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MUSTANG Calibrator Analysis

bsm apr 2008

• MUSTANG Calibrator Analysis
  • Intro
  • Results
  • Model Opacities
  • Notes on Individual Runs
    • TPAR_14
    • TPAR_15
    • TPAR_17
    • TPAR_18
    • TPAR_19
    • Run 1
    • Run 2
    • Run 3
    • Run 4
    • Run 5
    • Run 6
    • Run 8
    • Run 9
    • Run 10

Intro

OBJECTIVES

• evaluate relative calibration stability
• evaluate sensitivity to focus position (TBD)
• evaluate stability of telescope pointing (TBD)
• evaluate stability of telescope focus (TBD)
• evaluate beam shape stability
• independently determine opacities and compare to archival values. (insufficient data for individual runs)
• secondary: get an idea of the influence of the weather (TBD)
• secondary: get an idea of the influence of scan patterns and feedarm stability (TBD)

Method: identify scans within +/- 1.5 mm of best focus (as determined from the subsequently adopted focuses -- perhaps I should determine this myself however). Apply standard (38 Jy per 1.2 volt cal above the atmosphere) calibration and image using offsrcpolyfit (fitting explicitly for the pulse tube terms as a sin/cos linear combination). A zenith opacity of 0.13 was assumed for all data -- the model values don't appear reliable to me at the level that there are deviations from this (see the model taus for each session plotted below, along with comments from the observer log file). Fit the image to a Gaussian; also perform aperture photometry within 20" radius of the peak in the map for an independent estimate. 210 calibrator observations were selected to be looked at, all collected during nominally useful sessions. The calibrated images were examined and assigned a "Quality Code" ranging from 0 to 3, indicating: 0-- not an observation of the type it claims to be; 1-- something obviously very wrong; 2-- ok but not great (some visible artifact or beam distortion is evident); 3-- great observation (no visible image artifacts or beam distortions). Only observations with quality codes greater than or equal to 2 are used.

Location of data: Analysis resides at gb:/home/scratch/bmason/parscr/srcs

History

• 02apr08: selected dataset per above criteria
• 04apr08: finished first pass through imaging and fitting these data.
• 21apr08: figured out enough of the weird things going on to post first results.

Results

In all there were 128 calibrator observations of suitable quality (qc >= 2) on the following sources

• 0530+135 (orion pointing calibrator): 40
• 3c279 (1256-0547): 25
• Mars: 32
• Saturn: 13
• 0738+1742: 9
• 0958+6553: 5
• 0854+2006: 3

This analysis focuses on 0530+135 and 3c279, because they are bright, compact, and well-sampled relatively speaking. Statistics for the measurements of these sources are summarized in the following table.

Plots of the measured flux densities as functions of elevation, time, beamwidth, and so forth follow have been placed at http://www.gb.nrao.edu/~bmason/mustang/srcanalys.html

A few things to note or keep in mind:

• Both of the integrated flux quantities (the volume of the fitted Gaussian beam, and the aperture photometry) must be normalized by a fiducial beam, here taken to be 8 arcseconds. The median beamwidth for the good source observations is more like 9.5 arcseconds, resulting in a bias in the "flux scale" relative to the image peaks.
• The fitted beam volume and aperture photometry measurements show weak if any trends
• The aperture photometry values are consistently 20% higher than the fitted beam volume. This appears to be due to the error beam, which is not a uniform disk 30' across but is rather somewhat more concentrated than that (based on Bill's latest beam maps). This bias aside the aperture photometry and beam volumes track each other fairly well. (Note that this is a distinct effect from the bias due to different assumed beam sizes)
• the peak fluxes, in contrast, show variation with elevation and beamwidth. however, the variation with beamwidth is less strong than what one would expect if the volume of the core beam were conserved. The value of the highest pixel in the image tracks the peak of the fitted gaussian quite well.
• There is an interesting hint of a dip in the peak flux right around 45 degrees elevation (the rigging angle of the surface). The integrated flux quantities do not show this so it's not, for instance, a variation in opacity. This needs further confirmation.
• Ignore the labels on the y-axis -- use the legend in the lower right corner to determine what has been plotted. All y-axis units are Janskys (when width is plotted, which is in arcseconds).
• When looking for trends, bear in mind that variability is an issue. To minimize this compare data collected on runs near to each other in time, which tend to have similar colored points in the plots. A sense of intrinsic source variability can be obtained by looking at the integrated fluxes vs time. It appears that 3c279 varies significantly over the epoch of observations.
• As Simon discovered, the angular diameters of both Mars and Saturn vary significantly over the observing runs

Model Opacities

I used Ron's CLEO tool to extract (with 2 hour sampling) the 90 GHz opacities (average of Lewisburg, Elkins, and Hot Springs) for the entire period of early December 2007 - end of March 2008. These were then interpolated onto the MJD's of individual observations. Plots of the model opacities on individual nights, along with notes from the log file pertaining to the weather, are shown here. An ascii file with all of the opacities for the season at the 2 hour sampling is attached to the end of this page.

