sharc-ii data reduction workshop sharc-ii drw 11/08/2004 darren dowell attila kovacs colin borys...

SHARC-II Data reduction Workshop

SHARC-II DRW 11/08/2004

QuickTime™ and aYUV420 codec decompressorare needed to see this picture.Darren DowellAttila KovacsColin BorysDarek LisMin YangJon Bird

Outline GOALS Caltech success stories Software Requirements and Installation

Overview of available software Installation overview Scripting with CRUSH

CRUSH vs SHARCSOLVE General SHARC-II Calibration

Opacity (tau) estimation Calibrators at 350 micron Stability of calibration

Calibrating your data Aperture Photometry PSF Photometry Example

Map tweaks and presentation Pointing, Calibration, Coadding, Cropping, and Mosaicing Making publishable images with IDL

Chopped data Lessons learned Tips for taking better data Miscellaneous notes


Goals


1. Transfer expertise from Caltech to other usersWhy? To promote publication of SHARC-II data

2. Transfer expertise from other users to CaltechWhy? Users tend to be familiar with the issues involved.

3. Learn about difficulties users have with instrument/dataWhy? To improve the system.

4. Improve data acquisition techniquesWhy? Improve efficiency of SHARC-II observations

Caltech Success Stories


The next few slides present results from observations conducted by members of the Caltech SHARC-II group. They span a variety of flux levels and redshifts, and are meant to illustrate the full range of SHARC-II’s abilities.

SLUGS (z<0.05)


• Dunne et al. have characterized the SED of 106 IRAS selected galaxies at 850m

• Of those, only 17 were detected by SCUBA at 450 m, and it was noted that the data supported a 2-component SED fit.

• SHARC-II has detected roughly 60/65 targeted so far.

• They are so easy to detect that they now are done as poor-weather backup.

• 0.5h @ 225~0.06

• 1.0h @ 225~0.08

• 0.5 Jy< S350 < 3 Jy

• crush -faint -compact

Spitzer HLIRG (z~1.5)


• In follow-up observations of Spitzer selected objects, we discovered an object with an apparent luminosity above 1013.5 L.

• It has an SED similar to Arp220, but at at a redshift of 1.5.

• This object has sparked interest in “Silicate Dropouts” as a way to select high-z starbursts.

• 0.5h @ 225~0.06

• S350 = 226 ± 45 mJy

• CHOPPED observing• sharcsolve reduction

Stanford sample (0.1<z<1.0)


• The Stanford sample was compiled from cross-correlation of the faint-IRAS catalog and the FIRST 21cm radio catalog

• The sources are ULIRG’s lying within redshift range of 0.1 and 1; NIR morphologies of these objects reveal they tend to be interacting systems

• FIR/submillimeter fluxes were obtained for the first time on these targets, so were SED fits in the FIR

2h @ 225~0.05

S350 = 44.1 mJy

Td = 40.9 K , = 1.5

Fomalhaut Debris Disk


• 3.0h @ 225~0.039

• SWEEP (Lissajous)• crush -deep reduction• Peak fluxes: 150

mJy/beam• Integrated flux: 1.2 Jy• Consistent with thin,

uniform dust ring

K. Marsh et al. (2004-5)


Johnstone & Bally (1999)

4 hr.

1.2 mm PWV

18 hr.

1.0 mm PWV

rms: 0.3 Jy/beam

rms: 1 Jy/beam

rms: 0.3 Jy/beam

rms: 0.3 Jy/beam

mosaic of BOX scans

Houde et al. (2004)

Orion

• Selected by IRAS 100 mm flux and proximity using criterion of Surace (2004).

• Perhaps analogues to z>1 ULIRGs.

• Lissajous scans in typically t225×airmass = 0.05-0.10.

• Observations of 14/42 sources complete, to be reported by J. Bird and D. Dowell.

5×1010 Lsolar

Low-z Interacting Galaxy Survey



Chopped High-z survey

• CHOP in azimuth 39″/1.39 Hz plus slow SWEEP

• parallactic angle rotation of 77° washes out negative beams in sharcsolve reduction

• 8.6 hrs, median tau225 = 0.044• rms = 10 mJy/beam in middle• 2 sources are 80 mJy each• Definite and probable SCUBA

850 m sources marked with stars

High-z SCUBA sources


LE12LE21

LE31 LE2

• 3-4h @ 225<0.06

• 350 = 5 mJy


Software and RequirementsCRUSH is Java based and written and maintained by A. KovacsAvailable on web pageHas been successfully used on:• Windows• Mac OSX• Linux• SolarisSHARCSOLVE is C based and written by D. Dowell (phasing out?)Available only by special requestHas been successfully used on:• Mac OSX• Linux• SolarisAncillary software written by C. Borys.Available on web pageHas been successfully used on:• Mac OSX• Linux• GCC compatible, so in principle could be compiled on other platforms. (C. Borys)

