
The total-power output fro m one receiver channel during a 4.85 GHz scan. The system temperature T 60 K includes receiver noise, atmospheric emission, spillover, leakage through the reflector mesh, etc.
National Radio Astronomy Observatory July 11, 2005 ­ Single -dish Summer School

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Running-median baselines have removed atmospheric emissio n, spillo ver, 1/f no ise, and extended sources.

National Radio Astronomy Observatory July 11, 2005 ­ Single -dish Summer School

Beam-switching
The SNR 3C 10 imaged at 10.7 GHz by horizontal scans only (top) and by dual-beam basketweaving (bottom). Basketweaving references: Sieber et al. 1979, A&A, 74, 361 Emerson & Grave 1988, A&A, 190, 353 (see Chris Salter)

National Radio Astronomy Observatory July 11, 2005 ­ Single -dish Summer School

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Future single-dish continuum projects
· Penn Array on GBT
64-element = 3 mm bo lo meter camera, 8 arcsec resolution can map 15 arcmin X 15 arcmin with = 0.2 mJy in 1 hour circumstellar disks, S-Z clusters, protogalaxies,...

· ALFA on Arecibo
7-element = 21 cm coherent array, 3 arcmin resolution full-Stokes large-area continuum survey Galact ic loops, Faraday tomography, transient sources
National Radio Astronomy Observatory July 11, 2005 ­ Single -dish Summer School

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