1. SOFIA Polarimetry Pow-Wow (Darren’s slides)
Yerkes, Northwestern, U. Chicago
July 27-30, 2007
Version: Jul 30, 9:00 PM

2. SOFIA, HAWC, and Hale 1997: First SOFIA instruments funded
HAWC m camera funded (Harper)
Hale polarimeter not funded (Hildebrand)
2006: SOFIA canceled
2006: SOFIA reinstated
2007: airplane modifications (telescope) complete; moved to NASA/Dryden in Southern California
2009: first science flights

3. SOFIA 2.5m IR telescope

4. The Roads to SOFIA Polarimetry
Resume advertising, e.g., SPIE San Diego: Aug. 2007
Polarimeter technology development proposal to JPL ($0.2M):
Work must be done at Caltech or JPL
Convince SOFIA to “up-scope” HAWC ($1M): 2008?
SOFIA first science flights: 2009
First light for HAWC: 2010?
First light for HAWCpol: 2011?
Proposal to SOFIA 2rd Instrument Call ($10M): 2010?
First light for SuperHAWC: 2014?

5. HAWCpol and SuperHAWC (a.k.a. Hale)
Took a guess for maximum field of view of SOFIA/SuperHAWC m
5-20˝ resolution
384 pixels
0.8, 1.3, 3.3´ field of view
single-polarization m
5-20˝ resolution
5000 pixels?
2.9, 4.8, 10.0´ field of view
dual-polarization

6. Schedule -- Friday Friday - Yerkes Observatory 373 W. Geneva St.
Williams Bay, WI
Morning: 9 am -- 1 pm
1) Welcome, Overview/Schedule of next few days -- Dowell, Vaillancourt
2) Intro. to HAWC, details on optics -- Vaillancourt, Wirth
3) Variable-delay Polarization Modulator (VPM) -- Chuss, Novak
4) latest on new detectors -- Chuss
5) cold, achromatic HWPs -- Jones
Box Lunch provided.
Afternoon: 1: pm
1) Competition/Complementarity -- Dowell
2) T-tauri disks -- Novak, Lazarian/Cho, Whitney
3) Turbulence -- Hildebrand

7. Schedule -- Saturday & Sunday
Saturday - Yerkes
Morning: 9 am - 1 pm
1) Finish technical topics not covered Friday morning
2) Software, operations, etc. -- Dotson
3) technical aspects of a HAWC upgrade -- group
Sunday -
Northwestern University
Dearborn Observatory
2131 Sheridan Rd.
Evanston, IL
1) view labs, VPMs, Hertz
2) continue discussion of HAWC mod.'s -- group

8. Schedule -- Monday Monday - University of Chicago
Enrico Fermi Institute
Astronomy & Astrophysics Center (AAC) - Rm. 123
5640 S. Ellis Ave.
Chicago, IL
Morning: 9 am - 1 pm
1) Extragalactic -- Jones
2) Intro. to polarization spectrum -- Vaillancourt
3) Grain Alignment Theory -- Lazarian, Cho
4) Low-mass YSO's -- Novak, Looney
5) Polarization and line-of-sight B-field measurements -- Crutcher
Box Lunch provided.
Afternoon: 1: pm
1) Connection between dense/diffuse ISM, small/large scales -- Crutcher
2) DR21 massive star formation site -- Kirby
3) TELECON: 2:30 PM, , passcode
4) additional science topics group
5) discussion, identify favorite topics to go in SPIE paper, paper organization
6) paper/review writing progress - identify action items

9. Technical Meeting Summary
Long-range goal is a facility dual-polarization far-IR polarimeter/camera with ~5000 pixels: “Hale” or “SuperHAWC”.
We should not lose sight of that as we pursue an interim solution.
Among meeting attendees, there is unanimous interest in an interim solution “HAWCpol” which has 384 pixels and is single-polarization.
Eventual goal is for HAWCpol to be a facility observing mode.
Two options were considered for adding polarization capability to HAWC. Both are still promising and will be investigated further:
continuously rotating half-wave plate(s) followed by grid(s) in the HAWC cold pupil wheel
“variable polarization modulator” based on wire grids and mirrors in the HAWC warm fore-optics

10. In the interest of the HAWC camera achieving first light as soon as possible, the development of polarization hardware should be accomplished in parallel.
e.g., new pupil plate with rotating half-wave plate(s) designed and tested at JPL/Caltech
e.g., polarimetry foreoptics with VPM designed and tested at JPL/Caltech or Northwestern or Goddard (?)
Integration could be after delivery to SSMOC.
For the software control component of the polarimeter, impact on HAWC staff would likely be more immediate (before delivery to SSMOC). This aspect is difficult to develop in parallel, considering experience advantage of Yerkes/Goddard.