Minimum requirements to run all the software are:Java 1.4.1 (for CRUSH)gcc version 3.2.3cfitsio libraries (http://heasarc.gsfc.nasa.gov/docs/software/fitsio/fitsio.html)

Other nice software include:IDL or graphic (for plotting)DS9, GAIA (starlink) for displaying fits files.

http://heasarc.gsfc.nasa.gov/docs/software/fitsio/fitsio.html


Overview of Ancillary software : 1

header_update : alters header keywords in maps generated by CRUSH.

boxscan : helps calculate BOX_SCAN parameters for SHARC-II observations.• See SHARC-II web page for more details

sharccal : applies a calibration to a reduced sharc2 signal and noise mapsharccal [-c scalefactor] [-o offset] [-v] [-u units] raw.fits calibrated.fitsIf no options, it will use the builtin calibration factor (V2JY in fits file)Output signal = scalefactor*(raw map + offset)FITS keywords added or modified:NAME value comment---- ----------- ------------------V2JY scalefactor calibration factorCALAP T calibration applied?OFFAP T|F offset applied?OFFSET value offset value (only if OFFAP=T)BUNIT unit Units of output image

sharcgap : tests a raw sharc2 data file for timing gapssharcgap startidx stopidxNeeds to be run from the directory in which data is stored. It checks consecutive data points to see if they are spaced by more than 1% of the expected time.Expected time is 36ms, but is calculated explicitly from the first HDU.

sharcsmooth : Performs a PSF fit to a reduced SHARC2 map.This will be described later in the calibration section.


Overview of Ancillary software : 2

sharclog : Gets basic information from a SHARC-II raw data filesharclog startidx stopidxNeeds to be run from the directory in which data is stored.It scans the header of each file to provide a summary of the data (similar to Darren’s)

sharcstat : computes basic statistics on a reduced SHARC2 mapsharcstat file.fits

> sharcstat zw247_2.fits

NX NY N s_mean s_stddev rms_mean rms_stddev

118 76 5049 0.00049829 0.14564 0.023233 0.0072745

N = number of pixels with data in them (checks for NaN).S_ corresponds to mean and standard deviation of the SIGNAL mapRms_ corresponds to mean and standard deviation of the NOISE map.

sharctau : uses Jon Bird's tau fits to estimate tau for a given SHARC2 file. You also need the taufit filessharctau [-v] datafile taufileCan be run from anywhere> sharctau -v /home/bigdisk1/sharc2-012900.fits /scr/borys/sharc/tau225_sep2003.fit

# DD/MM/YYYY HH:MM UT/24 TAU225 FITTAU

# 30/09/2003 12:06 0.50 0.051 0.068> sharctau /home/bigdisk1/sharc2-012900.fits /scr/borys/sharc/tau225_sep2003.fit

0.068

Note: tau225 is read from file. Fittau is at the frequency appropriate to the input taufile.


• Create a convenient place for the CRUSH installation. • Use logical links to point to the most recent version.• CRUSH can ONLY be run from the directory in which it is installed.

istari (7:45am) [/scr/borys/sharc/attila] >ls -lalrwxrwxrwx 1 borys cittgp 10 Nov 5 08:21 crush -> crush-1.34drwxr-xr-x 3 borys cittgp 4096 Oct 3 07:16 crush-1.33drwxr-xr-x 3 borys cittgp 4096 Sep 22 09:39 crush-1.33b2drwxr-xr-x 3 borys cittgp 4096 Oct 6 15:48 crush-1.34drwxr-xr-x 2 borys cittgp 4096 Aug 31 23:13 datadrwxr-xr-x 3 borys cittgp 4096 Oct 28 00:35 develdrwxr-xr-x 2 borys cittgp 4096 Feb 13 2004 MaiTau

istari (7:48am) [/scr/borys/sharc/code/bin] >ls -la-rwxr-xr-x 1 borys cittgp 6793 Aug 27 14:31 boxscan-rwxr-xr-x 1 borys cittgp 16548 Aug 27 14:10 sharccal-rwxr-xr-x 1 borys cittgp 784529 Mar 26 2003 sharcextract-rwxr-xr-x 1 borys cittgp 766548 Aug 27 14:31 sharcgap-rwxr-xr-x 1 borys cittgp 770786 Aug 27 14:31 sharclog-rwxr-xr-x 1 borys cittgp 770704 Aug 27 14:32 sharcsmooth-rwxr-xr-x 1 borys cittgp 16164 Aug 27 14:13 sharcstat-rwxr-xr-x 1 borys cittgp 766589 Aug 27 14:32 sharctau

• Create a convenient place for the ancillary software. • Add the directory to your PATH variable • These programs can be run from anywhere.

