SOFIA Polarimetry Pow-Wow(Darren’s slides)

Yerkes, Northwestern, U. ChicagoJuly 27-30, 2007

SOFIA, HAWC, and Hale• 1997: First SOFIA instruments funded

– HAWC 50-200 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

SOFIA 2.5m IR telescope

The Roads to SOFIA Polarimetry• Resume advertising, e.g., SPIE San Diego: Aug. 2007• Polarimeter technology development proposal to JPL

($0.2M): 2007-2009– 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?

HAWCpol and SuperHAWC (a.k.a. Hale)

• 50-200 m• 5-20˝ resolution• 384 pixels• 0.8, 1.3, 3.3´ field of view• single-polarization

• 50-200 m• 5-20˝ resolution• 5000 pixels?• 2.9, 4.8, 10.0´ field of view• dual-polarization

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: 1:30 -- 5 pm• 1) Competition/Complementarity -- Dowell• 2) T-tauri disks -- Novak, Lazarian/Cho, Whitney• 3) Turbulence -- Hildebrand

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• ---------------------• Morning: 9 am - 1 pm• 1) view labs, VPMs, Hertz• 2) continue discussion of HAWC mod.'s -- group

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: 1:30 -- 5 pm• 1) Connection between dense/diffuse ISM, small/large scales -- Crutcher• 2) DR21 massive star formation site -- Kirby• 3) TELECON: 2:30 PM, 877-661-1951, passcode 727100• 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

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

• 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.

• 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?

Science Meeting Summary• HAWCpol provides unique information on the

following topics:– Giant molecular clouds at the subcriticalsupercritical

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 ~ nH

0.5 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.

Next-Generation FIR Detectors

SCUBA 2 Detector Array

• Sub-array: 1280 pixels• 1 array = 4 sub-arrays = 5120 pixels• Woodcraft et al. (2004) & Duncan et al. (2003) SPIE papers

~200 mm

~250 mm

SCUBA 2 Magnetic Shielding(Hollister et al. 2006)

• Requirements:– 100 nT over 0-200 Hz at

detector/SQUID multiplexer• JCMT environment: 150 T

SCUBA 2 Warm Electronics

• U. British Columbia (Halpern group)• 1 box per sub-array (1280 pixels)

Plan C:Stepped Half-Wave Plate

Hardware• We already have a working design for a

stepped half-wave plate:

– (Rennick, Vaillancourt, et al.)

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.

Competition and Complementarity

Far-IR/(sub)mm polarimetry in the 2010’s

• SCUBA2 POL2 (2008): 450-850 m, 8-14˝• CMB surveys

– Planck (2009): 850 m, 5´, full sky• HAWCpol (2011): 50-200 m, 5-20˝• ALMA (2012): 350-10000 m, 0.1˝• Cornell Caltech Atacama Telescope 25m?

(2015): 200-2000 m, 2-20˝• SPICA?? (2018): 50-200 m, 4-14˝

mid-IR polarimetry

• Chris Packham is considering a polarization upgrade to FORECAST

sensitivity and wavelength

sensitivity and resolution

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

Orion at Planck resolutionOMC1 at SOFIA

resolution

Andromeda Galaxy (M31) at Planck resolution

ALMA polarimetry

• 0.1” resolution: 10 AU at 100 pc

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 1983 + 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.

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

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

SCUBA 2 POL2 details

• http://www.phys.umontreal.ca/~eric_bissonnette/dokuwiki/doku.php?id=scuba2:scuba2

• http://www.roe.ac.uk/ukatc/projects/scubatwo• Bastien et al., CASCA, 2005

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´

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 = 0.0083, 0.00097

• AV = 51, 21 at 450, 850 m

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, 0.013 MJy/sr rms in Q

(P)=0.3% for:– 8, 4.3 MJy/sr

• Tdust = 20, 20 K:– mm = 1.610-4, 1.910-4

• AV = 3.5, 11 at 850, 1380 m• all-sky survey• resolution: 5´

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 = 0.0060, 0.0063, 0.0047

• 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˝

ALMA details• http://www.alma.nrao.edu/info/sensitivities/• http://www.eso.org/projects/alma/science/

bin/sensitivity.html• 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˝

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, 0.0038, 0.00075

• 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˝

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 = 0.0022 at 100 m

Turbulence for Dummies

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?