11. Estimated cost of HAWCpol is $1-2M.
We have not identified a method of funding HAWCpol other than as an upgrade to HAWC through the SOFIA program.
Could be envisioned as one element of a multi-wavelength program to measure polarization with SOFIA. (Also FORECAST upgrade?)
However, “seed” funding from alternate sources may be leveraged:
$0.2M proposal to JPL internal funding to build and test prototype polarimeter?
NASA ROSES: improved far-IR polarization technique for SOFIA, BLAST, and future space missions?
NSF: improved polarization technique for submillimeter astronomy?

12. Science Meeting Summary
HAWCpol provides unique information on the following topics:
Giant molecular clouds at the subcriticalsupercritical transition.
Hypothesis: GMCs form along magnetic flux tubes, and only when enough mass has built up do they gravitationally draw in the field.
Supporting observation: B  constant for nH < 103 cm-3, then ~ nH0.5 cm-3 for nH > 103 cm-3. This threshhold corresponds to AV = 5-10.
Supporting observation: B parallel to Galactic plane in synchrotron, optical, and diffuse millimeter dust emission, but not in dense cores.
Role of HAWCpol: good column density sensitivity, good resolution of clouds, selection of warm and cold dust
Technique: Compare field direction to general Galactic field (from optical or Planck). Survey clouds that can be mapped out to AV ≤ 5.

13. Next-Generation FIR Detectors

14. SCUBA 2 Detector Array Sub-array: 1280 pixels
~200 mm
~250 mm
Audley et al. (2004) paper: subarrays are 41 x 52 mm
Sub-array: pixels
1 array = 4 sub-arrays = 5120 pixels
Woodcraft et al. (2004) & Duncan et al. (2003) SPIE papers

15. SCUBA 2 Magnetic Shielding (Hollister et al. 2006)
Requirements:
100 nT over Hz at detector/SQUID multiplexer
JCMT environment: 150 T
Cryogenic high-permeability shielding: Metglas

16. SCUBA 2 Warm Electronics
U. British Columbia (Halpern group)
1 box per sub-array (1280 pixels)

17. Plan C: Stepped Half-Wave Plate

18. Hardware
We already have a working design for a stepped half-wave plate:
(Rennick, Vaillancourt, et al.)

19. Data Analysis
I claim we can deal with variations in atmospheric transmission:
(slide on “total power” calibration)
But we still have no solution for sky noise.

20. Competition and Complementarity

21. Far-IR/(sub)mm polarimetry in the 2010’s
SCUBA2 POL2 (2008): m, 8-14˝
CMB surveys
Planck (2009): 850 m, 5´, full sky
HAWCpol (2011): m, 5-20˝
ALMA (2012): m, 0.1˝
Cornell Caltech Atacama Telescope 25m? (2015): m, 2-20˝
SPICA?? (2018): m, 4-14˝
CHECK WAVELENGTHS AND DATE FOR ALMA

22. mid-IR polarimetry
Chris Packham is considering a polarization upgrade to FORECAST

23. sensitivity and wavelength

24. sensitivity and resolution

25. An all-sky polarization survey!
Planck is expected to become the “IRAS of polarimetry”.
full-sky survey at 5´ resolution
850 m best for dust polarization
By end of 2010, should have enough data to achieve (P) = 0.3% for AV ≥ 4
OMC1 at SOFIA resolution
Orion at Planck resolution
Andromeda Galaxy (M31) at Planck resolution

26. ALMA polarimetry
0.1” resolution: 10 AU at 100 pc

28. AV Sensitivity Assumptions
I chose to consider sensitivity to extended emission (column density) rather than point sources, thinking that polarization maps are needed for most of the science.
Ratio of  to AV (Hildebrand Dickman 1978):
() = AV/750 (100 m/),  < 250 m
() = AV/1900 (250 m/)2,  > 250 m
Dust temperature:
B peaks at  = 3670 m K / T
Assume T = 3670 m K / 
Also assume T bottoms out at 20 K (affecting  > 180 m).
This is enough information to relate MJy/sr to AV.
Should study recent Schnee papers for latest on tau(lambda) vs A_V.