Installation


#!/bin/cshcd /scr/borys/sharc/attila/crushecho “PROCESSING ic5634”./crush -faint -compact -name=ic5634_1.fits 14176 14177 >! ic5634_1.log./crush -faint -compact -name=ic5634_2.fits 14182-14185 >! ic5634_2.log./coadd -out=ic5634.fits ic5634_1.fits ic5634_2.fits >! ic5634.log sharcsmooth ic5634.fits ic5634_smooth.fitsmv -f ic5634* /scr/borys/sharc/projects/slugs/CRUSH/maps/.

1) -outpath= OR REDUCED_MAP_PATH in crush.cfg• This will change the path in which the file is saved, but not alter the name itself. i.e. it

will keep the form OBJNAME.SCAN1.SCAN2…SCANN.fits• This filenaming structure is sometimes inconvenient (e.g. GAIA)2) -name=/path/to/mapdir/map.fits• This will alter the name to one of your choosing. You can include a path here as well. If

used, outpath is ignored.

The necessity of running CRUSH from its install directory makes file management slightly tricky. Ways of manipulating output name include:

RECOMMENDATION: use scripts and the -name= option

Note the 2 different ways of specifying scans to analyze

Scripting


At this point in the workshop, Attila gave a presentation on CRUSH.Download that separately and review it before proceeding.

CRUSH

• Pointing– Different treatment of the case that the IRC Reference Pixel is not the

middle of the array (16.5, 6.5)

• Calibration– CRUSH and sharcsolve use completely different units, so cannot mix.– CRUSH corrects for dependence of detector gain on detector loading,

so resulting tau relations should look “normal” to SCUBA and SHARC users: (SHARC II, 350 m) ≈ 25(225 – 0.01)

– sharcsolve does NOT correct for gain change, so tau scaling looks “too big”: (SHARC II, 350 m) ≈ 32(225 – 0.01)

• Chopped reduction– sharcsolve differences with respect to chopper as first step.– CRUSH treats secondary chopping as merely another pointing offset.– Relative advantages of two approaches under study.


Important Differences between CRUSH and

SHARCSOLVE


Tau and Calibration

• Calibration at short sub-mm wavelengths is challenging,

but necessary.

• In the next few slides, we present our procedure for

estimating the atmospheric opacity, and then discuss the

overall calibration uncertainty for SHARC-II

• Then we provide a more detailed example of how to obtain

the calibrated flux for a specific observation.


SHARC-II Calibrators• Availability of calibration sources has always been a problem in sub-mm observations,

particularly at shorter wavelengths (can’t use BLAZARS, etc)

• We use primary calibrators (Mars, Uranus, and Neptune) to bootstrap the calibration of the

secondary systems.

• For stationary objects, we can use repeated observations to derive averages.

• For solar system objects, we need to consider the changes in distance and solid angle

over time.

TB = T1AUr(-1/2)

S() = B(TB)

• T1AU is derived by evaluating TB given all the other parameters (r is the heliocentric

distance in AU, is the solid angle as seen from Earth, and B is the Planck

function evaluated at the appropriate frequency (typically 350 micron). These

values are provided by the JPL Horizons System: http://ssd.jpl.nasa.gov/cgi-bin/eph

• We have used these relations to extrapolate the fluxes for all days between 2002 and

2010.

• These calibrations are available for download for the SHARC-II web page

http://ssd.jpl.nasa.gov/cgi-bin/eph

• Tau Dippers are noisy by nature (single measurement every ~10 min).

• Fits for both the 225Ghz and 350 micron data exist for every SHARCII night to date.

• Least square polynomial fits over a large range of each night (almost always covering the entire observing time).

• Images of these fits are located on the SHARCII website (www.submm.caltech.edu/~sharc).

• When reducing your data, observers should look at these tau fits as a FIRST step, so that they may determine the best fit to use and what was happening in the atmosphere at the time of observation.


Tau Fits


Typical 350 micron fit. Residuals are located on bottom of plot. Typical fit ranges from 2 to 20 hours UT. Notice that the X axis is in fraction of a day.

Tau Fits


Keep an eye on the 225GHz and 350 micron fits…they CAN differ

Fits from both tippers on the same night.