• TPAR_14modelTau.png: cold and clear
  

• TPAR_15modelTau.png: 95% clear, clouds come in at end of run
  

• TPAR_17modelTau.png: clearish and calm
  

• TPAR_18modelTau.png: clear w/ground mist at start, perhaps some clouds toward middle/end in the west, definite fog at end
  

• TPAR_19modelTau.png: sky obscured at start, more clear at end
  

• AGBT08A_056_01modelTau.png: no info in logs, but from the data an excellent night
  

• AGBT08A_056_02modelTau.png: partly cloudy, clearing towards the middle
  

• AGBT08A_056_04modelTau.png: clear cool and calm
  

• AGBT08A_056_06modelTau.png: weather overcast and windy by the end
  

• AGBT08A_056_08modelTau.png: clear calm; high then clouds towards the end
  

• AGBT08A_056_09modelTau.png: mostly clear w/a few high then clouds
  

• AGBT08A_056_10modelTau.png: partly cloudy at start; mostly clear towards the end
  

Notes on Individual Runs

TPAR_14

Tower problems at start; blower on for the whole run; cold and clear.

calib scans

• 6,7 -- blank,cal.

• Mars: 13-18. 19,20,21-- detspeed test. 22+23 normal.
• 0530: 27, 32-36, 40 @ probable nominal focus (2mm). many others in that sequence
• 0530: 83. 86-90 detspeed. 91-95- full daisy
• 0530: 98 -- quick daisy at new focus +5mm
• Mars: 114-117 full daisies

NOTES

• after scan 103/104 (both aborted) array was rebiased -- needs accounting for

TPAR_15

Blower discovery. latter half promising

• Mars: 39,43.
• 0530: 47,50. 56. 58. 67, 71.
• Mars: 74,77 (10mm)
• Saturn: 80, 82 (5mm)
• 0902: 89, 102, 109, 111
• Saturn: 111, 122

TPAR_17

good weather but focus confusion at end

• 0532: 14,17 (possible focus weirdness). 27,28, 35. 45.
• 0830: 51,66 , 69
• 3c279: 78, 92,93 , 94. total focus confusion.

TPAR_18

pretty decent though possibly some dew/frost issues

• 0854: 50,55,57, 60, 65 (no zernike?),
• Mars: 80
• 3c279: 84, 90, 97=107 (varying periods and radii), 113.
• 1120: 118-123

TPAR_19

Mixed

• 0530: 12, 19, 23, 38
• Mars: 42, 49-59
• 3c279: 86, 91, 100
• 1549: 115, 124, 135

NOTES

• after scan 13-- col 0 was rebiased. (probably superconducting before that)

Run 1

Great run

• Mars: 9, 10
• 0530: 12, 23, 38, 53 (there is some focus choosing weirdness going on in these).

Run 2

Great run

• Mars: 11
• 0530: 14, 28, 33, 36, 45, 50, 59, 64, 73

Run 3

very windy

Run 4

good run

• Mars: 5, 12,
• 0530: 15, 20,21, 30, 33,35; 45, 50, 60, 65

Run 5

poor weather

Run 6

good wx till very end

• Mars: 6, 11
• 0530: 24, 27, 37; 45,

Run 8

good run

• Saturn: 7,8,10; 43, 48
• 0825: 12, 24, 26, 39
• 3c279: 51, 54, 77, 83, 86

Run 9

good till end

• 0958: 6,9, 16, 18, 30, 32, 44, 46
• Mars: 56, 59-61
• saturn: 67, 64
• 3c279: 70, 75-78 (clouds in some of this)

Run 10

lots of focusing, with fairly narrow coverage and small steps. these data probably need separate consideration.

• Mars: 7, 14
• 0530: 17, 20, 29, 34,35,36, 38, 50,51,52, 63,
• 0738: 65,66,67, 71, 81, 85,86,87, 90,91,92, 94, 98,99,100, 102,103,104, 117, 118, 119
• Saturn: 130, 131, 132, 138
• 3c279: 141, 145,146,147
• 0958: 151, 166, 174, 175, 177, 179, 187

-- BrianMason - 02 Apr 2008

Attachment:	Action:	Size:	Date:	Who:	Comment:
TPAR_14modelTau.png	action	5748	21 Apr 2008 - 14:38	BrianMason
TPAR_15modelTau.png	action	5378	21 Apr 2008 - 14:38	BrianMason
TPAR_17modelTau.png	action	5083	21 Apr 2008 - 14:39	BrianMason
TPAR_18modelTau.png	action	5248	21 Apr 2008 - 14:39	BrianMason
TPAR_19modelTau.png	action	5164	21 Apr 2008 - 14:39	BrianMason
AGBT08A_056_01modelTau.png	action	5901	21 Apr 2008 - 14:39	BrianMason
AGBT08A_056_02modelTau.png	action	5210	21 Apr 2008 - 14:40	BrianMason
AGBT08A_056_04modelTau.png	action	5318	21 Apr 2008 - 14:40	BrianMason
AGBT08A_056_06modelTau.png	action	5210	21 Apr 2008 - 14:40	BrianMason
AGBT08A_056_08modelTau.png	action	5607	21 Apr 2008 - 14:40	BrianMason
AGBT08A_056_09modelTau.png	action	5881	21 Apr 2008 - 14:41	BrianMason
AGBT08A_056_10modelTau.png	action	6630	21 Apr 2008 - 14:41	BrianMason
mustang06-07wx.txt	action	35846	21 Apr 2008 - 15:54	BrianMason