1. Hale, a Multi-Wavelength, Far-Infrared Polarimeter for SOFIA
C. Darren Dowell (Caltech)
J. A. Davidson (USRA/SOFIA)
J. L. Dotson (NASA-Ames)
R. H. Hildebrand (Chicago)
G. Novak (Northwestern)
T. S. Rennick (Chicago)
J. E. Vaillancourt (Wisconsin)
George Ellery Hale – measured magnetic field strength in Sun in 1908.

2. Outline Prior work on Kuiper Airborne Observatory SOFIA possibilities
Hale design and development
Hale astronomy
2002 August 27
Hale/SOFIA

3. M17 – a Site of High-Mass Star FormationB
We see the polarized continuum from aligned dust grains.
One of three magnetic field models in the paper.
100 mm – Dotson (1996)
2002 August 27
Hale/SOFIA

4. Sgr A Circum-Nuclear Disk
100 mm – Hildebrand et al. (1993)
2002 August 27
Hale/SOFIA

5. Polarimetry from SOFIA
# pixels
q (60 mm)
FHWM
q (100 mm)
NEFD
(Jy s1/2)
Stokes/KAO 32
22 ´´
35 ´´
100
Hale/SOFIA
384 to 4096
6 ´´
10 ´´ 1
Hale can detect sources × fainter than was possible with Stokes.
No polarimeter in first-round SOFIA instruments.
We will propose Hale at next funding opportunity (2005).
NEFD improvement: factor of 10 for telescope area (0.9m to 2.5 m), factor of 10 for system quantum efficiency.
100x fainter for point sources. 40x for extended if small, up to 600x if large and we have 4096 pixel array.
2005 as of Aug ( from E. Becklin).
2002 August 27
Hale/SOFIA

6. Bolometers as Far-IR Detectors
Bolometers have quantum efficiency 50% from l = 50 mm to 200 mm and no recombination noise.
Progress is being made on multiplexed bolometers; on the verge of seeing ~32×32 arrays.
2002 August 27
Hale/SOFIA

7. Bolometer Development
NASA/Goddard – 384 bolometers
(Voellmer, Dowell, Moseley, SPIE 4855)
JPL – 144 bolometers
(Glenn, SPIE 4855)
UC Berkeley – 1024 element demo
(Lee, SPIE 4855)
NIST – 1600 element demo
(Holland, Duncan, Reintsema, SPIE 4855)
US only shown; also work in Europe.
Technology mostly driven by ground-based (sub)millimeter and space FIR-mm applications.
2002 August 27
Hale/SOFIA

8. Hale Design Considerations
Observing simultaneous, orthogonal polarization states required:
Two detector arrays.
Multi-wavelength capability required:
Passbands at 53, 88, 155, and 215 mm.
To field a powerful instrument within a SOFIA budget, need to control costs:
Use HAWC cryostat and filter designs.
Take advantage of detector array development driven by other projects.
Can’t afford to pay full development costs for detectors.
2002 August 27
Hale/SOFIA

9. Need for Two Arrays
350 mm – Dowell et al. (1998)
Sky noise (unpolarized) is subtracted away in measurement of polarized intensity.
2002 August 27
Hale/SOFIA

10. CND: Multi-Wavelength Capability Gives Additional Information about Magnetic Field Structure
38 microns: streamers and inner edge of disk
350 microns: outer parts of disk and surrounding molecular clouds
38 mm – Latvakoski et al. (1999)
350 mm – Serabyn et al. (1997)
2002 August 27
Hale/SOFIA

11. Far-IR Polarization Spectrum
No known single grain species will do this.
Multiple dust components with different polarization efficiencies are required.
Hildebrand et al. (1999)
Vaillancourt (2002)
2002 August 27
Hale/SOFIA

12. Prototype Half-Wave Plate Module
Average power dissipation is 22 mW.
Phytron motor.
Successful test of motor, bearing, and sensor at 4 K (Rennick, Vaillancourt – Chicago).
2002 August 27
Hale/SOFIA

13. Pupil Wheel with 5 HWP Modules
2002 August 27
Hale/SOFIA

14. Hale Opto-Mechanical System
With two wheels, can change magnification for different passbands.
Detector size: 15 cm x 15 cm x 7 cm (according to paper).
2002 August 27
Hale/SOFIA

15. HAWC Cryostat
Design is advanced.
2002 August 27
Hale/SOFIA

16. Magnetic Pinches in Massive CoresB B
Orion (500 pc): 1 arcminute = 0.15 pc
DR21 (2500 pc): 1 arcminute = 0.73 pc
Supercritically-collapsed 1 pc “clumps” discussed by Shu, Adams, & Lizano (1987)?
2002 August 27
Hale/SOFIA

17. Low-Mass Stars Examples from 1.3 mm survey by Motte & André (2001)
Low-Mass Stars PP I I
Examples from mm survey by Motte & André (2001)
Pre-protostellar clouds
Class 0: envelopes
Class I: disks (53 mm) & envelopes (155 mm)
Class II: disks I II I PP
Sources in Taurus. I I
2002 August 27
Hale/SOFIA

18. Polarimetry of Extragalactic Sources
NGC 891
NGC 1068
CHECK CALCULATIONS FOR NGC 891.
Grayscale in NGC 1068 is CO.
nuclear starburst
450 mm – Papadopoulos et al. (1998)
edge-on spiral – 850 mm – Alton et al. (1998)
Both can be mapped to s(P) = 0.3% in reasonable amount of time.
2002 August 27
Hale/SOFIA

19. Infrared Cirrus ~50 MJy/sr typical for brighter cirrus.
ISO 150 mm
Bernard et al. (1999)
In addition to finding out magnetic field structure, we can test models for the polarization spectrum. Also cosmological implications.
~50 MJy/sr typical for brighter cirrus.
s(P) = 1% in 3 hr. for 100´´×100´´ co-added region.
Requires largest possible detector arrays for accurate sky subtraction.
2002 August 27
Hale/SOFIA

20. Conclusion
Hale/SOFIA will cross new threshholds for magnetic field and dust studies at 100 mm:
Envelopes and disks of low-mass (proto)stars
Dusty galaxies
Infrared cirrus
Tests of models of polarization spectrum
Hale will also provide more detailed information on more traditional subjects:
Galactic center
Turbulence
2002 August 27
Hale/SOFIA

21. 2002 August 27
Hale/SOFIA

22. Three Dust Components
2002 August 27
Hale/SOFIA

23. Two Dust Components
Observational evidence for T,b correlation: Lis et al. (1998)
2002 August 27
Hale/SOFIA