• CRUSH uses the MaiTau server to obtain the fitted tau. • Parses through fit table (see below). Available online in

conjunction with the tau fits. • CRUSH’s output will inform you if a fit for your file was

found and what value was retrieved. “Got Mai-Tau! tau(350um) = X”


By default, MaiTau looks at the 350 micron fits. Use “-taufit=” option to choose which fit, or not to use a fit at all.

CRUSH and Tau

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Problem:Much variability.

Mai Tau success story on Mon R2

Below are maps made from individual scans of MonR2 (provided by D. Benford). The raw tau recorded in the file was used.



Mai Tau success story on Mon R2

Below are maps made from individual scans of MonR2 (provided by D. Benford). Opacity this time was provided by MaiTau.

MaiTau helps!

• Perform aperture photometry on calibrators with “known” fluxes.

• “Known” fluxes are obtained from HORIZONS.• CRUSH’s default output is in Volts- constant Volts to

Janskys applied (crush.cfg).• By comparing known flux with CRUSH reported flux, we

obtain a conversion factor.


Want to determine how stable that conversion factor, and thus calibration, is over time.

SHARC-II and Calibration

Plot shows conversion factor of calibrators taken during the August-September 2004 run.

Conversion factor is consistent to within:

21.3% for all

18.8% for Neptune

19.2% for Uranus


Calibration Stability

Calibration is consistent over a wide range of elevations.

You do not need to take calibration scans at the same elevation as your science.


Calibration Stability

• Tau fits: Important for understanding what is happening to the atmosphere during observation.

• Always look at the tau fits as a first step towards calibration and reduction.

• CRUSH calibration is now consistent to within 20% and improving.

• Calibration is consistent over the range of telescope positions.

• In the next few slides, we concentrate on object specific calibrations.


Calibration/Tau summary

PSF Photometry is the most often used technique for point source extraction in SCUBA maps (particularly high-z projects). It is mathematically equivalent to “convolving with the beam”, except it also takes into account the pixel-to-pixel noise differences. The procedure is very straightforward. Start at a given pixel (i,j), and calculate the following statistic:

S and N are the signal and noise maps respectively. This is simply a LLS fit, and it is easy to derive the best fit value and error for the PSF’s amplitude, A. This can be extended to include an offset parameter as well.The ancillary program sharcsmooth performs this function. It assumes a purely Gaussian, with a default (but user settable) FWHM of 9”. (see imagetool as well)The map answers the following statistical question: what is the best fit amplitude to a Gaussian centered at a given pixel? There are consequences to this assumption. i.e., for pixels near the peak of a source, the assumption that that given pixel is the center of a source is wrong.


Calibration : PSF

€

χ 2 =A ⋅PSF(dx,dy) −S(i+dx, j +dy)( )

2

N (i+dx, j +dy)2dy=−W

W

∑dx=−W

W

∑

Source extraction with a “smoothed” map is done by setting a SNR threshold to search for sources in the field.

Aperture Photometry is another popular choice, most often used on sources that are readily visible in the map, or if some other astrometric marker is available on which the aperture can be centered.

There are 3 circular radii to choose. In order of increasing value they are: source, inner sky, and outer sky. The annulus defined by the last two radii are used to estimate the mean sky level AND the scatter of pixels. The central aperture is used to sum up the flux contained within it (after correction for the mean sky offset). The error on the flux estimate is related to the RMS of the pixels in the sky annulus, and the number of pixels in both the aperture and annulus. Aperture radii usually chosen via “curve of groth”, annuli choosen to minimize noise while still providing a good estimate of sky background and RMS.

Given that the pixel to pixel errors are dominated by residuals in the sky estimation and not shot and photon noise as they are in optical CCD work, the equations are simpler. Note that CRUSH and SHARCSOLVE do provide a “noise” map, but I have always found that the RMS scatter in the “signal” pixels is higher than what the weight map implies. Thus I assume a uniform weight per map pixel, and calculate this weight via the RMS of the signal map. (implications for PSF fitting…)

It is not yet clear to me that sky estimation is necessary. CRUSH and SHARCSOLVE do a pretty good job of returning “zero” for a map mean when we look at blank sky. However, experience has also shown that well detected sources sometimes have a negative “bowl” around them.