29. Sensitivity Assumptions 2
Usually, point-source sensitivities (Jy s1/2) are quoted for instruments.
To convert to MJy/sr s1/2:
Assume a (/D)2 effective pixel (nearly optimal for point-source detection).
57% of the the power from a point-source is incident on the pixel, for a perfectly efficient telescope.
Then MJy/sr s1/2 = Jy s1/2  (D/)2  0.57

30. Sensitivity Assumptions 3
Quoted point-source sensitivities (Jy s1/2) are usually for the camera only, without a polarimeter in the beam.
Effects of polarimeter:
Often, one polarization is undetected, so 50% of the light is lost.
Often, another 20% of the light is lost due to imperfect polarimeter elements. Assume it is a “cold” loss.
Net effect is to worsen Jy s1/2 by a factor of 1/sqrt(.4): NEFD(pol) = 1.6 NEFD(cam)
For a single- or dual-polarization polarimeter:
(P) = sqrt(2) NEFD(pol) / (F t1/2)
(P) = 2.3 NEFD(cam) / (F t1/2) for converted camera
I’m pretty sure about that second-to-last equation. For dual-pol, see Platt et al. (1991) and Novak et al. (1989)

31. SCUBA 2 POL2 details
Bastien et al., CASCA, 2005

32. SCUBA 2 details Audley et al. (2004) hints at the following:
450 and 850 microns
6˝ pixels at each wavelength (/D and /2D)
32 x 40 x 4 pixels at each wavelength
Resolution: 8˝ and 14˝
Field of view (equiv. diameter): 8.1´

33. SCUBA 2 POL2 sensitivity Audley et al. (2004), point source:
113, 21 mJy s1/2 at 450, 850 m
extended source:
72, 3.7 MJy/sr s1/2
converted camera, (P)=0.3%, t = 3600 sec for:
920, 47 MJy/sr
Tdust = 20 K:
submm = ,
AV = 51, 21 at 450, 850 m

34. Planck polarimetry details
Planck Scientific Programme, p. 4&10:
TCMB/TCMB in Q = 29.8, 9.8  10-6 at 850, 1380 m
convert to MJy/sr:
0.024, MJy/sr rms in Q
(P)=0.3% for:
8, 4.3 MJy/sr
Tdust = 20, 20 K:
mm = 1.610-4, 1.910-4
AV = 3.5, 11 at 850, 1380 m
all-sky survey
resolution: 5´
sigma(P) ~ sigma(Q)

35. HAWC polarimeter details
point source with HAWC:
2.0, 1.3, 0.7 Jy s1/2 at 53, 88, 215 m
extended source with HAWC:
2500, 600, 54 MJy/sr s1/2
converted camera, (P)=0.3%, t = 3600 sec for:
32000, 7700, 690 MJy/sr
Tdust = 69, 42, 20 K:
FIR = , ,
AV = 2.4, 4.2, 7.6 at 53, 88, 215 m
Field of view, assuming 384 /2D pixels
0.8, 1.3, 3.3´ equivalent diameter
Resolution: 5, 9, 22˝

36. ALMA details http://www.alma.nrao.edu/info/sensitivities/
point source with ALMA:
10, 2.0 mJy s1/2 at 450, 850 m
extended source with ALMA (1˝):
540, 110 MJy/sr s1/2
already single-polarization, (P)=0.3%, t = 3600 sec for:
4200, 860 MJy/sr
Tdust = 20, 20 K:
submm = 0.038, 0.018
AV = 230, 390 at 450, 850 m (1˝)
Field of view, assuming 12 m telescope
9, 18˝ FWHM
Resolution: as good as 0.1˝
Are they actually planning to do polarimetry?

37. CCAT polarimeter details
point source with CCAT:
150, 14, 5.8 mJy s1/2 at 200, 350, 850 m
extended source with CCAT:
1300, 41, 2.9 MJy/sr s1/2
converted camera, (P)=0.3%, t = 3600 sec for:
17000, 520, 37 MJy/sr
Tdust = 20, 20, 20 K:
submm = 0.12, ,
AV = 180, 14, 16 at 200, 350, 850 m
Field of view, assuming 5000 /2D pixels
1.1, 1.9, 4.7´ equivalent diameter
Resolution: 2, 4, 9˝

38. SPICA polarimeter details
100 m extended source:
0.3 MJy/sr s1/2
dual-polarization, (P)=0.3%, t = 3600 sec for:
2.4 MJy/sr
Tdust = 37 K:
FIR = 2.9x10-6
AV = at 100 m

39. Turbulence for Dummies

40. Simple Questions
Is this a correct, simple-minded summary of C.F. method:
(), , (v)  B (and hence B2/8)
How does one identify Alfven waves?
How much of the turbulent energy density do they carry?
Is there a simple correspondence between () and E(B) / E(tot)?
What do magnetic fields look like after supercritical collapse? Near the end of the ambipolar diffusion process?