Calibration : Aperture


Calibration : Aperture

€

RMS =1

Nmi −m( )

i=1

N

∑2

S =1

NSmi

i=1

N S

∑

F = mi −S( )i=1

N A

∑

σF = RMS ⋅ NA ⋅ 1+NANS

⎡

⎣ ⎢

⎤

⎦ ⎥

1/2

N = Number of pixels in map under consideration. (notnecessarily the full map…one may exclude edges for example)NA = Number of pixels within the apertureNS = Number of pixels within the sky annulusmi = flux in a given map pixel, iF = estimated aperture fluxF = associated noise estimateS = estimated sky background per pixelI = pixel index which runs over the relevant pixels in

the map

Important caveat: This procedure assumes that the pixels are uncorrelated. This is NOT the default procedure for CRUSH, and one has to use -convolve=-1 to force this. Otherwise, the RMS calculation will be lower then it is supposed to be (you’ve essentially smoothed the map). If you do not use the convolve flag, the RMS should be increased by a factor of sqrt(N), where N = the number of pixels that fall within the area of the convolving function. By default, we use an 8” beam, with noise calculated for ~4.8” pixels, which therefore requires a sqrt(1.33)*(8/1.4) = 6.6 increase in RMS (and consequently the total error budget).


Aperture vs. PSFSo which should you use, and what are some caveats?

POINT SOURCESPOINT SOURCESIf the PSF is varying (ie, DSOS not functioning or not turned on), APERTURE is probably the safer choice.If CHOPPING, care must be taken to keep the annulus away from the offbeams (a concern for SHARCSOLVE, not CRUSH), hence PSF might be a good choice.

What do I use? Aperture, almost exclusively, but use the PSF smoothed map for presentation.

EXTENDED SOURCESEXTENDED SOURCESPSF, since it essentially gives you Flux/beam.

CAVEATSIn deep integrations, there are some issues related to correlated sky signal still in the map. (more from Attila)


Calibrating your data

The principles involved with calibrating SHARC-II data are applicable to all data from other sub-mm telescopes.

Ingredients• Good estimates of the atmospheric opacity for all science and calibration observations• A decent collection of calibrators (different objects, airmasses, etc.)• A CHOICE IN HOW YOU WILL EXTRACT FLUXES FROM YOUR DATA. What is done to the science map must also be done to the calibration.

EXAMPLE: Reduction of a local IRAS galaxy: MRK 331• Scans 9125-9127, taken on Jan 15, 2003, at UT 04:54• PSF photometry to be used


Calibration Example 1

Using sharclog, (or by some other log or by looking at the header), I find the UT time and date the data were taken, and then go to the SHARC-II web page to get the tau-fit plot for that night.

The data were taken at UT 04:30 (~0.20 fractional day). Fits look OK, so I will not override MaiTau.

Next I run CRUSH to make the map

> ./crush -faint -compact -convolve=-1 -name=mrk331.fits 9125-9127 >! mrk331.log> sharcsmooth mrk331.fits mrk331_smooth.fits> cat mrk331.logcrush -- Comprehensive Reduction Utility for SHARC2 Author: Attila Kovacs <[email protected]> Version: 1.34-1

Scan 1: Reading /home/bigdisk1/sharc2/sharc2-009125.fits... Got Mai-Tau! tau(350um) = 1.3088 83 HDUs, 16439 x 36ms frames -> 9.9 minutes total. Filtering 13.4Hz on noisy pixels. DownSampling -> 5479 frames

[MRK331] observed at 2003-01-15T04:54:01.949 RA = 23:48:54.0 DEC = 20:18:29.0 (1950.0) = 23:51:26.7 = 20:35:10.1 (2000.0) AZ = 277:44:54.5 EL = 57:01:57.9 RAO = 0.0 DECO= 0.0 AZO = 0.0 ZAO =-0.0 FAZO=-104.0 FZAO=-30.0 Rotator = 60.0 RotZero = 60.0 Pointing Center = 16.5,6.5 Rotation Center = 18.5,8.6 Parallactic Angle = 85.0 tau225 = 0.053 tau = 1.835 Plate Scale = 4.93"x4.77"


Calibration Example 2


Calibration Example 3• Now I check the logs for that date to see which calibrators were done.• In this particular case, I will only pick the one closest to the science observation, but you should reduce ALL of them and ensure that they seem reasonable.

> ./crush -compact -convolve=-1 -name=oh231.fits 9140 >! oh231.log> sharcsmooth oh231.fits oh231_smooth.fits

• The sharcsmooth program does a PSF fit to each pixel, so to calibrate, I load the image in GAIA (or DS9) and determine the brightness of the peak. In this case it is 3.378 units.•The true flux of OH231.8 is 19.4±1.9 Jy (10% calibration uncertainty).•Hence the scale factor is: 19.4/3.4 = 5.7 •Now we need to scale our image:

> sharccal -c 5.7 -u Jy mrk331_smooth.fits mrk_cal.fits • Finally I open up GAIA, and look at mrk_cal.fits. By looking at the Signal and RMS maps, I see that the brightest pixel is:1.80 ± 0.02 JyIn this case the calibration uncertainty dominates the error budget, so I simply quote 1.8 ± 0.2 Jy.


Map Tweaks

Making the maps is the first step, and you may need/want to perform some of the tweaks presented on the following

slides.

• Two options for pointing correction:– Apply knowledge of improved telescope pointing model at time

of running CRUSH:• crush -FAZO=-120.0 -FZAO=40.0 …

• See “MEMO: SHARC II Pointing at Nasmyth Focus Using CRUSH (Dowell, Nov. 2004)” on web page/Data Analysis.

– Align images after CRUSH*:• Use header_update utility (on web page under “Software utilities”)

• header_update image.fits RAP 1.0• header_update image.fits DECP -1.0• Doesn’t change WCS of image; however, pointing corrections will

be applied in coadd

*Attila says: Use jiggle


Tweaks-Pointing Correction

• CRUSH defaults to producing FITS images in nV, corrected for detector nonlinearity and atmospheric absorption.

• Based on results for calibrator (reduced/analyzed the same way), one can re-scale image before or after coadd:– sharccal -c 5.0 uncal.fits cal.fits– sharccal is on web page / Software utilities

• One can also change units of image:– sharccal -u Jy/beam input.fits output.fits– Just updates BUNIT keyword.– CRUSH recognizes: V, nV, Jy/beam, Jy/arcsec**2, and Jy/sr

• CRUSH imagetool will do these operations in future.


Tweaks-Calibration

• Use CRUSH’s coadd routine:pushd .; cd crushdircoadd \ ../data/SGRASTAR.16938to16947.cal.fits \ ../data/SGRASTAR.16948to16957.cal.fits \ ../data/SGRASTAR.16960to16969.cal.fitspopd; mv crushdir/../data/SGRASTAR.coadded.fits .

• By default, images are weighted, but “zero levels” are not adjusted. (This is likely to change in future.)


Tweaks-Coadding

• Use imagetool to cut noisy edges off map:– Example:

pushd .; cd crushdirimagetool -minexp=0.25 ../data/SGRASTAR.coadded.fitspopd

– Modifies image rather than making a new copy, unless -out option is used.

– imagetool is part of CRUSH.– Note other options to imagetool (e.g., -clip).


Tweaks-Cropping

• To mosaic many maps with signal in them (e.g., bright Galactic clouds), I find that adjusting the zero levels before coadd improves the appearance of the image.

• I find the mode of the image intensity distribution and subtract it off:– The mode can be found crudely with ds9.– sharccal -c 5.0 -o 0.1 uncal.fits cal.fits


Tweaks-Mosaicing


; read in the highest resolution image firstimg_vla=readfits('../J1428p3526.fits',hdr_vla)CX=281 ; center of source in X dimensionCY=282 ; center of source in Y dimensionHW=100 ; half width of box to extract

HEXTRACT,img_vla,hdr_vla,CX-HW,CX+HW,CY-HW,CY+HW

img_350=readfits('../../059/set_16301_smooth.fits',hdr_350) ; read in sharc imagehastrom,img_350,hdr_350,img_350p,hdr_350p,hdr_vla,MISSING=0 ; make image match size/shape of VLA

loadct,0 ; black and white color tablegamma_ct,1.0,/CURRENT ; normal gamma stretchimg_350p=bytscl(img_350p,min=-0.05,max=0.07) ; choose plotting rangeset_plot, 'ps'device , filename='sharc.eps', /encap, xsize=10., ysize = 10., $ yoffset = 1., BITS_PER_PIXEL=8, COLOR=1imcontour, img_350p, hdr_350p, levels=0, xtitle=' ', ytitle=' ',$ ; plot the axis charsize=1.2,charthick=3,/nodata,subtitle=' ',COLOR=0,$ XSTYLE=4,YSTYLE=4tvimage,img_350p,/overplot,/keep_aspect; display the image ; overlay radio contoursimcontour, img_vla, hdr_vla, levels=[2e-4,3e-4,4e-4],xtitle=' ', ytitle=' ',$ charsize=1.2,charthick=3,/noerase,subtitle=' ',C_THICK=3,C_COLOR=0,COLOR=0, $ XTHICK=2,YTHICK=2

XYOUTS,10,10,'350 + VLA contours',charsize=1.5,charthick=3DEVICE, /close

Everyone has their own way of turning maps into publication style images.I use IDL and the astrolib library (http://idlastro.gsfc.nasa.gov/homepage.html)IDL is not free, but it is very versatile.

Publishable Images

http://idlastro.gsfc.nasa.gov/homepage.html


Publishable ImagesIDL> @sharc.idl% READFITS: Now reading 561 by 561 by 1 by 1 array% HEXTRACT: Now extracting a 201 by 201 subarray% READFITS: Now reading 201 by 201 array% HPRECESS: Header astrometry has been precessed to 2000.0000% LOADCT: Loading table B-W LINEAR

Other packages in use at Caltech:• Graphic• GAIA (A free starlink package)

More complicated example:• Multiple contour sources• Astronomical coordinates• Object labelling


Chopped vs. Unchopped?• In principle a 2-beam chopping observation increases the noise by sqrt(2) because of spending half the time on source. But this can be recovered by folding back in the flux from the “off” beam, as long as it lands on the array.

• In general, we have had good success chopping and reducing the data with sharcsolve. Attila only recently added chopped data support in CRUSH, though it seems to work. Once tested more rigorously, we will likely phase out sharcsolve completely.

• We strongly encourage people who want to chop to discuss it with one of us.

Chopping is best suited for observations of point sources when the atmosphere shows signs of strong variability.

We have not yet shown that chopping offers a substantial improvement.

Comparison of Chopped Data

Stars denote sources detected by SCUBA, and 2 are well detected by SHARC-II. In this case, CRUSH and SHARCSOLVE both do a good job recovering the same map.

• Poor choices for focusing telescope:– Many protostellar/UCHII things, especially NGC2071. Even

IRAS16293-2422 is slightly elliptical.– Saturn, Jupiter, Venus– Better choices: Mars (usually), Uranus, Neptune, Callisto

(usually), Ganymede (often), Ceres, Vesta (sometimes), Pallas (sometimes), CRL618, CRL2688, IRC10216, OH231.8, ARP220

• Poor choices for pointing: NGC 2071 (Use CRL618, HLTAU, or OH231.8 instead)

• Poor choices for flux calibration: NGC 2071, blazars• Moons: Callisto or Ganymede is usually observable.

Titan is hard to observe cleanly; don’t bother with it.


Lessons learned (1)

Don’t Focus/Point/Calibrate With It!SHARC-II DRW 11/08/2004

Avoid NGC 2071

• For best looking large maps, map full area in as short a time as possible. Mosaics of fields under different conditions and scan patterns tend to have obvious “stitches”.

• The following projects have proven difficult; embark on them at your own risk:– High dynamic range

• CSO beam at 350 microns.• Negative artifacts surrounding bright sources.

– Faint, widely extended emission, due to ripples in reduced image.

– Be careful integrating total emission; use exactly the same procedure for source and calibrator, and use a “sky” aperture.


Lessons learned (2)

Ripples and Mosaic Stitches in Box Scan of Source with Low Surface Brightness

• crush -deep gets rid of ripples, but also some extended structure.

12′


M51

Problem:Large scale low-level baseline



Bad Pixel flagging• Bad pixels that are not properly flagged by CRUSH end up tracing the scan pattern on the final

map. Sometimes this is hard to see since by default CRUSH smooths the output.

• I recommend reducing each scan separately with -convolve=-1 in order to see if bad pixels are

corrupting any of the data. If so, remove them from the list of scans you use to make the

combined map. CRUSH 1.35 is meant to have a better algorithm for flagging bad pixels.

Right: Map of MonR2 with a bad pixel clearly influencing the output. (map courtesy of D. Benford)

Negative Halo Surrounding Bright Sources

• Negative intensity is ~3% of peak intensity.SHARC-II DRW 11/08/2004

• DSOS:– Use it!

• Beam shape at 350 m becomes nearly independent of ZA.

– Check that you are using correct procedure:

• Wait until telescope near outside ambient temperature, then init. (Assumes that telescope at that time has the same shape as during the holography.)

• Make sure you get into agent mode before observing. Easy to check with dsosm monitor screen.

• When significantly changing ZA, wait for new dish setting to activate and settle (again with dsosm). Otherwise, your calibrator may have the wrong PSF.

• Turn off DSOS at the end of the night.


Tips for taking better data (1)

• UIP source catalogs– Enter before you get to 14,000 ft.– Check the coordinates and equinox with VERIFY.

• Please use the existing CAL_* sources for extrasolar calibrators. This makes it easier for the staff to identify pointing/calibration scans to study, e.g., pointing model. The CAL_* sources are now loaded automatically from USER:[SHARC]SHARCCAL.CAT upon INST SHARC2.

• Get started quickly with the “Cheatsheet” on the web page.

• Focus and pointing tend to drift early in the night. Check every ~45 minutes until ~8 PM. After that, focus is usually stable (check every ~2 hours). Still should check pointing every ~1 hour, especially if observing faint sources.



• “SHARC Tau”: Use Bolometer Power Mean on Bolometer Means window to convert to 225×airmass. This is useful in cases that skies may be clearing rapidly early in night.

• Please report problems, even minor ones, to [email protected]




Miscellaneous Notes

In the next few slides, we present some information that is related to the workshop and SHARC-II in

general, but was tangential to the material already presented.

Dependence of Gain on Atmospheric Loading

• Nasmyth move was successful, and we’ll stay there for foreseeable future.

• In early September, a glue joint in the amplifier for rows 9-12 separated, breaking ~300 micro-wires in the process.– The glue joint has been

repaired and reinforced.– We’re now working on the

micro-wires, with expectation of returning to normal by the January run.

– September run was carried out in its entirety, with ~2/3 mapping speed.

Instrument status

• The move to Nasmyth forced a revisit of how we calculate pointing corrections. See the documentation on the SHARC-II web page for a full report.

• Top: as observed, (FAZO) = 3.7″• Bottom: after model applied, (FAZO)

= 2.1″• Model fit and method of correcting

data: web page memo• Use CRUSH exclusively to apply the

model if not pointed on center of array (16.5, 6.5).


Sept 2004 Pointing T-Terms


Temperature Effects on Pointing (Hiroko)

CSO/SHARC II Sidelobes (350 m)

• Sidelobe spots as bright as 5% of peak intensity.

~160″



BOXSCAN

There are a number of constraints on the scan pattern:1. It turns out that by starting the scan from the center of the map, the map size cannot be perfectly

square, otherwise the scan will hit a corner, and the algorithm will fail.2. There is also a choice in how far apart the intersection points are. You want them to be less than

the size of the SHARC array (to ensure the whole map gets sampled), but having them too close together means it will take longer to complete a scan.

3. The scan rate should be fast enough to close out the scan in a reasonable time, but not so fast as to smear the beam. Also, faster scans mean it is harder for the telescope to handle rapid change in direction at the boundaries.

Want a rectangular pattern instead of a box? This is straightforward, but ask me for details.


BOXSCAN To help plan your scan, download, and compile the program boxscan.c.

Here is an example of it in action: I want to scan a 10x8 arcminute region, relatively finely.

I start with a 10 arcsec spacing, and a 40 arcsec/sec scan rate:> boxscan 600 480 10 40BOX_SCAN 600.000 471.429 40.0 45 : 23.33 minutes# WARNING: scantime exceeds 15 minutes

Hmmm...that won't work. Scan length is too long. I'll try a larger spacing (20.0 arcsec)> boxscan 600 480 20 40BOX_SCAN 600.000 457.143 40.0 45 : 11.31 minutes

That's better, but now I wonder if 40arcs/sec is too fast. I'll try an even larger spacing and a slower scan speed:> boxscan 600 480 25 30BOX_SCAN 600.000 494.118 30.0 45 : 13.20 minutes

Enter the scan command dirently into the UIP, and set the integration time as suggested (perhaps adding on 0.2 minutes for overhead). Wondering what the "45" is in the "BOX_SCAN" output? It is the angle at which the scan starts. This should always be 45. Consult with us if you want to try other things.

http://www.submm.caltech.edu/~sharc/operating/boxscan.c

http://www.submm.caltech.edu/~sharc/operating/boxscan.c

SHARC-II/CRUSH Simulations


Source Fluxes Recovered within 1%

100 mJy Ring surrounding compact star in 1 hour10' x 10' Billiard Ball Scan.

Imperfect cleaning offaint large scale structures

100 mJy CompactLissajous Sweepin 1 hour

Imperfect cleaning offaint large scale structures

Tom Tyranowski (visiting student) wrote a data simulator, which we use to test the performance of CRUSH. If you are interested in using it, contact us.

• Get rid of negatives around bright sources.• Find mode of an image• Calibration cheatsheet• example graphic link/script on web page• Improved CRUSH default -chopped reduction• Memory problem in 1.34? (z=6.5 source)• Bolometer scrambling test• CRUSH email exploder• Resume simulations; release simulation code.• sharcsolve (for Johannes): independent tau for each scan• Hoping for better pixel flagging in v. 1.35• Update CAL catalog in UIP.

To-Do list

sharc-ii data reduction workshop sharc-ii drw 11/08/2004 darren dowell attila kovacs colin borys...

Documents

drw 11082004le12le21le31le23

caltech sharc

range of sharc

publication of sharc

efficiency of sharc

highz starbursts

highz scuba sourcessharc

chopped highz surveychop